Electrostatic Motor Debugging



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EMOTOR | DEVICE
DESIGN HINTS
Electrostatic Motor Debug/RepairSo you've built it and it
doesn't work! Rats!
(Actually, homemade devices rarely work correctly the very first time.)
Detailed debugging is down below, but first
read these:

1. DON'T MAKE MAJOR CHANGESFirst, did you build your motor to be
somewhat like the one I described in the instructions? It can seem boring to
simply copy someone else's idea exactly. It's easy to insert many improvements
as you go. This makes the motor YOURS and no longer mine. But if your device
doesn't work, what then? Maybe one of your improvements actually made the motor
not work. If your motor isn't made from three 2-liter plastic pop bottles with
aluminum foil glued to them, then I probably cannot help you debug it unless you
hire me to come out to your house and take a look. The solution? First build a
motor like mine, since we KNOW that this one works. Then, after you have a
working motor, go and add all your alterations and improvements one at a time
and see what happens. (In the electronics kit business, when the customers make
additions to a device BEFORE making it work first, it's called "Ego
Improvements.")

2. USE A RELIABLE POWER SUPPLY AT FIRSTNext, what are you using as a
power supply? Before trying feeble power supplies like balloons/wool,
electrophoruses (electrophori?), or Kelvin waterdroppers, try something fairly
powerful such as a VandeGraaff machine, neg-ion gen, or the foil-on-TV-screen trick. Get
the motor working with a known-good power supply before going off to try your
own power supply ideas. This way you'll know to not blame the motor when the
fault might be high humidity or a weak power supply. These motors need more than
5,000 volts DC to operate. This can be easily provided by a hefty "static
electric" source.

3. BATTERIES WON'T WORKThis motor needs a "static electric" power
supply (in other words, a power supply that puts out high voltage at low
current.) Use a TV screen, or a VandeGraaff Generator, or a Negative Ion Generator. I
found that my motor would not turn unless the voltage was at least 5,000 volts
(and 7,000 volts was much better.) Batteries cannot run this motor unless you
have about 4,000 of them hooked in series! (4000 times 1.5 volts is 6,000 volts)


4. TESLA COILS WON'T WORK (or will they?) Tesla coils are no good
because they are high-voltage AC and this motor requires high-voltage DC.
Maybe this is not true! [e-mail] reports that his pop-bottle
motor starts turning when the motor is placed near his large, floor-standing
Tesla coil, while one bottle of the motor is connected to ground. Weird! Do
Tesla Coils actually emit some microamperes of direct current into the air?
Possibly. If so, then in theory a Tesla Coil could run this motor, but only if
some corona-rectification is allowed to occur, and not if wires are used to
connect the motor directly to the Tesla Coil terminals. But even that might be
OK! Somebody with a TC should try it. (I tried it with a tiny solid-state tesla
coil from a Plasma Sphere, but it would not run the motor.)

5. BOTTLE ROTATES EASILY, FRICTION MUST BE VERY LOW Other possible
problems: does the center bottle turn very freely? VERY VERY freely? It must.
Here's a way to judge whether its friction is low enough. Get the bottle
spinning slowly by hand, turning about once per second, then let go. It should
keep turning for one or two revolutions or more. If not, friction is far too
high. Check out the metal point bearing and make sure it hasn't drilled itself
into the metal bottle cap. Don't use a plastic bottle cap, the plastic is too
soft to provide a good bearing. The bottle must turn VERY easily, otherwise the
feeble electrostatic forces won't be able to move it. I highly recommend using a
tiny glass test-tube as a bearing. Glue it upside-down in the bottle cap. Don't
let the bottle slam down onto the metal rod, or the sharp point will break the
test tube! Some sort of tiny, metal, cup-shaped object might also work OK. A
metal thumbtack with point removed? Also put a little oil near the bottom of the
metal rod where it rides against the hole in the rotor bottle's bottom.


ORGANIZED DEBUGGINGIf it still won't work, then you need to look for
the problem. Use this "debugging sequence" below.
Note: if you hate making sparks with your knuckles, then hold a metal object
in your hands (use a quarter, or a pop can), and jump the spark to the metal.
Painless!


