$15 Jewelry box
$10 Mod Podge & glitter
$30 High-torque servo
$40 Standard servo x 3
$60 Arduino Mega
$30 Ping))) sensor
$35 Gyroscope (optional)
$25 Accelerometer (optional)
Mini bar clamps
1/8" nuts and bolts
22-Gauge solid wire
I began with a thrift store jewelry box. I always start with some small furnishing: a table, chair, cinderblock. The compartments on this one are fun to work with. Under the lid was a compartment designed for rings: I ripped out the felt and padding to make room for the electronics.
After some horrifically failed attempts with spray glue and varnish, I had an easy time glittering the renovated interior using Mod Podge. I don't know why I ever stray from the stuff in crafty glueing, because I always return to it. Not pictured is the iridescent Martha Stewart glitter I ran out of in my many failures. Pictured is the Barbara Trombley art glitter I bought to replace it, which is much more monochromatic, and better suited to the task.
The main update to this iteration (besides the glitter) is a high torque shoulder motor. It only takes 5V but has an 800mA drain, so needs its own power supply. I assembled a platform using MakerBeam (mini aluminum t-slot with connectors: the most useful stuff in my studio). Since I have four servos and might want more, they're running off an Arduino Mega.
The first motor had no trouble carrying the second. I've actually only used hot glue and zip ties to connect each arm segment to the servo horn of its joint: a shortcut I'll regret soon enough. The proper solution is drilling a few holes into the servo horns and bolting them into the MakerBeam. Hose clamps work too, but are a bit bulky.
These are the three major components: shoulder, elbow, and wrist. The wrist has two motors and I'm on the fence about giving the shoulder another motor as well. There's space allotted for one in the MakerBeam shoulder socket. It'd be nice to have more lateral motion, but it's definitely challenging to motorize. Tom Sachs had a good suggestion to motorize the canvas instead.
After bolting the shoulder to the lid of the jewelry box, I attached the two arm segments. Next, I wired everything in for another test. I made the jumpers (connecting the servo wires to the breadboard) in the last iteration using intercom wire and header pins. I used gingham tape to flag the wires so I always know which motor is which. Tidy wiring is especially important in projects that need to travel to galleries. I absolutely hate perf board and designing custom PCB is at the top of my need-to-learn list.
I used hot glue again to attach the sensors to the brush holder. You really can't beat hot glue as a temporary solution, but you can never rely on it as a permanent fix. But this is a tricky one: I need those sensors to be exactly where they are, and can't add bulk. Unlike at the servo horn joints, the glue is never under stress here, so it's unlikely to fail. The real solution is to design a hand on the MakerBot that can hold the sensors, a brush, and the servo horn.
With a moving arm, it's easy for wayward wires to get entangled. I treat them like a spinal cord, and use zip ties to progressively bundle. They need to be tight enough to minimize snares, and loose enough to allow the arm its full range of motion. Done right, the bundle will also help keep the arm at midline.
I hate dealing with cords slightly less than I hate dealing with batteries, so you won't see many cordless tools in my studio. You will see a lot of 5/8" and 3/8" increments of things: an unanticipated but noticeable pattern in my projects. A 5/8" hole is a good fit for both a USB Type B header and Neko's wire bundle, so I drilled one for each.
Clockwise from top: black 12V DC plug connecting Arduino to wall; beige USB A/B cable connecting Arduino to computer; white 5V DC plug connecting breadboard to wall; yellow motor signal wires; green sensor signal wires. Circuit diagram below. These are all the wires needed so far, with plenty of room for additions. I've got an RGB LED strip and a color detector in the wings.
Reinstalled the drawers, cleaned up my work area— this is Neko's arm in mine, ready to paint.