Good variable-speed spinner device

[Prof Wonmug]

I want to make some "spinners" with my granddaughter. These are disks with various patterns that do interesting things when spinning. Some change colors: yellow and blue wedges turn green, all colors turn white. Some appear to spin backwards. Some are spirals. Benham disks generate colors from black and white:

's_top These can be made with toothpicks like a top, but the best effects are achieved with more controlled spin speeds. Most of them work best at fairly low speeds (150-300 rpm).

I have an old Makita cordless drill, which works OK, but the speed is difficult to control precisely and it's way overkill. I also have a Dremel tool, but its slowest speed is like 2000 rpm, which is way too fast.

Does anyone know of a simple tool, like a cordless screwdriver, that has better speed control and goes down to 150 RPM?

Or does anyone have a better suggestion?

Is there some kind of simple turntable?

I need speeds of 150 to 1,000 rpm (I think).

How much trouble would it be to build a simple hand-cranked turntable either gear or belt driven?

[Han]

Prof Wonmug wrote in news: [e-mail]:

We have a whole lot of hand-operated "tops". One of them does have black ink/paint patterns on it that seem to change in a weir wy into different colors, depending on the top's speed. It's disk is 3 1/8" in diameter. On the bottom is "The Toycrafter" whimsical whirligig, 1985. It's named Benham's wheel. It was (once upon a time) $1.99 at World of Science.

[Bob F]

How about using old 12 volt DC fans out of computers. With a variable resister fed from a 5 volt power supply to power them, you might be able to get the speeds you want.

[ransley]

An old record player at 78 speed? Or a bigger pulley on the motor and it will go faster.

[norminn]

An old fan or a Dremel rotary tool. Of course, you could rig some blades on the perimeter so it spins when the wind blows.

[Steve B]

I would try to find a motor from an old sewing machine. Variable speed from very slow to very fast. Should be easy to get pulleys and the drive belts are like big O rings, and available cheap at sewing places. With some ingenuity, it might be possible to stack pulleys, like a drill press, and change from one to another quickly and safely. All on one shaft.

If you can find an old machine WITH the foot control, you got the motor AND the variable speed control, and all for probably $10 at a yard sale. Maybe buy one that's on the fritz, but the motor works. That's all you want anyway. Then it would probably be only $5. Take the motor and speed control, and use the rest for a boat anchor.

Steve

[Prof Wonmug]

Interesting idea. Can I get a variable resistor gizmo from Radio Shack?

Do you know roughly the range of resistance I would need for a PC fan motor?

Can I buy wire with the right resistance/inch and make a simple slider or dial mechanism? About how much resistance/inch would I need?

[Existential Angst]

That's an elegant idea. Steve's sewing machine motor is also good.

A catchall-way, and generally useful for a variety of diy science/shop stuff, is a garden variety lab variac, typically rated at 7.5 amps. Excellent speed control, for the right kind of motor. If you got a bell transformer, or even some power adapter for a cheapie printer or sumpn (which would also likely put out DC), you just plug this into the variac and you'll have all thelow voltage DC you want. Or, you could just put a battery charger into the variac. Or just a rectifier, altho you'd have less control in the low V ranges.

Some nice variacs, with built-in voltmeters!

The older types should be cheaper. Some of those prices are ridiculous, but that seems to be the Internet Way.

[Prof Wonmug]

I think we have an old record player in the attic. Main downside here is 110 VAC. I'd rather work with low power if I'm taking it apart. Also, I'd have to find a way to make it variable.

[Prof Wonmug]

Another clever idea. Thanks.

[Existential Angst]

Look for a 1W to 5 W "potentiometer" -- which is basically a mini-version of the variacs I described.

shows a 500 ohm

1/2 W potentiometer, which might do -- heh, for $1.48. Probably you want a resistance of about 10x the motor resistance, so you'll have to measure the muffin fan motor resistance, which I would guess would be about 50 ohms, so this potentiometer might do well, if the wattage is sufficient. See also "slide potentiometers", which has a link at the bottom of that page.

[Prof Wonmug]

Thanks for everyone's suggestions. This led me to more searching.

One possibility is to buy something like an Erector Set. They have kits with 6V motors and the pieces to build the turntable or chuck mechanism. This is probably the easiest. I'll go to a hobby store or toy store and poke around.

I also found companies that specialize in micro motors. If the Erector Set doesn't work out, I'll try that.

[Prof Wonmug]

Thanks. I think this could be made into a great little science project. Lots of potential to learn optics, electronics, physics, mechanics, ...

[gfretwell]

I think the easiest solution is a junked cordless drill. It already has the speed control and when the battery dies, most people just throw them away. Get a small DC power supply, like a big wall wart to run it. Most will also run just fine on AC so you could use a doorbell transformer. You don't need a lot of power to spin it without a load.