My wheel is working again
I've just opened it to check what's broken and thankfully only the cogwheel of the FF motor had slipped down the axle. So I put it back on and now it's all fine.
I also took some pics from the inside of the DFP. It's really interesting, for example they put a special sensor just to check when the wheel is centered to avoid the decalibration problems of the previous Logitech wheels.
Pic 1: The opened wheel. Circuit board with USB, power and pedal connectors on the left. The FF motor with the optical sensor on the right.
Pic 2: The optical sensor. It's identical with the ones used in traditional ball mice, technically nothing special. Why can't they use such a sensor in the pedals too? It isn't that expensive.
Pic 3: The circuit board with the microcontroller in the middle.
Pic 4: The steering axle with ball bearing. The cograil is just for turning limitation. Coming out of the steering axle is the wire for the wheel buttons and two lights. On the far left is the "centered"-sensor.