Electric Motor

Current design of DC motors requires some method of alternating the direction of current to ensure continuous rotation of the output shaft; this can be in the form of brushes, commutators, or digital control. Additionally, the orientation of the wires and magnetic fields in typical DC motors induces an electromotive force (EMF) in the direction opposite of the applied voltage. This is known as back-EMF and restricts the current that can be supplied to a motor. The goal for this project was to build a proof of concept for a direct current (DC) electric motor that does not require a any switching method to operate in a steady state and eliminates back-EMF. It accomplishes this by using stators that wrap around the rotor and generate a magnetic field that aligns with the magnetic field generated by permanent magnets in the rotor.

I created models of the motor in a software called Alibre, which can be seen in the pictures below. I began by modeling the rotor which was sized to fit permanent magnets that I already had available. The rotor was then divided into four pieces that could be fit through the stators and bolted together. I then modeled the stator so that it wrapped around the rotor and split them in half so that they could be 3D-printed more easily. The biggest challenge was connecting the rotation of the rotor to an output shaft without interfering with the stators. To accomplish that, I turned the rotor into a ring gear and meshed it with a set of internal gears that connected to the final drive gear. To complete the design, I added in the bearings, pins, coils, and housing. Lastly, I 3D printed the parts, ordered the necessary hardware and assembled it all together.

Isometric View

Isometric View with Cover Removed

Front View with Cover Removed

Cross Section View

Exploded View

Overall, this was a fun design to explore, but it has several drawbacks that may prevent it from being a viable alternative to traditional motors. The first drawback is the increased overall complexity of the motor. The split rotor and subsequent gear chain would increase manufacturing costs and inefficiencies as well as providing additional failure points. Second, the connection between the rotor and the output shaft limits the amount of coils that can be used in the motor. Traditional designs are able to achieve a more significant density of coils and leave less empty space within the motor. Some adjustments to the design may be able to mitigate these drawbacks, but it is difficult to say if it will be enough to make the design a commercially viable alternative.

3D-printed Components and Hardware Assembled with Window to Inspect Rotation of the Rotor

Alternate View of 3D-printed Prototype

Back View of Prototype Showing Solder Connections between Coils