box for a kit of parts, including precut body pieces and
To complete the PropBot, you’ll need the hardware
listed in Table 1 to put all the pieces together. Except for
the skids and riser standoffs, I’ve specified 4-40 size
hardware for everything. While 4-40 machine screws and
nuts are a little harder to find than 6-32 hardware, their
smaller size makes them better candidates for a small
robot. Another advantage: They weigh less. A lighter robot
can go farther on a set of batteries.
If your local home improvement store doesn’t have the
4-40 hardware, you can always get it online; again, refer to
the Sources box for a small selection of Web retailers that
carry miniature fasteners. Tip: When searching the local
digs for miniature nuts and screws, try the smaller
hardware stores first. They’re more likely than the “big box”
retailers to have what you’re looking for.
In addition to the assembly hardware, at a minimum
you need the additional components in Table 2 to build
your PropBot. Some additional parts will be needed to
complete other functionality of the robot. We’ll cover those
parts in upcoming installments as they are described and
Assembling Your Robot
With the body pieces constructed (or purchased) and
all other parts in hand, you’re ready to build your PropBot.
Note that not all of the components listed in the tables are
used in this first installment. Some — like the piezo speaker
and switches — are covered in later parts of this series.
Before assembly, you may wish to use 150 grit
sandpaper to smooth the edges of the base parts.
Orient the bottom deck so that the holes are aligned as
shown in Figure 3. Note that the holes for each servo are
not symmetrically placed on the deck. This is to
accommodate the offset of the servo drive shaft. While
there is technically no “front” or “rear” of the PropBot, for
the purposes of assembly, the top of the illustration in
Figure 3 is the front and the bottom is the rear.
Insert a servo into a servo mount by sliding it back-end
first through the mount. The fit may be tight, depending on
the make and model of the servo. (As necessary, enlarge
the rectangle for the servo using a file or coarse
sandpaper.) Do not force the servo into the mount or the
mount may be damaged. Secure the servo to the mount
with 4-40 x 1/2” screws and hex nuts (Figure 6). You can
use four screws for each servo, or only two. When using
two screws, position them on opposite corners of the servo
mounting flange as shown.
Repeat for the opposite servo and mount. Be sure to
construct the second servo and mount in mirror-image
to the first! Refer to Figure 8 in Step 3 to see how the
motors should be inserted into the mounts.
Using 4-40 x 1/2” machine screws and nuts, attach
two plastic L brackets to each of the servo mounts. You’ll
make a “left” and a “right” mount assembly.
• For the left mount assembly, the motor shaft should
face to the left and toward the “top” of the deck (as
referenced in Figure 4). Attach the L brackets to the
right side of the mount.
•For the right mount assembly, the motor shaft should
face to the right, also toward the top of the deck.
Attach the L brackets to the left side of the mount.
SERVO 09.2014 55
Servos and servo mount hardware
6 4-40 x 1/2" pan head machine screw
16 4-40 hex nut
4 3/4" x 3/4" plastic angle bracket*
Propeller Activity Board mounting standoff hardware
4 3/4" to 1" (approx.) length nylon standoffs, 4-40 thread
4 4-40 x 1/4" pan head nylon machine screw
4 4-40 x 1/2" flat head machine screw
2 6-32 cap (acorn) nut, nylon (preferred) or steel
2 6-32 x 3/4" or 1" pan head machine screw
4 6-32 hex nut
Deck risers (standoffs)
4 6-32 x 3" pan head machine screw
8 6-32 nuts
4 2-1/4" lengths of clear rubber (aquarium pump) tubing, 0.25" O.D., 0.170" I.D., available at most home improvement stores
* For the 3/4" x 3/4" plastic angle brackets, you can substitute the nearest
smallest metal L brackets available. The plastic brackets weigh a little less.
1 Parallax Propeller Activity Board
2 Standard-size servos, continuous rotation, Futaba compatible splined hubs (ex: Parallax 900-00008)
2 2-1/2" or 2-5/8" wheels with Futaba compatible hubs (ex: Parallax 28114 or 28109)
4 x AA battery holder for non-rechargeable cells, with 2.1 mm
center-positive barrel connector (ex: Parallax 700-00038) or 5 x AA
battery holder for rechargeable cells, with 2.1 mm center-positive
barrel connector (ex: Parallax 753-00007)
4 or 5 AA batteries (four alkaline or five rechargeable)
1 Miniature piezo speaker (ex: Parallax 900-00001)
2 Snap action leaf switch (standard size)
1 12" length three-wire (signal, power, ground) extension (ex: Parallax 800-00120)
Misc Jumper wires (ex: Parallax 800-00016)
Misc 12" length of 0.25" O.D. (outside diameter) aquarium tubing