[apalrd]

About the drivetrain:

The drivetrain is very simple. There are 6 pieces of sheet metal (0.050" 6061 T6) which make up a fairly standard square with 2 wheel bays of approximately standard width (I believe 3", don't quote me on that). At each corner, a stiffener plate (0.050" 6061 as well) is used to maintain the center-center distance between a single large CIM with Vex 11t pinion and the Vex omni wheel and 72t gear (held together with versakey parts). The axle is 1/2" 7075 round, dead, taped in the end for a 1/2-20. I can give more details on the exact fabrication if you want.

The omni wheels were replaced every 2 tournaments or sooner, we simply replaced the entire axle-bearing-wheel-gear assembly and had a complete set of identical spares (including axle spacers) in the pit.

We found that the CIM could twist, so we added wood blocks between the CIM and front/rear chassis rail to keep the gear spacing correct. This was done manually by sound, the whole drivetrain is very quiet when running.

We initially used Vex encoders with Vex 2.75" omni wheels as floating odometry wheels, but quickly removed them for weight savings and ran time-based autonomous programs (we did do voltage compensation to try to keep it reasonably consistent). There are no sensors in the drivetrain.

The catapult is a single welded frame, which bolts on top of the chassis to provide significant stiffness. With the 4-omni drive, we don't care about stiffness nearly as much as we did with drop-center traction wheel drives.

The strategy behind the drivetrain was basically to be able to maneuver out of any situation easily enough to prevent direct pushing. We believe this achieved it in the lights, simplest way possible, without any articulating systems. By preventing direct pushing, we also removed the need for a multi-speed gearbox, allowing the 'corner modules' which are extremely light, simple, and efficient.

I can answer more questions if necessary.