For the first draft I can think of timer and sprinkler valves. For off the shelf components, I have to use one timer per day to activate something. Water is a good counter weight to bring food down from somewhere. Tubes can be custom made easily. Now sprinkler timers have 7 day program and each has at least alternate day programs. So I can save half the number of timers. I wasn't expecting too much of a vacation, just a weekend get away or up to a week will be good enough. It turn out that one timer per two days isn't a reality and so many custom pipes become a nightmare.
Then came the thought of a toy car coming out from somewhere to bring the food. A car each day. But now cars all come with remote control, so I have to rip off the remote control to get to the electronics, which adds to another level of unreliability. And also, the battery saving features in the cars may do something unexpected.
Fry's save the day. Now instead of an Outpost website, they put their name on it. I found toy motors online and found it in their stores too. Motors are everywhere, but theirs are kits, complete with gears box and mounting screws. Surprisingly it's purely made in Japan, and I don't know how they justify the low tech manufacturing, though the plastic gears are rather precise.
At the end, it become something like this, for each day:
- One AC 7 day timer - reliable and easy to program, you can't go wrong
- One AC to DC adaptor - to get 3 V for battery operated motor. With the exchangeable plugs, the motor wires can be clipped to the plugs without soldering.
- One motor with low gear ratio and mounted wheel.
- One heavy plank wood beam 1" x 2" in cross section
- A tray large enough for one portion of dog food
- Sewing thread to pull the tray
- A table in the yard
- Optionally a large bowl to receive the dog food
The gear ratio has to be low enough that the motor is powerful enough to overcome friction, and powerful enough to pull the thread to breaking point after the dog food is delivered to the ground. Since the thread is attached to the wheel and to the tray, the string thread has to break or it will be chaos. The mounted wheel isn't important as long as the thread has something to tie to. The powerful motor will ensure that the thread will coil up somewhere and pull the tray along the beam.
The beauty of it is the reliability. If anything fails the dog just miss one meal. Unlike the other feeders, the dog will starve for a week and die.
I have been thinking of improving it so it can be used daily to save labor. However, you need something like a grain screw as in the commercial feeders. If I can find something like that, I can attach it to an electric drill, which could be rather reliable. Though the amount of dog food delivered will not be exact.
There are also other toy motor kids that allow you to build a conveyor belt for example. You might be able to build a single feeding machine instead of 7 machine if you leave for a week. For reliability, you can use two machines, one for the even and one for the odd days.