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Anyone done the 360deg servo mod?

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  • mikesuthy
    Hi guys, I looking for some feedback from anyone who has used modified servos (continuous 360deg operation) as the base for a wheeled robot. I considered
    Message 1 of 13 , Aug 1, 2007
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      Hi guys,

      I looking for some feedback from anyone who has used modified servos
      (continuous 360deg operation) as the base for a wheeled robot.

      I considered cordless drill motors but decided against them due to noise
      / weight / and power requirements.

      So now looking at modified servos ... actual HS-425BB ... dual ball
      bearings ... medium torque ... and relatively cheap $30AU.

      Anyone had experience with servos used like this?

      What kind of lifetime do you get?

      How noisy etc?

      Mike.



      [Non-text portions of this message have been removed]
    • Ed Okerson
      I have used these on beginner mini-sumo robots with much success. So far I have never replaced one, and the robot was built about 3 or 4 years ago. They
      Message 2 of 13 , Aug 1, 2007
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        I have used these on beginner mini-sumo robots with much success. So far
        I have never replaced one, and the robot was built about 3 or 4 years ago.
        They aren't very loud, and have decent torque, just don't expect a lot of
        speed. I did not use the nice ball bearing ones either, so yours should
        be even quieter and last longer, as long as you keep your robot small
        enough.

        Ed Okerson

        >
        > Hi guys,
        >
        > I looking for some feedback from anyone who has used modified servos
        > (continuous 360deg operation) as the base for a wheeled robot.
        >
        > I considered cordless drill motors but decided against them due to noise
        > / weight / and power requirements.
        >
        > So now looking at modified servos ... actual HS-425BB ... dual ball
        > bearings ... medium torque ... and relatively cheap $30AU.
        >
        > Anyone had experience with servos used like this?
        >
        > What kind of lifetime do you get?
        >
        > How noisy etc?
        >
        > Mike.
        >
        >
        >
        > [Non-text portions of this message have been removed]
        >
        >
        >
        > Visit the SRS Website at http://www.seattlerobotics.org
        > Yahoo! Groups Links
        >
        >
        >
        >
      • Ray Xu
        I’m not sure if this site will help you… HYPERLINK http://servocity.com/html/rotation_modification_difficul.html http://servoc
        Message 3 of 13 , Aug 1, 2007
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          I�m not sure if this site will help you� HYPERLINK
          "http://servocity.com/html/rotation_modification_difficul.html"http://servoc
          ity.com/html/rotation_modification_difficul.html



          ______________

          Ray Xu

          Electric/Robotics Engineer

          HYPERLINK "mailto:rayxu@..."rayxu@...



          _____

          From: SeattleRobotics@yahoogroups.com
          [mailto:SeattleRobotics@yahoogroups.com] On Behalf Of mikesuthy
          Sent: Wednesday, August 01, 2007 4:55 AM
          To: SeattleRobotics@yahoogroups.com
          Subject: [SeattleRobotics] Anyone done the 360deg servo mod?





          Hi guys,

          I looking for some feedback from anyone who has used modified servos
          (continuous 360deg operation) as the base for a wheeled robot.

          I considered cordless drill motors but decided against them due to noise
          / weight / and power requirements.

          So now looking at modified servos ... actual HS-425BB ... dual ball
          bearings ... medium torque ... and relatively cheap $30AU.

          Anyone had experience with servos used like this?

          What kind of lifetime do you get?

          How noisy etc?

          Mike.

          [Non-text portions of this message have been removed]




          No virus found in this incoming message.
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          5:26 PM



          No virus found in this outgoing message.
          Checked by AVG Free Edition.
          Version: 7.5.476 / Virus Database: 269.11.0/929 - Release Date: 7/31/2007
          5:26 PM



          [Non-text portions of this message have been removed]
        • Rob Purdy
          I used them in some of my ant weight bots( 1#). worked great. Gotta be careful though not all servos can be hacked because some have only patially cut gears
          Message 4 of 13 , Aug 1, 2007
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            I used them in some of my ant weight bots( 1#). worked great. Gotta be careful though not all servos can be hacked because some have only patially cut gears so it can't do a 360 deg. rotation. Depending on your application there are also some some small gearmotors that might work for you too. Lynx motion has some. What size bot is this for?

