[FrankJ]

Tension springs are legal. It up to you to properly apply them. The robot inspector can decide that the design utilizing springs is unsafe. Unsafe can be springs, exposed propeller blades, exposed shooter wheels, ETC.

[T12] refers to springs on the robot.

[R34] Non-electrical sources of energy used by the ROBOT, (i.e., stored at the start of a MATCH), shall come only from the following sources:
A. compressed air stored in the pneumatic system that is legal per R79 and R80,
B. a change in the altitude of the ROBOT center of gravity,and
C. storage achieved by deformation of ROBOT parts.

[R34-C] is commonly known as a spring. It can be compressed/tensioned at the start of the match.