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Originally Posted by Coach Doug
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Great paper!
The last time I coached FTC was for HotShot. The drive train the kids built had 4 motors, 1:1 to 3" wheels. For what it's worth, if maneuverability is all you want, 2 motors 1:1 to 3" wheels is just as good.
The kids wanted to push through defense, so the obvious choice was 4 motors that year. Yet by accident, they discovered (and I learned by watching/coaching) what it takes to make a great defensive robot.
The drive train wheel base was, from what I could tell, somewhat constrained by the rest of the mechanisms. There were 4 drive traction wheels and 2 caster omni wheels. The 4 traction wheels were close to each other and were located at the front of the robot. The students understood that this helped put their center of rotation closer to the front of the robot -- thus the rear wheels were the casters.
This configuration meant that we couldn't push while going forward. So any time we were required to push, we pushed while moving in reverse. That's really when we realized that pushing in FTC is not only about having enough torque and traction, but
also about point of contact. You want your point of contact with the other robot done in such a way that it pushes down on your traction wheels, gaining you more traction. This meant that we reoriented one of our U-Channels so that it'd do exactly that -- it's not an angled wedge, but it was able to get under a robot or two just enough to provide us a traction advantage. It's how we pushed two great robots at once in a match during Championship Quals that year.
The third key to our success with pushing that year was the unorthodox wheels we had. There are a great variety of LEGO wheel/tire combinations on ebay and LEGO websites. Finding a tire that fits around a TETRIX wheel is a great challenge, but it's one that's well worth the search. It basically gave us a 1" wide
flat tire that meshed perfectly with the rubber foam tiles to give us a great amount of traction. We discovered the tire on accident since a student brought it in from his old home LEGO kit for use as a shooter wheel. Yet I remember reading about another team this year that also used them.
NOTE: no matter how great your defense is, in FTC if you do not have some sort of offense you will fall in the ranks very quickly. If you're not the alliance captain for an alliance, you won't make it to the championships -- so don't put defense as your only strategy
. The offensive mechanisms on our HotShot bot also added a good deal of weight right above the traction wheels.