Byi, The 3 servo mechanism is really cool, I've not seen anything like it before.

Tician, a thread rod and captive nut would be my first choice. But I haven't put it in because I'm not sure how to incorporate the limit switches. Your comments on pulleys have given me some ideas for getting the motor out of the way. I need to get a better idea of the general layout before I commit to anything. Space availability is a big factor in what is viable. (Hi, my name is captain obvious)

Since the target plates and turret both need to both go up above the legs I would like to avoid putting springs in the feet.

Thanks everybody for the feedback it is really encouraging.

Cheers,