of screws that held the front panels on, and eventually the
front panels were lost (Figure 5). However, the bots battled
on. I observed that every time a screw popped off, the
crowd would cheer. When a front panel was lost, they went
wild. It was pandemonium. I would tape the front panels in
place just so they could be torn off again. Nothing is cooler
than a bot dragging around part of its ripped off chassis.
One thing I took away from this experience is the idea
of designing a set of bots that could rip each other apart.
The PROCS design looks like a good place to start, but in
this application it’s really not. Because of the actuators and
microcontroller control, each cost over $2,000 to build. I
also thought they held up a little too well. I went back to
the drawing board.
What I came up with is what I call PBOD. This stands
for Plastic Bot of Destruction. The opening photo shows a
prototype that I have been working on, but I’m sure we can
make improvements. Let’s take a look at how this series will
The prototype shown at the beginning was a proof
of concept. Could I design and build a small inexpensive
bot that could be used in a radio controlled battle
scenario? The prototype showed it could be done. All of
the parts except for the electronics, hardware, and tires
were completely 3D printed. Although it’s a little sturdier
than what I eventually want, it helped me come up with
a set of goals for this project.
1. The PBOD has to be printed in ABS or PLA. If
machined, it has to be expanded PVC.
2. The frame cannot be made as a unibody frame. It
must be constructed with a base, with separate
sides and top.
3. The parts can be 3D printed, laser cut, or machined
with a CNC mill.
4. It must use a motor controller that is capable of
mixing the RC signals to control a differential drive
with two channels.
5. A four-channel radio should be able to control the
robot and weapons.
6. No projectile weaponry. No fire or explosives.
Flippers, spinners, or hammers are okay.
7. The wheels must fall into the same rules as the
frame. With the exception of the tread material, they can
be foam rubber, rubber, or some other soft material to
allow for traction.
These goals are only a starting point; once the
weaponry is complete and the PBOD has a few battles
under its belt, we can make changes.
You can see the prototype in action at
Now that I have a working prototype and a set of
goals, I have chosen the gear I will use to construct the
I decided on the Sabertooth dual 12 amp motor driver
from Dimension Engineering (Figure 6). While 12 amps is
overkill for the bot we will be building in this series, it
allows for a great deal of expansion in the future.
• 6V to 25V input (2s to 6s LiPo)
• Synchronous regenerative drive
• Ultra-sonic PWM switching
• Thermal and over-current protection
• Lithium protection mode
• Built-in RC mixer
44 SERVO 11.2013