pic: Frog Force 503 Omnitank Drivetrain (rAC)

[Chris is me]

It's perfectly possible to use 25 chain for an articulating drive module, provided you keep two things in mind:

1. Be sure that the chain run pivots with the axle. Easiest way to do this is to put a double sprocket coaxial with the pivot axle, running one loop of chain from this to the wheel and the other loop from this to your gearbox. Otherwise you could be stretching and loosening the chain with each articulation.

2. You want to be careful with the modules flexing under load, especially if the traction wheel is on the articulated axle rather than the fixed axle. There's some "fun" bending moments at play if you don't have a rigid, well supported module. To me, the best / coolest way to accomplish this with a WCD frame is to use a U-shaped module which almost hugs the drive tube (plus some delrin sliders at the contact points) - that way at least in theory the forces transfer nicely to the frame.

It looks like 503 is doing both of these things in this prototype. Overall, nice job. Looks sweet. I'd consider pivoting on the omni wheel if you can, but that does make gearing really messy and annoying.