traditional armor can emerge from
a tough battle with just cosmetic
Ablative armor is designed to
negate damage by being damaged!
Ablation is the removal of material
from vaporizing or chipping. The
materials are tough, but with low
hardness. Ablative plates are
efficient at dissipating energy,
transmitting less of an impact to
the rest of the bot compared to
traditional armor. They work well
against blunt spinners. They also
can be effective against drum bots,
whose typically small teeth eat
chunks out of the armor instead of
launching the robot. Thick wooden
plates can work as ablative armor,
however, they result in a lot of
visible damage that can cost points.
Make sure the judges know your
armor is supposed to ablate.
Another disadvantage is that it has
to be changed frequently.
Reactive armor, as the name
implies, reacts against blows. One
example is rubber layered metal
sandwiches. This works as a shock
mounted armor, dissipating energy
within the armor itself. A number of
reactive types (such as the explosive
type found on military tanks) or high
potential capacitive discharge types
are ruled out by most event’s tech regs.
Completing our trio of threes,
there are three typical types of drive
systems: treads, legs, and wheels.
Tank-style treads give excellent
32 SERVO 07.2009
traction and are difficult to high-center. However, they waste a lot
of energy when turning and can
be slow during turns. Treads are
also prone to getting knocked off.
They do show well, and are quite
fun to drive.
Legs have several disadvantages. They are complex to build
and control, and usually not sturdy
enough to survive combat. They
also raise the center of gravity of
the bot, leaving them prone to
tipping. The advantage is that
most events give a large weight
allowance — up to 100% — for true
walkers (as opposed to shufflers).
In the very rare event where the
bot is off-road or on a very uneven
surface, legged walkers might show
Wheeled bots are the overwhelming design in combat today.
Wheel types include pneumatic,
(often foam filled), solid, or foam
(typically used in smaller bots).
Two main types of steering are
used (Yep, breaking our string of
threes). Ackerman steering —
common to automobiles — uses
fixed drive on two wheels with a
smaller motor for steering. This is
a very effective system for high
speeds, allowing straight driving.
Turning in tight quarters can require
the “back and fill” technique,
leaving it vulnerable to attack.
Tank-style steering is much
more popular. Each side — no matter how many wheels — is driven
separately. This means to go
straight, each must have identical
speed which is often difficult to
calibrate. Turning is accomplished
by having one side at a different
speed, or even running in the
opposite direction. This allows for
very maneuverable robots.
Tank drive bots usually use two
or four driven wheels. With two
wheels, a lot of weight can be saved.
Another form of support is usually
implemented, like a caster, ball
transfer, or slide. In this design, the
wheels work best if they’re near the
center of gravity for traction and quick
turning. If a secondary support is
not used and if the wheels are off
the center of gravity, the bot is a
“front dragger” or “rear dragger”
which fits nicely with an offensive or
defensive wedge design (Photo 6).
Multi Wheel Drive
Often, all four (or more) wheels
are driven, making the bot easier
to drive straight. This also allows
redundancy against damage. A few
robots use six or even eight wheels.
While being very stable, these do
suffer from turning friction
problems like a tank tread.
Professor Marco has a nice
dissertation on the theory of c.g.
versus drive wheel placement, which
is worth reading in the book.
Another major design factor is
invertibility. This affects the drive
system — among other things —
because the wheels might need to
be greater in diameter than the
thickness of the structure. Another
solution is to have an “SRiMech” or
Self Righting Mechanism. This can
be a hoop, pole, or active element
to flip the bot back over. This
includes wedges or spikes on any
flat sides of the bot, so it can’t get
balanced on a side or end.
Chapter 2 concludes with
a long section on tools and
equipment, again worth a read.
This short summary covered
21 pages of dense and fascinating
material. To get the whole knowledge
base, join the over 4,000 people who’ve
downloaded the tutorial so far.
Look for summaries of other
chapters on other topics in future
editions of SERVO’s Combat Zone. SV