As I mentioned earlier, I don't have much experience in designing any mechanical devices that move, so I knew this part of the project would be the most difficult for me. With that in mind, I started here so I knew if this project would even be possible.
I started this project when a friend was visiting. We dug through my junk pile and found a bunch of motors and linear actuators. We started with the linear actuators. One was meant to open a valve, so the travel distance wasn’t enough for this project. Another one used a motor and gears to move in and out. It might’ve worked but was slower than I liked. One motor was too fast. The other one I found started smoking when we powered it up. While searching for something else, I found the motor I ended up using. I can’t remember exactly where I got it but given that I had it stored with some lawn mower parts, I think it was from a broken hedge trimmer. It runs well from 12V, has a nice-sized gear for connecting to other things, and came with a mounting bracket, so I decided to use it.
At some point late into the project, I realized I could probably have used a broken drill and cut down on a lot of problems I encountered (at least it would’ve been easier to control), so keep that as an option if you decide to make anything similar.
The next task was converting the rotation of the motor to a clapping motion. I knew the motor spun too fast as is, so I’d have to connect it to a bigger gear to slow the output down. I searched through my stuff and found that a lid for a jar of nuts was about the right diameter and had ribs for grip that could be used as teeth for the belt. I filled the jar with a piece of wood to strengthen it, but I made it too tight and it ended up cracking the lid. I remade the lid with a smaller piece of wood and filled the gap with hot glue. I drilled a hole in the middle based on the lid’s injection molding fill port (because it was dead center) to use as the rotation axis. I used a belt from a broken printer for a while until it broke and then I ordered a wider one that was the same length from Amazon.
How to make the gear.
My original design used a teardrop shape as the cam because I thought it would be better to gently pull the arm away, but I found out that if the motor over-rotated then the hands would end up with a slight gap between them and ruin the illusion of clapping. In the above video, you can see how the wide part of the cam hits the bar and the hands pull away from each other.
A pill-shaped cam worked better in my case because it would quickly pull the hands apart and release them into the closed position with 75% of the gear’s rotation left as leeway.
The motor came with a mounting bracket, but I had to remake it so it would more easily to mount to a piece of wood. I drilled a 1.5" hole into the wood (the exact size of the motor) and screwed the bracket into the wood to hold it in place. This worked, but the belt would sometimes come off. By adding some metal to the front of the motor so it was tilted away from the gear, it would pull the belt into the wood so it could not pop off. Below is a video of the first time I got the gear to spin using a square. You'll see a scrap piece of metal with "COOL" laser cut into it to replace the square in my final design.
The next task was mounting the bar so the cam would move it back and forth. I’m still basically using my original idea (see above video) where a piece of wood on the bottom and a loosely-fit zip tie provide the axis for the bar to move around. I now use a bungee cord to pull the bar towards the cam to let it snap in and make it clap.
I also had to make a small angled piece to keep the bar from falling past the gear (this is the anvil-shaped piece to the left of the large gear in the above video). Another piece of wood shaped like a bridge also keeps the bar from coming off (this is the light colored piece in the second video above). I ended up mounting the limit switch to this area because it is well constrained and the bar always moves in the same way in this area.
The motor driver and limit switch will be discussed in another log.
One hand is taped to the bar. The bungee cord is attached to this hand so it doesn’t rotate. I made another mount from a piece of wood to hold the second hand in place where the first hand can crash into it after spinning around.