Quote:
Originally Posted by GeeTwo
With omnis, I would agree with you. However, mecanums generate as much side force as forward/reverse force by design even when the robot is driving directly forward. With octanum, I'd consider the traction wheels as having less sideways loading under most conditions, probably only exceeding the peak mecanum side load when being T-boned. And in that case, the solution is to switch to mecanum and strafe your way out of the t-bone, or at worst into a legal pin that (under most years' rules) is time limited.
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First things first, if your solution to a design problem is to drive around the failure mode, that's just plain bad design. You should never have a robot designed in a mechanically weak manner just because the driver "shouldn't" have the robot in that mode when you expect damage. You can't bet your drivetrain on perfect play.
The strafing force a mecanum wheel puts on the robot is very different than the force of being pushed to the side in traction mode. When being pushed in traction mode, the full weight of the robot resists motion until static friction is broken. When strafing in omni / mecanum mode, there is no such resistance - the wheels are rotating and the rollers are allowing the motion to happen.
Finally, while you are technically right that mecanum wheels exert as much force in the sideways direction as they do in the forward / back direction, it is worth noting that this is ~70% of the peak force a traction wheel of the same gearing would put in the forward direction, assuming the same CoF for both wheels (which is also not true, all commercially available mecanum wheels have a lower effective CoF than most high traction wheels).
It is simply more robust to put the omni wheel on the pivot and the traciton wheel at the axle.