Octagonal WCD

[Jared]

Originally Posted by Ty Tremblay

It was quick and dirty, but here's what I did:

A worst case scenario of running into a robot at full speed with a high COG could lift the back 4 wheels off the ground. I chose this as starting point. Assuming a full weight robot with bumpers and a battery (~150lbs), that means we've got about 75lbs on each of the two wheels still contacting the ground.
[/url]

75 lbs is a very conservative worst case. If I were doing a quick simulation, I would put something like 300 pounds and aim for a factor of safety of around 2. Driving over a bump like 2012/2010 may see the entire weight of the robot drop on one wheel. You may see more than 150 lbs of load if your robot falls or roughly tips down onto that wheel. In 2013, we bent an axle when we smashed a wheel into the pyramid corner. I'd also be worried about the hex bearing's inner race in this situation.

SW simulation express isn't the right tool for this. IIRC, it doesn't support bearing fixtures, so you can't simulate torque on the shaft and the load of the robot. Also, it doesn't take into account the effect of strain rate (how quickly the part is being loaded), which will reduce the tensile strength of the material significantly.

If you're concerned that your cantilevered wheels are too weak, you can just add an additional plate on the inside with another bearing. It's likely worth the extra .5 pounds, rather than having the panic of replacing a wheel/bearing between elimination rounds.