Quote:
Originally Posted by RobotsThatWork
You mean the strafing module, right?
We took inspiration from 148's strafing module (from their 2014 robot, Vader). The module itself spins on the axle that's powered by the CIM. So when the CIM is powered, the module spins down until a wheel contacts the wheel. The CIM will exert enough force to push down the module enough to have the ground exert a normal force on the wheel (which is what traction is dependent on) before the torque of the CIM spins the omniwheel.
At least that's how I understood it while designing this. We haven't actually done more serious math outside of a simple free body diagram. If someone from 148 or anyone with experience with this type of strafing module could explain more/clarify/prove me wrong, that would be awesome.
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My understanding of 148's strafing module design is that it works even better than that. The wheel in contact with the ground rotates in the opposite direction as the module itself tips, meaning that the wheel is basically driving itself into the ground. For an intuition of this, consider the boundary cases (module tilt angles close to 0 degrees and close to 90 degrees). While the omni wheel would just skip along the ground if it made contact while the module was barely tilted, at close to 90 degrees it would actually be able to lift the robot up, supporting most of its weight. Obviously one would want to design for a tilt angle somewhere between these extremes, but they illustrate what's going on very well. The great thing about this design is that the normal force on the strafing wheel varies drastically depending on what the robot is doing, so you only have high normal force on the strafing wheel when high torque is applied to it.
For those more knowledgeable than I: Is my understanding correct?
Edit: As far as I can tell, it would follow from this understanding that, in theory, a tilt angle from horizontal of greater than the inverse tangent of the wheel-to-ground coefficient of friction would guarantee that the wheel wouldn't slip (Well, until the point at which the linear relationship between torque and normal force ends because there simply isn't more weight available for the strafe wheel to support). However, in reality, friction is also a fickle beast and is highly dependent on the exact conditions of the interaction at any given time.
In the absence of a valid game hint, the natives in CD tend to get restless and resort to this sort of pun-ishment of one another. - David Brinza [more] 
15-11-2015, 22:01
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