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Originally Posted by monsieurcoffee
It seems like one prevalent method that will be used this year to get onto the platforms will be to utilize big wheels. I tried to calculate how big such a wheel would be needed using a 130lb robot but didn't come up with a way to do it. Can someone with a deeper physics background explain the method?
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The short story is that any 4-wheel driven drive train could climb up the 6" lip assuming the coefficient of friction is high enough and the motor torque was high enough. However, the true problem is in "bottoming out" ie where the bottom of your robot or some component will actually scrape along the edge of the step before your back wheel climbs the back step.
To ensure this doesn't happen you can just choose a wheel size that has a radius larger than what you wish to climb, and mount it such that the bottom of your frame is taller than the 6" step- you're able to let both wheels stay in constant contact with the ground.
However, one should note that there exists a
very real fear of tipping. A robot with a high center of gravity could potentially tip while attempting a feat such as this. If you would like some calculations for when tipping occurs, please let me know.
I hope this (briefly) points you in the right direction.
As to Cory's comment about 2/3's... I've never heard of such a thing, though I know that a wheel with a radius higher than the step size will have a mechanical advantage, since you simply need to rotate about the point, as opposed to climb the wall.
Good luck!
Matt