I finished the motor mounts. Where at first I tried with the same plastic material as I used for the center part of the frame, I now opted for some more aluminium. The result is quite acceptable I think.
It also turned out that the frame is quite straight. With all four engines mounted all arms are resting without wobbling on the table on the screws. Might be that I have somewhere inherited some of the carpenter skills of my granddad. Or it’s just plain luck. Given that I cannot drill a hole anywhere I actually want it, I guess it’s luck 🙂
Next on the list: soldering the speed controllers to the engines.