SERVO 09.2015 29
design involved many hours of finding
places in the mechanism where
weight could be removed. This
process resulted in a fairly skeletal
appearance to the whole structure,
while still maintaining a decent
amount of strength and protection in
key areas. While not light enough to
make weight as-is, the design was
finalized at this point and drawings
were prepared for fabrication.
With the knowledge that the bot
wouldn’t be underweight as it was
designed, a few changes were made
to the main structure of Spanky.
Among the changes were switching
from 2” wide to 1.5” wide Colson
wheels (along with the removal of
some support ribs and the cutting of
treads into the wheels), the removal
of some excess chunks of steel in the
main chassis design, and a switch
from steel top and bottom armor to
titanium of the same thickness.
At this point, the steel part
drawings were sent to
www.discountsteel.com for laser
cutting. The 7075 aluminum and 6AL-
4V titanium were also ordered from
www.amxinc.com, respectively. The
titanium and aluminum parts were
waterjet cut locally a few weeks after
the stock was delivered. Once
everything was on-hand, it was time
for the on-site fabrication and
assembly to begin.
The weapon uses some 2x1”
rectangular tubing as the mounting
adapter. The tubing is cut to length,
drilled with the mount pattern, then
pressed and welded to the steel
The next step of construction was
the modification of the acme nut. One
corner of the nut had to be shaved
down to ensure that it would clear the
mounting adapter when installed. This
modification was quickly handled with
an angle grinder and a 24 grit
The next step in the modification
process was the welding of the 1/2”
rods to the nut. As part of this
process, the sides of the nut were
slightly counter-bored on a mill to
allow the shafts to slip partially into
the profile of the nut. The point of
this was to ensure a more robust joint
between the components.
Each shaft had two passes around
the entire perimeter with a tig welder.
The first pass joined the shaft to the
nut with minimal filler material. The
second pass included the use of filler
material to further reinforce the
connection. This resulted in some
warping, but not enough to cause
issues with the overall assembly.
Following this, the front support
bracket was assembled. This piece
consists of two bushings, a 7075
aluminum plate, and two sections of
large size nutstrip. This assembly slides
over the motor shaft and leadscrew
before being sandwiched between the
two side plates.
With the core components all
The finalized weapon design. It’s not
underweight yet, but it’s close enough.
After pressing the tubing into the
mount plate, it’s ready for welding.
Drilling the main attachment point
for the assembly.
Acme nut after being ground down.
One of the shafts prior to the
second weld pass.
The assembled front support bracket.