            Rob


            To: SeattleRobotics@yahoogroups.comFrom: mikesuthy@...: Wed, 1 Aug 2007 09:55:24 +0000Subject: [SeattleRobotics] Anyone done the 360deg servo mod?




            Hi guys,I looking for some feedback from anyone who has used modified servos(continuous 360deg operation) as the base for a wheeled robot.I considered cordless drill motors but decided against them due to noise/ weight / and power requirements.So now looking at modified servos ... actual HS-425BB ... dual ballbearings ... medium torque ... and relatively cheap $30AU.Anyone had experience with servos used like this?What kind of lifetime do you get?How noisy etc?Mike.[Non-text portions of this message have been removed]



            [Non-text portions of this message have been removed]
          • Jonathan Peakall
            I have used them on several bots. As others have said, they aren t fast, but they work well enough. Parallax sells pre-modified servos. I like them because
            Message 5 of 13 , Aug 1, 2007
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              I have used them on several 'bots. As others have said, they aren't fast,
              but they work well enough. Parallax sells pre-modified servos. I like them
              because there is a small hole which gives access to the pot using a
              screwdriver. You can use this pot to adjust the "zero" point of the servos.
              Meaning that you send a train of 1500uS pulses to the servo and use the pot
              to adjust until the servo stops moving. This way you can "sync" both servos
              to stop using the same pulse length.

              I find that to get a 'bot using servos to run as straight as possible, you
              need to tweak the length of pulses, as all servos I have encountered are a
              little differnent. On my current 'bot, I made a stand with a tachometer for
              both servos, using an IR led and photo transistor. My wheels have holes in
              them already, so it is easy ot measure the actual speed of the wheels.

              Jonathan

              ----------------------------------------------------------------------
              Some people are like a Slinky .. not really good for anything,
              but you still can't help but smile when you shove them down the stairs.
              ----------------------------------------------------------------------
              ----- Original Message -----
              From: "mikesuthy" <mikesuthy@...>
              To: <SeattleRobotics@yahoogroups.com>
              Sent: Wednesday, August 01, 2007 1:55 AM
              Subject: [SeattleRobotics] Anyone done the 360deg servo mod?


              > Hi guys,
              >
              > I looking for some feedback from anyone who has used modified servos
              > (continuous 360deg operation) as the base for a wheeled robot.
              >
              > I considered cordless drill motors but decided against them due to noise
              > / weight / and power requirements.
              >
              > So now looking at modified servos ... actual HS-425BB ... dual ball
              > bearings ... medium torque ... and relatively cheap $30AU.
              >
              > Anyone had experience with servos used like this?
              >
              > What kind of lifetime do you get?
              >
              > How noisy etc?
              >
              > Mike.
              >
              > [Non-text portions of this message have been removed]
              >
            • mikesuthy
              Excellent feedback/info ... agreed that it should be better with dual bearings ... interesting though that the next servo up (HS-475) uses Karbonite gears but
              Message 6 of 13 , Aug 1, 2007
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                Excellent feedback/info ... agreed that it should be better with dual
                bearings ... interesting though that the next servo up (HS-475) uses
                Karbonite gears but only has one ball bearing.

                Mike.


