After a couple of bad crashes I rebuilt the ZMR250 with a ZMR250 v2 frame from FPVModel.com. The carbon fiber is a lot better quality and the power distribution board really helped clean up the wiring. Finally, I decided to try Boris B's "Betaflight" fork of Cleanflight and the Luxfloat PID controller. I'm impressed. I did only the smallest amount of tuning to the stock settings and the quad is flying very, very well.