be attached to the end of a pole.
Both methods have been effective in
The main difficulty with this
design is that translational movement
while the weapon is active is difficult.
There are solutions to this, though.
Most systems that attempt to fix this
problem rapidly adjust the speed of
individual wheels to cause it to slowly
move in the desired direction.
Vertical spinners mostly come in
two varieties: bar and disk. Both do
basically the same thing. The idea
with a vertical spinner is to use the
ground to your advantage.
When a spinning object hits a
robot, half the energy goes to each
robot. Vertical disks use the ground to
absorb that energy while the
opponent only has its weight to resist
Vertical spinners require a lot of
strength in the frame that
supports the weapon to
avoid damage during
impacts. Many vertical
spinners have a support
going down from the
shaft of the spinning disk
to help absorb the impact.
Vertical spinners are
prone to gyroscopic issues
when turning. If you try
to turn too quickly with a
vertical spinner, it may tip
to one side. You risk
either flipping over or
losing traction as the
wheels are lifted off
The hazard here is
that when you are
doing this, the other
robot is able to better
position itself for a
counter attack. Vertical
spinners tend to have
wide drive systems to
counteract this force.
Drum weapons are the cousin of
the vertical disk. Unlike vertical disks,
drums tend to have a fairly small
diameter. They are also normally very
wide, often covering the majority of
one side of a robot.
Gyroscopic forces become less of
an issue with the drum design. They
also have a much wider impact area.
Drums are often spun at a higher
RPM than other spinners. Drum robots
don’t rely on one big hit. Drums are
meant to get to speed quickly and hit
many times in rapid succession.
A common drum variant referred
to as an ‘eggbeater’ removes the
drum portion of the design, using just
the impact bars and supports in the
structure of the weapon.
The horizontal spinner is a wide
category. It includes shell spinners,
overhead spinners, front mounted
spinners, and undercutters.
Shell spinners have a rotating
mass that surrounds the chassis of the
robot. These spinners develop a high
amount of kinetic energy when
spinning due to the large mass of the
spinning object. The shells also double
as kinetic armor when the weapon is
operational. Shell spinners are most
effective when the shell is short in
height. A low center of gravity keeps
them stable after powerful impacts.
Overhead spinners normally use
bars. This weapon is not as powerful
as a shell spinner, but it’s easier to
build and weighs less. The weight
savings allows for a stronger drive
system or frame. The simplicity makes
it an easier project for a new robot
builder. These weapons — when used
right — can be extremely effective.
Front mounted spinning weapons
are almost identical to overhead
spinners. Instead of having the blade
on the top of the robot, it’s mounted
into a frame that comes out one side
of the bot. This allows the blade to be
lower to the ground, and the robot
that wields it to be taller without
Undercutters do just what the
name implies. The idea with this
weapon is to remove the wheels and
anything else sticking out the bottom
of the opposing robot.
Undercutter blades ride close to
the ground which makes them
difficult to avoid in a match. The
blades often have a material beneath
the bar to prevent them from hitting
the arena floor.
All horizontal spinners have
problems with over- and
under-steering. When you
spin a large mass at a
high velocity, it causes the
chassis to want to rotate.
The rotation of the
weapon will cause the
robot to turn much faster
in one direction and have
trouble turning in the
other. It will also have
some difficulties driving in
a straight line. SV
Drum/Beater. Photo courtesy of David Moulds.
Photo courtesy of
24 SERVO 02.2018