While the design for the chassis has changed, it still
goes together as shown in the last article. A couple things
led me down the road for this particular design.
Originally, I was using a Dimension Engineering
Sabertooth 2 x 12 RC motor controller. While you can still
use this controller (as I kept the hole pattern in the chassis
bottom), I added a second set of holes that will allow you
to mount the smaller Sabertooth 2 x 5 RC motor controller
shown in Figure 7. This motor controller can easily control
all the motors in the PBOD. Its smaller size yields more
space inside the chassis for a battery or other payload.
You can get more information on both the 2x12 and
2x5 controllers at www.dimensionengineering.com.
I was able to test a couple different motors available
from SparkFun (Figure 8). Of the motors I tested, the
ROB-12007 and ROB-12008 work the best in the PBOD. The
ROB-12007 will make your PBOD faster, but it will have less
torque. This is good for smooth surfaces with a lot of room.
The ROB-12008 is slower, but yields more torque. It works
well on surfaces with
more traction like rugs
and carpets. It is also
easier to control and
capable of precision
movements. I have used
both two and three cell
Li-PO batteries with
success. The size of these
motors allowed me to
place both of them at the
rear of the PBOD. This
adds a much larger
payload area inside, plus
makes access to the motor
controller easier for motor
hookup. You can get
more information on the
motors at www.sparkfun
Start by installing the
two end chassis parts to
the bottom chassis part as
shown in Figure 9. Use
four nylon #6-32 x 3/8”
machine screws and four
hex nuts to secure them.
Install the two sides
using five #6-32 x 3/8” nylon machine screws and hex nuts
on each side as shown in Figure 10. Notice the orientation
of the motor cutouts. They are located at the rear of the
bot. The rear bottom part is the end with the controller
cutout. The end with the small slot is the front of the bot.
Place a washer on six #6-32 x 1-1/2” machines screws
and insert them into the six lower holes (three on each
side) from the inside; refer to Figure 11. Add lock washers
and #6-32 hex nuts, then tighten. Don’t over-tighten or you
stand a chance of damaging the plastic.
Place a washer on a #6-32 x 1” machine screw and
insert it into the top hole opposite the motor cutout
(Figure 12). Add a lock washer and hex nut. Tighten the
nut. These are the two idler gear axles.
Place a #2 washer on two #2-56 x 1/2” machine
screws and insert them into the two holes as in Figure 13.
Add a second washer to each screw and secure with a
#2-56 nut. Finger tighten only.
SERVO 01.2014 49
Figure 9. Figure 10.