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Miniature accelerometers and impact measurement

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  • sean14powell
    Hello, I need a little bit of computer geekery and I was hopeful someone here had some relevant experience. Once upon a time we were discussing ways of
    Message 1 of 22 , Jan 3, 2007
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      Hello,
      I need a little bit of computer geekery and I was hopeful
      someone here had some relevant experience. Once upon a time we were
      discussing ways of measuring the impact felt by a combatant when hit
      by a ballista bolt. A number of different methods were discussed but
      ultimately all of the macroscopic measuring devices measure momentum
      and not impulse or impact. We theorized that it would be nice to have
      one of those boxing impact machines that measure how hard a boxer can
      punch.
      Recently I've been asked to help a friend with a similar
      project but involving reproduction steel weapons and reproduction
      steel armor. I started looking into the punching impact sensors and
      found a LOT of other information. Apparently air-bag sensors are
      accelerometers and the massive increase in air-bags in vehicles has
      drastically reduced the cost of producing accelerometers. They have
      also gotten much smaller. Smaller to the point they put them inside
      the GLOVES of boxers to measure impact while sparring. Even more
      exciting, these puppies now come in blue-tooth wireless variants.
      Theoretically this device www.microstrain.com/g-link.aspx
      could be mounted to a ballista bolt and fired at a person or a target
      and record impact force at better then 2000 samples per second.
      Regrettably they are rather expensive.
      Alternately there are cheaper versions like:
      http://www.ertco.com/shock101_shock_recorders.html that might be
      useful if placed on the target.
      My question for the group is: Does anyone have any experience
      with high-speed data acquisition, wireless communication devices,
      and/or accelerometers in general? I would like some assistance
      designing an apparatus to measure actual impacts from (potentially
      deadly) steel on steel combat without it actually being deadly to the
      testers.
      Thank you much,
      Sean
    • Bruce S. R. Lee
      Makes me think of the Myth Busters TV program - as well as the hi-tech electronic gadgets, they use a type of parcel label that is used by shippers to prove
      Message 2 of 22 , Jan 3, 2007
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        Makes me think of the 'Myth Busters' TV program - as well as the
        hi-tech electronic gadgets, they use a type of parcel label that is
        used by shippers to prove how badly the couriers beat up their
        parcels. It seems to consist of a dye or chemical encapsulated in a
        way that will cause the capsule/s to break at a predetermined 'g'
        force is experienced, causing the label to change colour. I've seen
        them use labels rated from about 5 G to 100 G in their shows, and
        they seem to be pretty reliable.

        While not discussing an exact price, they have indicated they are
        pretty cheap - they'd want to be if you were going to stick them into
        every carton you shipped out.

        regards
        Brusi of Orkney

        At 05:30 AM 4/01/2007, you wrote:

        >Hello,
        >I need a little bit of computer geekery and I was hopeful
        >someone here had some relevant experience. Once upon a time we were
        >discussing ways of measuring the impact felt by a combatant when hit
        >by a ballista bolt. A number of different methods were discussed but
        >ultimately all of the macroscopic measuring devices measure momentum
        >and not impulse or impact. We theorized that it would be nice to have
        >one of those boxing impact machines that measure how hard a boxer can
        >punch.
        >Recently I've been asked to help a friend with a similar
        >project but involving reproduction steel weapons and reproduction
        >steel armor. I started looking into the punching impact sensors and
        >found a LOT of other information. Apparently air-bag sensors are
        >accelerometers and the massive increase in air-bags in vehicles has
        >drastically reduced the cost of producing accelerometers. They have
        >also gotten much smaller. Smaller to the point they put them inside
        >the GLOVES of boxers to measure impact while sparring. Even more
        >exciting, these puppies now come in blue-tooth wireless variants.
        >Theoretically this device www.microstrain.com/g-link.aspx
        >could be mounted to a ballista bolt and fired at a person or a target
        >and record impact force at better then 2000 samples per second.
        >Regrettably they are rather expensive.
        >Alternately there are cheaper versions like:
        ><http://www.ertco.com/shock101_shock_recorders.html>http://www.ertco.com/shock101_shock_recorders.html
        >that might be
        >useful if placed on the target.
        >My question for the group is: Does anyone have any experience
        >with high-speed data acquisition, wireless communication devices,
        >and/or accelerometers in general? I would like some assistance
        >designing an apparatus to measure actual impacts from (potentially
        >deadly) steel on steel combat without it actually being deadly to the
        >testers.
        >Thank you much,
        >Sean
      • scorch
        Shockwatch is what they re called, they tend to run about $2 each in case lots. According to the Shockwatch site, they are available in 10, 15, 25, 37.5, 50,
        Message 3 of 22 , Jan 3, 2007
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          Shockwatch is what they're called, they tend to run about $2 each in
          case lots. According to the Shockwatch site, they are available in 10,
          15, 25, 37.5, 50, 75 & 100 G varieties. There are also clip-on versions
          in 25, 50, & 75 G flavors.


          Eoin







          Makes me think of the 'Myth Busters' TV program - as well as the
          hi-tech electronic gadgets, they use a type of parcel label that is
          used by shippers to prove how badly the couriers beat up their
          parcels. It seems to consist of a dye or chemical encapsulated in a
          way that will cause the capsule/s to break at a predetermined 'g'
          force is experienced, causing the label to change colour. I've seen
          them use labels rated from about 5 G to 100 G in their shows, and
          they seem to be pretty reliable.

          While not discussing an exact price, they have indicated they are
          pretty cheap - they'd want to be if you were going to stick them into
          every carton you shipped out.




          __________________________________________________
          Do You Yahoo!?
          Tired of spam? Yahoo! Mail has the best spam protection around
          http://mail.yahoo.com

          [Non-text portions of this message have been removed]
        • Thorolfr inn smithr
          Myth Busters uses Shockwatch brand indicators. There is also another shipping damage indicator called drop-n-tell which can be reused several times -Thorolfr
          Message 4 of 22 , Jan 3, 2007
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            Myth Busters uses "Shockwatch" brand indicators.
            There is also another shipping damage indicator called drop-n-tell which can be reused several times

            -Thorolfr inn smithr

            Bruce S. R. Lee wrote:
            > Makes me think of the 'Myth Busters' TV program - as well as the
            > hi-tech electronic gadgets, they use a type of parcel label that is
            > used by shippers to prove how badly the couriers beat up their
            > parcels. It seems to consist of a dye or chemical encapsulated in a
            > way that will cause the capsule/s to break at a predetermined 'g'
            > force is experienced, causing the label to change colour. I've seen
            > them use labels rated from about 5 G to 100 G in their shows, and
            > they seem to be pretty reliable.
            >
            > While not discussing an exact price, they have indicated they are
            > pretty cheap - they'd want to be if you were going to stick them into
            > every carton you shipped out.
            >
            > regards
            > Brusi of Orkney
          • Danny Miller
            Yep. Not hard at all. In fact we can probably get some free samples of the accelerometers if you play your cards right. Actually unless there s some
            Message 5 of 22 , Jan 3, 2007
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              Yep. Not hard at all. In fact we can probably get some free samples of
              the accelerometers if you play your cards right. Actually unless
              there's some complicating factor an accelerometer should probably be
              available for under $20.

              The deceleration rate is only one factor in an imact. In the case of a
              ballista bolt head made with a compressible head, different parts of the
              head decelerate at different rates. In a UHMW head, I suspect the
              deceleration rate may be basically the same but it's hard to say for
              sure. I suspect that being hit with 6 oz of UHMW at 100 fps is probaby
              softer than being hit with 6 oz of a rock at 100 fps even if the impact
              area is identical and that would be due to the UHMW compressing on
              impact to limit the peak forces, even if the compression is very light.

              There's peak force and a total profile. Peak force is really easy. A
              total profile is tricky because you need a super high speed ADC and
              controller as well as a high speed accelerometer.

              Actually now that I think about it, the "high speed" accelerometer
              probably constitutes the complicating factor I alluded to before. Even
              a car collision happen like a few milliseconds to read. So if the head
              stops over the course of an inch, at 100 fps the whole impact is done
              with in under a millisecond. The interesting "peak" of force may happen
              over an order of magnitude less. If the accelerometer doesn't respond
              fast enough, the amplitude of the acceleration will be inaccurately
              low. The common accelerometers I know do not have a very high frequency
              response.

              The device need not be wireless, I can already tell you wireless isn't
              called for. The microcontroller can be mounted on the projectile and
              store the data so you can recover it from a laptop.

