44 SERVO 06.2016
marking your motor patterns.
Manufacturers don’t often change
their pattern, but they could without
notice. Also, an asymmetric hole
pattern is used on the Turnigy motors
I bought (2209-980Kv Outrunners). I
want the wiring harness of the motors
to face towards the inside of the
drone, but the hole spacing changes if
you rotate the motor mount 90°. Just
be careful and triple check this!
After marking, I used a center
drill in a drill press to make a divot
that ensures the drill bit doesn’t
“walk” and the holes end up in the
wrong place (Figure 2). A spring-loaded center punch could do the job
just as easily. I used a 1/8” pilot drill
for all the holes, then drilled them to
their final sizes.
Once all the holes are drilled, it’s
a good idea to clean up the burrs and
sharp edges. I used a #2 center drill to
clean and taper the outside face of
the holes, and the mill file to remove
burrs inside the channel. I also labeled
the arms to designate forward and
aft, as well as the wide and narrow
motor mount patterns.
Figure 5. A speed square is an easy way to make sure that your motor arms are
square with the body of the drone. Be sure the edge you use as a reference is actually
square, as well!
Figure 3. I clamped the spacers together
to be sure they were straight and
identical. Try to find straight stock when
shopping at the hardware store. I also
wrote a note to myself so I would drill
these as 1/4” deep blind holes.
Figure 4. Cut the base plate out of
1/8” plywood and drill the four 1/8”
holes to mount the motor arms.