Solution’s Advantages and Impact
Axial Reluctance Motor. We have manufactured a Phase I prototype that uses a radial reluctance motor for pitch control while its spin control is achieved using a pulley driven by an engine shaft/external motor. Our Phase II prototype will use two axial reluctance motor designs – one for pitch control and one for spin control.
Axial motors are regarded by many as the future of electric motors because of their power density which grows with the cube of rotor diameter (whereas that of radial motors grows with the square of diameter). Established market solutions use rare-earth magnets which are plagued by supply chain issues tied up with China. Incipient market solutions for axial reluctance use soft magnetic composites (groups of iron particles that are embedded in an insulating layer to avoid eddy currents); these nevertheless are relatively complex to manufacture and have magnetic permeability that does not even rise to that of laminated 1010 electric steel let alone that of nickel/cobalt mixes.
The use of SMC seems to be the only recognized solution for realizing a permanent-magnet-free motor in axial reluctance form. The insulating layer between electric steel laminations appears to have presented a cognitive barrier to attempting a laminated axial reluctance motor. The effective air gap presented by the 0.5-micron airgap between laminations would eventually add up significantly over a tall, laminated stack if flux were to flow axially through them – however, axial reluctance motors are generally noted for being much shorter than their radial counterparts. For instance, a 21kW axial reluctance motor made from SMC is only 3” high – creating an effective additional air gap of 0.03 mm if the rotor were instead laminated (with a design intent air gap of 0.8mm this only incurs a 4% increase). When considering that each iron particle, in an SMC motor, has an insulating layer that varies from 100nm to 600nm, we conclude that the added air gap from an SMC motor will be significantly larger than that of an axial flux motor made of laminated steel.
“A failure of others” appears to have left this very simple solution unrealized in research and market activity– we have seized on it by filing a provisional patent claiming patent-law bases like “the failure of others” and “skepticism of experts.” An axial reluctance motor made from laminated steel will enjoy the benefits of existing industrial processes, domestic supply and the low-cost point of electric steel – with the possibility for using nickel/cobalt laminations that can have magnetic permeability as high as 38 times that of electric steel. We will likely partner with Yeadon Energy Systems Inc. to use their pre-existing expertise in motor design. We have a solution to address stress in the lamination stack in the context of axial flow.
Cool Mechatronic’s research intent for Phase II is an EMCP fan but the possibility for one of the best motor topologies available on the market has also emerged.