Cross section view of mechanical design
A single modulator lam stack
V1 of the modulator cage
Outer Stator
Interior Permanent Magnet Rotor
Machined aluminum parts for housing
The modulator cage was 3D printed using carbon fiber reinforced poly carbonate. It took many versions to get the cage to be strong enough, with the final version actually having a thin bridge on both the inside and outside to increase the stiffness. The housing was machined out of 6061 aluminum and the shafts out of non-magnetic 300 series stainless steel.
Optimizing Modulator Retention Strategies
One of the biggest issues in magnetic gear design is finding a way to hold the modulator pieces in place. The difficulty stems from a few reasons. Firstly, the air gap between the modulator rotor and the inner and outer rotors are often in the order of 0.5 mm or 1 mm which makes creating a structure very space constrained. Secondly, the support structure can not be ferromagnetic (since that would disrupt the magnetic fields going through the modulators) which limits the material choices that we have. Lastly, due to the first reason, the force on each modulator can be in the order of kilonewtons which in combination with the second reason makes the design very difficult.
In this project I tried to remedy this issue by evaluating various modulator shapes separately for both low and high pole count designs. By optimizing the modulator shape, the negative of that could be taken and made into the support structure.
The modulator shape chosen for the prototype
Fully assembled prototype
Video demonstrating the gearing action
The main metric that was tested on the prototype was the slip torque rating. In this case, the gear slipped at an average of 76.3 Nm which was within about 2.5% of what my simulations predicted. Additionally, the high-speed side was spun up to 1800 RPM just to verify that the mechanical structure would remain intact (which it did thankfully).
Some of the other designs that were also considered for the modulator shapes. Each has their own advantages and disadvantages which can be found in the accompanying paper below.
A much more detailed explanation and analysis can be found in my research paper on this topology. The paper can be accessed via IEEE Xplore or directly.