John, Actually, I see nothing wrong with your solution. Have at it!
But having said that, I see 3 ways to handle the situation:
1. Install and program a stepper motor. (Expensive) It always "knows" where it is in the cycle. And you can program it to stop or start anywhere you want.
2. Install a sensing system to detect slack in the cables. This is what you have done. Down side: Not doing it properly will allow too much slack and take you back to the original problem. I think you have that covered.
3. Maintain tension on the cable, and use something else to detect the lowered position. This is what I had in mind. You add a moving pulley with a weight on it. The weight can move up and down in a trough or other guide. There is a stop at the top of the guide to prevent the pulley from getting out of position, but still allowing the cable to move. The cutoff switch is somewhere near the bottom of the trough. When the bridge goes up, the pulley goes up, and hits the stop. Your upper limit switch determines how high the bridge goes. When the bridge goes down, the pulley stays up b/c the cable is under tension from the bridge. One the bridge is down and seated, the weight keeps the cable under tension and pulls the pulley down until the limit switch in the trough is activated. End sequence.
Chris
LVHR
