Magnetically levitated pulse motor

Latest update:  5/21/2015               Return to the motor selection page  

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Vew of motor running

While many of us have played with magnets as kids (young and old) we most likely never could find much to really do with them.

We immediately noticed that if you have two magnets things got more interesting. Attraction and repulsion of the north and south poles of the magnets being most noticeable.  But we usually still didn't figure out a use for that feature. Moving one magnet with the other one under the kitchen table was fun though.

I decided to experiment with a few different electric motor designs as a learning experience with low input power. All these motors are based on electrical design knowledge that has been developed since 1832. 

There are many enthusiasts building small magnetically levitated motors. You can find videos of these motors on YouTube. The following link is to a "Mendocino" motor which uses rotating solar cells to power a magnetically levitated rotor shaft. The basic layout uses a stationary magnetic field with rotating coils on the armature. Solar cells rotate with the coils and do the commutating of the drive voltage. While these motors are unique they do operate on well founded principles.

Another class of home built motors are "pulsed" motors which rotate the armature with magnets attached using a stationary drive coil.  Various methods are used to time when the coil is energized to keep the motor running.  The levitated motor I built which is shown on the left uses the rotating magnets themselves to trigger the solenoid coil drive circuitry as a blocking oscillator

The  motor uses many common parts from my pre-owned collection of stuff.  The lowest drive voltage this motor runs on is 0.6 volt resulting in 0.177 milliwatts input power. No trickery, just careful design design of the drive circuitry.

The metal 1/4" x 20 threaded bolt is being levitated by Neodymium magnets at each end of the bolt. In other words, the affect of magnetic repulsion is supporting the rotating parts in mid air.

The motor is running in the picture while being powered by a garden night light solar cell. The motor and solar cell were inside my house on an overcast day at the time! The solar cell was located just to the right when the picture was taken.

Purpose of this site:

The purpose of these pages is to present the theory of how a levitated pulse motor works and describe how you can build one for yourself. I've learned quite a bit about building a stable levitating system and will I explain what I've learned in the "Magnet theory & rotor construction" article.

I also will [hopefully] debunk the over-unity claims that some people make for these motors when used to charge batteries.  You will NOT discover how to make a perpetual motion machine here or anywhere else I suspect.  But these motors are a great learning experience and will give you a good hands on understanding of practical electronics and magnets.

I will NOT attempt to teach you electronics as there are many sites that can be Googled that go into electrical theory and design.  Amateur Radio sites are a good source of common electrical designs.  Most have schematics and some have construction articles.

Talking Electronics has hundreds of circuits with explanations etc that you might find interesting.  There is a lot of good information there.  Resistor color codes, how the circuits work etc.

If I present some formulas or terms you aren't familiar with please use that as a reason to use Google to find out what they mean.  The math I use will be very basic to electrical design to keep the site geared toward non-professional experimenters.

I'd read all the articles I've presented here several times until you really understand what it's all about if you want to build one of these motors but aren't familiar with how to do it. 

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Quick review of what I've done so far

At first I didn't want to wind a many turn coil so I searched around in my pile of used stuff and found a normal car relay which has a solenoid coil that was designed to operate on the 12 volt DC car battery system.  The coil has a resistance of 150 ohms and worked better than several other coils I tried.  At first I just pulsed the coil with a square wave function generator set to 24 Hz.  I usually set the generator to 2 volts or less output. The generator has a 50 ohm output impedance so driving the 150 ohm coil was no problem.

I then built a simple transistor drive circuit that is common on YouTube and got the motor running with the relay solenoid.  The motor would not run below ~1.5 Vdc input which is commonly used.  The circuit took more milliamperes to run at that voltage than I would have liked.  But using a relay solenoid is a quick way to get a motor to run.

I finally found the specifications for a home made solenoid drive coil while watching this YouTube video posted by Lidmotor. He has some good videos on YouTube.  No b.s.  Just straight talk of what he's done. Thanks Lidmotor.

I have an article here explaining the details of the coil I made.

I did not end up exactly using the common circuits on YouTube since I wanted my motor to run on very low voltage and current. Basically I just biased the transistor differently to reduce the running current.

Two other things I want to investigate is a simple circuit to make the motor self starting and a way [hopefully] to eliminate the vertical wall that the rotor bearing touches. That is not an easy thing to do without a lot more circuitry and not drawing more power at the same time.

