chain with spikes sticking off of one
side. After finding that there was no
readily available product, I designed
my own teeth that would be cut from
1/16” steel plate and welded to
normal #40 roller chain.
Meeting the 20 ft/s speed
limitation for Robot Battles meant that
a relatively slow gearbox was needed.
After looking at several options, an
off-the-shelf 20:1 planetary gearbox
with a 775 sized brushed motor
(similar to the Robot Power Magnum-
775 which was out of stock at the
time) was chosen to drive the
The first and longest step in
assembling the chainsaw was welding
the teeth in place. Each of the 24
teeth was welded to the riveted roller
chain. After welding the teeth in
place, the rivets on the opposite side
of the tooth were welded to minimize
the chances of the rivets coming out
After that, the saw paths were
cut from the tubing using an angle
grinder, then the front guards were
welded on. The gearbox mount was
made by splitting a section of 2” x 1”
rectangular tubing. Once the gearbox
was bolted into place, it was then
welded to the main body of the
At this point, the chainsaw was
fully functional and the whole
assembly was weighed. There was
enough weight to spare to allow the
addition of some structural supports
to the side of the tube to help prevent
bending, and some catch flanges that
are intended to grab onto the
opponent as the saw pulls them
toward the main body of the robot.
Spanky went to Motorama 2014
and wound up with a 1-2 record.
Overall, the performance was
reasonable, however, a few design
issues became apparent during the
DragonCon Robot Battles.
First, the chainsaw teeth were
somewhat prone to bending, and
during a match the front of the bar
was rammed into the wall, bending
the teeth outward and locking up the
weapon. To fix this, the teeth are
being bent inward, slightly shortened,
and a small guard spike will be added
to the front of the chainsaw arm to
prevent it from coming directly into
contact with an arena wall.
The circular saw proved to be
fairly reliable with the only major issue
coming when I used a commercial
blade with vibration reducing cutouts.
The cutout near the arbor snapped
out and effectively immobilized the
blade as almost no torque was
transmitted from the shaft to the
blade. Not using anti-vibration blades
should effectively eliminate that issue.
One other minor upgrade planned
is to move to a Ragebridge two-channel ESC for the drive system as
the current limiting
should protect the
drive motors from the
current peaks that
resulted in excessive
heat and eventual
motor failure when
fighting aggressively at
30 SERVO 05.2014
A view of the front of the chainsaw showing the teeth
prior to final welding with the standoffs that prevent the
blade from digging into the ground.
The back side of the chainsaw assembly
with catch flanges and side supports
The completed chainsaw assembly as
used at Motorama 2014.
Installed circular saw motor and mount.