Test for low friction. Verify that the rotor bottle turns freely,
and that the tips of the commutator wires to not drag against it as it
rotates. To make friction lower, some people attach a pencil point to the
metal rod, so that the bottle cap is riding on the pencil point. Graphite is a
lubricant, like oil. Or you can glue an upside-down glass test-tube to the
bottle cap of the rotor bottle. The metal point of the rod then rides against
smooth glass.

Reduce the commutator gap Verify that the tips of the commutator
wires are VERY CLOSE to the surface of the rotor bottle. Tiny sparks will be
jumping from the wires to the patches of foil. If the gap between the foil and
the wire tips is too big, then your motor will only work if you use a VERY
hi-volt supply, like a VandeGraaff generator. If the gap is small, then even a
feeble power supply will make your motor spin. It pays to use a well-centered
bottom hole in the rotor bottle. That way the surface won't move so much as it
turns, and you can move the wire tips closer in.

Test the TV-screen for proper opration. Try removing the
electrostatic motor, then placing the end of your ground wire very close to
the end of the wire from the TV screen. VERY close, like a 1/16 of an inch
between them. When you turn the TV on or off, you should see little sparks
jump between the ends of the wires. If you don't, then there is something
wrong with the TV, or the connections, or the ground. If you get sparks, but
the motor won't turn, then the problem is with the motor.

Test for high voltage Use the TV method to power your motor. Hook
everything up. Turn the TV on, then immediately bump the foil on the TV screen
with your knuckle. If you get no spark, then your motor has a short somewhere,
or humidity is letting charge leak across the insulating surfaces. Sometimes
there is an invisible leakage path between the foils on the rotor bottle. Use
a razor knife to trim the foils to give 1/2 inch spacing between the foils on
the rotor bottle. Then use something to scrape the plastic between the foils
to remove all traces of glue, crud, etc., from the plastic bottle.

Listen for proper sparking first give the rotor bottle a slow spin.
Let it coast, then immediately turn the TV on or off to create the high
voltage. You should hear little clicking noises as sparks jump between the
commutator wire tips and the rotor foils. If you DON'T hear any clicking, then
the high voltage is being shorted out somehow. If you DO hear clicking, then
almost everything is working, but there isn't enough force to turn the rotor.
Maybe your TV screen is too small, or friction in the rotor bearing is too
high, or the middle bottle is much higher than the side bottles. Or maybe it's
way too humid out, and you need to move into an air-conditioned room.

Test for motor voltage. If you did get a spark from the TV, then
next hook up the motor to the TV and to ground. Turn the TV on or off to
generate another burst of hi-voltage, then bump your knuckle against the foil
on the stator bottle that's connected to the TV. If you feel no spark, then
the connection between the TV and the stator bottle foil is probably bad bad,
or maybe there is a short circuit in the motor.

Test for good ground. If you do get a spark from that stator
bottle, then turn the TV on or off again to make more hi-voltage, and bump the
grounded stator bottle with your knuckle. You should get no spark. If you DO
get a spark, it means that your source of electrical ground is bad, or there
is a bad connection between the "ground" bottle and the distant earth.

What's left? If all these tests work out OK, yet the bottle will
not turn, then the only causes could be bearing friction (use a glass test
tube in the bottle cap), or power supply voltage is too low (try a TV set with
a bigger screen and bigger foil, or locate a tabletop VandeGraaff generator:
ask your local High School physics teacher.)
Note: if you hate making sparks with your knuckles, then hold a
metal object in your hands (use a quarter, or a pop can), and jump the spark to
the metal. Painless!

