a side wall. This results in significantly better
energy transfer, meaning a harder hit and more
damage.
Vertical spinners generally spin either a bar
or a disk weapon, and commonly switch between
the two depending on the opponent they’re
facing. Disks are more popular because they
store more energy for a given mass, but they’re
vulnerable to horizontal spinners. Doubling the
spinning speed of a weapon results in four times
the kinetic energy, so vertical spinners will often
deploy asymmetrical, single-tooth weapons in
order to maximize their “bite.” This allows them
to save weight while increasing the energy stored
in the weapon.
One problem vertical spinners can suffer from
is gyroscopic forces on the robot due to the high
momentum of the weapon. Like a bike wheel, the
spinning weapon acts as a gyroscope and resists
the robot’s turning motion. Turn too fast, and one
end of the robot “floats” off the ground. This effect
can be used to self-right some robots but it can
also flip a robot upside down. Because of this
effect vertical spinners need to limit their turning
speed, or turn in large arcs. These handicaps can
give other robots an advantage.
DRUM SPINNERS
These weapons also spin vertically but they’re
wider, with smaller diameters, and can spin at
much higher speeds. Drum spinner robots are
mostly driven with two-wheel drive and have
smaller and more compact frames than any
other weapon type (Figure
B
), but their geometry
is especially prone to float when turning.
Because the weapon on a drum spinner
protrudes past the frame of the robot, their
ground clearance is not as important as other
vertical spinners. Most robots get away with a
small piece of metal pointed toward the ground
to stop other robot’s wedges from getting under,
but even that’s not absolutely necessary to be
competitive.
There are several popular ways to make
the drum weapon. The first is to fabricate a
single-piece drum out of a hardened steel. This
is difficult without highly specialized tools. An
easier way is to mount hardened steel “teeth” to
a drum using bolts, but these weapons have to
be manually balanced which takes considerable
time. The easiest way is by layering hardened
steel disks with spacers made from a softer
material, such as aluminum. This simulates the
large impact face of a unibody drum while also
storing a large amount of energy in the rotating
mass of the weapon.
BEATER BAR SPINNERS
Beater bars are a weapon type that sits between
verticals and drums. They span most of the width
of the bot, like a drum, but they can store more
energy with a larger diameter, like a vertical
spinner. The general idea behind a beater bar is
to maximize the moment of inertia (MOI) of the
weapon while keeping the weight low. This is
achieved by removing most of the material on the
inside of the weapon, and keeping the outermost
material, as mass further from the axis of
A B
Caleb Kraft
29
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