              Others have noted that the sensor can be on the target. You could have
              a gambeson on top of some clay for example, mounted on a FORCE sensor,
              backed up against something sturdy. It's also possible to use an
              accelerometer on the target but there are some complex issues with that
              which can easily compromise the meaningfulness of the measurement.

              Now steel-on-steel is different than ballista bolts. Just what do you
              want to use this measurement for?

              Oznog

              sean14powell wrote:

              > Theoretically this device www.microstrain.com/g-link.aspx
              >could be mounted to a ballista bolt and fired at a person or a target
              >and record impact force at better then 2000 samples per second.
              >Regrettably they are rather expensive.
              > Alternately there are cheaper versions like:
              >http://www.ertco.com/shock101_shock_recorders.html that might be
              >useful if placed on the target.
              > My question for the group is: Does anyone have any experience
              >with high-speed data acquisition, wireless communication devices,
              >and/or accelerometers in general? I would like some assistance
              >designing an apparatus to measure actual impacts from (potentially
              >deadly) steel on steel combat without it actually being deadly to the
              >testers.
              > Thank you much,
              > Sean
              >
              >
              >
              >
              >
            • Danny Miller
              Well lemme do some basic estimation for a projectile 100 fps (1200 inch/sec) projectile (that s pretty fast for a ballista I think) decelerating over 1 in. At
              Message 6 of 22 , Jan 3, 2007
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                Well lemme do some basic estimation for a projectile

                100 fps (1200 inch/sec) projectile (that's pretty fast for a ballista I
                think) decelerating over 1 in. At that speed it would take at 0.833e-4
                sec to pass it, let's say it takes 5x longer to complete an impact which
                puts us at 4.2e-3 sec.

                1G being a deceleration of 32 ft/sec^2. So I get (100 fps / 32
                f/s^2)/time=7500 G's.

                So, I'm sure my estimates are wildly inaccurate for a number of reasons,
                but not inaccurate enough to completely rule out 100G's.
                I fear that the magnitude of the deceleration may be another very
                difficult factor for selection of an accelerometer, in addition to the
                frequency response that accelerometer would have to have.

                I should have started from the idea of a constant deceleration and
                calculated from there. Ah well, you get the idea.

                Oznog

                scorch wrote:

                > Shockwatch is what they're called, they tend to run about $2 each in
                > case lots. According to the Shockwatch site, they are available in 10,
                > 15, 25, 37.5, 50, 75 & 100 G varieties. There are also clip-on versions
                > in 25, 50, & 75 G flavors.
                >
                >
                > Eoin
                >
                >
              • Danny Miller
                OK this may be a better way to estimate it:
                Message 7 of 22 , Jan 3, 2007
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                  OK this may be a better way to estimate it:
                • Danny Miller
                  (trying again...) OK this may be a better way to estimate it: 96fps, this requires 3 G-seconds to stop regardless of how you stop it. I put in a 0.1ft
                  Message 8 of 22 , Jan 3, 2007
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                    (trying again...)
                    OK this may be a better way to estimate it:

                    96fps, this requires 3 G-seconds to stop regardless of how you stop it.
                    I put in a 0.1ft deceleration distance (1.2 in).

                    Assuming the most ideal possible case, where it decelerated evenly over
                    the available distance (never happens, not ever close) I get 1500G's
                    over 2msec to bring it to a stop.

                    It would be good to understand how far off the "constant decelertion"
                    estimate is. Even a spring would start out at zero force/acceleration
                    and linearly increase the force/acceleration as distance decreases.
                    Closed cell foam is much less linear. So I would suspect for the most
                    ideal, tuned computer-modelled impact plan on twice that for a peak
                    deceleration. For real world padding, 5, 10, 20, who knows.

                    The G forces are of course linear with distance. If you had twice the
                    dist to stop, you could do it with with 750 G's.

                    Oznog
                  • Chris Larsson (Hrelgar)
                    I recently saw a mythbusters where they measured force over time via something called a force plate. They were measuring the impact of a frozen turkey being
                    Message 9 of 22 , Jan 3, 2007
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                      I recently saw a mythbusters where they measured force over time via
                      something called a force plate. They were measuring the impact of a
                      frozen turkey being dropped. They got a pretty decent force curve, so
                      I was thinking this impact timeframe should be similar to what we're
                      doing. I found it on a website:

                      http://www.vernier.com/probes/fp-bta.html

                      3500 N max force capability sounds about right for what I calculated
                      earlier for max force of impact of a bolt. $200 plus $60 for the
                      interface is a tad expensive but seemed a reachable expense.

                      A plus would be to use it to compare impact of bolts with impacts of
                      other weapons such as swords, polearms, etc.

                      Any thoughts?

                      Hrelgar
                    • graywolf
                      What I d like to see along with our testing is a Blind Test , say with Sir Stick Jock believing he is showing his prowess with Good and Bad Hits and not
                      Message 10 of 22 , Jan 3, 2007
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                        What I'd like to see along with our testing is a "Blind Test", say with Sir
                        Stick Jock believing he is showing his prowess with "Good and Bad Hits" and
                        not knowing it will be compared to Siege Missiles. It would readily dispel
                        the "You hit too hard and should be banned" Bull.

                        I had hoped to see this direction taken 2 years ago but, then like now,
                        economics is the problem. Any who can accomplish this program will be doing
                        a great service to Siege.

                        Graywolf
                        (SGEK Ret.)


                        ----- Original Message -----
                        From: "Chris Larsson (Hrelgar)" <igelkottinus@...>
                        To: <SCA-Siege@yahoogroups.com>
                        Sent: Wednesday, January 03, 2007 11:02 PM
                        Subject: [SCA-Siege] Re: Miniature accelerometers and impact measurement


                        > I recently saw a mythbusters where they measured force over time via
                        > something called a force plate. They were measuring the impact of a
                        > frozen turkey being dropped. They got a pretty decent force curve, so
                        > I was thinking this impact timeframe should be similar to what we're
                        > doing. I found it on a website:
                        >
                        > http://www.vernier.com/probes/fp-bta.html
                        >
                        > 3500 N max force capability sounds about right for what I calculated
                        > earlier for max force of impact of a bolt. $200 plus $60 for the
                        > interface is a tad expensive but seemed a reachable expense.
                        >
                        > A plus would be to use it to compare impact of bolts with impacts of
                        > other weapons such as swords, polearms, etc.
                        >
                        > Any thoughts?
                        >
                        > Hrelgar
                        >
                        >
                        >
                        > --
                        > [Email to SCA-Siege-unsubscribe@egroups.com to leave this list]
                        > Yahoo! Groups Links
                        >
                        >
                        >
                        >
                      • Danny Miller
                        It s interesting but limited in its applicability IMHO. First off the surface area of the impact is not represented. Impact area directly affects the pain
                        Message 11 of 22 , Jan 3, 2007
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                          It's interesting but limited in its applicability IMHO.

                          First off the surface area of the impact is not represented. Impact
                          area directly affects the pain potential. Of course with a sword, the
                          impact area is highly variable in reality anyways. A hit to the forearm
                          is a much more concentrated area than across the back.

                          Second the dynamics of the flesh and the force distribution are not
                          represented. For example, if the force plate is lightweight and rigid,
                          dropping a large ball bearing on it with no injury potential at all
                          could easily measure a very narrow spike of hundreds, even thousands, of
                          pounds.

                          Oznog

                          graywolf wrote:

                          >>I recently saw a mythbusters where they measured force over time via
                          >>something called a force plate. They were measuring the impact of a
                          >>frozen turkey being dropped. They got a pretty decent force curve, so
                          >>I was thinking this impact timeframe should be similar to what we're
                          >>doing. I found it on a website:
                          >>
                          >>http://www.vernier.com/probes/fp-bta.html
                          >>
                          >>3500 N max force capability sounds about right for what I calculated
                          >>earlier for max force of impact of a bolt. $200 plus $60 for the
                          >>interface is a tad expensive but seemed a reachable expense.
                          >>
                          >>A plus would be to use it to compare impact of bolts with impacts of
                          >>other weapons such as swords, polearms, etc.
                          >>
                          >>Any thoughts?
                          >>
                          >>Hrelgar
                          >>
                          >>
                          >>
                          >>
                          >>
                          >
                          >
                        • Oskar der Drachen
                          Just as a wrench in the works, I had an opportunity to put a speed meter used for archery under the nose of my arbalest, it clocked 147 fps, and that was with
                          Message 12 of 22 , Jan 4, 2007
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                            Just as a wrench in the works, I had an opportunity to put a speed meter
                            used for archery under the nose of my arbalest, it clocked 147 fps, and that
                            was with a 20oz wood and steel bolt. A (16oz-) plastic fantastic would have
                            moved out considerably faster, (slowing down faster too, but that's Problem
                            part #2). I was using a heavier than SCA combat rated draw, but when scaled
                            down the plastic bolt would still have moved equally as fast.

