Electromagnetic wheel motors possible in theory, but unlikely in practice

by James Huang


Recent news coming out of the world cyclocross championships in Belgium last weekend has confirmed the first documented case of what the UCI refers to as technological fraud as well as one of the primary suspected methods — a small electric motor and battery, hidden inside the frame, that directly drives a bevel gear on a modified crankset spindle.

Setups like what was found on Belgian Femke Van den Driessche’s bike have long been suspected. With only relatively simple mechanical and electrical components required, they can be small, cheap, easy to install, and easy to hide.

A recent report in Italian newspaper La Gazzetta dello Sport, however, suggests that direct-drive motors like that are only the tip of the iceberg with far more advanced systems already allegedly in use — namely, one that turns the rear wheel itself into an electromagnetic motor.

La Gazzetta’s anonymous source on the subject claims the system can produce up to 60 watts of extra power, available on demand, at a substantial cost of €220,000.

It sounds outlandish, particularly since it doesn’t function like a traditional motor, but it’s far from impossible.

How it would work

The infographic La Gazzetta used to depict this “electromagnetic wheel” doesn’t make much sense on its own. Not only is there no power source depicted, but the embedded wires wouldn’t generate any forward propulsion, even if there was a power source.

Infographic by La Gazzetta showing an “electromagnetic wheel"
Infographic by La Gazzetta showing an “electromagnetic wheel”

“The motor diagrams show wires, presumably carrying current going around a wheel underneath the tyre [with] no coils or loops parallel to the tube,” British journalist and Cardiff University physics graduate Josh Owen Morris told CyclingTips.

“In an electric motor, the direction of the electric current is at right angles to the direction of motion. If your current is going in the same direction as you supposedly want to travel, you’re going to struggle, to say the least.”

That said, it is possible, even if only in theory, to drive the rear wheel using electromagnetism by turning it into either a switched-reluctance motor or the circular equivalent of a magnetically levitated high-speed train.

Either scenario would require a specially modified rim with inserts embedded at precise intervals.

Depending on mechanism used, those inserts would be either some type of ferrous material, or strong magnets.

Electromagnets would then be housed inside the chainstays and/or seatstays, connected to an internal battery and some type of central processor (CPU), presumably connected to a wireless controller.

For an electromagnetic wheel to be possible in real life, electromagnets would be needed inside the chainstays and/or seatstays, connected to an internal battery and some type of central processor (CPU), presumably connected to a wireless controller.
For an electromagnetic wheel to be possible in real life, electromagnets would be needed inside the chainstays and/or seatstays, connected to an internal battery and some type of central processor (CPU), presumably connected to a wireless controller.

If current is pulsed through those electromagnets at the correct frequency, one could essentially create a wireless motor with no visible parts.

Why it’s unlikely

Whichever method is used, turning a rear wheel into an electromagnetic motor is far easier to do in theory than in practice.

In addition to the physical hardware that would have to be developed (including a custom molded rim that would presumably mimic that of the supplying team sponsor), the frequency of the applied current would have to be unfailingly precise, so as not to turn the desired speed-boosting motor into a resistance-adding generator.

“In order to keep the weight low and have it work reasonably well, you’d need thin strips of magnetics around the rim,” Dave Pfieffer, an electrical engineer at Ball Aerospace in Boulder, Colorado, told CyclingTips. “The inductive side of the motor would likely be inside the chainstays or seatstays. As an engineer, you’d then want a tight clearance between the seatstays/chainstays and the rim for maximum efficiency.

“The real question is how much are the magnetics and induction motor elements going to weigh? I bet it’s all possible to keep the total system weight under 2kg (4.4 lbs), but at what cost? To keep the weight down, you’d need some very hard-to-manufacture magnetics. They’d need to be small, thin, and lightweight, yet generate strong magnetic fields. You’d then have to get them in the wheels. Basically I’d say yes, it’s theoretically possible, but I’ll put this in the ‘I’ll believe it when I see it’ category.”

So, is an electromagnetic wheel possible? Yes, in theory.

Whether or not such a thing has actually been used in practice is another question entirely, but as we’ve already seen, truth can be stranger than fiction.


Video: Switched Reluctance Motor

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