I use the mechanical O K retracts in the smaller planes, A Kyosho Zero 25 size built in 1990 and the one in my avatar, about 8 yrs old. Never had any trouble with the mechanical part of them. Bend the wire gears back once in a while on a less than perfect landing Bend them back forward and go again. This is on grass. They are made for Hobbico. Normal Futaba retract servo.