                            There are probably some reliable archery speedos around and about where some
                            enterprising Siege people could lay their hands on them, why not start with
                            a database of basic "muzzle velocity" figures across a range of machines?
                            We don't really know how fast these rounds are do we?

                            Oskar

                            ----- Original Message -----
                            From: "Danny Miller" <dannym@...>
                            To: <SCA-Siege@yahoogroups.com>
                            Sent: Thursday, January 04, 2007 1:07 PM
                            Subject: Re: [SCA-Siege] Miniature accelerometers and impact measurement


                            > Well lemme do some basic estimation for a projectile
                            >
                            > 100 fps (1200 inch/sec) projectile (that's pretty fast for a ballista I
                            > think) decelerating over 1 in. At that speed it would take at 0.833e-4
                            > sec to pass it, let's say it takes 5x longer to complete an impact which
                            > puts us at 4.2e-3 sec.
                            >
                            > 1G being a deceleration of 32 ft/sec^2. So I get (100 fps / 32
                            > f/s^2)/time=7500 G's.
                            >
                            > So, I'm sure my estimates are wildly inaccurate for a number of reasons,
                            > but not inaccurate enough to completely rule out 100G's.
                            > I fear that the magnitude of the deceleration may be another very
                            > difficult factor for selection of an accelerometer, in addition to the
                            > frequency response that accelerometer would have to have.
                            >
                            > I should have started from the idea of a constant deceleration and
                            > calculated from there. Ah well, you get the idea.
                            >
                            > Oznog
                            >
                            > scorch wrote:
                            >
                            >> Shockwatch is what they're called, they tend to run about $2 each in
                            >> case lots. According to the Shockwatch site, they are available in 10,
                            >> 15, 25, 37.5, 50, 75 & 100 G varieties. There are also clip-on versions
                            >> in 25, 50, & 75 G flavors.
                            >>
                            >>
                            >> Eoin
                            >>
                            >>
                            >
                            >
                            >
                            > --
                            > [Email to SCA-Siege-unsubscribe@egroups.com to leave this list]
                            > Yahoo! Groups Links
                            >
                            >
                            >
                            >
                          • sean14powell
                            The key would be putting a wireless accelerometer on every helm (or possibly every weapon) used in crown tourney. Link the data to a high speed camera with
                            Message 13 of 22 , Jan 4, 2007
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                              The key would be putting a wireless accelerometer on every helm (or
                              possibly every weapon) used in crown tourney. Link the data to a high
                              speed camera with synchronized clock. Now you can tell exactly how hard
                              someone was hit. NO MORE RHINOS! :)

                              Realize that there are ALWAYS people out there from light hitting areas
                              that will say "Some jerk in a red and black tabbard hit me WAY too
                              hard." but since there is no way to identify the attacker it gets lost
                              in the shuffle. Siege engineers stand clearly on the side-line next to
                              the weapon in question and can easily be identified as the villan.
                              Regretably it's just part of the game we have to live with.

                              Remember, this was THEIR GAME FIRST. We asked them to change their
                              rules so we could play, and somewhat reluctantly they did. Now that we
                              are here it behoves us to be gracious guests in their game. Lets take
                              it upon ourselves to be better then they are. Lets us measure, and
                              experiment and find the safest goldilock middle ground between too hard
                              and too soft so they have no basis of complaining until the last of the
                              dissenters will be identified by all as whining childish currs and
                              ignored by all...

                              Sean

                              --- In SCA-Siege@yahoogroups.com, "graywolf" <f.miller19@...> wrote:
                              >
                              > What I'd like to see along with our testing is a "Blind Test", say
                              with Sir
                              > Stick Jock believing he is showing his prowess with "Good and Bad
                              Hits" and
                              > not knowing it will be compared to Siege Missiles. It would readily
                              dispel
                              > the "You hit too hard and should be banned" Bull.
                              >
                              > I had hoped to see this direction taken 2 years ago but, then
                              like now,
                              > economics is the problem. Any who can accomplish this program will
                              be doing
                              > a great service to Siege.
                              >
                              > Graywolf
                              > (SGEK Ret.)
                            • graywolf
                              !!!!!!!!?????? graywolf wrote: ??????!!!!!!!! WHOA, Hold it. Not my comment... My comment was meant to say: We are accused of hitting too hard with Siege. I
                              Message 14 of 22 , Jan 6, 2007
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                                !!!!!!!!?????? "graywolf wrote:"??????!!!!!!!!

                                WHOA, Hold it. Not my comment...

                                My comment was meant to say: We are accused of hitting too hard with Siege.
                                I believe the testing, if done, will go far to say Siege, as we apply it,
                                hits less hard than a "Good Blow".

                                graywolf

                                ----- Original Message -----
                                From: "Danny Miller" <dannym@...>
                                To: <SCA-Siege@yahoogroups.com>
                                Sent: Thursday, January 04, 2007 1:31 AM
                                Subject: Re: [SCA-Siege] Re: Miniature accelerometers and impact measurement


                                > It's interesting but limited in its applicability IMHO.
                                >
                                > First off the surface area of the impact is not represented. Impact
                                > area directly affects the pain potential. Of course with a sword, the
                                > impact area is highly variable in reality anyways. A hit to the forearm
                                > is a much more concentrated area than across the back.
                                >
                                > Second the dynamics of the flesh and the force distribution are not
                                > represented. For example, if the force plate is lightweight and rigid,
                                > dropping a large ball bearing on it with no injury potential at all
                                > could easily measure a very narrow spike of hundreds, even thousands, of
                                > pounds.
                                >
                                > Oznog
                                >

                                >
                                > >>I recently saw a mythbusters where they measured force over time via
                                > >>something called a force plate. They were measuring the impact of a
                                > >>frozen turkey being dropped. They got a pretty decent force curve, so
                                > >>I was thinking this impact timeframe should be similar to what we're
                                > >>doing. I found it on a website:
                                > >>
                                > >>http://www.vernier.com/probes/fp-bta.html
                                > >>
                                > >>3500 N max force capability sounds about right for what I calculated
                                > >>earlier for max force of impact of a bolt. $200 plus $60 for the
                                > >>interface is a tad expensive but seemed a reachable expense.
                                > >>
                                > >>A plus would be to use it to compare impact of bolts with impacts of
                                > >>other weapons such as swords, polearms, etc.
                                > >>
                                > >>Any thoughts?
                                > >>
                                > >>Hrelgar
                                > >>
                                > >>
                                > >>
                                > >>
                                > >>
                                > >
                                > >
                                >
                                >
                                >
                                > --
                                > [Email to SCA-Siege-unsubscribe@egroups.com to leave this list]
                                > Yahoo! Groups Links
                                >
                                >
                                >
                              • Sean Powell
                                Relax GW, I m sure it was an editing mistake, especially as Hrelgar s signature is right at the bottom of the post. Personally I DON T think that it s too
                                Message 15 of 22 , Jan 6, 2007
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                                  Relax GW, I'm sure it was an editing mistake, especially as Hrelgar's
                                  signature is right at the bottom of the post.

                                  Personally I DON'T think that it's too limited in it's application. The
                                  Heavy Weapon fighters have known subjectively for YEARS that momentum isn't
                                  necessary for scoring a killing blow, it's peak acceleration. I want a good
                                  crisp stick for crown tourney, not a broom. I want clackers on my mace head.
                                  I want an UN-padded pole weapon rather then a padded one. Now most of this
                                  is directed at head hits as the most common of the killing blows but the
                                  fighting community has become used to the sting of a sharp 'Crack' hitting
                                  armor or exposed flesh rather then the "OOOMPH" of a heavy padded blow. HW
                                  fighters frequently call padded pole-arm shots light that are landing with
                                  much more momentum then unpadded pole-arms.

                                  Honestly, I think our best option would be a bolt that weighs half as much
                                  but cranked up to a max range of 120 yards and a simple foam tip with
                                  something like a poker-chip on the striking surface. The shots should sting
                                  like snapping a heavy rubber band but not have the potential to break ribs
                                  or torque necks.

