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Re: #25 chain and sprockets

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  • arioch2k1
    There are a few problems with the chain and sprockets you are looking at on eBay. The sprocket doesn t have a keyway and the teeth are not hardened, this is
    Message 1 of 29 , Jul 25, 2013
      There are a few problems with the chain and sprockets you are looking at on eBay. The sprocket doesn't have a keyway and the teeth are not hardened, this is good indication that they are cheap Chinese products. I have bought chain and sprockets from a large local supplier for years and every time I forget to ask for US made products only, I seem to get the same cheap Chinese crap, the sprockets usually don't fit the chain's pitch properly and jam under load. You need a keyway to keep the sprocket from slipping on the shaft under load, the set screws are not meant to take any real load.

      --- In SeattleRobotics@yahoogroups.com, KM6VV <KM6VV@...> wrote:
      >
      > Sorry for the cross posts.
      >
      > I'm still trying to get a reliable motor drive on my 6WD Robomagellan.
      > Someone mentioned chain, so I'm researching. I've found #25 chain and
      > sprockets:
      >
      > http://www.ebay.com/itm/12-TOOTH-25-PITCH-1-4-BORE-SPROCKET-25BS12-1-2742-12
      > -A-/271033154180?pt=LH_DefaultDomain_0
      > <http://www.ebay.com/itm/12-TOOTH-25-PITCH-1-4-BORE-SPROCKET-25BS12-1-2742-1
      > 2-A-/271033154180?pt=LH_DefaultDomain_0&hash=item3f1ad5ba84>
      > &hash=item3f1ad5ba84
      >
      > http://www.ebay.com/itm/25-PITCH-ROLLER-CHAIN-10-25-10-25P-1-1163-25-/380227
      > 257478?pt=LH_DefaultDomain_0
      > <http://www.ebay.com/itm/25-PITCH-ROLLER-CHAIN-10-25-10-25P-1-1163-25-/38022
      > 7257478?pt=LH_DefaultDomain_0&hash=item58874f8486> &hash=item58874f8486
      >
      > But what do I do for adjusting the chain lengths and master links?
      >
      > OK, so I could probably machine the sprockets with CNC, but they're
      > cheap enough.
      >
      > Is the center-to-center and chain length calculations the same as timing
      > belt calculations? I'm looking for 3" C-C. I could use a calculator
      > for #25 chains.
      >
      > Would this chain drive be an improvement over .200" (XL) timing belts?
      >
      > Thanks,
      >
      > Alan KM6VV
      >
    • K Maxon
        Hello Alan,   For Protobot, the chain sprockets are good quality steel  that  have been nitrided to prevent corosion and  aid surface hardness /
      Message 2 of 29 , Jul 26, 2013
         
        Hello Alan,
         
        For Protobot, the chain sprockets are good quality steel  that  have been nitrided to prevent corosion and  aid surface hardness / wear.  (photo below). To answer your question on power, the motor can generate 32oz-in of torque while running  at  3,100rpm.  This power is then run through a 28:1 single stage planetary gear box before being applied to these chain sprockets that produce an additional 3:1 reduction.  That puts running torque at ~14ft-lbs (not accounting for frictional losses which are substantial) and about twice that near stall torque on  the motors.
         
         
        Installed, the gear and the  wheel  share the  same keyway on the shaft.
         
        One item to  consider when  when  leaving slack  on the chain is where the encoders are located in the drive train in relationship  to the motors as you may be introducing a 3'rd  order feedback delay term that is biased based on whether  the  chain is already loaded in a particular direction.  Just something to consider when building a robot with feedback and  control systems utilizing chain with slop that needs  to be taken up upon  reversing direction.
         
        -Kenneth

        From: KM6VV <KM6VV@...>
        To: SeattleRobotics@yahoogroups.com
        Sent: Thursday, July 25, 2013 7:25 PM
        Subject: Re: [SeattleRobotics] #25 chain and sprockets

        Hi Kenneth,

        Thanks for the comments.  I have adjustments for the motors, that could
        take care of it.

        How much power are you transmitting with your chain?  I read your
        Encoder article on making the 180 tooth sprocket.  What material?

        Mine is for powering the wheels; the 1st link from the motor to the
        first of three axles (DPA design).

        Alan  KM6VV

        On 7/25/2013 6:31 PM, K Maxon wrote:
        >
        >
        > Hello Alan,
        > There are two issues here:
        > The issue of precision  is not one of your ability to produce a
        > precision mechanism, but in lacking precision in the chain
        > construction.  It is not the center distances on the sprockets or the
        > sprockets themselves, but the precision problem comes from the chain.
        > All mass produced chain out there (smaller sizes) is produced from links
        > that are stamped from ribbon sheet steel.  This in combination with the
        > roll pins is a very low precision process and yeilds a non-consistent
        > chain even over a number of feet in the same chain.
        > The second issue is that chain is designed to stretch.  Chain stretches,
        > a  lot, under reasonably low loading.  In the first month of
        > operation, of my robot protoBot, I had to "take up" chain tension
        > 3-times and eventually ended up removing a full  link.  ProtoBot uses
        > #25 stainless steel roller chain.  It is only a guestimation on my part,
        > but  I believe that  a good  amount of the stretching took place during
        > abuse suffered during dialing in the software control system timing.
        > All that to say.... chain systems, that use cheap off the shelf -
        > comercial chain, should have a tension / slop take up system designed in.
        > -Kenneth
        >
        > *From:* KM6VV <KM6VV@...>
        > *To:* Seattle Robotics <SeattleRobotics@yahoogroups.com>
        > *Sent:* Thursday, July 25, 2013 12:38 PM
        > *Subject:* [SeattleRobotics] #25 chain and sprockets
        >
        > Sorry for the cross posts.
        >
        > I'm still trying to get a reliable motor drive on my 6WD Robomagellan.
        > Someone mentioned chain, so I'm researching. I've found #25 chain and
        > sprockets:
        >
        > http://www.ebay.com/itm/12-TOOTH-25-PITCH-1-4-BORE-SPROCKET-25BS12-1-2742-12
        > -A-/271033154180?pt=LH_DefaultDomain_0
        > <http://www.ebay.com/itm/12-TOOTH-25-PITCH-1-4-BORE-SPROCKET-25BS12-1-2742-1
        > 2-A-/271033154180?pt=LH_DefaultDomain_0&hash=item3f1ad5ba84>
        > &hash=item3f1ad5ba84
        >
        > http://www.ebay.com/itm/25-PITCH-ROLLER-CHAIN-10-25-10-25P-1-1163-25-/380227
        > 257478?pt=LH_DefaultDomain_0
        > <http://www.ebay.com/itm/25-PITCH-ROLLER-CHAIN-10-25-10-25P-1-1163-25-/38022
        > 7257478?pt=LH_DefaultDomain_0&hash=item58874f8486> &hash=item58874f8486
        >
        > But what do I do for adjusting the chain lengths and master links?
        >
        > OK, so I could probably machine the sprockets with CNC, but they're
        > cheap enough.
        >
        > Is the center-to-center and chain length calculations the same as timing
        > belt calculations? I'm looking for 3" C-C. I could use a calculator
        > for #25 chains.
        >
        > Would this chain drive be an improvement over .200" (XL) timing belts?
        >
        > Thanks,
        >
        > Alan KM6VV
        >
        >
        > ------------------------------------
        >
        > Visit the SRS Website at http://www.seattlerobotics.orgyahoo!/Groups Links
        >
        >
        > SeattleRobotics-fullfeatured@yahoogroups.com
        > <mailto:SeattleRobotics-fullfeatured@yahoogroups.com>
        >
        >
        >
        >
        >
        >
        >


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      • KM6VV
        Hi David, I think my chassis is stiff enough. I stressed it, and could not detect any dimensional change between the two timing belt pulleys. I ve got the
        Message 3 of 29 , Jul 26, 2013
          Hi David,

          I think my chassis is stiff enough. I stressed it, and could not detect
          any dimensional change between the two timing belt pulleys.

