Cheating is bad. If you use performance-enhancing drugs in an athletic competition, it isn't fair. You also can cheat through blood doping, to increase the supply of red blood cells. And if you're a cyclist, you can do what's called mechanical doping. This means adding equipment like an electric motor to gain an unfair advantage.

This actually happened.

The Union Cycliste Internationale, the sanctioning body for professional cycling, confirmed Sunday that a mechanically doped bike competed in the Cyclocross World Championship. This is unprecedented in pro racing, but it may become more common as the technology grows more sophisticated. The UCI adopted formal rules banning the use of motors last year.

Such a motor could tuck into a frame tube, a wheel hub, or the bottom bracket. To find motors in the past, race officials used X-rays or dismantled the bike. But how do you find a motor hidden in a bicycle without taking it apart? It seems that the UCI used some type of tablet to scan bikes. Just how would that work? Of course, the UCI doesn't want to reveal its methods, lest it help cheaters employ countermeasures. But we can do a little informed speculation, assuming UCI officials did indeed use a tablet.

Infrared Imaging

Yes, you can add an infrared camera to your smartphone or tablet (example: FLIR One or Seek Thermal). This camera can detect IR radiation from an object in which hotter things give off different wavelengths of radiation. From this you can estimate the temperature of an object.

Here is an example of an IR image.

This shows two power adapters for laptops. The one on the right is being used and the one on the left is off. The plain fact is that electrical things get hot and you can detect this with an IR camera. If you want to use this method to find a hidden motor, the motor would have to be on, or recently used. A motor that is off and cold will be be undetectable.

Radio Frequency Electromagnetic Radiation

Why would an electric motor produce radio frequencies? First, the rider could have some type of radio frequency controller from the handlebars to the motor that would allow the motor to be turned on and off. This might be better than running wires through the frame (but I'm not sure why).

The other source of radio waves could be from the motor itself. Clearly you will have some type of oscillating electric current in the wires, and this could produce detectable radiation. However, an iPad or tablet might not be able to find these radio frequencies with the built in radios (for wifi and Bluetooth). You might have to add an external radio detector. Honestly, I don't think this is how the UCI searches for motors.

Magnets

Although it's possible to make an electric motor without permanent magnets, most motors have them. Actually, it's not too difficult to make your own electric motor. All you need is a battery, a coil of wire and one magnet. So, I assume that a hidden bike motor would also have a magnet.

Hopefully this won't come as a surprise, but magnets make magnetic fields. You can detect these magnetic fields with a normal compass—or the digital compass that is in most smartphones. But how far away would you have to be from a magnet to detect its magnetic field? For a simple test, I used the magnetic field sensor on my phone (using the xSensor app) and moved it towards a small neodymium magnet. You can see a significant change in the field at a distance of about 10 to 15 cm.

I think the magnetic field method of detection should work. It's better than the other two methods because you don't need an external device and the motor doesn't have to be on for the UCI to find it.

Looking at Performance

Could you just look at the cyclist's motion and determine if there is a hidden motor? I don't think so. Back in 2010, people were complaining that Fabian Cancellara's attacks were too powerful to be real. His apparent acceleration during a short stretch seemed to defy the limits of human performance. However, my analysis showed that Cancellera's acceleration and speed weren't that different from other riders. This doesn't mean he did or did not cheat, just that's it's difficult to know for sure whether someone is cheating.

But how much of a boost could you get from a motor? Let's make an estimate. Suppose you have a 200 Watt motor—that should be enough to give a nice acceleration increase. How long could you run a motor like this? It all depends on the batteries. The best batteries would be lithium-ion. 6These can store about 2.0 x 106 joules per liter. If I approximate a battery that is a cylinder 30 cm long with a radius of 1 cm, this would give a total energy storage of about 1.9 x 105 J. Now I can calculate the time this motor can run at 200 W.

That's about 16 minutes of runtime. Maybe you could get a bigger battery in your bike, but still I think 16 minutes is enough of a boost to make a difference in a close race.