how to automatically reverse the direction of a stopped gear motor and restart 12 hours later
Ah, the old chicken coop door circuit. I've linked to this so often on various forums, I wonder if I should just commercialize it and get it over with ;-)

The simplest way of doing this without involving electronics is to use two single pole double throw relays as an electromechanical H-bridge and two normally-closed limit switches that stop it when triggered. The relays are connected in such a fashion that activating one causes the motor to run in one direction until it hits a limit switch. The limit switch disconnects the relay coil and stops the motor. Then when the other relay is activated, the same thing happens in the other direction. The activation is done by two timers that provide contact closure outputs.



The inputs are "move door LEFT" and "move door RIGHT"
I first posted this design to www.backyardchickens.com about four years ago. I haven't built it myself, but the people who have say it works quite well and is simple enough for a non-technical person to understand.

Hope I described it well enough to understand.