Introduction: Upcycled Cat Feeder
Cat feeders feed cats! Cats, like most things that eat, like a bit of regularity in their feeding - this cat feeder helps maintain a schedule by lifting the cover on the next meal right on time. (Particularly handy if you have a crepuscular kitten, and you are not a morning person.)
This is a quick build with parts that are easy to find used - between my junk bin and Urban Ore the cost of materials was under $10.
There are two versions to this instructable - the one step wonder on the next page, and the somewhat more involved version on all the steps after. Let me know in the comments if that's a helpful format or just redundant.
Step 1: One-Step Wonder
Here's the breakdown, Rube Goldberg style:
1. The wall timer goes off, turning on the 2. drill which lifts 3. the pot lid revealing the cat food then lifts the 4. PVC pipe flipping the 5. switch and turning off the drill.
To reset, just use the handle of the screwdriver to lower the lid again and flip the switch down!
The build is pretty straightforward - a cordless drill provides the motor and gearing, the timer the timing, the switch the switch, and everything gets ziptied to a milk crate.
Want more? Read on!
Step 2: The Full Monty - Assemble the Parts
I've been promising my partner a cat feeder for the better part of two years, and with our anniversary coming up it was made clear that I would be in a bad way if there wasn't a cat feeder on or around that date. I spent a lot of time over the last years thinking about cat feeders, what we needed in one, and wondering if I could do it for less time and money than buying a new one. My restrictions were:
- Small footprint - can't be bigger around than 12"x12" or so.
- Easy to use - neighbors cat-sit periodically, they should be able to use it too.
- Failsafe, cat safe, safe safe. Can't harm the cat, the operator, or the surrounding environment. Can't pose a risk of flooding or burning down the house.
- Must deliver one serving of food up to 12 hours into the future.
- BoM under $10
- Build time of under two hours, start to finish.
The last two were more bonus goals, but I managed to meet those also. Here's how I went about it, but your parts will vary, and this definitely isn't the "best" cat feeder out there - but it just might be the easiest.
- Drill, or other low voltage, geared DC motor
- Power supply suitable for the motor - a big inductive supply, not a switching one.
- Wall Switch
- Electrical box for the wall switch
- Wall timer, the kind with an outlet
- Milk crate
- 1" PVC
- 1/2" copper (or any 1/2" round or rectangular object)
- Zip ties
- Pot lid
- Junk screwdriver
- Crimps, wire nuts, soldering iron - some way to make electrical connections.
There are three little mechanisms that make this cat feeder work: the lifter, the cut-off, and the timer. You could combine the same or similar parts in countless ways to suit your situation, and make each out of whatever you have at hand. At the very simplest, you could use a water clock on a balance to provide the same function (this one failed the fail safe/ease of operation test), or you could go full arduino with a motor shield. Whatever you've got/floats your boat.
Step 3: The Lifter
Parts Used: Drill, Lid, Screwdriver
The lifter portion is a hacked-up formerly cordless drill wired into a coil-based transformer (wall wart).
Open up the drill, chop the trigger out, and crimp the wires from the the wall wart onto the motor leads - bonus points if you check and remember which side is positive.
The main reason for stripping the switch out of the drill is that we don’t need there to be a nice little variac inside of our winch. It should just haul at full speed when the power is on. (I also wanted it for another project)
Select a Phillips head screwdriver someone wrecked, and chuck it up in the drill - the dimensions aren't critical, but if it’s too long it might stick out and be inconvenient once the drill is on top of the milk crate.
You now have a corded winch made out of a cordless drill! Plug the wall wart in to make sure everything works, then move on the cut-off.
Cordless drills pretty cool. They will run on a wide range of voltages, are geared so they have plenty of torque, and have clutches so you can't blow them up. Unfortunately, they do run on rechargeable batteries that have a finite lifespan. Cordless drills without batteries are super cheap - this one was something like $5, ones that are more beat up or older can be had for even less.
A word on wall warts:
AC-DC power supplies used to all use big honking transformers, now many of them are switching power supplies. Switching supplies are smaller, generally use less power, and are smarter than transformer-based supplies. The little charger that came with your cell phone is a switching power supply. However, they are not as good at powering high current loads like a drill - they tend to freak out a little bit or not work at all. Big fat old-style transformers use transformers, which don't mind inductive loads the way switching supplies do, but they will draw more power when they are at idle. Since the transformer is on a timer we don't need to worry about the idle load, so just use a nice big old-fashioned wall wart.
Step 4: The Cutoff
Parts Used: Wall Switch (switch, box, cover), PVC slider (PVC pipe, bolt)
The cut-off uses a wall switch activated by a little segment of PVC as a limit switch.
Cut the positive wire to the drill about a foot from where it exits the body and strip the two new ends you’ve created. (Leave the negative alone, it’s not bothering anyone.) Stuff the wires through the back of the junction box and wire them into the switch. Now you have the switch part of the limit switch.
The little bit of PVC will toggle the switch when the lid runs into it and pushes it up into the switch. The length of the PVC is dictated by the distance between the bottom of the toggle in the up position to the inside of the milk crate, plus ¼” safety factor to avoid the lid jamming against the crate before the switch is off. This is actually pretty unlikely, since the contact is broken before the switch hits midway up, but a “half off” switch freaks people out, and is a bad thing from a design/usability standpoint.
The other concession to usability is the bolt screwed into the side of the pvc to keep it from falling all the way down - if it didn’t have that bolt, the pvc would likely fall down to the lid then jam on the way up without triggering the switch - no bueno. I located the screw to hold the PVC pretty high - the less distance something has to move, the less there is to go wrong!
One particularly fiddly bit is the ziptie that guides the pvc onto the switch - first, faceplates are brittle, be careful when drilling into them. Second, the loop needs to be sized so that you think it will be almost too slack. When it’s too tight, the PVC can ride against it, snag, and jam. Not a desired outcome. So keep that loop loosey goosey and it will be fine.
Now you have a winch and a way to stop it - all you need now is a way to turn it on at the appointed hour.
One of the important bits about electricity and pets is keeping the two separate - to that end all the wiring gets terminated either inside the drill casing (non-conductive) or inside the plastic switch box (also non-conductive) so that even if something does get pulled loose, there won't be exposed voltage.
Step 5: The Timer
Parts Used: Lamp timer.
This isn't too groundbreaking, timers are timers. The one pictured is analog, which is fine, but a bit noisy. I ended up swapping in a digital one. Plug the transformer in and you're set.
Step 6: Chassis
Parts Used: Milk Crate.
Here’s where you can have some fun.
You could hide everything in a box without too much trouble, or make an architectural piece by using your house as the milk crate. (I was angling for the floor to ceiling cat feeder art installation in our kitchen, sadly that was vetoed by the better half.) Mount it under the kitchen table, surprise and delight guests! Mount it under the couch, scare the kitten! Truly, the possibilities are endless.
I’ve mounted everything on a milk crate using zip ties. Milk crates are a great prototyping platform - they have a grid, they are robust, easy to clean, easy to add holes to, easy to make watertight (add a trash bag), have relatively standard dimensions. And they are virtually free.
That’s the cat feeder! I made this in under two hours, and most of that was figuring out which power supply I could part with and taking pictures. The best part is that the cat has stopped waking us up in the morning - she knows that when the lid is down on the feeder, food will appear promptly at 8. So far it’s worked flawlessly, everyone is happy, and the cat has a new robot best friend.