Question for EE types

[jyl]

I'm looking for opinions from electrical engineer-ish Pelicans.

The question is, if one can build a concealed electric motor into the rear rim of a modern bicycle.

The concept is: install rare earth magnets inside the carbon fiber rim, conceal windings in the seat stays and chain stays. Effectively treat the rim as the rotor and the stays as the stator. Assume you can conceal the battery and electronics in the frame tubes.

My feeling is that the distance between the stays and the rim (at least 20 mm at the closest point), and the limited surface area of the stays where they cross the rims, makes this impractical.

Here is an image: http://cdn.velonews.competitor.com/files/2015/06/29.jpg

What do you think?

[HardDrive]

One would think that the increased rotating mass of the magnets would make the system impractical.

There is already a system on the market with an electric motor hidden in the seat down tube that drives the cranks. And all of these systems are easily detectable.

[HardDrive]

Fabian Cancellara was accused of cheating using the system. I have not followed the matter closely.

Tour de France 2015: Cycling fears 'mechanical doping' poses increased threat to sport - Telegraph

[LEAKYSEALS951]

I like your idea- but one thing I have learned is that with a limited power supply, it is advantageous to be able to funnel it in through a point where you can utilize the gear system to get the right power curve. I had a 80 cc chinese motor on my bike, which didn't reach it's peak until I hooked it in through a triple front chainring and 9 in the back to really take advantage of the it's power band. I also had to disassociate the front chainrings from the cranks by adding a front freewheel so pedaling was supplemental and optional- not having the engine spinning the cranks and my feet at 120 rpm.

Maybe an electrical motor with a rim that large as the magnet would have so much torque it wouldn't matter?

I was just watching a video with a similar setup as the recently found bike which produced 250 watts ave- which is a NICE supplement to have.

Nice idea though- anything related to bikes like this I just love!

[wdfifteen]

To what end? Are you trying to ride to work without pedaling or trying to gain a small advantage in the Tour de France? It might give you the edge you need to win the TdeF, but doesn't sound like an easy way to get to work.

[aschen]

You don't have enough angular coverage of the wheel to have enough poles of windings to have an effective motor.


The down tube system in the news was slick packaging

[look 171]

Wow John, that's really clever of you to come up with that one. That's pretty damn cool idea.

[Willem Fick]

Originally Posted by HardDrive

Fabian Cancellara was accused of cheating using the system. I have not followed the matter closely.

Tour de France 2015: Cycling fears 'mechanical doping' poses increased threat to sport - Telegraph

I followed this very closely at the time, and must say footage of his performance in especially one finish-line group sprint provided a very credible smoking gun to me at least. The Cyclocross girl being found out in my mind certainly more than hints again that Cancellara was more than likely cheating.

Here's another nice link:

How Mechanical Doping Works in Cycling | Bicycling

[flatbutt]

That Vivax is very clever. But clearly intended as a cheating device. I wonder if they do software as well?

[jyl]

I'm finding the whole idea of building an undetectable motor into a bike just very interesting.

The UCI started out physically disassembling bikes (remove crank, use probe camera to look inside frame). They also started bringing portable xray machines to races. At the CX Worlds, they used a new "tablet app" to "scan" the bikes, any flagged as suspicious were disassembled. I think the app was an EMF detector, that uses the tablet's magnetic field sensor (enables the internal compass and attitude measurement) to look for the magnetic field from a motor's permanent magnets. Those sensors will also, I think, detect sufficiently large amounts of ferrous metal.

The existing internal motors (Vivax, Typhoon), which fit in the seat tube and drive the crank via a worm gear, would be easily detected with such a scanner. The Typhoon company actually helped the UCI develop the app. Then removing the seatpost would reveal the motor (and battery, if concealed there) and removing the crank would reveal the worm gear.

But the motor could be a type with no permanent magnet, I think. Use coils on both stator and rotor. And perhaps such a motor could be with no ferrous components, using copper windings, aluminum parts, ceramic bearings, some sort of plastic or fiber gear. So that might elude the scanner.

Then the battery could be hidden in the downtube. LiPo battery packs are small, light, and powerful. And we could fill the seattube with a Di2 shifter battery. So now, removing the seat post won't immediately reveal the motor.

Hmm, what to do about removing the crank? I can't think of a way to fool that test.

The motor-in-the-rim idea that I initially asked about was inspired by a newspaper article. An Italian reporter was told by someone, who claimed to build concealed bike motors, that hiding motors in seat tubes is so last decade, the state of the art for motor doping in bike racing is $200K "electro magnetic rims". So I started thinking about if this is really feasible. So far, I think "no" and the reporter got snowed. But I'm still thinking about it.

Anyway, any "rim motor" that uses magnets in the rim will be detected by the UCI's scanner too. And by simply lifting or spinning the wheel.