ORIGINAL: MinnFlyer
Something else worth noting is that you were using an 11x6 prop (After starting with a 12x6)
But the smallest prop recommended is a 12x7
Could be you were turning too many RPM.
I doubt that. The .55 AX is quite happy at much higher RPM than one could attain from using a 12x7 prop. A 12x7 prop is on the (too) large size for this one, IMHO.
-Robert