A cordless drill may make a good off the shelf actuator. They are pretty efficient and energy dense. Plus you can screw jack and/or jill with it.

Replace the trigger and reversing switch with your drive signals and relay.

Hi Andy, To give better advice I would need to know more. But here are some thoughts on solenoids and motors... By using solenoids you are injecting a short pulse of energy into the arm to move it compared to a longer pulse from something like a motor. Solenoids can use large amounts of power for sh...