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Andymark Mecanum Wheels Don't Work!

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  • Andymark Mecanum Wheels Don't Work!

    We purchased the 4" Standard mecanum wheels about 2 months ago. Our robot is 15 pounds. We tried gears, sprockets, and direct drive with different ratios. The sideways movement has not worked. Even after loosening and tightening the rollers. Typically it goes diagonally or spins in a very large turn circle. Our wheels and in an X formation. The program assigns each strafe to a different button. We did get it to work at a certain time but since then it hasn't worked. We've tried to eliminate every variable including the things we changed since they worked. We use Andymark 40 motors. Please help us because we've spent over a month on these wheels and need to get our robot ready for competition. Thanks for your help.

  • #2
    Mecanum wheels are weight sensitive, you need to have the same weight on each wheel to minimize bad behavior. The more expensive wheels work better (less sensitive to weight). My team successfully used the wheels you have for a couple of years in autonomous, but use the gyro to not rotate and a distance sensor to stop the diagonal movement. They have also done code where in teleop when strafing they use the gyro to stop the rotation. They have to manually adjust for the diagonal in teleop.

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    • #3
      The "common wisdom" is that the Andymark Standard Mecanum aren't that good but the HD Mecanum wheels are good. I have only used the HD version with my team so I am just repeating what I've read here or reddit.

      The mecanum wheels are weight sensitive so you need all 4 to have the same weight. If you are getting a "large turn circle" when straffing then you are close and I would call it good enough.

      A 15lb bot seems kind of light to me for mecanum wheels - you might do an experiment where you put more weight on - bring it up to 25 or 30 lbs and see if that helps. Mecanum works because of the friction and slipping occurring in the right way. So not enough (or too much) weight may cause problems. Make sure of course to balance the weight distribution. We have also see where there is a mechanical drag - say one chain has more friction than the others - that will cause a lot of problems with straffing smoothly.

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      • #4
        Our team is using 6 inches HD mecanum wheels. This is our first year using mecanum and we have had no complaints so far. The link below shows the robot in action (please see the first 30 seconds, the red alliance robot 10357 facing the camera) where it does fair amount of maneuvering involving, strafing, turning, forward and reverse during its autonomous routine - https://www.youtube.com/watch?v=meE3-Bwp0Gs
        As others have said, heavier is better. Weight of our 4 wheels itself is 10 pounds ! Few other things that we learnt - encoders are your best friend and watch your speed .

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