          I've got the spec sheet for the pulleys and chain; and I've done CAD
          drawings of different pulley sizes to see how they fit. I even
          considered machining up a pulley or two for tests while I thought I had
          some chain on a surplus bit in the garage. Found out the chain I had
          was #15, cute, but too small!

          Other then a few bicycles, I haven't played with chain, not that there's
          much to it. Actually good for robot hobbyists, as it's easy to machine
          pulleys, and you can adjust the chain length link by link!

          Is chain going to give me a little more torque, and not ratchet? That's
          what I need to take away from this.

          On 7/25/2013 9:23 PM, David Buckley wrote:
          >
          >
          > Alan
          > If you have a wimpy chassis you will find that chain doesn't jump teeth
          > as easily as toothed belt because the teeth are bigger.
          > Calculating the pitch length is just the same as for toothed belts and
          > remember you need the spec sheet to relate the pitch diameter to the
          > overall diameter whether the wheels are for chains or toothed belts.
          > Tension needs to be minimal and sprung, or you need slack, you need
          > slack in a chain otherwise it won't run smoothly, unlike a belt, and a
          > tensioner just stops it flapping around.
          > The slack also need to be minimal otherwise you get lots of flapping
          > around under electric braking or reversing.
          > You will probably find you can't run it nearly as fast as a belt unless
          > the axial alignment is spot on.
          > If you get significant chain stretch you should have chosen a bigger
          > chain or you have stressed it by over-tensioning it.
          > If that happens you need to replace the chain otherwise it damages and
          > wears the chain wheels, the end result is the chain jumps teeth and if
          > that happens at speed you could end up bending something like one of the
          > shafts, there is a lot of stored energy in a rotating motor/gearbox.
          > Did you never run a motor bike or work on an overhead cam engine with
          > chain drive to the camshaft?
          > DAvid
          >
          >
        • KM6VV
          I wasn t aware of the problems! Pictures are not real. I found sprockets at SDP, but they are out of stock. I have flatted shafts, can t really use the keys.
          Message 4 of 29 , Jul 26, 2013
            I wasn't aware of the problems! Pictures are not real.
            I found sprockets at SDP, but they are out of stock.
            I have flatted shafts, can't really use the keys.

            Alan KM6VV

            On 7/25/2013 9:43 PM, arioch2k1 wrote:
            > >
            > There are a few problems with the chain and sprockets you are looking at on eBay. The sprocket doesn't have a

            keyway and the teeth are not hardened, this is good indication that they
            are cheap Chinese products. I have bought

            chain and sprockets from a large local supplier for years and every time
            I forget to ask for US made products only,

            I seem to get the same cheap Chinese crap, the sprockets usually don't
            fit the chain's pitch properly and jam under

            load. You need a keyway to keep the sprocket from slipping on the shaft
            under load, the set screws are not meant to

            take any real load.
            >
          • KM6VV
            Hi Kenneth, I d better get SDP to order the sprockets. I have 9.5 kgf-cm (131 oz-in) of torque at 240 RPM from the motor (IG42 motors from SuperDroid). So
            Message 5 of 29 , Jul 26, 2013
              Hi Kenneth,

              I'd better get SDP to order the sprockets.

              I have 9.5 kgf-cm (131 oz-in) of torque at 240 RPM from the motor (IG42
              motors from SuperDroid). So maybe 8 Ft-lbs?

              http://www.superdroidrobots.com/shop/item.aspx/ig42-24vdc-240-rpm-gear-motor-with-encoder/840/

              My encoders are on the motors.

              I really didn't want slack, but if the drive doesn't ratchet, then I'm
              ahead. Still rather get the timing belt to work, but I haven't been
              able to add a tension wheel to the motor belt drive. Two level stacking
              of the motor pulley and axle pulley on each side of a central bearing
              limit the room for changing the the pulleys without an extensive
              re-design.

              And I just heard that there my not be another RoboGames...

              Thanks for the comments,

              Alan KM6VV

              On 7/26/2013 7:27 AM, K Maxon wrote:
              >
              >
              > Hello Alan,
              > For Protobot, the chain sprockets are good quality steel that have
              > been nitrided to prevent corosion and aid surface hardness / wear.
              > (photo below). To answer your question on power, the motor can
              > generate 32oz-in of torque while running at 3,100rpm. This power is
              > then run through a 28:1 single stage planetary gear box before being
              > applied to these chain sprockets that produce an additional 3:1
              > reduction. That puts running torque at ~14ft-lbs (not accounting for
              > frictional losses which are substantial) and about twice that near stall
              > torque on the motors.
              > http://nikita.argia.net/kmaxon/q50_0360.jpg
              > Installed, the gear and the wheel share the same keyway on the shaft.
              > http://nikita.argia.net/kmaxon/q50_113_001170.jpg
              > One item to consider when when leaving slack on the chain is where
              > the encoders are located in the drive train in relationship to the
              > motors as you may be introducing a 3'rd order feedback delay term that
              > is biased based on whether the chain is already loaded in a particular
              > direction. Just something to consider when building a robot with
              > feedback and control systems utilizing chain with slop that needs to
              > be taken up upon reversing direction.
              > -Kenneth
              >
            • arioch2k1
              McMaster-Carr has good quality sprockets, roller chain and links also.
              Message 6 of 29 , Jul 26, 2013
                McMaster-Carr has good quality sprockets, roller chain and links also.

                --- In SeattleRobotics@yahoogroups.com, KM6VV <KM6VV@...> wrote:
                >
                > Hi Kenneth,
                >
                > I'd better get SDP to order the sprockets.
                >
                > I have 9.5 kgf-cm (131 oz-in) of torque at 240 RPM from the motor (IG42
                > motors from SuperDroid). So maybe 8 Ft-lbs?
                >
                > http://www.superdroidrobots.com/shop/item.aspx/ig42-24vdc-240-rpm-gear-motor-with-encoder/840/
                >
                > My encoders are on the motors.
                >
                > I really didn't want slack, but if the drive doesn't ratchet, then I'm
                > ahead. Still rather get the timing belt to work, but I haven't been
                > able to add a tension wheel to the motor belt drive. Two level stacking
                > of the motor pulley and axle pulley on each side of a central bearing
                > limit the room for changing the the pulleys without an extensive
                > re-design.
                >
                > And I just heard that there my not be another RoboGames...
                >
                > Thanks for the comments,
                >
                > Alan KM6VV
                >
                > On 7/26/2013 7:27 AM, K Maxon wrote:
                > >
                > >
                > > Hello Alan,
                > > For Protobot, the chain sprockets are good quality steel that have
                > > been nitrided to prevent corosion and aid surface hardness / wear.
                > > (photo below). To answer your question on power, the motor can
                > > generate 32oz-in of torque while running at 3,100rpm. This power is
                > > then run through a 28:1 single stage planetary gear box before being
                > > applied to these chain sprockets that produce an additional 3:1
                > > reduction. That puts running torque at ~14ft-lbs (not accounting for
                > > frictional losses which are substantial) and about twice that near stall
                > > torque on the motors.
                > > http://nikita.argia.net/kmaxon/q50_0360.jpg
                > > Installed, the gear and the wheel share the same keyway on the shaft.
                > > http://nikita.argia.net/kmaxon/q50_113_001170.jpg
                > > One item to consider when when leaving slack on the chain is where
                > > the encoders are located in the drive train in relationship to the
                > > motors as you may be introducing a 3'rd order feedback delay term that
                > > is biased based on whether the chain is already loaded in a particular
                > > direction. Just something to consider when building a robot with
                > > feedback and control systems utilizing chain with slop that needs to
                > > be taken up upon reversing direction.
                > > -Kenneth
                > >
                >
              • David Buckley
                Hi Alan How long is a piece of string? Depends on how you cut it. If your belt jumps teeth something is wrong, poor alignment, wimpy chassis, putting in too
                Message 7 of 29 , Jul 26, 2013
                  Hi Alan
                  How long is a piece of string? Depends on how you cut it.
                  If your belt jumps teeth something is wrong, poor alignment, wimpy chassis, putting in too much torque for the number of teeth engaged etc etc,
                  Same goes for chain.
                  It is shock loads which cause a jump and you won't be able to measure the effects of them, you'll just notice the result.
                  How stiff is stiff? I remember somebody writing about most large hobby lathes lathes and remarking that if a cylinder that was just out of balance was held between centers and the tailstock centre was adjusted so it was just pressing enough to stop the piece revolving under gravity then with one finger pressing on the bed you could exert enough pressure to flex the bed so the piece would rotate under gravity!
                  Now consider doing the same by wacking the bed with a big hammer and sending a shockwave, would you be able to measure the deflection? In either case, not without exotic equipment you wouldn't.
                  What is the input torque? what is the belt/chain speed? What is the belt width? How many teeth are engaged on each wheel?
                  DAvid
                   
