RE: converting air to electric retracts.
Cheers for that Mustang I must admit I have run mine on 3 cells but thought it a bit fast so have used it on 2 cells since, but everything thing seems fine so far. Nice to hear your ok on 4mm thread I'll probably stick with the acme though because there not that expensive and are really smooth in operation and the way I make the nuts there's no backlash at all and as I said i can form the thread in each nut in less than 2 mins. Although machining the the outer part of the nut and the guide pin block takes a bit of time so all in all probably works out about the same overall time as cutting my own screws.
The pitch on these screws is a bit courser though at 1.25mm as opposed to 0.7 for 4mm thread. but they are beautifully made though, precision rolled from 303 stainless and a 125mm length is just £14. The price of a nut though was a bit high, I think about 50 odd pounds each, which is why I decided to experiment with making my own nuts from acetal (the bought nuts are made from some plastic also), and it proved to be remarkably easy to do. And I think that the loads that these are likely to be subjected to acetal is more than adequate.
I,m gonna copy your sketch and give it a try. This is my first foray into the Arduino and programming.
Windy