In Part 3 of this series, I had received most of the parts and started work on the chassis. Is this
part, I will put together the drive
motors, complete the rest of the parts,
and assemble the bot. I was on a tight
deadline as there was only four weeks
to go before the bot’s first event ... I
started by modifying the longer axles
I would use in the Banebots P60
gearboxes. The shafts had two grooves
added for the circlip (Figure 1) that
would retain the wheels, then was cut
off to length. I chose to add two
grooves and make the shafts a little
longer than planned to cover any
unforeseen problems. A longer shaft
could always be made shorter, but if I
cut them too short I would need new
shafts at very short notice.
The shaft is retained in the
gearbox by a 7/16” circlip (Figure 2).
These are easy enough to get off if you
have the right size tool, but it turned
out my pliers had pins that were too
large. In removing the clip by other
means, one of them pinged off never
to be seen again. Fortunately, my local
hardware store had a replacement. You
will need a set of pliers with 0.038” or
smaller tips for clips this small. I
ordered a set from McMasters.
The P60s come assembled, but you
must disassemble them and grease
them before they can be used. Be
careful to note how the various stages
go together; take a few pictures.
After swapping the shafts out by
removing the clip, pulling out the shaft,
and replacing it with the new shaft and
refitting the clip, I added grease to
each gear and the post it fits on to
(Figure 3) until I had the gearbox all
back together. I then fit the motor
plate to the motor with the
provided screws (Figure 4). I
used a little Loctite on the
threads to make sure they don’t
come loose in use. Don’t be
tempted to not do the Loctite.
I then attached the motor to
the gearbox with the four long
screws (again, use a little Loctite
on the threads) to complete the
drive motors (Figure 5). The motors
are a larger diameter than the
gearboxes, so you need a spacer block
if you want to mount them on a flat
panel like the base in my bot. So, I
machined a couple out of some scrap
aluminum (Figure 6).
The only critical dimension was the
thickness so that the axles will line up
correctly with the bushes in the chassis.
SERVO 05.2014 35
Is telus Rex
● by Pete Smith
Part 4: The Sprint to the Finish Line
FIGURE 4. Add plate to motor.
FIGURE 3. Re-assemble and grease.
FIGURE 1. Modifying the longer
motor shafts. FIGURE 2. Shaft retention clip.
FIGURE 5. Motors and gearboxes