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:
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
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?
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.
Interesting idea. Can I get a variable resistor gizmo from Radio
Do you know roughly the range of resistance I would need for a PC fan
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?
Look for a 1W to 5 W "potentiometer" -- which is basically a mini-version of
the variacs I described.
http://www.google.com/products?q=potentiometer&hl=en&aq=f 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
See also "slide potentiometers", which has a link at the bottom of that
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.
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.
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.
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.
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