Egg of Columbus

This is a replica of Tesla's Egg of Columbus currently on display in the Nikola Tesla museum in Belgrade. The museum also has Tesla's original device in their archives but is in dire need of restoration. This device was envisioned and constructed by Tesla to to demonstrate his rotating magnetic field principal which is used today in most of our modern electric motors.

Christopher Columbus story

In the story, Christopher Columbus attends a dinner which a Spanish gentleman had given in his honor. Columbus asks the gentlemen in attendance to make an egg stand on end. After the gentlemen successively tried to and failed, they stated that it was impossible. Columbus then placed the egg's small end on the table, breaking the shell a bit, so that it could stand upright. Columbus then stated that it was "the simplest thing in the world. Anybody can do it, after he has been shown how!"

Tesla's Egg of Columbus

Nikola Tesla, at the 1893 World's Columbian Exposition, demonstrated a device he constructed known as the "Egg of Columbus". It was used to demonstrate and explain the principles the rotating magnetic field model and the induction motor. Tesla's Egg of Columbus performed the feat of Columbus (without damaging the egg) by means of a rotating magnetic field. The egg spins on its major axis, standing on end due to gyroscopic action.

Brian's Egg of Columbus

In the spring of 2005 I became involved in the production of a stage play honoring Nikola Tesla and his achievements. With Tesla's rotating Magnetic Field being a key milestone in his life I sat out to try and recreate this demonstration device.

My plan was to first build a prototype using available materials and to determine how I was going to develop the Two-Phase power needed to drive an eventual replication of Tesla's device.

I started by gutting an old induction motor and re-connecting the field coils in a two-phase configuration.

Since I didn't have two-phase available to me I used a bank of capacitors to generate the second phase.

Suspending a small bar magnet into the core immediately showed me the magnetic field was NOT rotating.

Adding some instrumentation to the setup, a scope and a couple DMM's allowed me to see the two phases were woefully imbalanced. This imbalance was resolved by varying the capacitance on the generated phase and adding some resistance to the primary phase (in the form of a space heater).

Once I had the magnet spinning it was tome to move on to my main goal of spinning a ball and eventually an egg. What I found was the core of the motor focused the magnetic flux deep in the motor and this was something I'd have to consider during this testing and when constructing the finished piece. Using a small bowl allowed me to get a metal ball deep enough into the field so it would spin. Hurray!!!

If a little way in is good more must be better, right? Here I used a drinking glass to get the ball deeper into the field. It did spin better deeper in but was much harder to see.

With this device drawing nearly 2,000watts to spin a small metal ball it's not very efficient as a motor but that is not its purpose. But place a small compass in the center and it plainly demonstrates Tesla's Rotating Magnetic Field.

Now that I knew I could build it it was time to find a common and easily accessible material as a core to wind the four coils on. Reading Tesla's comments he specifies insulated iron wire to reduce eddy losses and heating but insulated iron wire is hard today. What I decided on was to use metal strapping material which is a steel band .500" wide and .100" thick with a heavy coat of paint on it which I'm hoping to use as insulation. Strapping material is not easily wound into the 10" diameter pieces I need so I needed to construct a winding jig.

Gluing the center of the jig to the fixed side plate (the propane tank and bag of lead shot are just for weight while the glue dries).

Due to an overabundant supply of projects, and not enough time, I haven't got back to winding the cores yet...