Regarding the HAcker A50-16L and problems with it, I think I found the problem.

First of, my engine is working fine but it was making strange sounds when spinning up or when changing from powering to braking.

I'm dutch so I dont know the terminology in English, but I'll try to explain the problem.

The rotor is locked to the hub with a small steel pin. The fitting of this pin isn't too tight, which means the rotor can move in respect to the hub. This makes the motor makes the nasty noises.

I can't really explane it, but luckily, I've got a movie explaining what the problem is. Here you can see it clearly:
http://www.youtube.com/watch?v=onzZA5Z-EnQ

I fixed this by glueing the whole together using UHU endfest 300.