                --- In SeattleRobotics@yahoogroups.com, "Ed Okerson" <ed@...> wrote:
                >
                > I have used these on beginner mini-sumo robots with much success. So
                far
                > I have never replaced one, and the robot was built about 3 or 4 years
                ago.
                > They aren't very loud, and have decent torque, just don't expect a
                lot of
                > speed. I did not use the nice ball bearing ones either, so yours
                should
                > be even quieter and last longer, as long as you keep your robot small
                > enough.
                >
                > Ed Okerson
              • mikesuthy
                Thanks ... yep, it is a good site. Mike. ... //servoc
                Message 7 of 13 , Aug 1, 2007
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                  Thanks ... yep, it is a good site.

                  Mike.


                  --- In SeattleRobotics@yahoogroups.com, "Ray Xu" <rayxu@...> wrote:
                  >
                  > I'm not sure if this site will help you… HYPERLINK
                  > "http://servocity.com/html/rotation_modification_difficul.html"http:
                  //servoc
                  > ity.com/html/rotation_modification_difficul.html
                  >
                  >
                  >
                  > ______________
                  >
                  > Ray Xu
                  >
                  > Electric/Robotics Engineer
                  >
                  > HYPERLINK "mailto:rayxu@..."rayxu@...
                • mikesuthy
                  I am planning to model it off the Octobot: http://www.robotstore.com/store/product.asp?pid=419&catid=1549 It will be running around for sometime ... Eventually
                  Message 8 of 13 , Aug 1, 2007
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                    I am planning to model it off the Octobot:
                    http://www.robotstore.com/store/product.asp?pid=419&catid=1549

                    It will be running around for sometime ...
                    Eventually with a wireless link back to a pc for mapping inteligence,
                    logging, control, etc.

                    Mike.


                    --- In SeattleRobotics@yahoogroups.com, Rob Purdy <kb7wnz@...> wrote:
                    >
                    >
                    > I used them in some of my ant weight bots( 1#). worked great.
                    Gotta be careful though not all servos can be hacked because some
                    have only patially cut gears so it can't do a 360 deg. rotation.
                    Depending on your application there are also some some small
                    gearmotors that might work for you too. Lynx motion has some. What
                    size bot is this for?
                    >
                    > Rob
                  • mikesuthy
                    Thanks for the hint ... the tacho idea is good ... Do you find the difference between the two servos can be taken up just with an offset or does it vary with
                    Message 9 of 13 , Aug 1, 2007
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                      Thanks for the hint ... the tacho idea is good ... Do you find the
                      difference between the two servos can be taken up just with an offset
                      or does it vary with the actual speed (and thus need a slope
                      adjustment also)?

                      Mike.

                      --- In SeattleRobotics@yahoogroups.com, "Jonathan Peakall"
                      <jpeakall@...> wrote:
                      >
                      > I have used them on several 'bots. As others have said, they aren't
                      fast,
                      > but they work well enough. Parallax sells pre-modified servos. I
                      like them
                      > because there is a small hole which gives access to the pot using a
                      > screwdriver. You can use this pot to adjust the "zero" point of the
                      servos.
                      > Meaning that you send a train of 1500uS pulses to the servo and use
                      the pot
                      > to adjust until the servo stops moving. This way you can "sync"
                      both servos
                      > to stop using the same pulse length.
                      >
                      > I find that to get a 'bot using servos to run as straight as
                      possible, you
                      > need to tweak the length of pulses, as all servos I have
                      encountered are a
                      > little differnent. On my current 'bot, I made a stand with a
                      tachometer for
                      > both servos, using an IR led and photo transistor. My wheels have
                      holes in
                      > them already, so it is easy ot measure the actual speed of the
                      wheels.
                      >
                      > Jonathan
                    • Ed Okerson
                      The problem with this approach is that the center point will change with battery voltage. A better solution would be to use encoders on the wheels like these:
                      Message 10 of 13 , Aug 1, 2007
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                        The problem with this approach is that the center point will change with
                        battery voltage. A better solution would be to use encoders on the wheels
                        like these:

                        http://www.acroname.com/robotics/parts/R238-WW01-KIT.html

                        With encoders you can measure the actual wheel velocity and adjust the
                        pulse width to ensure it is at the speed you want. If you don't want to
                        do the code yourself to monitor the encoders you can use the companion
                        controller:

