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Originally Posted by sanddrag
Can someone elaborate on exactly what the 116 drive is and how it works? This is the first I've ever seen of it.
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Start with a standard holonomic drive system, with four omnidirectional wheels at the center of each edge of the robot. Tilt the wheels over at an 82-degree angle, and cram them as far into the corners of the legal footprint as you can. The wheels now effectively run on the "edge" rather than the "outer face" of the wheel. The wheel is driven by mounting a 144-tooth, 20DP gear (with spokes and hub removed) to the "upper" side of the gear with 5/8" standoffs. This ring gear is driven by a Chiaphua motor with an 11-tooth gear, which is mounted on the same strut that supports the wheel/gear combination.
When you do this, a couple of things happen. The points of contact between the robot and the floor are spread way out. The resulting conservative support polygon is about 56% larger than it would be with a conventional orthogonal holonomic drive. Thus, the entire robot is considerably more stable. Also, by pushing the contact points farther out from the CG of the robot, you create a longer lever arm for the application of force when trying to turn the robot. Finally, by tilting the wheels over that far, the entire CG of the drive system and robot is dropped by about 3 inches. This increases the stability of the robot even further.
We played around with a few similar design concepts before converging on this version. We also had to play around with the particular compound used in the smaller wheels of the omniwheels. While several other teams that were using the AndyMark omniwheels were after harder mini-wheels, we actually wanted the softer compounds to maximize the traction we would get. Otherwise, we would spin out and create these really neat cresent-shaped burn marks on the carpet. That is why we ended up with the unusual white, slightly lower durometer, mini-wheels on our omniwheels (the picture above is from the Annapolis Regional, before we swapped out the mini-wheels for the Atlanta competition).
-dave