                                  As for the numbers and comparing to HW attacks. We can do a direct
                                  comparison to the delivered momentum of Peters Van Dorns original Bowling
                                  Ball experiments: http://sca.org/ti/articles/1994/issue110/BlowCalib.html
                                  and if we do (assuming my quick calculation were correct) a 1 lb bolt
                                  traveling at 90f/s (near the end of it's arc) will impart as much momentum
                                  to a bowling ball as slightly above medium power. A 1 lb bolt traveling at
                                  130f/s (near the beginning of it's arc) will impart significantly more
                                  momentum to a bowling ball then the hardest hitting fighters. I'll try to
                                  access my numbers from work and post them a little later. This is the
                                  calculation that I think will benefit the most from knowing the velocity of
                                  the bolt at different points in it's flight path.

                                  As for my non-siege application: I expect to get VERY high peak loads,
                                  probably tons, but only occurring for mili-seconds. I expect to deform
                                  striking edges on hardened steel swords and dent spring tempered
                                  breast-plates. I want to shatter a lance when the crenellated tip strikes a
                                  frog-mouth jousting helm. Maybe I can even get up to proofing breastplates
                                  with musket balls. I figure if I can do this I must be able to measure
                                  impact from a ballista. :)

                                  Sean

                                  -----Original Message-----
                                  From: SCA-Siege@yahoogroups.com [mailto:SCA-Siege@yahoogroups.com]On
                                  Behalf Of graywolf
                                  Sent: Saturday, January 06, 2007 9:59 AM
                                  To: SCA-Siege@yahoogroups.com
                                  Subject: Re: [SCA-Siege] Re: Miniature accelerometers and impact
                                  measurement


                                  !!!!!!!!?????? "graywolf wrote:"??????!!!!!!!!

                                  WHOA, Hold it. Not my comment...

                                  My comment was meant to say: We are accused of hitting too hard with Siege.
                                  I believe the testing, if done, will go far to say Siege, as we apply it,
                                  hits less hard than a "Good Blow".

                                  graywolf

                                  ----- Original Message -----
                                  From: "Danny Miller" <dannym@...>
                                  To: <SCA-Siege@yahoogroups.com>
                                  Sent: Thursday, January 04, 2007 1:31 AM
                                  Subject: Re: [SCA-Siege] Re: Miniature accelerometers and impact measurement


                                  > It's interesting but limited in its applicability IMHO.
                                  >
                                  > First off the surface area of the impact is not represented. Impact
                                  > area directly affects the pain potential. Of course with a sword, the
                                  > impact area is highly variable in reality anyways. A hit to the forearm
                                  > is a much more concentrated area than across the back.
                                  >
                                  > Second the dynamics of the flesh and the force distribution are not
                                  > represented. For example, if the force plate is lightweight and rigid,
                                  > dropping a large ball bearing on it with no injury potential at all
                                  > could easily measure a very narrow spike of hundreds, even thousands, of
                                  > pounds.
                                  >
                                  > Oznog
                                  >

                                  >
                                  > >>I recently saw a mythbusters where they measured force over time via
                                  > >>something called a force plate. They were measuring the impact of a
                                  > >>frozen turkey being dropped. They got a pretty decent force curve, so
                                  > >>I was thinking this impact timeframe should be similar to what we're
                                  > >>doing. I found it on a website:
                                  > >>
                                  > >>http://www.vernier.com/probes/fp-bta.html
                                  > >>
                                  > >>3500 N max force capability sounds about right for what I calculated
                                  > >>earlier for max force of impact of a bolt. $200 plus $60 for the
                                  > >>interface is a tad expensive but seemed a reachable expense.
                                  > >>
                                  > >>A plus would be to use it to compare impact of bolts with impacts of
                                  > >>other weapons such as swords, polearms, etc.
                                  > >>
                                  > >>Any thoughts?
                                  > >>
                                  > >>Hrelgar
                                  > >>
                                  > >>
                                  > >>
                                  > >>
                                  > >>
                                  > >
                                  > >
                                  >
                                  >
                                  >
                                  > --
                                  > [Email to SCA-Siege-unsubscribe@egroups.com to leave this list]
                                  > Yahoo! Groups Links
                                  >
                                  >
                                  >




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                                  Yahoo! Groups Links
                                • Chris Larsson (Hrelgar)
                                  ... forearm ... I definitely agree. However, I think we could factor this in by estimating the average surface area of impact for each weapon. For example, a
                                  Message 16 of 22 , Jan 7, 2007
                                  • 0 Attachment
                                    --- In SCA-Siege@yahoogroups.com, Danny Miller <dannym@...> wrote:
                                    >
                                    > It's interesting but limited in its applicability IMHO.
                                    >
                                    > First off the surface area of the impact is not represented. Impact
                                    > area directly affects the pain potential. Of course with a sword, the
                                    > impact area is highly variable in reality anyways. A hit to the
                                    forearm
                                    > is a much more concentrated area than across the back.
                                    >

                                    I definitely agree. However, I think we could factor this in by
                                    estimating the average surface area of impact for each weapon. For
                                    example, a bolt is 2.5 in. in diameter yielding about a 5 sq. in.
                                    striking surface. A sword is about 1.25" by about 2" yielding about a
                                    2.5 sq. in. striking surface.

                                    > Second the dynamics of the flesh and the force distribution are not
                                    > represented. For example, if the force plate is lightweight and rigid,
                                    > dropping a large ball bearing on it with no injury potential at all
                                    > could easily measure a very narrow spike of hundreds, even
                                    thousands, of
                                    > pounds.

                                    Well, I think that's the nice feature of this thing. It looks like you
                                    end up with a force curve over time. I think the area under the curve
                                    represents the energy dissipated. A short high spike as you describe
                                    would have a high maximum force but a relatively small area under the
                                    curve. I'm guessing that one should be able to create a formula which
                                    factors in the force curve over time, energy dissipated, and impact
                                    area to come up with something useful for comparison purposes.

                                    >
                                    > Oznog
                                    >
                                  • Danny Miller
                                    Impact area is what often surprises people about their designs. This is why I designed an impact board by putting styrofoam wallboard over a heavy, supported
                                    Message 17 of 22 , Jan 7, 2007
                                    • 0 Attachment
                                      Impact area is what often surprises people about their designs. This is
                                      why I designed an impact board by putting styrofoam wallboard over a
                                      heavy, supported piece of plywood. You find that many LARP arrow
                                      designs which feel sturdy in fact push very hard in the center if you
                                      hit hard enough, making a very high force right in the center. Unless
                                      there is a very rigid 2.5" plate in there somewhere, the force per unit
                                      of area will vary greatly across the head.

                                      A round sword such as rattan is VERY difficult to predict the impact
                                      area. It is a narrow line and does not undergo much flattening at all
                                      under typical forces. So against a hard surface you might well see 1/4"
                                      x 2" for a stellar 0.5 sq in. I think that's what carbon paper will
                                      tell you. However, flesh is not a hard surface. The flesh and clothing
                                      is the padding, and conforms around the weapon's diameter to distribute
                                      the force as well as slow it down gradually.

                                      The total energy dissipated we can already predict from
                                      1/2(mass*velocity^2). I've thought about if we can discount the peaks
                                      as being due to the hard plate surface and conclude we cannot. It could
                                      be due to the way it impacts on real flesh. The peaks were the point of
                                      the test and discounting or reshaping them to fit our theories
                                      invalidates the data entirely.

                                      I believe the proper Mythbusters setup would be a force plate with a
                                      lightweight but rigid radius of "bone" material around it to replicate
                                      the curve of a thigh or the side of the rib cage. It must be
                                      lightweight or its inertia will slow plate down and thus dampen the
                                      observed force at the back even though the front surface observes high
                                      forces. The front should have about 3/8" of "Dragon Skin" on top of it
                                      to replicate the way skin conforms to the weapon and provides some
                                      capacity to slow it down. Dragon Skin is a pourable silicone which
                                      feels fairly close to human flesh. I can only hope it responds
                                      similarly at high speeds. Otherwise we're gonna have to chop up a pig
                                      here and place the bloody mess on the force plate (and again I fear the
                                      inertia of it will dampen the observed force).

                                      The force distribution is still unmeasured. A small diameter heavy rod
                                      (rebar?) with a tremendous ability to bruise someone may measure less
                                      total force than a wide, flat padded sword. In some ways the
                                      silicone-over-"bone" model will help show it because it's easy to bottom
                                      out under high PSI of a rebar strike, then the remaining energy makes
                                      very high peak forces as it goes to the bone, whereas a distributed,
                                      conformal impact will use the impact absorption of a great deal of the
                                      silicone.

