Tony, I have given the auto line tensioner a bit of thought. Measuring with a three pulley sort of thing and a strain gauge on the moveable pulley or an optical sensor approach should be pretty feasable and low cost. Two problems remain: a motor controller will be very expensive for any analog sort of approach - power FETs ain't that cheap! Which leaves a bang bang sort of controller. Stability issues should be manageable BUT, the pulses to the solenoids will be many and pretty fast unless we use some sort of micro processor to intelligently control things.
I don't have the machining tools or skill to make the sensor but in theory it should be fairly simple. I have some crude ideas. The design must allow for fast line speeds and have low mass / inertia on the sensor. The controller should be pretty cheap as it is a simple 4 bit micro and a FET or relay to control the winch solenoid. I envision a small box for the controller which has its own battery supply and plugs between the foot pedal and the winch. The tension is adjusted at the sensor which sits astride the return winch line about 50 feet out. The pilot pulses as he wishes. If the tension gets too high - the winch pulses itself. Anyone with a machine shop want to have a go at making a reasonable cost line tension sensor? I could breadboard up the rest in crude form and see what happens and refine the controller from there. I have two advantages: I fly with the Orlando Buzzards who are really good guys and like to compete and have pretty good weather. I am an electrical designer so that helps a bit. It is possible that a cleverly made sensor would have nothing more on it electrical than a really good micro travel switch and that switch would be in series with the pedal. If the stability / solenoid pulse rate issues are not too bad that alone might work. It should be pretty low cost - if less than $100, should be real practical for most contests to have such a thing. Just thoughts. Comments? Merry Christmas Everyone! Jim MacLean
