Important! The PAB can be powered via USB (when
connected to your PC for programming) or from a 9 VDC
“transistor” battery. Neither is suitable for running the
motors of your PropBot. The reason: The motors may draw
too much current for these sources to handle. Use AA cells
when operating the robot on its own. If you don’t want to
wear down the batteries while programming, connect a
7. 5 to 9 VDC wall adapter to the PAB. The adapter should
be rated at one amp or higher.
Constructing the PropBot
Let’s now turn to building the PropBot. Construction is
straightforward, requiring only one square foot of material.
You need to cut four pieces total:
1 Bottom base with small cutouts for the wheels
1 Top base
2 Servo mounts
A cutting and drilling diagram for the main top and
bottom decks is provided in Figure 4; Figure 5 shows a
cutting and drilling guide for the servo mounts.
You can use 1/4” plywood or (my preference) 6 mm
expanded rigid PVC plastic. The plastic is lighter weight, and
if purchased locally from a plastics distributor, is often
cheaper than wood. In a pinch, you can use 1/4” thick
foam-core construction board. This method provides an
easy way to construct quick prototypes, but you’ll want a
more hearty material for a longer-lasting design.
Either way, plywood and PVC can be readily cut using
ordinary wood tools. I suggest a coping saw for working by
hand, but recommend a motorized table scroll saw for the
fastest and most accurate cutting. You can use any type of
drill — all holes are 1/8” unless otherwise indicated. Some
hole locations are critical, so follow the old adage: Measure
twice, cut (or drill) once.
When marking off the holes for the activity board in
the top deck, use the PAB for the hole locations. If you’d
prefer not to do the cutting and drilling, see the Sources
54 SERVO 09.2014
Figure 5. Cutting and drilling template for the servo mounts.
Figure 4. Cutting and drilling template for
the top and bottom decks of the PropBot.
Exact position is not critical, except for the
holes marked with a red frame.