Ibuilt my first robot back in 2001. It was an Antweight (one pound) robot called 3-letter-word. After I
finished the Ant, I decided to start on
a simpler project and built my
heavyweight (220 pound) robot
named 4-letter-word. It started life as
a tough steel box with what we
thought was an indestructible
thresher. It was cool, but the thresher
was promptly thrashed in the first
It then fought the next event as a
simple pushy box. That was neither
cool nor successful. For the third
event, we added an aluminum disk
with steel blocks on the end. That was
both cool and mildly successful.
In the fourth event, I forgot the
belt for the disk at home, and the
weapon was damaged in our first
fight before we could get a new belt.
Without the disk, we were back to
being a pushy box and not cool or
It was a good ride and I learned a
ton about robots, and used that
knowledge to build dozens more in
the Insect weight classes, but I retired
the heavyweight. It spent the next 8-
10 years lying in a slumber.
When the folks at USF announced
Southeast Combot Championships in
Tampa, I knew it was time to pull the
old bot out from under the
workbench and put it back together.
The first task to be completed was a
I surveyed the mechanics and it
was in pretty rough shape. The
wheelchair motors had been removed
and were sitting in a box; two of the
four tires were cut up; and the
batteries had long ago given up their
sealed-lead acid (SLA) souls to the
recycling center in the sky.
I decided most of the robot
would remain the same, but with
technology updates here and there,
and some modifications to make the
design more robust.
The first major modification was
to change the drivetrain from four-wheel drive (4WD) to two-wheel drive
(2WD). This seems counter-intuitive,
because the 4WD gave the bot
additional traction when pushing, but
that additional traction negatively
affected turning. Being able to face
your opponent is important.
The next major change was going
from 24 volts’ worth of SLA batteries
to 30+ volts of lithium polymer (LiPo)
batteries. The battery upgrade should
improve the speed,
and offers about a
40 pound weight
savings over the
planned upgrade is
the addition of a
With only five
many repairs left to make, the
hammers ultimately ended up getting
sacked. It was a shame because they
were mechanically complete. They just
needed to be plumbed, but I simply
didn’t have time to finish.
Some of the systems that I had
10 years ago remained in the robot.
They’ve earned the right to stay as far
as I see it. The wheelchair motors
have seen plenty of abuse, but they
provide good torque and the price is
The wheelchair motors are
controlled by an RSGSS speed
controller, which went obsolete back
in like 2003.
I really don’t know why it isn’t still
30 SERVO 07.2015
Renewing Old Iron
● by Matt Spurk
Old Iron vs. Bear Tooth.