Twitchy, Your E-waste Friend

He's cleaner than a hamster, and has more personality than most reptiles, and is much smarter than this dog I used to have. Plus, he's made out of junk and is lots of fun to build.


The human population can be (and arguably should be) divided into two groups: those of us who take apart hard drives, and those of us who do not. I sit squarely in the first group, alongside my two aspiring-mad-scientist sons. Perhaps we should be given an island somewhere, so we don't disturb the rest of the populace? At least until we take over the world via some sinister super-laser... BWAHAHAHAHAHA... but I digress.

As most HDTA's (Hard Drive Taker-Aparters) have discovered, you can't get a hard drive motor to spin continuously using a battery or other DC source, because it's a stepper motor that uses a controller on the hard drive's circuit board for a high-speed spin. But you can get the motor to jerk from one pole to another by connecting one terminal of a battery to one of the motor's three terminals, then poking a wire from the other terminal of the battery back and forth between the other two hard drive terminals. Useless? Of course! But this is the phenomenon that gave birth to Twitchy: a self-motivating randomly-switching boingy apparatus, whose own random motion contributes to more random motion. Measurements and specific materials aren't very important here, so feel free to improvise!

Materials:
Hard drive motor
24-36" scrap Cat-5 network cable.
12" insulated, stiff copper wire (thickness doesn't matter much)
Wire clothes hangar
6" Fishing line
5V power supply
Small "zip" ties
Eyeball, hair, or other personality-enhancing items

Tools:
Torx wrenches
Pliers: standard, needle-nosed
Vice grips
Wire cutters
Wire strippers
Soldering stuff
Hot Glue gun

Prepare the Hangar:
Cut off the part with the twists, straighten.

Prepare the Cat-5:
Pull one or two "twisted pairs" of wire out of your length of CAT-5 cable, for two reasons: 1. making room for the hangar, and 2. gathering more materials: save the skinny little wires you remove; you'll need them later. Since you're pulling through four twisted pairs that are also twisted to each other, it can take some effort: you may need to clamp the remaining pairs into a vice or vice grips, then pull on the ones you're removing with pliers. Now thread the straightened hangar through the CAT-5.

Eviscerate a deceased hard drive. Chances are good, regardless of the state of the platters and their data or the circuit board or the pins or anything else, the motor is just fine.
You'll need to bust out the torx wrenches and be prepared to remove little silver stickers to reveal hidden screws. Save the screws for later!
Here are some swell photos of a typical disassembly:
http://www.takeitapart.net/archives/hard-drive/
The most difficult part to remove is the actuator arm (which holds the read/write heads, just like the arm of a record player holds the needle). This generally requires some amount of poking, prodding & prying, so watch your knuckles! Save the magnets because they're ultra-strong, but careful not to pinch your fingers. Save the platters because they are quite possibly the most aesthetically pleasing piece of junk you'll ever see, and they make great wind chimes or earrings for elephants or coasters or throwing stars for ninjas-in-training or delicious donuts to feed to your robot. Save the actuator assembly to make a Windbelt,
Like thisthis or thisthis or thisthis.
...or a Robo-RoosterRobo-Rooster.
Still more hard drive salvage ideas herehere...
Find the motor in your pile of shiny hard drive bits: it's the silver piece that looks like a flying saucer. Screw something onto it, a straightened paperclip or similar-sized piece of copper wire, that will serve as an "un-balancer," an arm upon which you will place a small amount of weight that will be constantly thrown to and fro in random, twitchy fashion. I used a paperclip with a circle of copper wire soldered to it's end.
Strip the ends of two 6" lengths of the skinny, flexible wire you harvested from the CAT-5. Solder one wire to each to two terminals of the hard drive motor. These wires can be twisted together (or remain twisted, if they were a pair to begin with).

Bend your CAT-5 into a graceful spiral. Trim all but two skinny wires (power!), which you'll leave longer, sticking out of both ends of your CAT-5. Affix the hard drive motor to the top of your spiral using zip ties (or wire, if your zip ties are too thick), threaded through the motor's mounting holes and around the CAT-5. Bend the stand until the motor is level. Solder one power wire to the remaining motor terminal, leave the other dangling for now.

