paper: Analysis of “a torque-actuated module” used for strafing in an H-drive.

[RyanCahoon]

Originally Posted by GeeTwo

By pivot axle, do you mean the drive axle (coming from the motor)?

Yes, sorry for the confusion.

Originally Posted by GeeTwo

This should be the same magnitude and direction as B, with slight adjustments for supporting the weight of the module and wheels. Because of the constraint of the drive bearings, any linear force (not torque, but that's assumed zero because of the bearings) applied to the module at these bearings can only act on the wheel in the direction shown for B.

Imagine that you have a beam supported on both ends, and you apply a downward force in the middle.



There are reaction forces on both ends of the beam, and the sum of all three force must be 0. I see this as the same case here: the beam is the module, one end is supported by the wheel bearings (and transitively by the wheel on the carpet), the other end is supported by the the bearings on the drive axle.

I think you have to separate the two, because only the part of the force that's being experienced at the wheel is ending up as normal force.

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I'm not sure if this is the correct analysis, but as a general point, I'm bothered that your derivation doesn't incorporate the distance between the drive axle and the wheel axle. If you increase this distance, then the torque load on the motor imposed by turning the wheel won't increase, but the torque load imposed by the normal force does. At some point, turning the wheel will be much easier for the motor than applying normal force, so the wheel will spin with very little normal force applied, causing the wheel to slip and the robot won't move.