                  ----- Original Message -----
                  From: KM6VV
                  Sent: Friday, July 26, 2013 5:34 PM
                  Subject: Re: [SeattleRobotics] #25 chain and sprockets

                   

                  Hi David,

                  I think my chassis is stiff enough. I stressed it, and could not detect
                  any dimensional change between the two timing belt pulleys.

                  I've got the spec sheet for the pulleys and chain; and I've done CAD
                  drawings of different pulley sizes to see how they fit. I even
                  considered machining up a pulley or two for tests while I thought I had
                  some chain on a surplus bit in the garage. Found out the chain I had
                  was #15, cute, but too small!

                  Other then a few bicycles, I haven't played with chain, not that there's
                  much to it. Actually good for robot hobbyists, as it's easy to machine
                  pulleys, and you can adjust the chain length link by link!

                  Is chain going to give me a little more torque, and not ratchet? That's
                  what I need to take away from this.

                  On 7/25/2013 9:23 PM, David Buckley wrote:
                  >
                  >
                  > Alan
                  > If you have a wimpy chassis you will find that chain doesn't jump teeth
                  > as easily as toothed belt because the teeth are bigger.
                  > Calculating the pitch length is just the same as for toothed belts and
                  > remember you need the spec sheet to relate the pitch diameter to the
                  > overall diameter whether the wheels are for chains or toothed belts.
                  > Tension needs to be minimal and sprung, or you need slack, you need
                  > slack in a chain otherwise it won't run smoothly, unlike a belt, and a
                  > tensioner just stops it flapping around.
                  > The slack also need to be minimal otherwise you get lots of flapping
                  > around under electric braking or reversing.
                  > You will probably find you can't run it nearly as fast as a belt unless
                  > the axial alignment is spot on.
                  > If you get significant chain stretch you should have chosen a bigger
                  > chain or you have stressed it by over-tensioning it.
                  > If that happens you need to replace the chain otherwise it damages and
                  > wears the chain wheels, the end result is the chain jumps teeth and if
                  > that happens at speed you could end up bending something like one of the
                  > shafts, there is a lot of stored energy in a rotating motor/gearbox.
                  > Did you never run a motor bike or work on an overhead cam engine with
                  > chain drive to the camshaft?
                  > DAvid
                  >
                  >

                • KM6VV
                  Hi Ceal, Yes, I d like to see the design for the chain tensioner! I haven t found the chain breaker on Andy-Mark yet. I m about to order some #25 sprockets
                  Message 8 of 29 , Jul 26, 2013
                    Hi Ceal,

                    Yes, I'd like to see the design for the chain tensioner!
                    I haven't found the chain breaker on Andy-Mark yet. I'm about to order
                    some #25 sprockets and chain. Andy-Mark says made in USA.

                    I don't like the idea of back-driving my 'bot, I suspect the Traxx drive
                    shafts to the wheels are a possible future weak point. DPA had to swap
                    his out for metal ones, I'd like to put off that exercise until I get a
                    RoboMagellan race or two in first (if that happens).

                    Granger looks pretty pricy for the chain breaker, might look elsewhere
                    for that. I didn't remember Tim using chains.

                    Alan KM6VV

                    On 7/26/2013 9:29 AM, Ceal wrote:
                    > Alan, I see Tim already provided the info about the chain
                    > breaker/relinker with master links. We purchased one of those at
                    > Grainger years ago. Not sure if that is comparable price-wise or not. I
                    > have an account at Grainger by us in Berryessa (San Jose) if you need
                    > one from them. I even used it, so if I can use it, most folks can. :)
                    > Also, Tim designed this neat chain tensioner that we used on several
                    > robots in years past for FIRST Robotics Competition (FRC). Sort of like
                    > an aileron on a plane, as he told me. But composed of parts
                    > off-the-shelf at OSH.
                    > The students on FRC teams who use chains learnd that chain tensioners
                    > are an important element in a robot chain-drive system. Alternatively
                    > the length of chain driven is so small and the wrap so much, it may not
                    > be as important. And of course FRC robots do get pushed around a bunch
                    > on the field. Your robot may not undergo that kind of stress. Andy-Mark
                    > sells one too.
                    > Tim has photographs of the design if you are interested. Some flat
                    > corner brackets and something else I'm drawing a blank on.
                    > ceal
                    >
                  • kevinr
                    Try your local bicycle shop for chain, master links, and the breaker you need. Kevin. KD5ONS
                    Message 9 of 29 , Jul 26, 2013
                      Try your local bicycle shop for chain, master links, and the breaker you need. 
                          Kevin.  KD5ONS


                      On 7/26/2013 12:02 PM, KM6VV wrote:
                       

                      Hi Ceal,

                      Yes, I'd like to see the design for the chain tensioner!
                      I haven't found the chain breaker on Andy-Mark yet. I'm about to order
                      some #25 sprockets and chain. Andy-Mark says made in USA.

                      I don't like the idea of back-driving my 'bot, I suspect the Traxx drive
                      shafts to the wheels are a possible future weak point. DPA had to swap
                      his out for metal ones, I'd like to put off that exercise until I get a
                      RoboMagellan race or two in first (if that happens).

                      Granger looks pretty pricy for the chain breaker, might look elsewhere
                      for that. I didn't remember Tim using chains.

