View Full Version : Egg of Columbus

07-11-2009, 01:00 AM
I'm looking for some hints or plans to build a replica of Nikola Tesla's "Egg of Columbus". It's not particularly complex, but one of the unknowns to me so far is if it is single phase or poly-phase. Almost everything he did was poly-phase , but I'm not convinced this is necessary.

For those reading about this for the first time, Tesla had a copper egg made and he placed it in the field of a multi-winding toroidal core reactor. The egg, being asymmetrical, will spin owing to induced magnetism from eddie currents, and as it spins, the egg shape causes it to stand up on the fat end. the name comes from a parlor trick Columbus pulled on a group.

A picture being worth a paycheck...


07-11-2009, 01:08 AM

Any help?



07-11-2009, 01:17 AM
I'd seen those, but none answer the question. As said, most of it is pretty straight forward stuff, but none of what I've read so far describe the applied power. I think this would be a good project for scouts and first years at Hogwarts if single phase works, but if it's poly-phase then that puts it out of reach for the average home owner.

Edit: This project is much simpler than Tesla made it, but AC was his life so he did this in an awkward way by using electricity and not magnets. Today this can be done with rare earth magnets spinning under the dish out of sight, but that's too unclever and doesn't make a good scientific point. Tesla spent a good part of his life promoting AC power against Edison's DC grid, and it would have been a disastrous failure if not for AC motors, and later, poly-phase motors. The invention of the rotating magnetic field is in my mind one of the few sacred inventions of all time.

So while I could replicate this project in spirit by using a disk with lots of rare earth magnets on it I'm purist enough to want to repeat the principles as well as the function by using electrically generated magnetic fields. And I may have to ask someone with a CNC machine to turn a copper egg for me :)

07-11-2009, 04:41 AM

perhaps you need a Curate's egg. I have lots!!!


Will these do?

A couple (lots!!) of these will do me!!

This is more likely to be me or my lot:

07-11-2009, 06:14 AM
So while I could replicate this project in spirit by using a disk with lots of rare earth magnets on it I'm purist enough to want to repeat the principles as well as the function by using electrically generated magnetic fields. And I may have to ask someone with a CNC machine to turn a copper egg for me

This is a trap, right? Where does this trail of bread crumbs lead?

Spin a disk with lots of rare earth magnets on it near a bunch of solenoids. That is your poly phase power supply. It can be sitting across the room if need be. The wires connect to identical solenoids at the other end and arranged in the same pattern. That then makes the egg spin.

I happen to be making a power supply of that exact type right now. BTW, if you are lazy then just use an electric motor connected to a car alternator and by pass the diodes. Instant three phase AC power. You will need a bit of DC for the field winding.

I will be testing my generator in a couple of days and if it performs as I expect I will post it.

Weston Bye
07-11-2009, 06:36 AM
It appears that Tiffie's Wikkipedia reference explains it:

Tesla's device used a toroidal iron core stator on which four coils were wound. The device was powered by a two-phase alternating current source (such as a variable speed alternator) to create the rotating magnetic field. The device operated on 25 to 300 hertz frequency.
The fields would have been 90 out of phase, in a quadrature relationship. Such signals should be obtainable with a circuit similar to a static phase converter, providing 90 phase lag rather than 120.

07-11-2009, 08:04 AM
The college I went to had a demo of this in the electrical lab. They used 3 phase power applied to three separate coils arranged on a bench, 120 degrees apart, with the egg in the center. It was powered from a 3 phase variac. As the power was 60 hz, the egg did not spin fast enough to stand up on end, but it was a cool and interesting demo.

07-11-2009, 09:01 AM
you could probably do the same thing inside a 3 phase motor stator. We uesd to check windings by pulling the rotor, applying power and dropping a bearing in the stator and watching it run around the ID of the stator

07-11-2009, 11:56 AM
I didn't consider a quadrature configuration as two-phase is less handy and obviously missed the two-phase reference. Thanks! I have quite a bit of experience with quadrature devices and many homes still have them in their living rooms (television deflection yokes). Generating the two phases seems best accomplished with electronics as I don't have a good winding facility here though some starting caps could probably get the job done for this low power requirement. The frequency is a problem as pointed out. I need to get my head around three phases - I think the center of magnetic force walks off center which doesn't happen in a quadrature (just saw Bmyer's comment on that very point - wouldn't do to drag the egg around the dish).

I wonder how many setups is required to turn a copper egg... A tracer lathe would be one solution in the pre-CNC days. Three at least, I think.

07-11-2009, 12:15 PM
This is what I am building right now. It will generate two phase power. It is made partly from a remachined pole piece from a cheap ceiling fan. The rotor is Lexan with supermagnets (in color) and pole pieces. The output is AC of course and will be rectified to charge the batteries in my e-trike.


It will weigh much less than a regular automotive alternator and put out perhaps 1/4 the power which is sufficient for my needs.

07-11-2009, 12:38 PM
Interesting design - it could easily be a reciprocating linear rail with hollow cylindrical coils with magnets on a shaft. Such an arrangement would make it an interesting presentation piece. The logic can be reversed in which it becomes a motor-generator by powering the half the coils. The electrical equivalent of a Snow engine. http://www.youtube.com/watch?v=tn7u6xoeIMs

Speaking of Snow engines, had dinner with HSM'rs Jim and Jan Dunmeyer and saw the photos of his Snow engine project. Yikes! Those are huge.

07-11-2009, 01:24 PM
Jim and Jan stopped here as well. What an incredible project that is. It makes restoring a locomotive look like a warm up excercise. Great people and we had a good time discussing projects. I had the honour of having them as the first guests to park in my new RV parking space. :)