Magnetism loss in brushless motors
 

I know in brushed we could get the magnets zapped again and I just wondered if this would also help in brushless so is it advisable to change the rotor say every year to get the magnetism back to when the motor was new?

Maybe I should have given a reason behind the question and that is my Peak 6.5 motor was very quick to begin with and now it seems that the acceleration is not there and I have checked the bearings and I have tried different speedo's and bearings but the motor does not seem to have the notchiness that it one had which I assume is down to the rotor loosing magnetism when getting hot maybe someone else has an idea of what the problem could be?

The only way, as far as I'm aware, that the rotor of a brushless motor can diminish in strength is if it's been overheated. Overheating can easily cause the rotor to demagnetise, but other that that...they should never lose strength. Pretty much all RC-specific brushless motors use Neodymium as their rotor material, which is a permanent rare earth magnet and should never lose strength on its own, unlike those in most brushed motors.

If your Peak motor appears to have been losing strength, then you've probably either overheated it a little at some point, or perhaps your cells are going a bit soft? Then again, if it was "notchy" when you first got it, then this points to the motor having been overheated. :(