Hi Nigel,
In retrospect I would have implemented the "full loop" drive chain approach, but I was worried about what happens at the fully open & fully closed positions and the amount of play this system has. However, the limit switches take care of this as they switch off the power and any play is taken up by gravity. The drive system I implemented, requires accurate placement of the limit switches and no allowance for error, which is a daunting, as if I had a limit switch failure it would keep trying to drive the shutter past it's stop. To overcome this I have checked the ampage under full load and fused 1 amp above this load.
Have a look at a more powerful truck windscreen motor, although I would have though a standard windscreen motor would have sufficed. What sort of sliding mechanism is your shutter using at the moment?
Just an update. After a few discussions with Hugh Gillespie regarding the electrical gremlins I had, I now have a fully functioning shutter system and are now implementing the safety systems ready for a fully automatic system.
BTW the Magic Wire system works a treat
Steve