                      Alan KM6VV

                      On 7/26/2013 9:29 AM, Ceal wrote:
                      > Alan, I see Tim already provided the info about the chain
                      > breaker/relinker with master links. We purchased one of those at
                      > Grainger years ago. Not sure if that is comparable price-wise or not. I
                      > have an account at Grainger by us in Berryessa (San Jose) if you need
                      > one from them. I even used it, so if I can use it, most folks can. :)
                      > Also, Tim designed this neat chain tensioner that we used on several
                      > robots in years past for FIRST Robotics Competition (FRC). Sort of like
                      > an aileron on a plane, as he told me. But composed of parts
                      > off-the-shelf at OSH.
                      > The students on FRC teams who use chains learnd that chain tensioners
                      > are an important element in a robot chain-drive system. Alternatively
                      > the length of chain driven is so small and the wrap so much, it may not
                      > be as important. And of course FRC robots do get pushed around a bunch
                      > on the field. Your robot may not undergo that kind of stress. Andy-Mark
                      > sells one too.
                      > Tim has photographs of the design if you are interested. Some flat
                      > corner brackets and something else I'm drawing a blank on.
                      > ceal
                      >


                    • KM6VV
                      Thanks. Sprockets are good price, chains are 3X more. I ll have to figure out the shipping. The do have the individual links stuff too. Alan KM6VV
                      Message 10 of 29 , Jul 26, 2013
                        Thanks.

                        Sprockets are good price, chains are 3X more. I'll have to figure out
                        the shipping.

                        The do have the individual links stuff too.

                        Alan KM6VV

                        On 7/26/2013 11:13 AM, arioch2k1 wrote:
                        > McMaster-Carr has good quality sprockets, roller chain and links also.
                        >
                        >
                      • Kevin Ross
                        Bike shops almost never deal with #25 chain, they are using #35 chain. Save yourself the trip, they won’t have what you are looking for. Best chain breaker
                        Message 11 of 29 , Jul 26, 2013

                          Bike shops almost never deal with #25 chain, they are using #35 chain. Save yourself the trip, they won’t have what you are looking for.

                           

                          Best chain breaker is part 6051K15 from McMaster Carr. It is $28 there. You can get pretty much an identical part from Amazon for $12 using

                          http://amzn.com/B004HKIU4C . I have used both, they both work fine. Amazon also has some inexpensive chain, http://amzn.com/B004HKITHA, which I have used and it also worked just fine.

                           

                          McMaster Carr or MSCDirect are the two best traditional places to go for #25 chain supplies. AndyMark.com is also a good supplier. We use all three of them in FIRST.

                           

                          If you want really lightweight large hubless sprockets, AndyMark has some decent ones that are very inexpensive. They are water jetted out of .090 aluminum. They work fine for robotics.

                           

                          If you were designing a machine that was intended to be used for years with a big service life, then you will want to go with hardened sprockets. If you are building a hobby robot, don’t worry so much about that. Your duty cycle is going to be so low, it won’t matter.

                           

                          From: SeattleRobotics@yahoogroups.com [mailto:SeattleRobotics@yahoogroups.com] On Behalf Of kevinr
                          Sent: Friday, July 26, 2013 12:09 PM
                          To: SeattleRobotics@yahoogroups.com
                          Cc: Alan Marconett; Sherline CNC; Sherline
                          Subject: Re: [SeattleRobotics] Re: #25 chain and sprockets

                           



                          Try your local bicycle shop for chain, master links, and the breaker you need. 
                              Kevin.  KD5ONS

                          On 7/26/2013 12:02 PM, KM6VV wrote:

                           

                          Hi Ceal,

                          Yes, I'd like to see the design for the chain tensioner!
                          I haven't found the chain breaker on Andy-Mark yet. I'm about to order
                          some #25 sprockets and chain. Andy-Mark says made in USA.

                          I don't like the idea of back-driving my 'bot, I suspect the Traxx drive
                          shafts to the wheels are a possible future weak point. DPA had to swap
                          his out for metal ones, I'd like to put off that exercise until I get a
                          RoboMagellan race or two in first (if that happens).

                          Granger looks pretty pricy for the chain breaker, might look elsewhere
                          for that. I didn't remember Tim using chains.

                          Alan KM6VV

                          On 7/26/2013 9:29 AM, Ceal wrote:
                          > Alan, I see Tim already provided the info about the chain
                          > breaker/relinker with master links. We purchased one of those at
                          > Grainger years ago. Not sure if that is comparable price-wise or not. I
                          > have an account at Grainger by us in Berryessa (San Jose) if you need
                          > one from them. I even used it, so if I can use it, most folks can. :)
                          > Also, Tim designed this neat chain tensioner that we used on several
                          > robots in years past for FIRST Robotics Competition (FRC). Sort of like
                          > an aileron on a plane, as he told me. But composed of parts
                          > off-the-shelf at OSH.
                          > The students on FRC teams who use chains learnd that chain tensioners
                          > are an important element in a robot chain-drive system. Alternatively
                          > the length of chain driven is so small and the wrap so much, it may not
                          > be as important. And of course FRC robots do get pushed around a bunch
                          > on the field. Your robot may not undergo that kind of stress. Andy-Mark
                          > sells one too.
                          > Tim has photographs of the design if you are interested. Some flat
                          > corner brackets and something else I'm drawing a blank on.
                          > ceal
                          >





                        • KM6VV
                          Hi David, I used leverage to try and deflect the chassis about the two shafts. Probably not a perfect test, I must agree. I couldn t measure with a dial
                          Message 12 of 29 , Jul 26, 2013
                            Hi David,

                            I used leverage to try and deflect the chassis about the two shafts.
                            Probably not a perfect test, I must agree. I couldn't measure with a
                            dial caliper.

                            The shock (stress) of a turn is what is apparently over-stressing the
                            belts.

                            Approximately 8 ft-lb of torque, 240 RPM, .375 XL belts. 3" C-C. 20
                            tooth 1:1 pulleys, so 10 teeth of each engaged.

                            I'm still open for a belt solution. I'm even looking harder to add a
                            tensioner.

                            Alan KM6VV

                            On 7/26/2013 11:36 AM, David Buckley wrote:
                            >
                            >
                            > Hi Alan
                            > How long is a piece of string? Depends on how you cut it.
                            > If your belt jumps teeth something is wrong, poor alignment, wimpy
                            > chassis, putting in too much torque for the number of teeth engaged etc etc,
                            > Same goes for chain.
                            > It is shock loads which cause a jump and you won't be able to measure
                            > the effects of them, you'll just notice the result.
                            > How stiff is stiff? I remember somebody writing about most large hobby
                            > lathes lathes and remarking that if a cylinder that was just out of
                            > balance was held between centers and the tailstock centre was adjusted
                            > so it was just pressing enough to stop the piece revolving under gravity
                            > then with one finger pressing on the bed you could exert enough pressure
                            > to flex the bed so the piece would rotate under gravity!
                            > Now consider doing the same by wacking the bed with a big hammer and
                            > sending a shockwave, would you be able to measure the deflection? In
                            > either case, not without exotic equipment you wouldn't.
                            > What is the input torque? what is the belt/chain speed? What is the belt
                            > width? How many teeth are engaged on each wheel?
                            > DAvid
                            >
                          • KM6VV
                            Thanks, I ll do that. Alan KM6VV
                            Message 13 of 29 , Jul 26, 2013
                              Thanks, I'll do that.

                              Alan KM6VV

                              On 7/26/2013 12:08 PM, kevinr wrote:
                              >
                              >
                              > Try your local bicycle shop for chain, master links, and the breaker you
                              > need.
                              > Kevin. KD5ONS
                              >
                            • KM6VV
                              I think you re right Kevin. I just placed an order for stuff from Amazon, had some other stuff to get. Alan KM6VV
                              Message 14 of 29 , Jul 26, 2013
                                I think you're right Kevin.

                                I just placed an order for stuff from Amazon, had some other stuff to get.

