pic: Wheel 4 V1.2

[Brandon Holley]

Originally Posted by Raul

OK, be careful with this. If the wheels will be used in a swerve/crab application on carpet and your wheels will have a decent CoF, the spokes need to be beefier than you think.

Just to reiterate what Raul is saying here...

If you are using solidworks or inventor you have built in tools that allow you to do some quick FEA on your wheel. Instead of guessing at something being too beefy or not beefy enough, why not do some analysis?

For starters when it comes to wheels I do this:
Knowing that a wheel can only exert a certain amount of force on the ground and vice versa we can use the coefficient of friction with the wheel and ground as a starting point. The wheel will be under the most load when it is being pushed sideways along the carpet RIGHT before it loses traction with the ground. So estimate the weight of the robot and determine the normal force on one wheel. Then you will be able to determine the frictional force acting on your wheel. Use this as a baseline (ie safety factor = 1). You can then put this exact force on your wheel in Solidworks Simulation (or some other FEA software). Support the wheel right where the shaft would be and start your analysis. You are definitely going to want to bump the safety factor for a FIRST robot, and especially since this is just a rough calculation. To do that just multiply your frictional force by 3, 4 or 5 or whatever you want. Look at your stresses, compare them to the yield stress of the material you are using. Look at your deflections, make sure they seem reasonable (ie not half an inch or something like that, you want to be in the couple of thousandths range). Look at your stress concentrations and see if there is some simple geometry fixes you may be able to incorporate to alleviate them.

Analysis is a very powerful tool that starts taking things from a guessing game to concrete answers. I highly recommend learning to use it effectively. Keep in mind though that analysis isn't everything, and one small assumption you make can throw off your whole analysis.

Good luck, the wheel looks great so far.

Brando