Insert the machine screws through the L bracket, then
through the servo mount. Secure on the other end with a
nut. Before tightening, be sure the bottom of the L bracket
is flush with the bottom edge of the servo mount.
Attach the left mount assembly to the bottom deck
using 4-40 x1/2” screws and nuts. The screws should come
up from the underside of the deck, through the L bracket
as shown in Figure 7. When orienting the mount assembly,
be sure the servo shaft is centered in the wheel well cutout.
Align the assembly so it is parallel with the wheel well
cutout, then tighten all screws.
Repeat the same procedure for the right mount
assembly. Figure 8 shows how the completed servos and
mounts should look on the bottom deck of the robot.
Attach the front and rear skids as shown in Figure 9.
Each skid uses a 6-32” machine screw, hex nut, and acorn
(cap) nut. You can adjust the height of the skid by
loosening or tightening the machine screw in the hole. If
you need greater height adjustment, use a longer machine
screw, then tighten it into place using nuts on both the top
and bottom of the deck.
Important: Properly leveled, the robot should have a
slight “teeter tot” forward and back. If the skids are level to
the wheels and one another, the bot will not steer properly,
and it could get caught up in even the smallest of
obstacles. Conversely, if there’s too much teeter tot
movement, adjust the skids so they are closer in length to
Attach the wheels to the servos. Each wheel is secured
with a small self-tapping screw that is supplied with the
servo. Note that the servo shaft is splined, and this spline
matches the wheel hub. Be sure to press the wheel onto
the shaft firmly while tightening the screw. Do not over-tighten the wheel mounting screw, but be sure the wheel is
Secure the AA battery holder to the mounted servos
using small strips of double-sided tape or Velcro hook-and
loop fastener as depicted in Figure 10.
Add four deck risers to separate the top and bottom
decks in a tower configuration. These risers are made using
3” machine screws and rubber tubing.
Start by cutting to length four pieces of 0.25 O.D. clear
or milky white aquarium tubing. Trim each piece to about
2-1/4”. For each of the four risers, thread the screw from
the bottom deck. Place a length of the cut tubing over the
screw and lightly compress the tubing by hand-tightening a
nut over it. Do the same for all four risers. When it’s time to
attach the top deck, position it over the machine screws
and secure with four more nuts. Hand-tighten only. See
Figure 11 for assembly details. Figure 12 shows the
56 SERVO 09.2014
Figure 6. Use 4-40
machine screws and nuts
to secure each servo to
its servo mount.
Figure 7. Each
servo mount attaches
to the bottom base
of the PropBot
with a pair of
Figure 8. The PropBot bottom base showing mounted servo
motors. Note the orientation of the motor shafts relative to the
front of the robot (the front is pointing left).