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!
Step 1: Materials, Tools
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
Pliers: standard, needle-nosed
Hot Glue gun
Step 2: Prepare the Hangar & CAT-5
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.
Step 3: Prepare the Motor
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:
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).
Step 4: Make a Stand
Step 5: The Pendulum
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.
Step 6: Make a Switch
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.
Step 7: Prepare the Power Supply
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.
Step 8: Mount Your Twitchy to Something
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.
Step 9: Test & Tweak
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.
Step 10: Add Personality
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!
Step 11: Evolve
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!