                        http://www.acroname.com/robotics/parts/R279-WC-132.html

                        Ed Okerson

                        >
                        > Thanks for the hint ... the tacho idea is good ... Do you find the
                        > difference between the two servos can be taken up just with an offset
                        > or does it vary with the actual speed (and thus need a slope
                        > adjustment also)?
                        >
                        > Mike.
                        >
                        > --- In SeattleRobotics@yahoogroups.com, "Jonathan Peakall"
                        > <jpeakall@...> wrote:
                        >>
                        >> I have used them on several 'bots. As others have said, they aren't
                        > fast,
                        >> but they work well enough. Parallax sells pre-modified servos. I
                        > like them
                        >> because there is a small hole which gives access to the pot using a
                        >> screwdriver. You can use this pot to adjust the "zero" point of the
                        > servos.
                        >> Meaning that you send a train of 1500uS pulses to the servo and use
                        > the pot
                        >> to adjust until the servo stops moving. This way you can "sync"
                        > both servos
                        >> to stop using the same pulse length.
                        >>
                        >> I find that to get a 'bot using servos to run as straight as
                        > possible, you
                        >> need to tweak the length of pulses, as all servos I have
                        > encountered are a
                        >> little differnent. On my current 'bot, I made a stand with a
                        > tachometer for
                        >> both servos, using an IR led and photo transistor. My wheels have
                        > holes in
                        >> them already, so it is easy ot measure the actual speed of the
                        > wheels.
                        >>
                        >> Jonathan
                        >
                        >
                        >
                        >
                        > Visit the SRS Website at http://www.seattlerobotics.org
                        > Yahoo! Groups Links
                        >
                        >
                        >
                        >
                      • Jonathan Peakall
                        I run the servos on regulated power, so that never changes. I have need for good dead reckoning with this bot, so the reduced speed is worth the consistency.
                        Message 11 of 13 , Aug 1, 2007
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                          I run the servos on regulated power, so that never changes. I have need for
                          good dead reckoning with this 'bot, so the reduced speed is worth the
                          consistency. Encoders would be nice though. I find that adjusting the servos
                          to the zero point, then using my tach stand to characterize the servos is
                          enough. Offset is accurate enough for me, but a greater degree could be
                          achieved with a slope factor.



                          ----------------------------------------------------------------------
                          Some people are like a Slinky .. not really good for anything,
                          but you still can't help but smile when you shove them down the stairs.
                          ----------------------------------------------------------------------
                          ----- Original Message -----
                          From: "Ed Okerson" <ed@...>
                          To: <SeattleRobotics@yahoogroups.com>
                          Sent: Wednesday, August 01, 2007 7:48 PM
                          Subject: Re: [SeattleRobotics] Anyone done the 360deg servo mod?


