Nonstoprc, you mentioned that the ESC was emitting single beeps before you disconnecting the battery. Have you had the opportunity to check out the error codes in the User Guide for the CC120, yet? If they are the same as the error codes for the CC HV80, then I would agree with Dave Lockhart, in that the ESC did not cause the problem. The single beeps seem to indicate that the motor jammed or locked up. Last year while flying in a contest, in the middle of a maneuver, the same thing happened to my NEU F3A engine that had about 70 flights logged. After taking the engine apart, we discovered that the cooling fan was not working. After an email discussion with the "powers that be at Neutronics", I was told that the special "glue" that secures the cooling fan had failed. Five or so flights prior, I had noticed that the engine was a lot hotter than normal after a seven and a half minute flight, but I attributed that to the 103 degree Texas temps. Neutronics repaired the engine free of charge. The only thing to be concerned with is due to their workload at Neutronics, it usually takes 2 to 3 weeks to get your engine back.