I spent the evening working on the mechanicals for an automatic dry cat food dispenser. It consists of a screw-driven slide with a 2 inch hole. The assembly will be placed under a large cat food bucket with a hole in the bottom, with a chute directing dispensed cat food into a bowl.
At the moment the screw is driving the slide simply by threads cut directly into the wood. If necessary I will embed a nut in the slide, but I'm hoping the forces will be low enough that the wood will be sufficient. I've got the motor coupled directly to the screw. This means I'm using a far larger motor than is really necessary for this job. Unfortuantely I didn't have any gear drives that were really suitable. Also unfortunately I didn't have any reasonable way to couple the motor to the screw, so I just bored the end of the screw out to the diameter of the motor shaft and put some Loctight in it. This obviously won't last long, but it was a quick fix. I'll need to come up with something interesting to couple the shafts. Maybe it would be interesting to cast a three-part coupler for this.
The next part of the project will be the electronics for driving the motor. This will consist mostly of some end switches for the slide and an h-bridge driver for the motor. I'll probably put an AVR into it, just because they're cheap and I've got a bunch lying around looking for work. On the other hand, since it just needs to cycle once per input trigger, it might be fun to do it with something more rudimentary with some basic logic.