I am a mechanical engineering student from Texas A&M and have a set of complete plans and force calculations for a jack in the box. I want to build it so badly but do not have the time, money, or place to display it. If any one is interest PM and ill send you a scan of the calculations. It uses a scissor mech to lift. I had the idea for a awhile but wondered how much force it would take to lift quickly and if it would be do-able. turns out it is, assuming the prop doesn't get to big. It was more of a proof of my knowledge after learning this stuff in my Statics and Particle Dynamics class.