Burnt controllers motors
A 2 amp controller may burn out since the GWS-A motor pulls close to that on 8 cells. Also, make sure that the prop is sized for the gear ratio of the motor. An oversize prop will make the motor pull a lot of extra current.
A 5 amp controller should work with no problem. What brand is it? I've had good results from GWS, Jamara, and Jeti controllers.
If you are going to be doing a lot of electrics, I recommend getting a wattmeter from Astroflight or a similar one. That will tell you if the problem is too many amps for the controller, or if the controller's a faulty one.
Good luck!