                                      Oznog

                                      Chris Larsson (Hrelgar) wrote:

                                      >--- In SCA-Siege@yahoogroups.com, Danny Miller <dannym@...> wrote:
                                      >
                                      >
                                      >>It's interesting but limited in its applicability IMHO.
                                      >>
                                      >>First off the surface area of the impact is not represented. Impact
                                      >>area directly affects the pain potential. Of course with a sword, the
                                      >>impact area is highly variable in reality anyways. A hit to the
                                      >>
                                      >>
                                      >forearm
                                      >
                                      >
                                      >>is a much more concentrated area than across the back.
                                      >>
                                      >>
                                      >>
                                      >
                                      >I definitely agree. However, I think we could factor this in by
                                      >estimating the average surface area of impact for each weapon. For
                                      >example, a bolt is 2.5 in. in diameter yielding about a 5 sq. in.
                                      >striking surface. A sword is about 1.25" by about 2" yielding about a
                                      >2.5 sq. in. striking surface.
                                      >
                                      >
                                      >
                                      >>Second the dynamics of the flesh and the force distribution are not
                                      >>represented. For example, if the force plate is lightweight and rigid,
                                      >>dropping a large ball bearing on it with no injury potential at all
                                      >>could easily measure a very narrow spike of hundreds, even
                                      >>
                                      >>
                                      >thousands, of
                                      >
                                      >
                                      >>pounds.
                                      >>
                                      >>
                                      >
                                      >Well, I think that's the nice feature of this thing. It looks like you
                                      >end up with a force curve over time. I think the area under the curve
                                      >represents the energy dissipated. A short high spike as you describe
                                      >would have a high maximum force but a relatively small area under the
                                      >curve. I'm guessing that one should be able to create a formula which
                                      >factors in the force curve over time, energy dissipated, and impact
                                      >area to come up with something useful for comparison purposes.
                                      >
                                      >
                                      >
                                      >>Oznog
                                      >>
                                      >>
                                      >>
                                      >
                                      >
                                      >
                                      >
                                      >
                                      >


                                      [Non-text portions of this message have been removed]
                                    • Chris Larsson (Hrelgar)
                                      ... as much ... should sting ... break ribs ... A couple of issues.... The energy of the bolt is mass times velocity squared. So, for example, if you halve the
                                      Message 18 of 22 , Jan 7, 2007
                                      • 0 Attachment
                                        --- In SCA-Siege@yahoogroups.com, "Sean Powell" <powell.sean@...> wrote:
                                        >
                                        ....
                                        > Honestly, I think our best option would be a bolt that weighs half
                                        as much
                                        > but cranked up to a max range of 120 yards and a simple foam tip with
                                        > something like a poker-chip on the striking surface. The shots
                                        should sting
                                        > like snapping a heavy rubber band but not have the potential to
                                        break ribs
                                        > or torque necks.
                                        >
                                        A couple of issues....

                                        The energy of the bolt is mass times velocity squared. So, for
                                        example, if you halve the weight but double the speed, then you in
                                        effect have doubled the energy that needs to be dissipated (I know you
                                        didn't say to double the speed, but I wanted to illustrate the point).
                                        In order to increase the range by 50%, you would need to significantly
                                        increase the speed to offset drag. I suspect that the 2 would offset
                                        each other or you may actually end up with more energy.

                                        If you increase the range, then you need to increase the playing area
                                        required. As it is (at least in the northeast), I'm finding it hard to
                                        find decent sites with the 120 yards of space required with the
                                        current 80 yard range (don't forget to factor in buffer areas), let
                                        alone finding 150-180 yards needed for a 120 yard range. I think I'm
                                        content with the current 80 yard range.

                                        > As for the numbers and comparing to HW attacks. We can do a direct
                                        > comparison to the delivered momentum of Peters Van Dorns original
                                        Bowling
                                        > Ball experiments:
                                        http://sca.org/ti/articles/1994/issue110/BlowCalib.html
                                        > and if we do (assuming my quick calculation were correct) a 1 lb bolt
                                        > traveling at 90f/s (near the end of it's arc) will impart as much
                                        momentum
                                        > to a bowling ball as slightly above medium power. A 1 lb bolt
                                        traveling at
                                        > 130f/s (near the beginning of it's arc) will impart significantly more
                                        > momentum to a bowling ball then the hardest hitting fighters. I'll
                                        try to
                                        > access my numbers from work and post them a little later. This is the
                                        > calculation that I think will benefit the most from knowing the
                                        velocity of
                                        > the bolt at different points in it's flight path.
                                        >
                                        .....
                                        >
                                        > Sean
                                        >

                                        The problem with the bowling ball is it only measures momentum, not
                                        damage potential. The limitations of this test were demonstrated a
                                        while ago. If you throw a lighter shot but follow through you can
                                        carry the ball as far or farther than a harder blow thrown with no
                                        follow through. Which one causes more damage? Hard to tell. Consider
                                        the most common case, the spear thrust. A short, very hard thrust can
                                        hurt a lot, but won't necessarily carry you over the haybale. But a
                                        long, not so hard thrust with a lot of follow through can send a 280
                                        pound fighter over the haybale, with no injury (I know, it's happened
                                        to me).

                                        For siege, A bolt with a dead tennis ball tip will cause injury, but
                                        should cause the bowling ball to go the same distance as a bolt with a
                                        good pool noodle tip (assuming the same level of bounceback). This is
                                        because the momentum is the same for both bolts (assuming the same
                                        weight, air resistance etc.). The difference is the amount of time
                                        over which the impulse is exerted on the bowling ball.

                                        I guess another problem is practical. The "sweet spot" for the ball is
                                        very small. You have to hit it exactly on center or the bolt will
                                        glance off the surface to some extent. It will be hard to tell whether
                                        you got an exact hit or slightly glancing hit, thus making it hard to
                                        achieve consistent results.

                                        Hrelgar
                                      • Danny Miller
                                        OK this is my territory again. I do foam LARPs and specialize in lighter-than-light technology. The added speed is tremendously useful for taking down people
                                        Message 19 of 22 , Jan 7, 2007
                                        • 0 Attachment
                                          OK this is my territory again. I do foam LARPs and specialize in
                                          lighter-than-light technology. The added speed is tremendously useful
                                          for taking down people before they can block or dodge. While being
                                          light does not change the energy, I do find it easier to build a safe
                                          arrow in light package.

                                          If you manage the drag, "light" can get very good range. I have made
                                          arrows that weight LESS than a 2018 arrow with a field point and they
                                          have gotten excellent range. However, it is tricky to get the
                                          aerodynamics this well tuned and foam has the added problem of liking to
                                          distort itself out of shape over time.

                                          Now you may find an undesirable difference. A light arrow of the same
                                          energy will not have the same momentum (note the difference between
                                          momentum and energy). This usually constitutes a more superficial
                                          "slap" on armor and I can tell the SCA would prefer to get knocked back
                                          a tad like a pillowfight. I have observed that my really light arrows
                                          will mostly stop on loose-hanging garb for example. That's supposed to
                                          count but people often assume that the arrow just caught the cloth
                                          itself as it went by (which is not a hit) as opposed to the straight-in
                                          shot it was. I've noticed people with loose hanging chainmail may not
                                          register it at all, thinking that was just the normal slap of chainmail
                                          as they ran.

                                          Well the effect is there anyways, it is not an all-pervasive problem.
                                          You seem to be so far on the high momentum end of the spectrum so as it
                                          have momentum-based concerns (torqued necks? ouch!) so a lighter
                                          projectile would definitely seem helpful.

                                          Note that the momentum difference cannot be entirely made up for with
                                          harder padding. Well like a very stiff head will make it hit harder for
                                          sure so it rings hard off of plate but then you are really rough on less
                                          armored portions of the body. Then again, I look at you guys' solution
                                          of the UHMW slug arrow and I guess it'd be hard to have a siege
                                          projectile be harder than that.

