How Stepchange motors work

The power density of conventional electric motors can be improved by increasing the switching rate of the electric coils. Unfortunately this results in higher rotor speeds, more precise bearing requirements, more windage losses in the rotor gap, more heating, higher rotational inertia and more expensive and heavier reducers to reduce the rpm to useful levels, which are mostly below 500 rpm.

The Stepchange motor does not have a high speed rotor. It operates by rotating a very small gap in the interface between a compliant material bonded to the output and an outer stator, on which electro-magnetic coils are mounted.  Rotating a gap is analogous to pushing out a fold in a carpet - so that when the fold reaches the far end the whole carpet has moved forward. Apart from the fold, the rest of the carpet remains in fixed contact with the floor. Similarly, a caterpillar on a twig arches its body and rolls the arch forward, thereby moving itself forward, but if the caterpillar were to be held stationary, the twig would move backwards instead of the caterpillar moving forward.

Both rotary and linear embodiments are described in the patent application, including actuation by electro-magnetic coils, piezos, electrostrictive materials, smart muscles, carbon nanotube muscles and physical input  etc. and both friction, and positive output.

In the Stepchange motor version illustrated on the Home page, the coil cores are the stator and face permanent magnets or magnetic material on, or in, a compliant material, such as rubber. The compliant material is the output to which a shaft or output ring is attached. In operation, the coils are activated in sequence, repelling the permanent magnets, opening a gap between the coils and the compliant material and moving the gap. Because the two sides of the interface that create the gap are of different lengths, the longer, compliant, side moves by the difference each rotation. The smaller the gap, the higher the reduction ratio.

In most embodiments the output is frictional. Friction may be increased by reversing the current, attracting the magnets to some the coils, instead of repulsing them. This increases the force between the two surfaces and so increases the friction. Because the contacting interfaces do not move relative to each other, there is no need for a bearing and curved or ribbed interfaces prevent axial displacement.

Note.  The video image is not to scale. It illustrates a reduction ratio of 20:1

Reduces >500 to 1

No bearings

No rotor

No airgap

The Stepchange Motor

No gears

Patent pending




Holds on power off 

Hollow shaft




Industrial machines



Stepchange Motor Ltd is a UK Start-up commercializing a novel electric motor by licensing

No precision parts