I want a hypnodisc
May 30, 2006 10:32 AM   Subscribe

How do I buy/build a hypnodisc with a stand and electric motor?

Googling this is tough because there's a lot of hypnodisc screensaver downloads out there.

Eccentric Genius can make a very cool one, a there's one on Ebay for $300 but I'm looking for a cheaper alternative.

One possible approach is to get a cheap electric fan and replace the fan with a hand-painted disc, but I'd want to slow down the motor somehow.
posted by RobotHero to Technology (9 answers total) 1 user marked this as a favorite

A few CDs, like Ethan Persoff's Snap! feature hypnodisc designs, and can be spin manually while held aloft with a pencil.
posted by Smart Dalek at 10:50 AM on May 30, 2006

Plug that fan into a dimmer switch. Presto!
posted by MrMoonPie at 10:59 AM on May 30, 2006

Stupid Home Depot site. Go to HomeDepot.com, search for item # 162668.
posted by MrMoonPie at 11:04 AM on May 30, 2006

MrMoonPie writes "Plug that fan into a dimmer switch. Presto!"

Most AC motors can't be slowed with a dimmer switch, they lose power not speed.

Now if you were to attach the disk to a DC motor a dimmer switch will work. A good source would be a cheap corded V/S drill.
posted by Mitheral at 11:39 AM on May 30, 2006

I made one as a kid from an old can opener, which was free and already geared perfectly, and an old record, which I painted. Today, I would download some spiral op art in vector form and then print it out to glue on the record.
posted by roboto at 1:25 PM on May 30, 2006

Best answer: Use a DC motor, gear it down a lot (perhaps use a worm gear), and/or lower the speed with a simple PWM (pulse width modulation) circuit. (Simple meaning around 5 components.)

Mount the disc so that it can freely (and silently) spin on the shaft. This has two advantages:
1. you can spin it by hand / fiddle with it without interfering with the motor and/or gears
2. the rotation of the disc will be silky smooth - no need to slowly ramp up the motor to avoid the disc leaping to full speed, it will gradually start to turn when the shaft is turning. Also importantly - the very slight but brief spiked variations in speed that you will get from an electric motor with mechanical linkages will be smoothed out, I think these momentary abberations would be visible and detract from the effect when the speed is low enough for a hypnodisk to look at its best.

Suggestion: For extra coolness, have the motor powered by a solar cell on the base of the mount. That way, the disk speed corresponds to the level of light in the area, and needs no batteries or wires. And also will respond to you somewhat, as your presense reflects or blocks more or less light.

I would suggest the low voltage DC route. Buy the motor, some wires, soldering iron, etc, and build it into an ornage mount/base that you get from scouring thrift stores for old ornate lamps and trinkets. How big did you want to make it? I assume a little desk one like Eccentric genius?
posted by -harlequin- at 1:37 PM on May 30, 2006

Also, for a free source of nice DC motors and gears, rip apart a busted old CD-ROM drive. The motor that spins the disk is usually no good (they're usually stepper motors, not DC motors, you can tell because they have lots of wires or connectors instead of just two wires), however the motor that operates the reading head and the motor that slides the tray, those are usually really good, and will run at 1.5V-6V (ie one flashlight battery to four). Regarding my other suggestion, they'll actually usually even run at 0.5v, which means a single solar cell can get them turning, if you're not comfortable stringing a series of solar cells into a panel)
posted by -harlequin- at 1:42 PM on May 30, 2006

Follow-up: this thread prompted me to play around with making one. I haven't finished it, but so far: the route I took was to use a solar cell or two and a DC motor from a CD-ROM drive. The use of a small solar cell meant that there was so little power available to the motor that gear reduction appears to be unnecessary - I'm using a CD-ROM disc as the disk to spin, and the weight/inertia of the disk, combined with the low power, keeps the speed down. Plus, because there is no battery to run down, and the current involved is so low, I can just use a potentiometer (variable resistor) for a speed control, which is very simple.
I'm also going to try putting in a light-dependant resistor as a way to regulate the speed - the brighter the sun, the more the LDR throttles the solar panel, so that the disk more or less maintains the speed you set, however this LDR-throttle idea is currently completely untested :)
posted by -harlequin- at 2:43 PM on July 5, 2006

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