                                Alan KM6VV

                                On 7/26/2013 1:34 PM, Kevin Ross wrote:
                                >
                                >
                                > Bike shops almost never deal with #25 chain, they are using #35 chain.
                                > Save yourself the trip, they won’t have what you are looking for.
                                >
                                > Best chain breaker is part 6051K15 from McMaster Carr. It is $28 there.
                                > You can get pretty much an identical part from Amazon for $12 using
                                >
                                > http://amzn.com/B004HKIU4C. I have used both, they both work fine.
                                > Amazon also has some inexpensive chain, http://amzn.com/B004HKITHA,
                                > which I have used and it also worked just fine.
                                >
                                > McMaster Carr or MSCDirect are the two best traditional places to go for
                                > #25 chain supplies. AndyMark.com is also a good supplier. We use all
                                > three of them in FIRST.
                                >
                                > If you want really lightweight large hubless sprockets, AndyMark has
                                > some decent ones that are very inexpensive. They are water jetted out of
                                > .090 aluminum. They work fine for robotics.
                                >
                                > If you were designing a machine that was intended to be used for years
                                > with a big service life, then you will want to go with hardened
                                > sprockets. If you are building a hobby robot, don’t worry so much about
                                > that. Your duty cycle is going to be so low, it won’t matter.
                                >
                                > *From:*SeattleRobotics@yahoogroups.com
                                > [mailto:SeattleRobotics@yahoogroups.com] *On Behalf Of *kevinr
                                > *Sent:* Friday, July 26, 2013 12:09 PM
                                > *To:* SeattleRobotics@yahoogroups.com
                                > *Cc:* Alan Marconett; Sherline CNC; Sherline
                                > *Subject:* Re: [SeattleRobotics] Re: #25 chain and sprockets
                                >
                                >
                                >
                                > Try your local bicycle shop for chain, master links, and the breaker you
                                > need.
                                > Kevin. KD5ONS
                                >
                                > On 7/26/2013 12:02 PM, KM6VV wrote:
                                >
                                > Hi Ceal,
                                >
                                > Yes, I'd like to see the design for the chain tensioner!
                                > I haven't found the chain breaker on Andy-Mark yet. I'm about to order
                                > some #25 sprockets and chain. Andy-Mark says made in USA.
                                >
                                > I don't like the idea of back-driving my 'bot, I suspect the Traxx
                                > drive
                                > shafts to the wheels are a possible future weak point. DPA had to swap
                                > his out for metal ones, I'd like to put off that exercise until I get a
                                > RoboMagellan race or two in first (if that happens).
                                >
                                > Granger looks pretty pricy for the chain breaker, might look elsewhere
                                > for that. I didn't remember Tim using chains.
                                >
                                > Alan KM6VV
                                >
                                > On 7/26/2013 9:29 AM, Ceal wrote:
                                > > Alan, I see Tim already provided the info about the chain
                                > > breaker/relinker with master links. We purchased one of those at
                                > > Grainger years ago. Not sure if that is comparable price-wise or
                                > not. I
                                > > have an account at Grainger by us in Berryessa (San Jose) if you need
                                > > one from them. I even used it, so if I can use it, most folks can. :)
                                > > Also, Tim designed this neat chain tensioner that we used on several
                                > > robots in years past for FIRST Robotics Competition (FRC). Sort
                                > of like
                                > > an aileron on a plane, as he told me. But composed of parts
                                > > off-the-shelf at OSH.
                                > > The students on FRC teams who use chains learnd that chain tensioners
                                > > are an important element in a robot chain-drive system. Alternatively
                                > > the length of chain driven is so small and the wrap so much, it
                                > may not
                                > > be as important. And of course FRC robots do get pushed around a
                                > bunch
                                > > on the field. Your robot may not undergo that kind of stress.
                                > Andy-Mark
                                > > sells one too.
                                > > Tim has photographs of the design if you are interested. Some flat
                                > > corner brackets and something else I'm drawing a blank on.
                                > > ceal
                                > >
                                >
                                >
                                >
                                >
                                >
                                >
                                >
                                >
                              • dpa
                                Hi Alan, I m trying to get up to speed on the problem you are attempting to solve. Seems like the starting point was that the timing belt driving the first
                                Message 15 of 29 , Jul 27, 2013
                                  Hi Alan,


                                  I'm trying to get up to speed on the problem you are attempting to solve. Seems like the starting point was that the timing belt driving the first stage of the robot's drive train is jumping teeth when you attempt to turn/rotate the robot. Since this is not a problem I have encountered with jBot, a very similar design, (http://www.geology.smu.edu/dpa-www/robo/jbot/) I started wondering why.

                                  I think the answer might be as follows. The motors you are using can produce more torque than the Pittman's on jBot (I don't have the numbers at hand but I believe this is true.) Since rotating a 6 wheel skid steered vehicle requires scrubbing the front and rear tires sideways, there is a lot of friction involved, much like tank treads.

                                  To that end, jBot uses "Road Rage" tires with very little tread, as we have discussed, which are relatively easy to scrub sideways. jBot, by design, also has very light wheel loading, on the order of 3+ pounds per wheel. I believe your robot is heavier, and also uses the stock EMAXX tires which are, by design, very hard to scrub sideways. Hence much more torque is required to rotate the bot that is required to rotate jBot.

                                  Since jBot is both lighter, has smoother tires, and weaker motors, the robot either rotates successfully or the motors stall, long before the point of jumping teeth on the timing belt. The stall condition is monitored by the microprocessor and handled as an error condition.

                                  Check out the video of jBot getting itself unstuck from various situations here:

                                  <http://www.geology.smu.edu/dpa-www/robo/jbot/jbot2/jbot_stuck_m1.mpg>

                                  and look at the escape around 1:30 into the video. You can see the motors stall and the robot react to that condition.

                                  From your description I believe that your robot would, in that same situation, not stall, but rather apply enough torque to jump the timing belt teeth. Too much torque for the condition, or so it would seem.

                                  Not sure how much any of this helps but it looks like what you are describing is a total systems design problem rather than a chain vs. timing belt or tensioning problem, having to do with available torque, your robot's tires and performance requirements, and the controlling software.

                                  You might try going to smoother tread wheels, lighten the robot if possible, and see'f you can monitor the motors to trade off torque vs. stall current and prevent the timing belt from jumping.

                                  In any event, good luck. jBot is looking forward to having a mate to play with...

                                  best regards,
                                  dpa






                                  On Thursday, July 25, 2013 1:10:56 PM UTC-5, KM6VV wrote:
                                  > Sorry for the cross posts.
                                  >
                                  >
                                  >
                                  > I'm still trying to get a reliable motor drive on my 6WD Robomagellan.
                                  >
                                  > Someone mentioned chain, so I'm researching. I've found #25 chain and
                                  >
                                  > sprockets:
                                  >
                                  >
                                  >
                                  > http://www.ebay.com/itm/12-TOOTH-25-PITCH-1-4-BORE-SPROCKET-25BS12-1-2742-12-A-/271033154180?pt=LH_DefaultDomain_0&hash=item3f1ad5ba84
                                  >
                                  >
                                  >
                                  > http://www.ebay.com/itm/25-PITCH-ROLLER-CHAIN-10-25-10-25P-1-1163-25-/380227257478?pt=LH_DefaultDomain_0&hash=item58874f8486
                                  >
                                  >
                                  >
                                  > But what do I do for adjusting the chain lengths and master links?
                                  >
                                  >
                                  >
                                  > OK, so I could probably machine the sprockets with CNC, but they're
                                  >
                                  > cheap enough.
                                  >
                                  >
                                  >
                                  > Is the center-to-center and chain length calculations the same as timing
                                  >
                                  > belt calculations? I'm looking for 3" C-C. I could use a calculator
                                  >
                                  > for #25 chains.
                                  >
                                  >
                                  >
                                  > Would this chain drive be an improvement over .200" (XL) timing belts?
                                  >
                                  >
                                  >
                                  > Thanks,
                                  >
                                  >
                                  >
                                  > Alan KM6VV
                                • KM6VV
                                  Hi David, Yes, first stage belt drive from motor to 1st axle. I put the drive aside for a while and worked on the sonar array and camera mountings. I agree
                                  Message 16 of 29 , Jul 27, 2013
                                    Hi David,

                                    Yes, first stage belt drive from motor to 1st axle. I put the drive
                                    aside for a while and worked on the sonar array and camera mountings.

