Linear actuators are getting easy to obtain and relatively cheap. The same cannot be said of linear servos. The two have a lot in common except for the ability to control the position precisely. The usual way the commercial servos do it is using a multi-turn potentiometer. I decided to take a different tack. And the best way to implement it is to take one apart and see how they can be engineered to provide servo operation.
The full sized linear actuators (500+ mm travel) I intend to use are expensive and I need six of them. A good approach would be to try it with smaller actuators (200m travel) and get some experience using them. The ones I opted for are shown below in retracted and extended state.