                                          Oznog

                                          Chris Larsson (Hrelgar) wrote:

                                          >--- In SCA-Siege@yahoogroups.com, "Sean Powell" <powell.sean@...> wrote:
                                          >
                                          >
                                          >....
                                          >
                                          >
                                          >>Honestly, I think our best option would be a bolt that weighs half
                                          >>
                                          >>
                                          >as much
                                          >
                                          >
                                          >>but cranked up to a max range of 120 yards and a simple foam tip with
                                          >>something like a poker-chip on the striking surface. The shots
                                          >>
                                          >>
                                          >should sting
                                          >
                                          >
                                          >>like snapping a heavy rubber band but not have the potential to
                                          >>
                                          >>
                                          >break ribs
                                          >
                                          >
                                          >>or torque necks.
                                          >>
                                          >>
                                          >>
                                          >A couple of issues....
                                          >
                                          >The energy of the bolt is mass times velocity squared. So, for
                                          >example, if you halve the weight but double the speed, then you in
                                          >effect have doubled the energy that needs to be dissipated (I know you
                                          >didn't say to double the speed, but I wanted to illustrate the point).
                                          >In order to increase the range by 50%, you would need to significantly
                                          >increase the speed to offset drag. I suspect that the 2 would offset
                                          >each other or you may actually end up with more energy.
                                          >
                                          >If you increase the range, then you need to increase the playing area
                                          >required. As it is (at least in the northeast), I'm finding it hard to
                                          >find decent sites with the 120 yards of space required with the
                                          >current 80 yard range (don't forget to factor in buffer areas), let
                                          >alone finding 150-180 yards needed for a 120 yard range. I think I'm
                                          >content with the current 80 yard range.
                                          >
                                          >
                                          >
                                          >>As for the numbers and comparing to HW attacks. We can do a direct
                                          >>comparison to the delivered momentum of Peters Van Dorns original
                                          >>
                                          >>
                                          >Bowling
                                          >
                                          >
                                          >>Ball experiments:
                                          >>
                                          >>
                                          >http://sca.org/ti/articles/1994/issue110/BlowCalib.html
                                          >
                                          >
                                          >>and if we do (assuming my quick calculation were correct) a 1 lb bolt
                                          >>traveling at 90f/s (near the end of it's arc) will impart as much
                                          >>
                                          >>
                                          >momentum
                                          >
                                          >
                                          >>to a bowling ball as slightly above medium power. A 1 lb bolt
                                          >>
                                          >>
                                          >traveling at
                                          >
                                          >
                                          >>130f/s (near the beginning of it's arc) will impart significantly more
                                          >>momentum to a bowling ball then the hardest hitting fighters. I'll
                                          >>
                                          >>
                                          >try to
                                          >
                                          >
                                          >>access my numbers from work and post them a little later. This is the
                                          >>calculation that I think will benefit the most from knowing the
                                          >>
                                          >>
                                          >velocity of
                                          >
                                          >
                                          >>the bolt at different points in it's flight path.
                                          >>
                                          >>
                                          >>
                                          >.....
                                          >
                                          >
                                          >>Sean
                                          >>
                                          >>
                                          >>
                                          >
                                          >The problem with the bowling ball is it only measures momentum, not
                                          >damage potential. The limitations of this test were demonstrated a
                                          >while ago. If you throw a lighter shot but follow through you can
                                          >carry the ball as far or farther than a harder blow thrown with no
                                          >follow through. Which one causes more damage? Hard to tell. Consider
                                          >the most common case, the spear thrust. A short, very hard thrust can
                                          >hurt a lot, but won't necessarily carry you over the haybale. But a
                                          >long, not so hard thrust with a lot of follow through can send a 280
                                          >pound fighter over the haybale, with no injury (I know, it's happened
                                          >to me).
                                          >
                                          >For siege, A bolt with a dead tennis ball tip will cause injury, but
                                          >should cause the bowling ball to go the same distance as a bolt with a
                                          >good pool noodle tip (assuming the same level of bounceback). This is
                                          >because the momentum is the same for both bolts (assuming the same
                                          >weight, air resistance etc.). The difference is the amount of time
                                          >over which the impulse is exerted on the bowling ball.
                                          >
                                          >I guess another problem is practical. The "sweet spot" for the ball is
                                          >very small. You have to hit it exactly on center or the bolt will
                                          >glance off the surface to some extent. It will be hard to tell whether
                                          >you got an exact hit or slightly glancing hit, thus making it hard to
                                          >achieve consistent results.
                                          >
                                          >Hrelgar
                                          >
                                          >
                                          >
                                          >
                                          >


                                          [Non-text portions of this message have been removed]
                                        • Sean Powell
                                          Thanks Hrelgar, I understand the KE=1/2M*v^2 rule. I m just not as worried about it. I think many SCA weapons have higher KE values and many probably have
                                          Message 20 of 22 , Jan 7, 2007
                                          • 0 Attachment
                                            Thanks Hrelgar,
                                            I understand the KE=1/2M*v^2 rule. I'm just not as worried about it. I
                                            think many SCA weapons have higher KE values and many probably have higher
                                            peak forces during impact. HW fighters are used to sticks that go "Crack" on
                                            impact. I'm worried about having too much momentum. Momentum isn't as well
                                            understood by the targets (uhm, I mean fighters) and some rough calculations
                                            indicate to me that we are anywhere from just over average to way too hard
                                            depending on range.
                                            Lighter ammo, faster velocity, more KE and less Mo. I think that's what we
                                            should be designing towards... but it's so hard to tell with only knowing
                                            part of our side of the equation and very very little about the HW side of
                                            the equation.
                                            I do see your point about max range. I'd love to duplicate actual siege
                                            engine range and performance one day... but I'll wait to do that with an A&S
                                            display only engine.
                                            Sean

                                            -----Original Message-----
                                            From: SCA-Siege@yahoogroups.com [mailto:SCA-Siege@yahoogroups.com]On
                                            Behalf Of Chris Larsson (Hrelgar)
                                            Sent: Sunday, January 07, 2007 12:37 PM
                                            To: SCA-Siege@yahoogroups.com
                                            Subject: [SCA-Siege] Re: Miniature accelerometers and impact measurement


                                            --- In SCA-Siege@yahoogroups.com, "Sean Powell" <powell.sean@...> wrote:
                                            >
                                            ....
                                            > Honestly, I think our best option would be a bolt that weighs half
                                            as much
                                            > but cranked up to a max range of 120 yards and a simple foam tip with
                                            > something like a poker-chip on the striking surface. The shots
                                            should sting
                                            > like snapping a heavy rubber band but not have the potential to
                                            break ribs
                                            > or torque necks.
                                            >
                                            A couple of issues....

                                            The energy of the bolt is mass times velocity squared. So, for
                                            example, if you halve the weight but double the speed, then you in
                                            effect have doubled the energy that needs to be dissipated (I know you
                                            didn't say to double the speed, but I wanted to illustrate the point).
                                            In order to increase the range by 50%, you would need to significantly
                                            increase the speed to offset drag. I suspect that the 2 would offset
                                            each other or you may actually end up with more energy.

                                            If you increase the range, then you need to increase the playing area
                                            required. As it is (at least in the northeast), I'm finding it hard to
                                            find decent sites with the 120 yards of space required with the
                                            current 80 yard range (don't forget to factor in buffer areas), let
                                            alone finding 150-180 yards needed for a 120 yard range. I think I'm
                                            content with the current 80 yard range.

                                            > As for the numbers and comparing to HW attacks. We can do a direct
                                            > comparison to the delivered momentum of Peters Van Dorns original
                                            Bowling
                                            > Ball experiments:
                                            http://sca.org/ti/articles/1994/issue110/BlowCalib.html
                                            > and if we do (assuming my quick calculation were correct) a 1 lb bolt
                                            > traveling at 90f/s (near the end of it's arc) will impart as much
                                            momentum
                                            > to a bowling ball as slightly above medium power. A 1 lb bolt
                                            traveling at
                                            > 130f/s (near the beginning of it's arc) will impart significantly more
                                            > momentum to a bowling ball then the hardest hitting fighters. I'll
                                            try to
                                            > access my numbers from work and post them a little later. This is the
                                            > calculation that I think will benefit the most from knowing the
                                            velocity of
                                            > the bolt at different points in it's flight path.
                                            >
                                            .....
                                            >
                                            > Sean
                                            >

                                            The problem with the bowling ball is it only measures momentum, not
                                            damage potential. The limitations of this test were demonstrated a
                                            while ago. If you throw a lighter shot but follow through you can
                                            carry the ball as far or farther than a harder blow thrown with no
                                            follow through. Which one causes more damage? Hard to tell. Consider
                                            the most common case, the spear thrust. A short, very hard thrust can
                                            hurt a lot, but won't necessarily carry you over the haybale. But a
                                            long, not so hard thrust with a lot of follow through can send a 280
                                            pound fighter over the haybale, with no injury (I know, it's happened
                                            to me).

                                            For siege, A bolt with a dead tennis ball tip will cause injury, but
                                            should cause the bowling ball to go the same distance as a bolt with a
                                            good pool noodle tip (assuming the same level of bounceback). This is
                                            because the momentum is the same for both bolts (assuming the same
                                            weight, air resistance etc.). The difference is the amount of time
                                            over which the impulse is exerted on the bowling ball.

                                            I guess another problem is practical. The "sweet spot" for the ball is
                                            very small. You have to hit it exactly on center or the bolt will
                                            glance off the surface to some extent. It will be hard to tell whether
                                            you got an exact hit or slightly glancing hit, thus making it hard to
                                            achieve consistent results.

