Fab – Motor Mounts


When I started this project, I was working with Carrie Wang on our Pcomp midterm. After brainstorming ideas, we decided to start experimenting with creating a robotic arm. I went to tinkersphere and bought this dual axis mount and tried it out on my servos. It was great!

It was difficult to settle on a concept but we decided to use brass rods I had to encircle the robot arm – a golden cage of sorts. As we talked, we thought concrete would be reaaaaallly cool to use as the enclosure… it’s cheap and readily available so how hard could it be? …. [answer: intimidating & hard to make a mold 😐 ]

First we sketched out the layout, and made a basic mockup with foamboard. We used the laser cutter to mark where we would need to cut.

To test the electronics, I found screws that fit the holes on the side of the servo, and screwed it into a piece of wood.

In addition, it became obvious that a continuous servo would not work as the “base”, because things would get tangled..

We tested a few interactive elements – like using light to have the servo move on its own. This worked ok but didn’t really give the movement I was hoping for. Carrie went out to acquire concrete and ended up being sold on pre made joint compound. Unfortunately at the same time, we were told this project would not be interactive enough for our midterm. So I moved ahead on my own.

To get the cavity, I bought a plastic box from muji along with .5 inch copper pipe. I first cut the copper pipe on the metal saw, and grinded it a bit. I drilled a hole in the plastic, then dremeled the hole to make the pipe fit. I hot glued the pipe in, then got to casting.

It was a disaster! The sheetrock was definitely not made for casting. And it didn’t solidify – even overnight. So that went to the trash. I was uncertain of what to do next… finally I figured I could do a layered laser cut base to hold everything. So I gave that a shot with cardboard.

It took a lot of layers but it worked! I noticed a few flaws – my cavity for the electronics wasn’t tall enough, and my cavity for the servo needed to allow for the wires to be removed easily. So I went back to the laser cutter and made adjustments to a few of the top layers. I also went ahead and started glueing the cardboard together.

From here, it was time to finalize my rod mount. I made a hole in a small block of wood to fit the rod in [this took me a few tries to find the right size], drilled pilot holes into it, painted, and used epoxy to set the rod inside.

This all went fine, except for forgetting to drill before painting. But as I was screwing into the wood, I started having problems. My screws were stripping, the holes weren’t lining up with my bracket, and I cracked the wood. My pilot holes were too small, threading the screws through the wood, and generating too much pressure. I managed to make the holes bigger… problem solved!

Now, I put it all together. I placed the motor into the top cavity, screwed it down, and got to wiring. To ensure there’d be enough current available, I set up an external power supply and two voltage regulators (one per motor). Here it is in action.

I glossed over a looot of details in getting this to work; tweaking code, struggling with esoteric roadblocks… Overall it turned out pretty good as a proof of concept. Some interactivity via motion tracking of a user would be nice. I still would like to paint the base and tweak the code.

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