[DonRotolo]

I think you might be asking the wrong question. Instead, it seems like you want to know "What's the maximum torque I can expect to have to transmit to the wheels?" - am I correct?

If so, the amount of frictional force the wheel can see is important, but if we assume the wheel is never going to slide - like a gear on a rack - then it becomes a question of how much torque you can generate with your motor(s), and considering your gear ratios. This simplifies the problem, and makes knowing the wheel configuration irrelevant.

If I'm wrong - I frequently am - please also remember to think about shock loads, which can be easily 2 to 4 times the regular load. Then a factor of safety, at least 2. Then remember to de-rate all the components that are not perfect shapes - for example, a hole or keyway in a shaft has a known and calculable effect upon it's strength and load capacity.

Another thing to consider would be to make a "fuse" - a part that will be the first to break, if necessary, but is easy to replace in a big hurry*, and of which you have plenty of spares. Like a shaft with a purpose-cut weakening groove.

Sounds like a very interesting project, good luck.

Don


*5 minutes is far too long. Ask Team 11 about their experience at Monty Madness, where they changed out a broken shaft that was about 30 minutes inside their robot in an absolutely amazing 7 minutes (I timed it). Unfortunately, the match started after 5 minutes, and so they couldn't get onto the field in time.