I think my Neu 1515 1y broke down ..

[suicideneil]

What you are looking for is the shaft being able to rotate inside the magnet, or the magnet around the shaft- just grip the shaft with some pliar or molegrips on the flat spot, and try to rotate the magnet by hand; it it feels loose or slips at all, then its like I said.

I doubt its the esc, especially if the motor does the same thing on two different ones.

Unloaded, the magnet is tight enough on the shaft to spin the rest of the drive train; loaded, the shaft slips and only the magnet rotates within the motor can.

Easy test; put the truck on a bench, and observe the spur & pinion gear when you try to prevent the wheels from turning by holding the truck in place (be brave!)- if you hear the motor spinning but the pinion & shaft dont, then you know whats up...

Final test would be a different (any) Bl motor on the same escs, just to see if the truck does move when you hit the throttle.