At first I built a crude levitating system using some low power ring magnets I had in my extensive electronics parts pile using a ball point pen and an aluminum TV antenna tube for the levitated part.  After that big accomplishment I ordered a stack of twenty N42, 1/2" x 1/4" - 1/8" thick Neodymium disk ring magnets from eBay which evolved into the motor at the top of the page.

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Bill of materials: 
(What you need to build this motor.)

Hopefully you'll have most of the materials already.  But here's the list of  the major parts and where I got them from.
  1. A base for your motor with a vertical surface.  I used a fiberboard like material that was originally a desk draw divider and a short length of 1" x 2" 90 degree angle aluminum for the vertical part..  Pieces of wood will work fine, or aluminum sheet metal.
  2. Four rubber stick on pads to go under the motor base.
  3. One 5" long 1/4" x 20 ferrous threaded screw. Mine had a flat blade screw driver slot in the head. A threaded rod can be used, the lighter the better.
  4. Six 1/4" x 20 nuts. The ones I used are aluminum for lightness.  Steel is OK but heavy. Nylon would be best for low weight.
  5. Two square 1/4" x 20 nuts.  These must be steel so the rotor magnets will stick to them.
  6. At least sixteen, N42 or higher number, 1/2" x 1/4" x 1/8" Neodymium ring magnets. I got mine from eBay.  The seller was zillionsof.  A pack of 20 was $11 with free shipping.
  7. Four 1/4" x 20 screws to hold stator magnets in place.  These can be any material although mine are nylon. Length will vary depending upon how you mount the magnets.
  8. One 1/8" steel ball. Mine is from a small ball bearing.  Or some other hard pointed object like the end of a ball point pen.
  9. Enameled coated magnet wire, 200' of AWG# 30, 75' of AWG#26.  My wire came from a sonar buoy and a TV degaussing coil.
  10. A plastic spool to wind the magnet wire on.  Hopefully one of the spools the wire came on will have enough room left to rewind both wires on it.
  11. Various small screws, washers etc. All my hardware is either stainless steel, aluminum or plastic (nylon).
  12. A small solar panel.  Mine is a 3.25 volts at 30 ma panel from a garden night light.
  13. If you want to be able to disconnect parts of the wiring you will need some plastic connectors.  Mine came from scrap computers.
  14. Several other metal parts which are not absolutely necessary for the eddy current generator to stabilize the free end of the rotor shaft.
After running the motor for quite awhile I noticed that the lowest voltage the motor would run on was 0.8 volt rather than my lowest reading of 0.58 volt.  I had an idea that it might be that the gauss level of the rotor magnets had gone down due to the closeness of the drive coil when I was running the motor on 5 volts with the coil spacing set for lower voltages.  I put a fresh set of four rotor magnets on the rotor and sure enough the lowest voltage the motor would run on went back down to 0.6 volt.

So it might be best if you try to get some higher gauss level magnets than the N42 I am using.  The higher the number the more powerful and expensive the magnets will be.

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Definitions of terms used:

Even though a levitation motor hasn't had much practical use compared to the billions of electric hp that have been installed around world, many of the terms used for the parts of a levitation motor are similar.  Since this website is geared to non-professional builders I am presenting this list so we are all talking about the same thing.
  1. Baseplate ................ The part of the motor that all the other components are mounted on.  Also includes a vertical wall for the rotor to bear against.
  2. Stator magnets ........ The magnets mounted on the baseplate that create the magnetic field that causes the rotating part of the motor to float in the air.
  3. Rotor shaft .............. On my motor it is the threaded screw that holds the rest of the moving parts of the motor in alignment.
  4. Levitating magnets .. The magnets mounted on each end of the rotor that react to the stator magnet's levitating magnetic fields.
  5. Rotor magnets ........ The magnets mounted on the rotor that actually cause the rotor to rotate.
  6. Drive coil ................ The coil that creates a pulsating magnetic field that drives the rotor magnets. May also be called a solenoid.
  7. Drive circuitry ......... The electronic circuit that causes pulses of current to flow through the drive coil.
  8. Eddy current ring .... A device used to suppress out of balance motion of the rotor shaft.
  9. Back EMF .............. The spike of voltage produced by most non resonant coils when the driving current is suddenly removed.
  10. Snubber .................. A simple electrical circuit placed across the terminals of a coil, relay, switch etc to suppress back EMF.
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