So long as the third element only needs to move in one direction, negative or positive, then it is fairly simple. Attached above is an example. You will need to loose the ".TXT" part of the file extension.

There is a "DRIVE" dial in the body that drives to motions. The channels that translate or rotate, have limits forced, so they can't go beyond zero in one direction. Each channel that is driven, is also slave the a channel in th body named "one", that channel serves to hold the driven channel back from expression untill a certain value is accumulated fron the DRIVE channel.

When the DRIVE dial goes beyond a value of 1, the green cube will start to move, beyond 2 the orange cube will move, and beyond 3 th cream cube will move.

It's late now, and I must go to bed. I will try to say more about it tomorow, if I get a chance.