SERVO 10.2017 27
structure and power trains to produce.
Phantom II went through about
12 distinct iterations in design before
we finally built it. The first version of
the design (shown in Figure 1) was
not much better than its predecessor.
A major part of the philosophy
for this build was to take some of the
better elements from common
undercutter designs and apply them
to our overhead spinner. The steps in
the right direction included a belt
driven weapon, a frame fastened by
screws and end-tapped holes,
legitimate metal armor, and a design
which could potentially drive inverted.
Invertibility was something we
prioritized in this design as we had
never seen an overhead bar spinner
do this before, and were eager to see
how it would play out.
Another major change was
including one wedge instead of four,
allowing for a smaller base footprint
and greater reach, while also giving us
more interior space for packing
internals inside the bot.
Lastly, the frame pieces and
armor were designed to be easily
fabricated with hand tools.
Our toolset included a drill, an
angle grinder, a Dremel, a jigsaw, and
some files and hand saws, so all of
the metal components (except for the
weapon bars) had to be fabricated by
modifying the custom-size aluminum
rectangles available for reasonable
cost from Onlinemetals.com.
Unfortunately, this version would
have sported a cantilevered 1/4”
diameter live shaft and only two rear
wheels which would have given it very
poor traction in the arena, and only
marginally better durability than the
first bot. In a never-ending effort to
reduce the robot’s cringe factor, we
went back to the Internet to do more
By about the fifth version of the
design (shown in Figure 2), the
internals had been rearranged to
make space for some better design
Four-wheel drive afforded us
much better traction, while keeping
the inverted driving feature given by
the exposed rear wheels. Each wheel
was driven by a 1: 22 Silver Spark
motor, making a total of four.
This is somewhat underpowered
for a Beetle, but is still an upgrade in
both speed and total torque from the
two 1: 35 Gold Sparks we used in the
Figure 1: The first version of the design,
featuring unrealistic expectations of rigidity
Figure 2: A later version of the
design, complete with unrealistic
expectations of how many parts
can fit in such a tiny space.
Figure 3: The first test-fit
of the internals. This was
helpful in determining
what could actually fit
inside the frame, so that
we could adapt the