                                    I agree with your analysis. And yes, our designs are very similar, as
                                    far as I've been able to tell. Hard to improve on your design!

                                    I never did get a good idea of the torque from your Pittman motors. I
                                    calculated 8 ft-lb at 240 RPM from my 24 V IG42 SuperDroid motors. Any
                                    idea what your motors put out?

                                    I first did a search for different belt materials; I have another set of
                                    belts to try as well. Hard to find the "Road Rage" you mentioned.

                                    I'm heavier, what with the Mini-ITX CPU and the sensor head.

                                    Good videos! I've studied them over and over.

                                    Thanks for the comments.

                                    Best regards,

                                    Alan KM6VV

                                    P.S. Let's schedule a play date for Jbot and HexaTraxx Moose once I get
                                    him running!


                                    On 7/27/2013 8:24 AM, dpa wrote:
                                    > Hi Alan,
                                    >
                                    >
                                    > I'm trying to get up to speed on the problem you are attempting to solve. Seems like the starting point was

                                    that the timing belt driving the first stage of the robot's drive train
                                    is jumping teeth when you attempt to

                                    turn/rotate the robot. Since this is not a problem I have encountered
                                    with jBot, a very similar design,

                                    (http://www.geology.smu.edu/dpa-www/robo/jbot/) I started wondering why.
                                    >
                                    > I think the answer might be as follows. The motors you are using can produce more torque than the Pittman's

                                    on jBot (I don't have the numbers at hand but I believe this is true.)
                                    Since rotating a 6 wheel skid steered

                                    vehicle requires scrubbing the front and rear tires sideways, there is a
                                    lot of friction involved, much like

                                    tank treads.
                                    >
                                    > To that end, jBot uses "Road Rage" tires with very little tread, as we have discussed, which are relatively

                                    easy to scrub sideways. jBot, by design, also has very light wheel
                                    loading, on the order of 3+ pounds per wheel.

                                    I believe your robot is heavier, and also uses the stock EMAXX tires
                                    which are, by design, very hard to scrub

                                    sideways. Hence much more torque is required to rotate the bot that is
                                    required to rotate jBot.
                                    >
                                    > Since jBot is both lighter, has smoother tires, and weaker motors, the robot either rotates successfully or

                                    the motors stall, long before the point of jumping teeth on the timing
                                    belt. The stall condition is monitored

                                    by the microprocessor and handled as an error condition.
                                    >
                                    > Check out the video of jBot getting itself unstuck from various situations here:
                                    >
                                    > <http://www.geology.smu.edu/dpa-www/robo/jbot/jbot2/jbot_stuck_m1.mpg>
                                    >
                                    > and look at the escape around 1:30 into the video. You can see the motors stall and the robot react to that

                                    condition.
                                    >
                                    >>From your description I believe that your robot would, in that same situation, not stall, but rather apply

                                    enough torque to jump the timing belt teeth. Too much torque for the
                                    condition, or so it would seem.
                                    >
                                    > Not sure how much any of this helps but it looks like what you are describing is a total systems design

                                    problem rather than a chain vs. timing belt or tensioning problem,
                                    having to do with available torque, your

                                    robot's tires and performance requirements, and the controlling software.
                                    >
                                    > You might try going to smoother tread wheels, lighten the robot if possible, and see'f you can monitor the

                                    motors to trade off torque vs. stall current and prevent the timing belt
                                    from jumping.
                                    >
                                    > In any event, good luck. jBot is looking forward to having a mate to play with...
                                    >
                                    > best regards,
                                    > dpa
                                    >
                                    >
                                  • David Buckley
                                    Hi Alan I tried to find max tension information for XL belts, I have it in a paper catalog somewhere, but where, I asked Google but all the suggested links had
                                    Message 17 of 29 , Jul 27, 2013
                                      Hi Alan
                                      I tried to find max tension information for XL belts, I have it in a paper catalog somewhere, but where, I asked Google but all the suggested links had data for metric Tx belts.
                                      All I can say is that Liberator http://www.davidbuckley.net/DB/Liberator/Liberator.htm is driven by 72 teeth .375 XL belts, with 10 tooth pulleys on the gearboxes and 60 tooth pulleys on the wheels, hence I only have less than 5 teeth in engagement on the drive pulleys - not really good. The motors are the usual 38mm dia. Far East ones. Top speed of Liberator is about 3 ft/sec. I haven't rebuilt it since its shades of J5 'dissasembly'! but I have just driven it round the workshop powered by a 4A battery charger, it won't drive with me on it, the motors stall, but was fine with a 56lb weight. No belt troubles at all.
                                      DAvid
                                       
                                       
                                      ----- Original Message -----
                                      From: KM6VV
                                      Sent: Friday, July 26, 2013 10:30 PM
                                      Subject: Re: [SeattleRobotics] #25 chain and sprockets

                                       

                                      Hi David,

                                      I used leverage to try and deflect the chassis about the two shafts.
                                      Probably not a perfect test, I must agree. I couldn't measure with a
                                      dial caliper.

                                      The shock (stress) of a turn is what is apparently over-stressing the
                                      belts.

                                      Approximately 8 ft-lb of torque, 240 RPM, .375 XL belts. 3" C-C. 20
                                      tooth 1:1 pulleys, so 10 teeth of each engaged.

                                      I'm still open for a belt solution. I'm even looking harder to add a
                                      tensioner.

                                      Alan KM6VV

                                      On 7/26/2013 11:36 AM, David Buckley wrote:
                                      >
                                      >
                                      > Hi Alan
                                      > How long is a piece of string? Depends on how you cut it.
                                      > If your belt jumps teeth something is wrong, poor alignment, wimpy
                                      > chassis, putting in too much torque for the number of teeth engaged etc etc,
                                      > Same goes for chain.
                                      > It is shock loads which cause a jump and you won't be able to measure
                                      > the effects of them, you'll just notice the result.
                                      > How stiff is stiff? I remember somebody writing about most large hobby
                                      > lathes lathes and remarking that if a cylinder that was just out of
                                      > balance was held between centers and the tailstock centre was adjusted
                                      > so it was just pressing enough to stop the piece revolving under gravity
                                      > then with one finger pressing on the bed you could exert enough pressure
                                      > to flex the bed so the piece would rotate under gravity!
                                      > Now consider doing the same by wacking the bed with a big hammer and
                                      > sending a shockwave, would you be able to measure the deflection? In
                                      > either case, not without exotic equipment you wouldn't.
                                      > What is the input torque? what is the belt/chain speed? What is the belt
                                      > width? How many teeth are engaged on each wheel?
                                      > DAvid
                                      >

                                    • Kevin Ross
                                      There has been quite of bit of study on belt vs chain in the FIRST community. Here is one paper: http://www.chiefdelphi.com/media/papers/2216 Another good link
                                      Message 18 of 29 , Jul 27, 2013

                                        There has been quite of bit of study on belt vs chain in the FIRST community. Here is one paper:

                                         

                                        http://www.chiefdelphi.com/media/papers/2216

                                         

                                        Another good link is from Gates:

                                         

                                        http://first.gatesprograms.com/assets/first/docs/pdfs/2013/first-tech-notes-2013.pdf

                                         

                                         

                                         

                                         

                                        From: SeattleRobotics@yahoogroups.com [mailto:SeattleRobotics@yahoogroups.com] On Behalf Of David Buckley
                                        Sent: Saturday, July 27, 2013 3:15 PM
                                        To: SeattleRobotics@yahoogroups.com
                                        Subject: Re: [SeattleRobotics] #25 chain and sprockets

                                         




                                        Hi Alan

                                        I tried to find max tension information for XL belts, I have it in a paper catalog somewhere, but where, I asked Google but all the suggested links had data for metric Tx belts.

