In 2009 I took a week off from work to build an Automatic Cat Feeder to ration food to the overweight household cat. This was a project built from need and it had a deadline because my girlfriend and I were heading out of town for Thanksgiving.
The requirements were simple: It needed to be easy to refill and dispense the correct amount of food twice daily. Early on I had an idea for a large rotating drum to dispense the food, it needed to be easily removable for refilling and heavy enough that it could sit on a motorized wheel and cause enough friction to be turned.
Figuring out a latch mechanism that dropped the correct quantity of food after one rotation was the first tricky part. I didn't want any electronics on the drum so it had to be completely mechanical. In the end I hot glued a small box to the outside of the drum which filled during rotation, when it started moving back towards the top a tab would be hit to fling a door open and drop the food out. A magnet held the door shut and gravity would shut the door when the box made it back to the top. I'm extremely proud of this mechanism and it worked perfectly.
|The dispenser mechanism! A marvel of engineering, hot glue, magnets and JB Quick Weld.|
With all the details figured out, hacking it together turned out to be pretty easy. The hardware store patiently cut a sheet of 1/4" MDF into pieces for me which formed the box, and I was able to glue the pieces together with gorilla glue. A small stepper motor and some electronics were harvested from a 5 1/4" floppy drive and I was able to control it with an arduino. The program couldn't have been more than 50 lines, I figured out how many steps it took for 1 revolution of the drum through trial and error. Then coded it to do that every 12 hours.
|The finished product. Seriously, we used it looking like this for several years.|
|The happy customer. My wife added a chute made from a mountain dew bottle.|
I did make a couple upgrades after these shots were taken. The stepper motor died so I upgraded to sparkfun's cheapest stepper and an EasyDriver stepper driver. I also added a reed switch to the box and put a magnet on the drum so that I didn't have to count steps, this was needed because depending on how much food was in the drum it would sometimes slip and require a different number of steps to get back to the top.