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Mecanum Wheels Insights — Parallax Forums

Mecanum Wheels Insights

ercoerco Posts: 20,259
edited 2012-04-17 12:58 in General Discussion
Rich's too-cool Kepler robot at Expo has me thinking about getting back on the mecanum robot train. I've had these Vex wheels for a while now. The rollers are at 45 degrees. Is there any advantage to a chassis aspect ratio that puts the wheels' contact points in a square instead of a rectangle? Seems like in some maneuver (pure spin or traverse) that may reduce scrubbing. Or perhaps mixing wheel speeds properly takes care of all that. So much to learn about using these wheels properly. Rich & Duane?

Comments

  • Duane DegnDuane Degn Posts: 10,588
    edited 2012-04-17 10:46
    The Rover 5 arrangement isn't quite square. The center of the wheels are about 8.5" apart side to side and about 6.5" front to back.

    Rich's robot looks like the wheels have more distance front to back than side to side.

    I wondered the same thing about a square aspect ratio. I haven't figured out any reason why a square arrangement of wheels would offer an advantage other than uniform stability in moving the various directions. I'd only think this would matter if you have a very top heavy robot.

    The power of Rich's motors lets his robot work fine without encoders. The weaker motors of the Rover 5 need the encoders to let the robot know if the wheels are actually moving or not.

    By the way, there was a bug in the program used by the robot when making the last videos posted of my Mecanum robot. The bug prevented accurate diagonal movement. I've fixed the bug but I didn't make a new video of the bug free movement.

    I've been switching out the board on my Mecanum robot and using a different radio control so I don't have it running right now. I'll make sure and post some new video once it's up and running again. I plan to add to the Mecanum robot the same record feature I added to my PropBOE-Bot.
  • W9GFOW9GFO Posts: 4,010
    edited 2012-04-17 12:58
    I've wondered the same thing. I came to the conclusion that it does not matter. After all, Airtrax makes their forklifts non square.

    The front and rear axles can be any distance apart and it will still strafe the same. The further they are apart the slower will be the yaw (turning).

    If you need the vehicle to drive a very precise path then you will need to account for the distance between the axles and the width of the wheel track in your program.
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