The battery tends to be hidden in a bidon. Motor is hidden in the down tube or the seat tube. It turns the crank, which then, after you hit the switch on your handlebars, turns the pedals. Quite simple, right? The motor can produce up to whopping 250 watts of power and that is going to make any hill climb much easier.
This system is nothing new and was already in use decades ago. Back then it was, due to the loudness of the motor, truly for recreational purposes only. With the advancement of the technology though, more and more allegations arise, that it’s used by the pros as well.
https://www.instagram.com/p/BBsNethuWCZ/
You can find quite a lot of material of self-spinning wheels online, so the question really is: Was Femke the only one? It sounds very unlikely…
Ryder Hesjedal – 2014 Vuelta
https://www.youtube.com/watch?v=ynLMfzLTc8M
Team Movistar member following the Femke Van Den Driessche scandal
https://www.youtube.com/watch?v=pD5YkqFGdwI