After converting to the BL motors I had problems with the behaviour of the DF:

When applying quick throttle the DF shake and rolled in one direction (mostly to the right) and when descending it tended to wobble like crazy and was hard to control.
I holded the DF down to the ground and applied throttle and noticed that the main rotor gear was pushing against the motor pinion causing the motor to run very hard.

After close inspection I found that the motor mounts where deforming to an oval shape because the motor adaptor is to small and hardly touch the motor mount.

Solution:
I cut rings of a broken standard motor and clued them inside the motor mounts to stabilize them so they cannot deform anymore.
Problem solved. No more shaking.

Bernd