Hi everyone I made an automatic door similar to the one suggested above and it works great. What you need is a submersible fountain pump, really cheap, then a water container to act like a reservoir, I used a big a plastic cereal container then a plastic 1 1/4 litre bottle, some plastic tubing and weights for your coop door. Step 1 make a sliding up down door on the entrance to the coop. Step 2 run a fishing line from the top of the door towards a power source, mine went 20 metres. Step 3 connect 1 1/4 litre bottle to line on an up down pulley system, I used the side of the shed with eye screws .step 4 have water pump in reservoir container with plastic tube coming from outlet of pump into the lid of the bottle, then an overflow from the bottom of the bottle, the bottle hangs upside down. When turned on the water pumps into the bottle filling it up and opening the door and then pulling down the string when the bottle gets full it overflows back into the reservoir and cycles around. The secret is to have the bottle set higher than the reservoir so when the power goes off the water then drains back into the reservoir and with a couple of weights , I used fishing sinkers on the door the door closes. The final step is you put a timer on the power source so your pump comes on when you want , say 6am opening the door, water cycles around all day but uses minimal power on those tiny fountain pumps and then you set power to go off whenever it suits water drains out and it shuts them in for the night. The biggest cost was the pump and it cost me $14. Cheers.