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?

• Schematic diagram
• Parts list
• Buying the Parts
• Close-up photographs

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.

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.