                                        All I can say is that Liberator http://www.davidbuckley.net/DB/Liberator/Liberator.htm is driven by 72 teeth .375 XL belts, with 10 tooth pulleys on the gearboxes and 60 tooth pulleys on the wheels, hence I only have less than 5 teeth in engagement on the drive pulleys - not really good. The motors are the usual 38mm dia. Far East ones. Top speed of Liberator is about 3 ft/sec. I haven't rebuilt it since its shades of J5 'dissasembly'! but I have just driven it round the workshop powered by a 4A battery charger, it won't drive with me on it, the motors stall, but was fine with a 56lb weight. No belt troubles at all.

                                        DAvid

                                         

                                         

                                        ----- Original Message -----

                                        From: KM6VV

                                        Sent: Friday, July 26, 2013 10:30 PM

                                        Subject: Re: [SeattleRobotics] #25 chain and sprockets

                                         

                                         

                                        Hi David,

                                        I used leverage to try and deflect the chassis about the two shafts.
                                        Probably not a perfect test, I must agree. I couldn't measure with a
                                        dial caliper.

                                        The shock (stress) of a turn is what is apparently over-stressing the
                                        belts.

                                        Approximately 8 ft-lb of torque, 240 RPM, .375 XL belts. 3" C-C. 20
                                        tooth 1:1 pulleys, so 10 teeth of each engaged.

                                        I'm still open for a belt solution. I'm even looking harder to add a
                                        tensioner.

                                        Alan KM6VV

                                        On 7/26/2013 11:36 AM, David Buckley wrote:
                                        >
                                        >
                                        > Hi Alan
                                        > How long is a piece of string? Depends on how you cut it.
                                        > If your belt jumps teeth something is wrong, poor alignment, wimpy
                                        > chassis, putting in too much torque for the number of teeth engaged etc etc,
                                        > Same goes for chain.
                                        > It is shock loads which cause a jump and you won't be able to measure
                                        > the effects of them, you'll just notice the result.
                                        > How stiff is stiff? I remember somebody writing about most large hobby
                                        > lathes lathes and remarking that if a cylinder that was just out of
                                        > balance was held between centers and the tailstock centre was adjusted
                                        > so it was just pressing enough to stop the piece revolving under gravity
                                        > then with one finger pressing on the bed you could exert enough pressure
                                        > to flex the bed so the piece would rotate under gravity!
                                        > Now consider doing the same by wacking the bed with a big hammer and
                                        > sending a shockwave, would you be able to measure the deflection? In
                                        > either case, not without exotic equipment you wouldn't.
                                        > What is the input torque? what is the belt/chain speed? What is the belt
                                        > width? How many teeth are engaged on each wheel?
                                        > DAvid
                                        >




                                      • KM6VV
                                        Hi David, Yeah, a .375 XL belt should have been able to do the job. What torque and RPM does your motor have? What size and type of tires? DPA thinks my
                                        Message 19 of 29 , Jul 27, 2013
                                          Hi David,

                                          Yeah, a .375 XL belt should have been able to do the job.  What torque and RPM does your motor have?  What size and type of tires? 

                                          DPA thinks my tires and greater motor torque is the problem.  I fully agree.

                                          Alan KM6VV

                                          On 7/27/2013 3:14 PM, David Buckley wrote:
                                          Hi Alan
                                          I tried to find max tension information for XL belts, I have it in a paper catalog somewhere, but where, I asked Google but all the suggested links had data for metric Tx belts.
                                          All I can say is that Liberator http://www.davidbuckley.net/DB/Liberator/Liberator.htm is driven by 72 teeth .375 XL belts, with 10 tooth pulleys on the gearboxes and 60 tooth pulleys on the wheels, hence I only have less than 5 teeth in engagement on the drive pulleys - not really good. The motors are the usual 38mm dia. Far East ones. Top speed of Liberator is about 3 ft/sec. I haven't rebuilt it since its shades of J5 'dissasembly'! but I have just driven it round the workshop powered by a 4A battery charger, it won't drive with me on it, the motors stall, but was fine with a 56lb weight. No belt troubles at all.
                                          DAvid
                                           
                                           

                                        • David Buckley
                                          Hi Alan No idea of the torque of the motor, the wheels are 6 dia vinyl. Although I just tested the chassis from a 4A battery charger I seem to remember that
                                          Message 20 of 29 , Jul 28, 2013
                                            Hi Alan
                                            No idea of the torque of the motor, the wheels are 6" dia vinyl.
                                            Although I just tested the chassis from a 4A battery charger I seem to remember that running from a battery the chassis would carry me. 2A per motor on stall is very limiting.
                                            However even running one motor from the battery charger trying to stop the wheel by hand is risky, ie at 4A for the motor.
                                            Gearbox output rpm is about 720rpm free running which with  10t/60t gives 2rps at the wheels.
                                            Motors and gearboxes are from car polishers, I think they take about 8 amps at stall.
                                            I modified  the output of the gearbox so the shaft runs in dual ball bearings.
                                            The motor/gearboxes were what was available at the time, they are noisy and are current hogs.
                                            The motors I used on the Cycler robots are much better, give 40Kg.cm stall torque on 24v taking 2A and free run at 80rpm at maybe 250mA and the gearboxes are very quiet.
                                             
                                            From the Gates-HTD_first-tech-notes-2013.pdf which Kevin linked a HTD belt on 20t at 240rpm should handle about 801 oz in (58Kg.cm). Now XL can't handle the same torques but even if they can only handle 1/3 of the torque that is still about twice as much as your gearboxes put out. Hence set up properly your belts shouldn't jump teeth regardless of what tires you are using.
                                             
                                            The other link which Kevin gave to chiefdelphi.com had a somewhat suspect report on belts versus chains. If you look at the pictures there are no tensioners on the belts drives and on the chain drives there is a tensioner on one of the chains but not on the others. The axle mountings are welded in place so no adjustment possible there and the tensioner must be needed because of construction inaccuracies. I think the report is a case of playing all the right notes but not necessarily in the right order.
                                             
                                            DAvid
                                             
                                             
                                             
                                            ----- Original Message -----
                                            From: KM6VV
                                            Sent: Sunday, July 28, 2013 6:48 AM
                                            Subject: Re: [SeattleRobotics] #25 chain and sprockets

                                             

                                            Hi David,

                                            Yeah, a .375 XL belt should have been able to do the job.  What torque and RPM does your motor have?  What size and type of tires? 

                                            DPA thinks my tires and greater motor torque is the problem.  I fully agree.

