Mounting DJI 4114 Motors to QUADframe Mounts

DJI 4114 motor

We decided to use DJI 4114 motors from the S800 for our hexacopter.  They are low KV motors which means they will hopefully draw fewer amps and give us longer flight times.  Unfortunately they have an odd bolt hole pattern and do not fit on the QUADframe motor mounts.

bolt hole patterns do not match up

The DJI wires come out of the bottom of the motor and hit the mounting plate.  So first I had to make a clearance cut in the mounts for the wires.  I put two mounts into my milling vise at a time and located the center line.  I then used a 0.50" end mill to drill through the two mounts leaving a 0.25" deep semicircle on the end of each mount.  The mounts are made of G10 which machines easily.

cutting clearance for motor wires

The next step was measuring the hole pattern on the motor.  The holes are in a triangular pattern.  After much careful measuring, I came up with the pattern below.

DJI bolt hole pattern

I used the DJI motor mounts that came with the motor to locate the bottom hole.  I centered the DJI mount over the QUADframe mount and marked the bottom hole.  I then drilled the bottom hole in each of the QUADframe motor mounts with a #30 drill bit.  With that done, I centered the chuck over the bottom hole and used the X and Y dials to position the bit to drill the other two holes according to the above pattern.

compare original (L) to modified mount (R)

holy cow, it fits!

Luckily all of my measurements were correct and the QUADframe mounts fit the DJI motors on the first try. However, the captive nuts just barely hit the bottom of the DJI motors preventing them from sitting flush on the mount.

captive nuts hit base of motor

So I needed to remove some material from the base of the motors.  I used a grinding wheel in my Dremel to carefully grind small notches in the base where they hit the captive nuts.  I taped up the motors with painters tape first to keep the metal dust out of the motors.  When finished, I blew the motors out with some canned air just to be sure.

small notch ground into base of motor

With that problem solved it was time to mount the motors back on the frame, right?  Wrong.  One motor mount screw was directly under one of the boom blocks.  I had to cut a clearance notch in each boom block so it would sit flush over the screw.  And the other boom block pinched the wires so I had to file a notch in those as well.

clearance cuts on boom blocks

Finally everything fit.  I used a little thread lock on the motor screws and screwed the motors to the mounting plates.  The motors mounted nice and solid; almost a factory fit.  A more elegant solution would have been to machine new motor mounting plates, but I'm under a deadline and don't have the time.  However I expect I will have some carbon fiber mounting plates custom made at some point.

finally mounted