Chapter 8: Barry's Magnetic Levitation

These coilguns with control circuits are great! Now... How can you use them for magnetic levitation?

This is slightly off-topic from coilguns, but magnetic levitation has many common design principles and is a little easier to build!

How Levitation Works

If you hold two permanent magnets close together, you see that one of them will jump strongly toward (or away) from the other. In 1842, Samuel Earnshaw expressed the perversity of inanimate magnetic objects in his theorem. It explains this frustrating behavior will always prevent you from suspending one permanent magnet above or below another, no matter how one arranges the two magnets. However, an active control circuit can get around this problem by rapidly adjusting the magnet's strength.

The general principle is straight forward: An electromagnet pulls a ball upward while a light beam measures the exact position of the ball's top edge. The magnet's lifting force is adjusted according to position.

As less light is detected, the circuit reduces the electromagnet's current. With less current, the lifting effect is weaker and the ball can move downward until the light beam is less blocked. Voila! The ball stays centered on the detector! It is a small distance across the photodetector, perhaps a millimeter or two, but this is sufficient to measure small changes in position. Of course, if the ball is removed the coil runs at full power. And conversely, if the light beam is blocked the coil is turned completely off.

This device uses two photodetectors: the "signal" detector looks for an interruption in the light beam, and the "reference" detector measures the background light. The circuit subtracts one signal from the other to determine the ball's position. The use of two detectors is my small contribution to advance the art of levitation. This design automatically compensates for changes in ambient light, and eliminates a manually adjusted potentiometer.

Barry's Maglev Demonstrator

Here's why I built one:

A nice entry for a science fair.
There are other fun levitation systems
There are some great wacko sales pitches for it!

How does it work?

So how was it all designed?

Circuit design for Infrared Emitter circuit
Circuit design for Photodetector circuit
Circuit design for Reference voltage circuit
Circuit design for Difference amplifier circuit
Concepts of Feedback loop control systems
Concepts of Feedback loop equations
Concepts of Bode plots to represent transfer functions
Concepts of Phase lead network circuit
Circuit design for Output amplifier circuit
Circuit design for Coil driver circuit
Circuit design for PWM coil driver circuit
Coil design of the Lifting coil
Levitator Simulation using PSPICE

How do you get it working?

How long does it take to build?
Constructing the wooden base
Connecting the power supplies
Using a printed circuit board
Setup and Adjustment overview
Testing the power supplies
Testing the infrared LED emitter
Testing the signal detector
Testing the reference detector
Adjusting the sensing resistor for the reference detector
Testing the difference amplifier
Testing the non-inverting amplifier
Testing the output transistor
Adjust, connect and test the lifting coil
Results and Further Work

Other Fun Levitation Systems

There are many ways to levitate objects magnetically. Here are some fun methods that I've used.

The simplest!	Guy Marsden's Levitation Kit is built on a single fan controller chip!
The best!	The Visual Levitation kit (read my review)
Do it yourself!	The Levitation Engine kit is an inexpensive start
Completely free!	Float your own Magnet over a hard drive (free!)
Fun toy!	The Levitron antigravity spinning top
Cheap and cheesy	Go to Edmund Scientific and search for "levitator"
Executive toys	SirTimeBenda has levitating globes and executive toys for sale

Comments? Send me your suggestions and circuit improvements! Send your levitator e-mail to Barry Hansen and put "levitator" in the subject line. Please note: I am not interested in antigravity theories, overunity devices, gravitic shielding or other types of fringe science. Thank you in advance for not asking.