                                            Alan KM6VV

                                            On 7/27/2013 3:14 PM, David Buckley wrote:
                                            Hi Alan
                                            I tried to find max tension information for XL belts, I have it in a paper catalog somewhere, but where, I asked Google but all the suggested links had data for metric Tx belts.
                                            All I can say is that Liberator http://www.davidbuckley.net/DB/Liberator/Liberator.htm is driven by 72 teeth .375 XL belts, with 10 tooth pulleys on the gearboxes and 60 tooth pulleys on the wheels, hence I only have less than 5 teeth in engagement on the drive pulleys - not really good. The motors are the usual 38mm dia. Far East ones. Top speed of Liberator is about 3 ft/sec. I haven't rebuilt it since its shades of J5 'dissasembly'! but I have just driven it round the workshop powered by a 4A battery charger, it won't drive with me on it, the motors stall, but was fine with a 56lb weight. No belt troubles at all.
                                            DAvid
                                             

                                             

                                          • David Buckley
                                            Kevin Great links, everyone new to belts and chains should read them. David ... From: Kevin Ross To: SeattleRobotics@yahoogroups.com Sent: Sunday, July 28,
                                            Message 21 of 29 , Jul 28, 2013
                                              Kevin
                                              Great links, everyone new to belts and chains should read them.
                                              David
                                               
                                              ----- Original Message -----
                                              Sent: Sunday, July 28, 2013 6:46 AM
                                              Subject: RE: [SeattleRobotics] #25 chain and sprockets

                                               

                                              There has been quite of bit of study on belt vs chain in the FIRST community. Here is one paper:

                                              http://www.chiefdelphi.com/media/papers/2216

                                              Another good link is from Gates:

                                              http://first.gatesprograms.com/assets/first/docs/pdfs/2013/first-tech-notes-2013.pdf

                                              From: SeattleRobotics@yahoogroups.com [mailto:SeattleRobotics@yahoogroups.com] On Behalf Of David Buckley
                                              Sent: Saturday, July 27, 2013 3:15 PM
                                              To: SeattleRobotics@yahoogroups.com
                                              Subject: Re: [SeattleRobotics] #25 chain and sprockets




                                              Hi Alan

                                              I tried to find max tension information for XL belts, I have it in a paper catalog somewhere, but where, I asked Google but all the suggested links had data for metric Tx belts.

                                              All I can say is that Liberator http://www.davidbuckley.net/DB/Liberator/Liberator.htm is driven by 72 teeth .375 XL belts, with 10 tooth pulleys on the gearboxes and 60 tooth pulleys on the wheels, hence I only have less than 5 teeth in engagement on the drive pulleys - not really good. The motors are the usual 38mm dia. Far East ones. Top speed of Liberator is about 3 ft/sec. I haven't rebuilt it since its shades of J5 'dissasembly'! but I have just driven it round the workshop powered by a 4A battery charger, it won't drive with me on it, the motors stall, but was fine with a 56lb weight. No belt troubles at all.

                                              DAvid

                                              ----- Original Message -----

                                              From: KM6VV

                                              Sent: Friday, July 26, 2013 10:30 PM

                                              Subject: Re: [SeattleRobotics] #25 chain and sprockets

                                               

                                              Hi David,

                                              I used leverage to try and deflect the chassis about the two shafts.
                                              Probably not a perfect test, I must agree. I couldn't measure with a
                                              dial caliper.

                                              The shock (stress) of a turn is what is apparently over-stressing the
                                              belts.

                                              Approximately 8 ft-lb of torque, 240 RPM, .375 XL belts. 3" C-C. 20
                                              tooth 1:1 pulleys, so 10 teeth of each engaged.

                                              I'm still open for a belt solution. I'm even looking harder to add a
                                              tensioner.

                                              Alan KM6VV

                                              On 7/26/2013 11:36 AM, David Buckley wrote:
                                              >
                                              >
                                              > Hi Alan
                                              > How long is a piece of string? Depends on how you cut it.
                                              > If your belt jumps teeth something is wrong, poor alignment, wimpy
                                              > chassis, putting in too much torque for the number of teeth engaged etc etc,
                                              > Same goes for chain.
                                              > It is shock loads which cause a jump and you won't be able to measure
                                              > the effects of them, you'll just notice the result.
                                              > How stiff is stiff? I remember somebody writing about most large hobby
                                              > lathes lathes and remarking that if a cylinder that was just out of
                                              > balance was held between centers and the tailstock centre was adjusted
                                              > so it was just pressing enough to stop the piece revolving under gravity
                                              > then with one finger pressing on the bed you could exert enough pressure
                                              > to flex the bed so the piece would rotate under gravity!
                                              > Now consider doing the same by wacking the bed with a big hammer and
                                              > sending a shockwave, would you be able to measure the deflection? In
                                              > either case, not without exotic equipment you wouldn't.
                                              > What is the input torque? what is the belt/chain speed? What is the belt
                                              > width? How many teeth are engaged on each wheel?
                                              > DAvid
                                              >




                                            • KM6VV
                                              Hi Kevin, Thanks for the PDF files. Yes, I could use the torque and HP limits for my belts as well. I m sure I looked at them some time ago before a picked
                                              Message 22 of 29 , Jul 28, 2013
                                                Hi Kevin,

                                                Thanks for the PDF files. Yes, I could use the torque and HP limits for
                                                my belts as well. I'm sure I looked at them some time ago before a
                                                picked my current belts. Maybe I am running them past their limits.

                                                On 7/27/2013 10:46 PM, Kevin Ross wrote:
                                                >
                                                >
                                                > There has been quite of bit of study on belt vs chain in the FIRST
                                                > community. Here is one paper:
                                                >
                                                > http://www.chiefdelphi.com/media/papers/2216
                                                >
                                                > Another good link is from Gates:
                                                >
                                                > http://first.gatesprograms.com/assets/first/docs/pdfs/2013/first-tech-notes-2013.pdf
                                                >
                                                >
                                              • David Buckley
                                                We have just been through the limits for your belts, even if they are only 1/3 as strong as HTD that is still twice as strong as your motors!!!!!!!!!!! ...
                                                Message 23 of 29 , Jul 28, 2013
                                                  We have just been through the limits for your belts, even if they are only 1/3 as strong as HTD that is still twice as strong as your motors!!!!!!!!!!!
                                                   
                                                  ----- Original Message -----
                                                  From: KM6VV
                                                  Sent: Monday, July 29, 2013 12:39 AM
                                                  Subject: Re: [SeattleRobotics] #25 chain and sprockets

                                                   

                                                  Hi Kevin,

                                                  Thanks for the PDF files. Yes, I could use the torque and HP limits for
                                                  my belts as well. I'm sure I looked at them some time ago before a
                                                  picked my current belts. Maybe I am running them past their limits.

                                                  On 7/27/2013 10:46 PM, Kevin Ross wrote:
                                                  >
                                                  >
                                                  > There has been quite of bit of study on belt vs chain in the FIRST
                                                  > community. Here is one paper:
                                                  >
                                                  > http://www.chiefdelphi.com/media/papers/2216
                                                  >
                                                  > Another good link is from Gates:
                                                  >
                                                  > http://first.gatesprograms.com/assets/first/docs/pdfs/2013/first-tech-notes-2013.pdf
                                                  >
                                                  >

                                                • KM6VV
                                                  Yeah, the XL375 belts should be able to handle .1 HP at 240 RPM. My motors aren t that powerful! Back to the drawing board. Alan KM6VV
                                                  Message 24 of 29 , Jul 28, 2013
                                                    Yeah, the XL375 belts should be able to handle .1 HP at 240 RPM. My
                                                    motors aren't that powerful!

                                                    Back to the drawing board.

                                                    Alan KM6VV

                                                    On 7/28/2013 6:17 PM, David Buckley wrote:
                                                    >
                                                    >
                                                    > We have just been through the limits for your belts, even if they are
                                                    > only 1/3 as strong as HTD that is still twice as strong as your
                                                    > motors!!!!!!!!!!!
                                                    >
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