Ihave employed pretty much the same design for three pound robots since around 2002. I take a
7-1/4” saw blade, attach a motor and
some tires, and call it done. So, when
my youngest son begged to have a
robot with a saw blade, I knew
exactly what he needed. I also knew
that I wanted to 3D print as much of
the robot as possible, so we had more
of a robot kit than a built from scratch
The construction of Scary! Scary!
SCARY! (that’s the full name as
decreed by my four year old son)
began with a beta set of Team Tiki
gearmotors that team member, Micah
sent me (see the accompanying part
review in this issue). The gearmotors
came with a red tire attached. I bolted
them onto a 1/8” thick aluminum
base with a 1/2” conduit clamp over
Micah installs a piece of heat
shrink over the gearbox and motor to
help prevent the two units from
separating. The heat shrink provided
me the extra benefit of being a nonslip surface under my motor mount
(a.k.a., conduit clamp). The red tires
were a set of Micah flip-flop tires.
I was a little concerned with the
wheels at first, because they were
very soft and I wasn’t certain how
well they would hold up to the big
spinners that were going to be at the
Orlando Maker Faire. To my surprise
they held up great, offered good
traction, and when one was
completely torn off I just super-glued
it back on.
Once the gearmotors were
mounted, I decided to wire up the
Once the drive was
sorted out, I started on
the weapon. The weapon
system that I have used
for the past couple events
is a very simple, very
cheap, very robust unit.
I started with a roller
blade wheel and trimmed
off most of the rubber,
then drilled four holes in
the side of the wheel.
Next, I bolted the wheel
to a piece of aluminum
angle. A 1/4-20 bolt
through the wheel became my
I wrapped the bolt with a thin
piece of aluminum duct tape to shim
it to the proper fit for the
bearings. After that, I slipped a
washer over the bolt and
tightened a threaded hub onto
the bearings. The hub contained
an O-ring groove and a lip that
secured the saw blade. I installed
the O-ring and saw blade, and
tightened a flanged nut down on
the saw blade which squeezed it
against the hub.
Once the weapon bearing
was installed, I moved on to the
weapon motor. I began by
installing an O-ring hub on the
weapon motor. In this case, it
was a printed hub. I tensioned
the belt and marked one hole.
I installed the motor with
just that one bolt to act as a
pivot point. I did this so I could
swivel the motor to adjust the tension
in the belt. When I was happy with
the belt tension, I marked and drilled
the remaining holes.
SERVO 12.2014 25
Scary! Scary! SCARY!
● by Matt Spurk
The assembled weapon system getting ready for
the first spin test.
The drive train with the 1/2" conduit clamp
snapped over the top.