With Ref to the Rc Truggy weakness of printed gears. A diff and drivetrain based on toothed belts would be more robust as the load is transmitted across many teeth. I have printed many of these toothed pulleys. Bevel gears are particularly weak, but diffs such as those used on the Schumacher Cat use belts (CAD model on Grabcad). Its also possible to print belts and they could be reinforced with carbon fibre fishing line as used in many delta repraps.