One evening while browsing eBay, I stumbled across a used “as-is” retired police robot. I thought it would be a great way to ease myself in this field by
restoring a professional robot first and take those lessons
into the next design.
So, I made an offer of $10,000 on the Remotec Andros
Mark 4. Quite a price, but not so bad considering that a
new one is over $250k. The list price on eBay was $20k,
but they took my offer. Remotec is the name in this field,
and they don’t sell to the public.
A week later, the machine came: 900 pounds including
all accessories (such as a tether cable unit, for example).
Some rubber tracks were broken, there was no
documentation, and it seemed like it had not been fired up
in a long time.
I called the company; unfortunately, they didn’t support
this model anymore with parts or documentation.
I decided to re-do all the electrical stuff and remote
control from scratch. I was facing 10 brushed DC motors,
but I felt pretty confident that I could handle that.
PARTS AND ARCHITECTURE
For RC, I decided to go with a traditional 12-channel
radio with a built-in video screen: the DEVO F12. I like
things that are compact, and having the screen right there
was nice. On the receiver side, I used the matching DEVO
RX1202. It’s stable and reliable, and much cheaper than the
fancy RC names.
For the signal processing, I decided to use the Teensy
3. 5 development board since I heard they are incredibly fast
(compared to my old time favorite, the Arduino Mega).
I decided to use two processors: one for the traction
wheels and the four “legs” (total of four motors); and one
for the arm.
The “Traction Teensy” was the receiver of all 12 PWM
channels using IRQ functions. The traditional PulseIn is very
slow for the processor. This Teensy would also communicate
eight of those values to the “arm” Teensy through an I2C
protocol. I don’t think that any Arduino model could deal
with all this stuff in a timely manner, but the two Teensy
boards did. I was really impressed.
Next, I realized that I didn’t have enough proportional
controls on the TX radio to deal with the wheel and arm
I was at the point where making “toys”
was not fulfilling anymore. I wanted to
put my skills to work for something
useful. I decided to design a
police/military robot. I knew that they
are very expensive, and I thought I
could do a prototype that would be
more affordable. I realized the
complexity — especially of the arm
assembly — so I was a bit hesitant.
Mitch and Emma Anderson, the father-daughter team
working on the robot arm. Here, they’re installing the
rifle module that can replace the grip unit.
The Making of
By Mitch Anderson
SERVO 02.2018 31