Quote:
Originally Posted by JesseK
Scaling up to large-scale applications (FRC, heavy-lift mobility, etc) has some foreseeable issues. The first and foremost is the noticeable skidding of the hemisphere as the robot changes directions. Even changing the speed/torque by rotating the gimbal causes localized skidding on each individual hemisphere due to the differences in radii that create the different "gear ratios". I don't know of every way to reduce the effect, but it implies that each individual application will have to account for the effect. The easiest way to account for it seems to be finding the best balance of traction & intentional slip. Another way could be to limit the rotation speed of the gimbal.
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Absolutely true. I wasn't questioning the notion of there being issues with scalability of the concept, but rather that the statement was made without even a modest attempt at calculations to prove his (very different) reasoning.
But building off of what you said, I'm curious as to how this would behave with softer tread materials on a soft surface (as likely to be the application in FRC). The deformation of both the tread and carpet under the weight of your robot would result in a contact patch larger than a single point (obviously). Because of that, different points in contact with the carpet are going to be moving at different speeds (and with different torques), meaning that there's going to be some slip in the drive of the wheel on the carpet. Depending on the radius of the hemisphere, the difference in speeds from one end of the contact patch to the other may or may not be marginal. It's possible that portions of your contact patch might interact with the carpet at closer to their coefficient of kinetic friction than their static friction.
In order to mitigate that, larger hemispheres could be utilized. But then the size and range of motion of your gimbal must increase accordingly, as well. Pretty soon that's eating up a considerable portion of your volume, especially compared to traditional drive systems.