stainless screws. Andros is supposed to
be rainproof, so all parts we used are
either aluminum, brass, or stainless; this
way, nothing can rust. It all worked out
well. The wheels are solid. I can ride on
the robot, and I’m 250 lbs.
CONTROLLING THE ARM
We discovered the arm was more
complex than the traction. Weighing 65
lbs on its own, we decided it would be
better to detach it from the robot and
install it on a separate table on wheels.
The first step was identifying the
wires coming out at the bottom; there
were about 45 of them. Emma and I sat
down patiently with the ohmmeter,
finding pairs of 2-3 ohms of resistance
between them (that is a motor). Next,
we applied 12V on each pair from a
battery and observed the motion. We
documented everything such as “base
rotation, right-left,” “shoulder rotation
extend-withdraw,” etc. Luckily, there was
no interruption in the wires, so
everything powered fine.
Next, I designed a circuit taking each
pair to an H-bridge controller (nothing
fancy; $16 on eBay), and I wrote the
software on the Teensy that would take
the RC signals and convert them to PWM
and motor direction commands. After all
was said and done, we connected all the
above-mentioned pairs to the H-bridges. It
all worked after a few hiccups, of course
(inverted wires, loose wires, minor stuff).
So, there we were, on our knees
with the remote picking up a 30 lb lead bar from the floor
with the arm fully extended. That is impressive! Most arms
are very limited in the weight they can hold.
While playing with it, the shoulder motor quit working.
It was turning, but the arm was not lifting. We took it apart
and discovered that the worm gear axle broke. We found
the Engel motors distributor and he told me it would take
eight weeks to get me one. There was no way we could
wait that long, so I went to a machine shop in my
We took the motor apart, and they welded an even
thicker axle instead. We put the worm gear back in, and it
now works like a charm; even stronger than before. The
repair was $180, but well worth it.
Finally, we put the arm back on the base of the robot,
reconnected the wires, and it worked.
CAMERAS AND REMOTE VIDEO
Andros was designed with two cameras: one on the
“hand unit,” and a fancier one (zoom, high-res) on the
“periscope” assembly in the back. They were both feeding
the signal in a switch that would take the video output and
send it as UHF to a receiver.
I didn’t like the idea of switching the video, so decided
to have two transmitters instead: one for each camcorder. I
used the Boscam 2W RF model — the maximum power they
make. I could then monitor both cameras (on two
monitors) or switch between them by toggling the power
to each transmitter — front or back. The front was easy — a
simple super wide FOV 600x400 cam.
For the back, I used an older Sony (HDR-SR10)
The first part of the project: The arm was detached, so we took care of the
traction and the four legs. We also built a ramp to drive the robot into the
family’s Volvo SUV. Since the robot weighs 280 lbs, we had to test the ramp
before attaching it to the car. It bent, but it held okay. The ramp solution
worked out well.
SERVO 02.2018 33