OTHER POSSIBLE PROBLEMSThe metal of the commutator wires must be
directly connected to the foil of their respective STATOR bottles. Commutator
wires are electrically a part of the stator foils, so when the power supply is
operating, both the wires and the stator foils acquire the same polarity of
charge imbalance. If the commutator wires don't make good contact with the foil
on their corresponding stators, either the stator foils won't get charged, or no
charge will flow down the wire to leap across to the rotor bottle. So, make sure
there is no plastic on either end of the commutator wires, and that bare metal
touches bare foil. If you have taped your commutator wires securely to the foil
of the stator bottles, make sure that there is no tape, hot glue, etc., between
the foil and the metal wire.
The commutator wire's tips need to be very close to the surface of the rotor
bottle, but should not scrape along it as it turns. The gap between the wire's
tip and the rotating bottle's surface must be as small as possible. If it is too
large, then the motor will operate successfully only if the power supply voltage
is raised high enough to force sparks to jump across the large gap. If the gap
is tiny, then even a weak supply will run your motor. If you ARE seeing tiny
sparks jumping between the wire tips and the rotor bottle foils, then the
spacing between commutator tip and rotor surface is probably OK, and the power
supply voltage is probably high enough. Apply power and give the center bottle a
slow spin by hand, and you should hear a slight clicking noise as the tiny
sparks jump. Lack of clicking noise indicates either too low a supply voltage,
or that something on the motor is providing an unwanted leakage path which
shorts out the power supply and reduces its voltage too much.
If you use a strong power supply such as a VandeGraaff or Wimshurst machine,
you can even try increasing the gap to one or two inches and the motor will
still run! In this case the electric current takes the form of silent streams of
charged air rather than sparks. Your motor then runs via sliding contacts made
of invisible ion-beams! Very hard even for scientifically-trained passersby to
figure out. <grin> However, first get the motor running before trying
this.
Make sure there is a complete circuit path between your power supply and the
motor. If you use a VandeGraaff, you must connect TWO wires between it and the
motor. One wire goes between the large sphere and the foil of one of the stator
bottles. The other wire goes from the generator's metal base and to the other
stator bottle's foil. If you use the TV set, connect one stator bottles' foil to
ground, connect the other stator bottle to the TV screen's foil. Wires can be
connected to metal surfaces by simply taping them there. (Make sure to strip any
plastic coating off the wire ends, you need metal-to-metal contact!) If you
attempt to use the wool/balloon method, connect the unused stator bottle's foil
to ground. (Hint: if ground is entirely unavailable, try spreading a few feet of
aluminum foil on the floor and connecting your motor to that.)
Are sparks jumping between the central rotor bottle and the FOIL SURFACE of
the stator bottles? This is bad. Or are your stator bottles too close or too far
from the rotor bottle? About 1/2 in. spacing seems to work OK. If this space is
too large, the electrostatic drive force will be greatly reduced. If this space
is too small, sparks will jump from the rotor bottle and act as a leakage path,
greatly reducing the driving voltage on the stator foils, and slowing or
stopping the motor.
If the humidity is high (above 40% to 50%), it's possible that your power
supply is being shorted out by leakage along the plastic surface of wires to
ground. Try using plastic cups to support your high-voltage connecting wires up
off the table surface. (Wires connected to ground need not be lifted.) Leakage
can also happen across the plastic surface of the bottles. This can be cured by
warming the exposed plastic parts with an electric blow dryer. (Don't heat them
up too much, or they will soften and distort!) Or, store the whole setup in a
cold, air-conditioned room for a couple of hours, then operate it in that room.
Or, wait to try again on a day which isn't as humid. Hint: if you rub a balloon
on your arm hairs and the charged balloon can make the arm-hairs rise, the
humidity is low enough. If no amount of rubbing with a balloon can lift your
arm-hair, then humidity is probably too high.
If you use a VandeGraaff generator or Wimshurst generator, try taping some
strips of tissue to the metal generator sphere so you can monitor the voltage.
Cut or tear out a 2" x 1/4" kleenex strip and tape one end to the metal, so the
strip hangs down. When the generator is operated, this strip should be repelled
from the metal and lift outwards. If it does not, it means that no high voltage
is being created. If high voltage is missing, first try totally disconnecting
the motor from the generator, then run the generator all alone. If the kleenex
still does not rise, then there is something wrong with the generator! Could be
high humidity. If so, you can warm the moving parts of the generator with an
electric blow dryer (open the vandegraaf sphere or base if necessary, and
blow-dry the belt while it's running.)
Finally, check for possible shorts throughout your entire motor. There must
be no surface connections between the three foils of the rotor bottle, and there
must be about 1/2" space between them. There must be no connections between the
foil on the stator bottle and the wooden base. Many sorts of tape count as a
"connection" because of their conductivity, so don't let any tape touch both the
wooden base and the foil of the bottles. The first motor I ever built would not
run no matter what I did. I discovered that the duct tape I used to connect
stator bottles to base was conductive. It was touching the wood base and the
stator foils. The wood base was conductive also, and the whole motor was shorted
out by the tape.






Created and maintained by Bill Beaty. Mail me at: [e-mail].
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