Springs?

Are there any restrictions or limitations on the springs we can use for the robot?

The only real restriction is Safety. If you use high strength Springs, plan for “spontaneous disassembly”. Shield it or run something down the middle to help contain pieces should it break. Do not modify springs - taking a garage door sprin and cutting it in hall is NOT safe. You’ll potentially introduce fractures or damage to the spring that would cause it to fail down the road. Don’t cut or drill into Springs either - removing material just introduces weak spots!