Thanks.
I need to look into those other plastics. I just happen to have a load of polycarbonate, but I am worried it will be brittle after machining.
What sizes of timing belt do you have? I'd like to keep some slip in the design, so I'll have a look at the green belting. I'm not sure how stretchy that is though. I might have to do a Gene and use a v groove on one part and timing teeth on the other pulley to still allow some slip.

I'm currently running 3s, so not even overvolting the motors. I thought I'd heard about people running one 10A per side, and the motors should only be ~6A stall, so I thought I'd be ok. I'm just looking now if I can squeeze 2 more ESCs in there. I think they'll fit, but wiring will be tight.