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A DIY motorized chicken (and duck) coop door that adapts to sunrise/sunset times, and can optionally be remote-controlled.

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A DIY motorized chicken (and duck) coop door that adapts to sunrise/sunset times, and can optionally be remote-controlled.

We have a backyard flock of chickens and ducks. They have a much healthier sleep cycle than most human adults do: wake up at sunrise, go to sleep at sundown. We love them dearly, but it's just not sustainable for us to get up at the crack of dawn all year, every day (during the winter? extra nope) to open their coop so they can access their food and water. Fortunately, we can automate a door.

Instructions and other writing in progress!

Additional documentation and process blog posts: https://sminliwu.github.io/projects/ChickenCoop/

We got our flock as two-day old chicks in April 2020 (our quarantine babies). They lived inside the house in a pen for four months until they were fully-grown, which gave us time to revamp the backyard shed into a proper coop. I began working on the automatic door almost immediately, starting first with the overall mechanical design. I was primarily inspired by the drawbridge mechanism in another DIY chicken coop project, which felt doable for my limited mechanical design experience. I can make a motor wind up a rope, sure.

First, determining the kind of motor I needed. ( reference for the physics calculations) I cut a piece of plywood to the necessary size, attached some length of rope, and weighed them both to estimate how much weight the motor needed to lift. I got 7.8 lbs/3.5kg, which I rounded up to 10 lbs to be safe. This converts to approximately 45-50 Newtons (N) of weight. However, the force applied (weight) isn't what matters here; it's the torque needed from the motor that's turning the winch winding up the rope. Torque depends on the size of the winch as well as the applied force:

Estimates for different winch radii and the amount of torque required from the motor to lift 50N: (ugh, why does the oz-in unit exist?)

I used 1cm as the smallest radius I could realistically make the winch, and I would definitely not make a winch bigger than 5cm, so this gave me the minimum and maximum torque that I needed the motor to deliver.

However, the more torque that a motor can deliver, the slower its speed (for gearmotors, at least?) when provided with the same amount of power. I wanted the door to take about 20 to 30 seconds to open/close -- too fast makes a bird guillotine, and too slow is just too inefficient. The lift time for the door depends, again, on the winch size, since a bigger winch with a bigger circumference will wind more rope in a single turn. The door would move approximately 40cm between its open and closed states, so we calculate:

We're ignoring the fact that the winch will wind slightly more rope with every successive turn, since the wound-on rope increases the total circumference, because this is estimation and not a physics derivation. For the same radii used above, and using 2π = 6, we estimate the motor speeds as:

So if the winch radius was 1cm, I needed a motor that could handle at least 80 oz-in of torque (stall torque) while still rotating at least 15 RPM. Looking at a range of 12V DC motors, this 30RPM 137 oz-in stall torque motor more than satisfied those requirements.