Winning Drive Train

[kramarczyk]

I thought this was a good year to really nail that whole Ff=mu*Fn into people's head, but to get it past my kids we had to do some quicky tests to prove it. See attached data.

We took the kitbot stuff plus some junk around the shop and created a simple test bed to determine if more wheels would generate more force. We were less interested in pushing people around than we were in making the most of our acceleration (F=m*a). We used the kitbot frame and successively mounted wheels on one side, first 2, then 3, finally 4. We would have done more but that's all the wheels we had. We then placed this on a piece of the FRP that was spec'd and massed up the frame with stuff from around the shop. Each of these items was weighed individually (introduces error). We tried to keep the mass as close to the wheels as possible, but still needed to have a student support the outrigger side by a piece of rope with the goal being to keep the frame level (introduces more error). A fishing scale on the rope allowed us to back calculate out the load on the wheels by treating the assembly as a simply supported beam. (i.e. total mass - mass on rope = mass on wheels)

Once we know how much weight was on the wheels we moved the scale to the rear of the frame, in-line with the wheels. We applied power to the wheels and measured the force generated on the scale. Change # of wheels and repeat. Based upon the data gathered and the acknowledged crudeness of the testing we all quickly concluded that more wheels did not significantly add more force.

Based upon the test data we gathered I would say that anyway you could generate and additional lbf of thrust would be important. I was told that 45 & 469 could get 5lbf and ~4lbf respectively... That's 50-60% more thrust than me.

"Foul, foul, I saw you use 6 wheels on your wide chassis at comps!" Read Chris Hibner's white paper, "Drive Train Basics (How to Be Sure Your Robot Will Turn)" It's not just about how much force, but where you put it sometimes that matters.