Solder a small length of thick wire onto your remaining piece of thin wire. Strip an inch of insulation from the bottom of the thick wire, and bend it with pliers to form a "V" of bare copper. Trim the thin wire so that both wires total only three or four inches, and solder the thin end to one of the power wires. Tie a knot in the wire and glue-gun it to the base of the motor, so that it's dangling straight down from the center.

The weight on the end of the pendulum can be anything, but I used a spacer that came from between the platters of the donor hard drive. Tie one end of a piece of fishing line to the weight, and the other to the copper "V." Bend the V up to pinch the string, forming a double-with copper area about 1/2" long.

The idea here is to form two copper rings connected to the terminals of the hard drive. Strip an inch of insulation from the end of a thick copper wire, form a loop (bend a nice circle with your needle nosed pliers), and solder the loop to the end of one of the the two skinny wires leading to the hard drive motor. Repeat for the other wire.

Bend another piece of thick wire around the loops and around the CAT-5 so that the loops are held out with the copper part of the pendulum running through them. Make sure that the loops are insulated from one another, but not from the pendulum.

Cut & strip the wires near the "jack" side, and join them to the wires you left sticking out of the bottom of your spiral stand. I used 5 volts, but you could probably get away with a variety of ratings.

At first I used a 9V battery and it worked surprisingly well (as well as being nice and portable, with the battery zip-tied to the last 2 inches of the CAT-5 providing a weighted "anchor"), but it didn't have the amperage to get past the resistance of the motor and kept stopping.

A wall-wart will give you a much perkier Twitchy.

I have it clipped to the corner of my cube, but you could zip tie it to a metal ring, a circle of plywood, or your own head.

The point is, the bottom edge of the CAT-5 stand needs to be planted firmly, or the added bounce will actually cancel out a lot of it's motion and bring it to a stop too quickly.

Plug your Twitchy in, and start fiddling with it. The two main variables are the weight on the un-balancer and the switch: experiment with different items stuck to the wire, and orient the loops of the switch in different ways. The motion created by the unbalanced motor and transferred to the springy stand causes the pendulum to rock and alternate randomly between connections, changing the motor's direction, and contributing to more motion.

Bending the copper rings around can increase sensitivity and overall twitchiniess. With proper tweaking, your Twitchy will keep itself running for long periods of time. Make sure that at rest, the pendulum is not touching either ring of the switch; as in, "off," to avoid overheating.

Over time, you might get some corrosion on the copper pieces that can slow things down: clean that off with a file or sandpaper or backhoe, and you're back in business.

I settled on a large googly-eye, and I think a tuft of fuzzy hair may be in order. Twitchy has a charming paranoiac quality, frantically trying to look in every direction at once.

Initially I left the googly-eye googling, but it quickly because evident that the constant rattling of the eyeball was too loud for the workplace, so I un-googled it by poking a hole in it from behind and taping the black part into place. Keep your eyeball rattling if you can get away with it, though.

Any personality components placed on the un-balancer will affect Twitchy's behavior, so keep weight in mind!

This Twitchy will often run for 15 minutes or so at a stretch, but since the motion is so random, it's bound to stop eventually. My co-worker Russ, Primary Twitchy Consultant, suggested a mechanism to poke Twitchy back to life when he settles: perhaps a capacitor that begins charging as soon as twitchy goes still, then discharges into the hard drive motor just enough to kick it back to life and start the twitching again. (I really should give Russ credit for his valuable contributions to the Twitchy Project, all made more remarkable by his numerous personal challenges: Besides his carnival-freak-like physical deformities, he has never been the same since the incident with the squirrels)

I like the idea, but I don't consider it stupid enough and would prefer something far less efficient: perhaps a separate motor or lever or electromagnet or relay that when triggered by the capacitor, would physically poke the pendulum into renewed twitchiness.

Maybe the jolt-it-back-to-life idea could compensate for the higher amperage requirements, and allow Twitchy to run on a 9 volt battery after all?

Twitchy could be powered by alternate means, he could be made with a laptop motor, he could be persuaded to stir your drink or wave a flag or scare away trick-or-treaters or frighten squirrels or signal aircraft or mount a make-you-sick webcam...

Let the evolution begin!

-Mike