Quote:
Originally Posted by craigboez
For wheels mounted in the correct configuration, I don't think that it's possible to rotate a bot about center if they are mounted in a square configuration. When summing moments about center they all cancel out when length = width. Only when you have a rectangular bot, where length != width, can you create one pair of moments not offset by the other pair.
This seems to be unconventional thinking, and I can't seem to find anywhere on CD that this has ever been stated. Am I missing something? Would anyone be willing to provide a vector analysis of a square 'bot rotating about center?
(It can be done using four identical wheels, but thats not what I'm after. Two "RH" and two "LH" wheels, mounted in an "O" configuration, cannot seem to create a moment about the center of a square bot).
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Consider a bot with 4 mecanum wheels mounted so that they have the "X" configuration when viewed from the top. Now drive both wheels on the left side forward, and both wheels on the right side backward, all at the same speed.
The front left wheel will be pulling forward and to the right. The rear left wheel will be pulling forward and to the left. The front right wheel will be pulling backward and to the right. The rear right wheel will be pulling backward and to the left. So, all 8 force vectors are pulling CLOCKWISE. The vectors do not cancel, they add. So the bot spins clockwise.
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