ErMaC_,
That is a great job on a massive Pep. Looks like it survived the first resin layer without major issues. How far do the arms need to extend? If it's just a few inches, then an RC airplane landing gear retract servo can do that. Same money for a version with metal gears inside as that actuator, but runs on 5 volts. I used one to extend the front shroud on my Spartan Laser and its proven fairly tough. You would need some electronics to send it commands.
Redshirt