                          > The problem with this approach is that the center point will change with
                          > battery voltage. A better solution would be to use encoders on the wheels
                          > like these:
                          >
                          > http://www.acroname.com/robotics/parts/R238-WW01-KIT.html
                          >
                          > With encoders you can measure the actual wheel velocity and adjust the
                          > pulse width to ensure it is at the speed you want. If you don't want to
                          > do the code yourself to monitor the encoders you can use the companion
                          > controller:
                          >
                          > http://www.acroname.com/robotics/parts/R279-WC-132.html
                          >
                          > Ed Okerson
                          >
                          >>
                          >> Thanks for the hint ... the tacho idea is good ... Do you find the
                          >> difference between the two servos can be taken up just with an offset
                          >> or does it vary with the actual speed (and thus need a slope
                          >> adjustment also)?
                          >>
                          >> Mike.
                          >>
                          >> --- In SeattleRobotics@yahoogroups.com, "Jonathan Peakall"
                          >> <jpeakall@...> wrote:
                          >>>
                          >>> I have used them on several 'bots. As others have said, they aren't
                          >> fast,
                          >>> but they work well enough. Parallax sells pre-modified servos. I
                          >> like them
                          >>> because there is a small hole which gives access to the pot using a
                          >>> screwdriver. You can use this pot to adjust the "zero" point of the
                          >> servos.
                          >>> Meaning that you send a train of 1500uS pulses to the servo and use
                          >> the pot
                          >>> to adjust until the servo stops moving. This way you can "sync"
                          >> both servos
                          >>> to stop using the same pulse length.
                          >>>
                          >>> I find that to get a 'bot using servos to run as straight as
                          >> possible, you
                          >>> need to tweak the length of pulses, as all servos I have
                          >> encountered are a
                          >>> little differnent. On my current 'bot, I made a stand with a
                          >> tachometer for
                          >>> both servos, using an IR led and photo transistor. My wheels have
                          >> holes in
                          >>> them already, so it is easy ot measure the actual speed of the
                          >> wheels.
                          >>>
                          >>> Jonathan
                          >>
                          >>
                          >>
                          >>
                          >> Visit the SRS Website at http://www.seattlerobotics.org
                          >> Yahoo! Groups Links
                          >>
                          >>
                          >>
                          >>
                          >
                        • mikesuthy
                          Both ways are valid ... a regulated supply may eat some battery power on the higher motor currents than just having cpu/logic circuitry regulated ... but then
                          Message 12 of 13 , Aug 2, 2007
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                            Both ways are valid ... a regulated supply may eat some battery power
                            on the higher motor currents than just having cpu/logic circuitry
                            regulated ... but then all wheels will have some slip pending on
                            acceleration, grip, floor type, etc.

                            My main drive is AI ... thus rather than dead reckoning I am thinking
                            of using/identifying landmarks (IR beacons) etc ... to let the bot
                            self locate .... sounds like fun!

                            Mike.


                            --- In SeattleRobotics@yahoogroups.com, "Jonathan Peakall"
                            <jpeakall@...> wrote:
                            >
                            > I run the servos on regulated power, so that never changes. I have
                            need for
                            > good dead reckoning with this 'bot, so the reduced speed is worth
                            the
                            > consistency. Encoders would be nice though. I find that adjusting
                            the servos
                            > to the zero point, then using my tach stand to characterize the
                            servos is
                            > enough. Offset is accurate enough for me, but a greater degree
                            could be
                            > achieved with a slope factor.
                            >
                            >
                            >
                            > --------------------------------------------------------------------
                            --
                            > Some people are like a Slinky .. not really good for anything,
                            > but you still can't help but smile when you shove them down the
                            stairs.
                            > --------------------------------------------------------------------
                            --
                          • mikesuthy
                            Hi ya, I bought 2 of the HS-425BB servos on the weekend ... just finished modifying them ... very easy as the website below suggests ... grinding off a bit of
                            Message 13 of 13 , Aug 6, 2007
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                              Hi ya,

                              I bought 2 of the HS-425BB servos on the weekend ... just finished
                              modifying them ... very easy as the website below suggests ... grinding
                              off a bit of plastic on one of the gears (recommend Dremel tool or
                              equalivant) ... made the job alot easier .... then removed the pot ...
                              one screw ... and replaced it with a 5k multiturn trim pot ... for
                              calibrating the zero point to 1.5ms .... in theory at least.

                              Now to write some test firmware ....

                              Mike.


                              --- In SeattleRobotics@yahoogroups.com, "Ray Xu" <rayxu@...> wrote:
                              >
                              > I'm not sure if this site will help you… HYPERLINK
                              > "http://servocity.com/html/rotation_modification_difficul.html"http://
                              servoc
                              > ity.com/html/rotation_modification_difficul.html
                              >
                              >
                              >
                              > ______________
                              >
                              > Ray Xu
                              >
                              > Electric/Robotics Engineer
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