Vibrations from the motors are the most common problem for areal photography and filming. The most common solution is to balance the propellers and the motors (search for instruction videos om YouTube on how to do this). But I decided to try another approach as well, namely to prevent vibrations from the motors to propagate to the frame. I'll use previous experience from building silenced computer chassies.
The key to this approach is to make sure that the motor and the screws holding the motor is insulated from the frame by vibration-damping material. Since the motors spinn at such high speed the vibrations are going to have high frequency. This means the material does not have to be so thick. I am going to use 1 mm rubber from an old bicycle inner tube.
For this I'm going to need:
The holes for the screws in the arm are going to be drilled up to accommodate not only the M3 screws but also the shrink tube around it. For good measure I made them 5 mm. I'll also need longer screws to allow for the washer, two layers of rubber and most likely also a prop-guard. M3x12 will do nicely.
Initially I planned on using four ordinary brass washers, but one large washer made out of 1 mm aluminium actually weights less and give better support.
The rubber mounted on the washer and secured in place by the shrink tube on the screws. To the right is the rubber for the motor. It's going to need a hole in the middle for the axis as well.
The finished assembly.