In general, you can do whatever you like in the construction of FIRST robots. The main rules, the ones that anyone designing the robot will need to know by heart, are:
- weight limits
- size limits
- only allowed motors are those in the kit (plus two more CIMs)
- electrical system except for sensors is mostly restricted to whats in the kit
- only allowed pneumatic stuff is either in the kit or orderable from a short list of places. (except for trivial stuff like hose, etc)
- price limit
- and, of course, generally safe designs are required.
That's really it. You are pretty much free to do anything within those rules.