Have you ever wondered how to use a motor in an environment where a traditional motor just won't work—like submerged in seawater, in a vacuum, or when you need to completely separate a tool from its motor to avoid contamination? That's the problem that sparked my latest project: building and testing a 3D printed magnetic gear. This isn't your typical gear with interlocking teeth; these teeth mesh using magnetism and can transmit power through a physical wall.

How Magnetic Gears Work

A magnetic gear is an ingenious piece of engineering made from three main parts: an inner magnetic rotor, a stationary magnetic field concentrator, and an outer magnetic rotor. My design uses a diametrically magnetized neodymium magnet for the inner rotor. As this inner rotor turns, its magnetic field interacts with a set of soft iron field concentrators. These concentrators focus the magnetic flux, causing the outer rotor to rotate in the opposite direction.

The magic is in the numbers. By changing the number of magnetic pole pairs on the inner and outer rotors, you can adjust the gear ratio. My design has four pole pairs on the outer rotor and one on the inner, giving me a 4:1 gear ratio. The number of concentrators is simply the sum of the inner and outer pole pairs (4 + 1 = 5).

The design was done in Fusion 360, where I could see how all the components fit together. The inner magnet and bearings are held within the stationary concentrator ring, which is made of soft iron. The outer rotor, also with bearings, fits over this assembly, completely separated from the inner components by the concentrator.

Building and Testing

With the design finalized, I fired up my 3D printers and got to work. Using a motor mount I designed, I hooked up a DC motor to the inner rotor. For a fun twist, I also printed a propeller and a helically grooved drum to test its performance.

My first test was to measure the gear's maximum torque. I attached a string to the drum and added small bearing weights one by one, increasing the current to the motor as needed. The gear performed impressively, but eventually, with a torque of 15 N·cm, the magnets slipped and the gear "unmeshed." This gave me a baseline for what was possible with the initial design.

Boosting the Torque

I wanted to see if I could squeeze more power out of it. The idea was to increase the magnetic flux flowing through the concentrator. I decided to wrap the outer face of the magnets with a layer of low-carbon mild steel. Using the wire bender I built in a previous project, I rolled strips of the steel plate into a perfect circle to fit inside the outer rotor. It was satisfying to reuse a tool in such an unexpected way!

With the new steel insert, I re-ran the torque test. The results were fantastic. My gear could now lift five bearings at the same current that had caused the old design to fail. The new maximum torque was somewhere between 18.9 and 22.3 N·cm, an improvement of 25-45%!

Power Output

Finally, I wanted to see how much power the gear could output. I attached the propeller and ran the motor at different voltages, measuring the power consumed. At 36V, the motor was consuming around 180W. Accounting for efficiency losses (I estimated about 80%), I figured the magnetic gear could output around 150 watts. This is a solid number, and I believe it could go even higher with a larger propeller or a more powerful motor.

Final thoughts

Ultimately, I've designed and built a working magnetic gear that can transmit power wirelessly through a physical barrier. The torque-boosting trick with the steel insert was a huge success. This project opens up possibilities for building tools that are completely sealed from their drive mechanisms, which is exactly what I was hoping for.