                                            Hrelgar



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                                          • Roderick McKraken
                                            The problem with light weight ballista bolts is that they deform too easily. We ve used ballista bolts made from golf tubes and 100 PSI siloflex. This stuff
                                            Message 21 of 22 , Jan 7, 2007
                                            • 0 Attachment
                                              The problem with light weight ballista bolts is that they deform too easily.
                                              We've used ballista bolts made from golf tubes and 100 PSI siloflex. This
                                              stuff gets bent when fighters step on the bolts. It can also curve just
                                              laying in the sun as the up side gets hot. This is why we went to the 160
                                              PSI siloflex and the gas pipe. These heavier tubes remain straighter and
                                              last longer. However, the problem now is that the heavier tubes with a
                                              tennis ball tip hit too hard within 40 yards range. So, now we are
                                              switching to foam tips. This has been one long learning curve.

                                              Roderick McKraken

                                              ----- Original Message -----
                                              From: "Danny Miller" <dannym@...>
                                              To: <SCA-Siege@yahoogroups.com>
                                              Sent: Sunday, January 07, 2007 1:15 PM
                                              Subject: Re: [SCA-Siege] Re: Miniature accelerometers and impact measurement


                                              > OK this is my territory again. I do foam LARPs and specialize in
                                              > lighter-than-light technology. The added speed is tremendously useful
                                              > for taking down people before they can block or dodge. While being
                                              > light does not change the energy, I do find it easier to build a safe
                                              > arrow in light package.
                                              >
                                              > If you manage the drag, "light" can get very good range. I have made
                                              > arrows that weight LESS than a 2018 arrow with a field point and they
                                              > have gotten excellent range. However, it is tricky to get the
                                              > aerodynamics this well tuned and foam has the added problem of liking to
                                              > distort itself out of shape over time.
                                              >
                                              > Now you may find an undesirable difference. A light arrow of the same
                                              > energy will not have the same momentum (note the difference between
                                              > momentum and energy). This usually constitutes a more superficial
                                              > "slap" on armor and I can tell the SCA would prefer to get knocked back
                                              > a tad like a pillowfight. I have observed that my really light arrows
                                              > will mostly stop on loose-hanging garb for example. That's supposed to
                                              > count but people often assume that the arrow just caught the cloth
                                              > itself as it went by (which is not a hit) as opposed to the straight-in
                                              > shot it was. I've noticed people with loose hanging chainmail may not
                                              > register it at all, thinking that was just the normal slap of chainmail
                                              > as they ran.
                                              >
                                              > Well the effect is there anyways, it is not an all-pervasive problem.
                                              > You seem to be so far on the high momentum end of the spectrum so as it
                                              > have momentum-based concerns (torqued necks? ouch!) so a lighter
                                              > projectile would definitely seem helpful.
                                              >
                                              > Note that the momentum difference cannot be entirely made up for with
                                              > harder padding. Well like a very stiff head will make it hit harder for
                                              > sure so it rings hard off of plate but then you are really rough on less
                                              > armored portions of the body. Then again, I look at you guys' solution
                                              > of the UHMW slug arrow and I guess it'd be hard to have a siege
                                              > projectile be harder than that.
                                              >
                                              > Oznog
                                              >
                                              > Chris Larsson (Hrelgar) wrote:
                                              >
                                              > >--- In SCA-Siege@yahoogroups.com, "Sean Powell" <powell.sean@...> wrote:
                                              > >
                                              > >
                                              > >....
                                              > >
                                              > >
                                              > >>Honestly, I think our best option would be a bolt that weighs half
                                              > >>
                                              > >>
                                              > >as much
                                              > >
                                              > >
                                              > >>but cranked up to a max range of 120 yards and a simple foam tip with
                                              > >>something like a poker-chip on the striking surface. The shots
                                              > >>
                                              > >>
                                              > >should sting
                                              > >
                                              > >
                                              > >>like snapping a heavy rubber band but not have the potential to
                                              > >>
                                              > >>
                                              > >break ribs
                                              > >
                                              > >
                                              > >>or torque necks.
                                              > >>
                                              > >>
                                              > >>
                                              > >A couple of issues....
                                              > >
                                              > >The energy of the bolt is mass times velocity squared. So, for
                                              > >example, if you halve the weight but double the speed, then you in
                                              > >effect have doubled the energy that needs to be dissipated (I know you
                                              > >didn't say to double the speed, but I wanted to illustrate the point).
                                              > >In order to increase the range by 50%, you would need to significantly
                                              > >increase the speed to offset drag. I suspect that the 2 would offset
                                              > >each other or you may actually end up with more energy.
                                              > >
                                              > >If you increase the range, then you need to increase the playing area
                                              > >required. As it is (at least in the northeast), I'm finding it hard to
                                              > >find decent sites with the 120 yards of space required with the
                                              > >current 80 yard range (don't forget to factor in buffer areas), let
                                              > >alone finding 150-180 yards needed for a 120 yard range. I think I'm
                                              > >content with the current 80 yard range.
                                              > >
                                              > >
                                              > >
                                              > >>As for the numbers and comparing to HW attacks. We can do a direct
                                              > >>comparison to the delivered momentum of Peters Van Dorns original
                                              > >>
                                              > >>
                                              > >Bowling
                                              > >
                                              > >
                                              > >>Ball experiments:
                                              > >>
                                              > >>
                                              > >http://sca.org/ti/articles/1994/issue110/BlowCalib.html
                                              > >
                                              > >
                                              > >>and if we do (assuming my quick calculation were correct) a 1 lb bolt
                                              > >>traveling at 90f/s (near the end of it's arc) will impart as much
                                              > >>
                                              > >>
                                              > >momentum
                                              > >
                                              > >
                                              > >>to a bowling ball as slightly above medium power. A 1 lb bolt
                                              > >>
                                              > >>
                                              > >traveling at
                                              > >
                                              > >
                                              > >>130f/s (near the beginning of it's arc) will impart significantly more
                                              > >>momentum to a bowling ball then the hardest hitting fighters. I'll
                                              > >>
                                              > >>
                                              > >try to
                                              > >
                                              > >
                                              > >>access my numbers from work and post them a little later. This is the
                                              > >>calculation that I think will benefit the most from knowing the
                                              > >>
                                              > >>
                                              > >velocity of
                                              > >
                                              > >
                                              > >>the bolt at different points in it's flight path.
                                              > >>
                                              > >>
                                              > >>
                                              > >.....
                                              > >
                                              > >
                                              > >>Sean
                                              > >>
                                              > >>
                                              > >>
                                              > >
                                              > >The problem with the bowling ball is it only measures momentum, not
                                              > >damage potential. The limitations of this test were demonstrated a
                                              > >while ago. If you throw a lighter shot but follow through you can
                                              > >carry the ball as far or farther than a harder blow thrown with no
                                              > >follow through. Which one causes more damage? Hard to tell. Consider
                                              > >the most common case, the spear thrust. A short, very hard thrust can
                                              > >hurt a lot, but won't necessarily carry you over the haybale. But a
                                              > >long, not so hard thrust with a lot of follow through can send a 280
                                              > >pound fighter over the haybale, with no injury (I know, it's happened
                                              > >to me).
                                              > >
                                              > >For siege, A bolt with a dead tennis ball tip will cause injury, but
                                              > >should cause the bowling ball to go the same distance as a bolt with a
                                              > >good pool noodle tip (assuming the same level of bounceback). This is
                                              > >because the momentum is the same for both bolts (assuming the same
                                              > >weight, air resistance etc.). The difference is the amount of time
                                              > >over which the impulse is exerted on the bowling ball.
                                              > >
                                              > >I guess another problem is practical. The "sweet spot" for the ball is
                                              > >very small. You have to hit it exactly on center or the bolt will
                                              > >glance off the surface to some extent. It will be hard to tell whether
                                              > >you got an exact hit or slightly glancing hit, thus making it hard to
                                              > >achieve consistent results.
                                              > >
                                              > >Hrelgar
                                              > >
                                              > >
                                              > >
                                              > >
                                              > >
                                              >
                                              >
                                              > [Non-text portions of this message have been removed]
                                              >
                                              >
                                              >
                                              > --
                                              > [Email to SCA-Siege-unsubscribe@egroups.com to leave this list]
                                              > Yahoo! Groups Links
                                              >
                                              >
                                              >
                                            • Jeffrey Blaisdell
                                              What if we shorten the bolts to lighten the weight? I understand they were once 3 feet, and 4 ft flies better, but with fins on the back end, 3 ft might be OK.
                                              Message 22 of 22 , Jan 8, 2007
                                              • 0 Attachment
                                                What if we shorten the bolts to lighten the weight? I understand they were once 3 feet, and 4 ft flies better, but with fins on the back end, 3 ft might be OK.

