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Re: #25 chain and sprockets

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  • 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 1 of 14 , Jul 27, 2013
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      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
      >
      >
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