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powered weapon (and occasionally
Brushless motors tend to have a
higher power-to-weight ratio and
much higher RPM, but often suffer
from “cogging” when geared with
low reduction and heavy attachments.
Cogging means instead of smoothly
accelerating, the motor sputters and
The simplified version of why this
happens is the large mass relative to
the torque of the motor results in the
controller and motor getting out of
sync preventing proper acceleration. In
weapons, this can result in slow or no
spin-up, and in drive systems it can
result in erratic low speed behavior.
Brushless drive systems are less
common as there are not many
controllers available that give quick
proportional forward and reverse
control, and the high RPMs can make
gearing systems more difficult than
with brushed motors.
However, some teams have found
success pairing brushless motors with
gearboxes designed for brushed
For a first build, wheels with tank
style steering are the simplest option.
Tracks and walking systems can be
built, but on your first build, getting
something working reliably should be
the focus. The two main wheeled
options are two-wheel drive and
anything greater than that — usually in
multiples of two.
Two-wheel drive robots will have
two powered points of contact with
the ground, and short of a balancing
robot, this means at least one non-powered point of contact will exist.
This can either be a piece of
chassis/armor dragging on the
ground, a skid, or a caster.
The best option will depend on
the exact design of the robot and
what arena it will compete in.
Robots with greater than two
driven wheels will likely have all points
of contact with the ground powered
with the exception of hinged
components that are meant to stay in
constant contact with the ground.
Chassis construction generally
takes one of a few different routes.
The first is an internal frame with
armor attached to it; the second uses
the frame members as armor, often
with connected plates of material
forming the structure; and the third is
unibody construction, where the
majority of the frame and armor are
cut from a single piece of material.
Building a chassis using an
internal frame with armor panels
mounted to it tends to be the heaviest
of the three options, though often will
be the most durable and easiest to
repair as the portions of the armor
most likely to be damaged are easier
to remove from the rest of the robot.
These frames typically involve a
welded frame with armor bolted to it.
Frame as armor construction is
generally in the middle when looking
at strength vs. weight. By reducing
the frame and armor into a single
part, you can reduce the size of the
machine and use relatively thick
materials in areas likely to come into
contact with weapons. Frames like this
are usually bolted together.
Unibody construction will typically
be the strongest per pound. However,
it’s also the most complicated to
manufacture, as all features will need
to be added to a single piece of
This often involves repositioning
the workpiece many times during the
Care must be taken to avoid
misalignment of holes as the
workpiece is moved. The good
strength-to-weight ratio — the best of
the three mentioned — is due to the
reduced need for fasteners to hold the
chassis together, and the lack of areas
only held on by hardware.
While there are many different
types of commercially available metals
on the market, there are only a few
that are well-suited to robot combat.
The four primary metal types used in
robot combat are steel, titanium,
aluminum, and magnesium. For each
type of metal, there is an alloy or set
of alloys that find common usage
since the mechanical properties of the
alloy are a better match for combat
• Steel: Steel comes in a huge
range of alloys and can have its
properties dramatically altered by heat
treating and tempering. That being
said, steel will likely be the toughest
armor option for a given shape.
However, it will also be the heaviest
Steel is frequently used for
weapons since high grade steels can
be heat treated to achieve a nice
balance of stiffness and strength
while not being so brittle that they
will readily shatter. Common steels in
robot combat are 4130, 4140, 1095,
and S7. There are many other steel
options out there, and often you can
find a specific alloy that is well-suited
to your application.
• Titanium: Titanium is a fantastic
material if you’ve got the budget and
the necessary tools. Grade 5 titanium
provides a great balance of light
weight and strength at the cost of
being difficult to work with and
• Aluminum: Aluminum is a fairly
light metal that’s easy to work with
and isn’t too expensive. There are
many grades of aluminum available,
but 6061, 2024, and 7075 are the
most common in robot combat
• Magnesium: Magnesium is the
lightest metal listed here. Magnesium
is fairly easy to machine, but heat
control is a must as it burns
energetically if it’s allowed to get hot