                                                Geoffrey

                                                ----- Original Message -----
                                                From: Roderick McKraken
                                                To: SCA-Siege@yahoogroups.com
                                                Sent: Sunday, January 07, 2007 11:50 PM
                                                Subject: Re: [SCA-Siege] Re: Miniature accelerometers and impact measurement


                                                The problem with light weight ballista bolts is that they deform too easily.
                                                We've used ballista bolts made from golf tubes and 100 PSI siloflex. This
                                                stuff gets bent when fighters step on the bolts. It can also curve just
                                                laying in the sun as the up side gets hot. This is why we went to the 160
                                                PSI siloflex and the gas pipe. These heavier tubes remain straighter and
                                                last longer. However, the problem now is that the heavier tubes with a
                                                tennis ball tip hit too hard within 40 yards range. So, now we are
                                                switching to foam tips. This has been one long learning curve.

                                                Roderick McKraken

                                                ----- Original Message -----
                                                From: "Danny Miller" <dannym@...>
                                                To: <SCA-Siege@yahoogroups.com>
                                                Sent: Sunday, January 07, 2007 1:15 PM
                                                Subject: Re: [SCA-Siege] Re: Miniature accelerometers and impact measurement

                                                > OK this is my territory again. I do foam LARPs and specialize in
                                                > lighter-than-light technology. The added speed is tremendously useful
                                                > for taking down people before they can block or dodge. While being
                                                > light does not change the energy, I do find it easier to build a safe
                                                > arrow in light package.
                                                >
                                                > If you manage the drag, "light" can get very good range. I have made
                                                > arrows that weight LESS than a 2018 arrow with a field point and they
                                                > have gotten excellent range. However, it is tricky to get the
                                                > aerodynamics this well tuned and foam has the added problem of liking to
                                                > distort itself out of shape over time.
                                                >
                                                > Now you may find an undesirable difference. A light arrow of the same
                                                > energy will not have the same momentum (note the difference between
                                                > momentum and energy). This usually constitutes a more superficial
                                                > "slap" on armor and I can tell the SCA would prefer to get knocked back
                                                > a tad like a pillowfight. I have observed that my really light arrows
                                                > will mostly stop on loose-hanging garb for example. That's supposed to
                                                > count but people often assume that the arrow just caught the cloth
                                                > itself as it went by (which is not a hit) as opposed to the straight-in
                                                > shot it was. I've noticed people with loose hanging chainmail may not
                                                > register it at all, thinking that was just the normal slap of chainmail
                                                > as they ran.
                                                >
                                                > Well the effect is there anyways, it is not an all-pervasive problem.
                                                > You seem to be so far on the high momentum end of the spectrum so as it
                                                > have momentum-based concerns (torqued necks? ouch!) so a lighter
                                                > projectile would definitely seem helpful.
                                                >
                                                > Note that the momentum difference cannot be entirely made up for with
                                                > harder padding. Well like a very stiff head will make it hit harder for
                                                > sure so it rings hard off of plate but then you are really rough on less
                                                > armored portions of the body. Then again, I look at you guys' solution
                                                > of the UHMW slug arrow and I guess it'd be hard to have a siege
                                                > projectile be harder than that.
                                                >
                                                > Oznog
                                                >
                                                > Chris Larsson (Hrelgar) wrote:
                                                >
                                                > >--- In SCA-Siege@yahoogroups.com, "Sean Powell" <powell.sean@...> wrote:
                                                > >
                                                > >
                                                > >....
                                                > >
                                                > >
                                                > >>Honestly, I think our best option would be a bolt that weighs half
                                                > >>
                                                > >>
                                                > >as much
                                                > >
                                                > >
                                                > >>but cranked up to a max range of 120 yards and a simple foam tip with
                                                > >>something like a poker-chip on the striking surface. The shots
                                                > >>
                                                > >>
                                                > >should sting
                                                > >
                                                > >
                                                > >>like snapping a heavy rubber band but not have the potential to
                                                > >>
                                                > >>
                                                > >break ribs
                                                > >
                                                > >
                                                > >>or torque necks.
                                                > >>
                                                > >>
                                                > >>
                                                > >A couple of issues....
                                                > >
                                                > >The energy of the bolt is mass times velocity squared. So, for
                                                > >example, if you halve the weight but double the speed, then you in
                                                > >effect have doubled the energy that needs to be dissipated (I know you
                                                > >didn't say to double the speed, but I wanted to illustrate the point).
                                                > >In order to increase the range by 50%, you would need to significantly
                                                > >increase the speed to offset drag. I suspect that the 2 would offset
                                                > >each other or you may actually end up with more energy.
                                                > >
                                                > >If you increase the range, then you need to increase the playing area
                                                > >required. As it is (at least in the northeast), I'm finding it hard to
                                                > >find decent sites with the 120 yards of space required with the
                                                > >current 80 yard range (don't forget to factor in buffer areas), let
                                                > >alone finding 150-180 yards needed for a 120 yard range. I think I'm
                                                > >content with the current 80 yard range.
                                                > >
                                                > >
                                                > >
                                                > >>As for the numbers and comparing to HW attacks. We can do a direct
                                                > >>comparison to the delivered momentum of Peters Van Dorns original
                                                > >>
                                                > >>
                                                > >Bowling
                                                > >
                                                > >
                                                > >>Ball experiments:
                                                > >>
                                                > >>
                                                > >http://sca.org/ti/articles/1994/issue110/BlowCalib.html
                                                > >
                                                > >
                                                > >>and if we do (assuming my quick calculation were correct) a 1 lb bolt
                                                > >>traveling at 90f/s (near the end of it's arc) will impart as much
                                                > >>
                                                > >>
                                                > >momentum
                                                > >
                                                > >
                                                > >>to a bowling ball as slightly above medium power. A 1 lb bolt
                                                > >>
                                                > >>
                                                > >traveling at
                                                > >
                                                > >
                                                > >>130f/s (near the beginning of it's arc) will impart significantly more
                                                > >>momentum to a bowling ball then the hardest hitting fighters. I'll
                                                > >>
                                                > >>
                                                > >try to
                                                > >
                                                > >
                                                > >>access my numbers from work and post them a little later. This is the
                                                > >>calculation that I think will benefit the most from knowing the
                                                > >>
                                                > >>
                                                > >velocity of
                                                > >
                                                > >
                                                > >>the bolt at different points in it's flight path.
                                                > >>
                                                > >>
                                                > >>
                                                > >.....
                                                > >
                                                > >
                                                > >>Sean
                                                > >>
                                                > >>
                                                > >>
                                                > >
                                                > >The problem with the bowling ball is it only measures momentum, not
                                                > >damage potential. The limitations of this test were demonstrated a
                                                > >while ago. If you throw a lighter shot but follow through you can
                                                > >carry the ball as far or farther than a harder blow thrown with no
                                                > >follow through. Which one causes more damage? Hard to tell. Consider
                                                > >the most common case, the spear thrust. A short, very hard thrust can
                                                > >hurt a lot, but won't necessarily carry you over the haybale. But a
                                                > >long, not so hard thrust with a lot of follow through can send a 280
                                                > >pound fighter over the haybale, with no injury (I know, it's happened
                                                > >to me).
                                                > >
                                                > >For siege, A bolt with a dead tennis ball tip will cause injury, but
                                                > >should cause the bowling ball to go the same distance as a bolt with a
                                                > >good pool noodle tip (assuming the same level of bounceback). This is
                                                > >because the momentum is the same for both bolts (assuming the same
                                                > >weight, air resistance etc.). The difference is the amount of time
                                                > >over which the impulse is exerted on the bowling ball.
                                                > >
                                                > >I guess another problem is practical. The "sweet spot" for the ball is
                                                > >very small. You have to hit it exactly on center or the bolt will
                                                > >glance off the surface to some extent. It will be hard to tell whether
                                                > >you got an exact hit or slightly glancing hit, thus making it hard to
                                                > >achieve consistent results.
                                                > >
                                                > >Hrelgar
                                                > >
                                                > >
                                                > >
                                                > >
                                                > >
                                                >
                                                >
                                                > [Non-text portions of this message have been removed]
                                                >
                                                >
                                                >
                                                > --
                                                > [Email to SCA-Siege-unsubscribe@egroups.com to leave this list]
                                                > Yahoo! Groups Links
                                                >
                                                >
                                                >






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