bought from a competitor in the US
via eBay. This set-up is sufficiently
powerful, fast, and reliable, but also
extremely cost-effective. The 40 MHz
radio control system used is cheap
and reliable, although we would
now buy a 2. 4 GHz system instead
if starting all over again, as it offers
more safety and convenience by
effectively eliminating the chances
of interference or loss of control.
The storage of the liquid CO2
used in the pneumatic system is critical,
so a certified fire extinguisher is used
for the main bottle and an identical
extinguisher (painted black) is used
for the buffer tank which allows the
use of the CO2 full bottle pressure to
be used if required; a change of pipe
work is the only modification needed.
The choice of pressure tanks used is
also very cost-effective. A standard,
high-pressure welding regulator is
perfectly capable of handling the
reduction to 200 psi. Likewise, the
perfectly capable Electronize weapon
switcher and 5/3 solenoid valve are
a neat and inexpensive solution that
has the option of going to 1,000 psi
with little modification.
Finally, we have incorporated a
simple but tidy charging system that
allows us to remove our safety link and
charge the batteries without turning a
single bolt. We use jack plugs hidden
under the arm of the bludgeon.
Development
After competing in several live
events in 2009, a number of updates
were needed. Firstly, the thick wall
steel box section used in the arm was
bending under the huge forces. The
arm was reinforced along its full length
with steel plate, which also added a
little more weight to the bludgeon.
This solved the bending problem in
Crossfire, and caused more bending
problems in the enemy robots (which
is a nice win-win situation for us). The
gears in the original boxes stripped
unexpectedly, so larger versions of
the same gear-motor were fitted
and have been reliable to date.
The cause of the failure was traced
to bolts coming loose in the gear
housing, allowing the drive worm to
wobble around and destroy the teeth
on the drive gear. This will not happen
again as all bolts now use thread lock.
(See Nick Martin’s article on thread
locking in this issue of Combat Zone).
Finally, the robot carries much
of its weight relatively high up, so
its center of gravity is higher than on
Edgehog. This means that it does
get flipped over a little easier and
often takes a few attempts to right
itself. This can be solved with some
welded fins strategically placed on
the outer shell, but the driver is happy
with the look of the robot and prefers
to leave the robot as it is for now.
We may add the fins for important
competitions in the future.
Does It Work?
Absolutely! All design targets
have been met. The machine has
been reliable, cost-effective, low
maintenance, and is easy to turn
around for the next fight. The armor
is just as impervious as we hoped
for, and the weapon is devastating
against many opponents — often
immobilizing them by bending the
chassis enough to lock up the wheels
or crush internal components.
The inspiration for the paint job
arose because we often wear combat
jackets at events which has become
an unofficial team uniform. The robot
looks great in the arena in contrast
to robots in primary colors or shiny
metallic, so Crossfire has proven to
be the perfect successor to and
companion of our veteran Edgehog,
who has still not retired and will be
fighting again in 2010. SV
Resources
www.robotpower.com
www.battlepacks.com
www.electronize.co.uk
www.futaba.com
www.xbotz.com
MAN UFACTUR IN G:
Keeping Your Stuff T gether
● by Nick Martin
Since screws were invented over 2,000 years ago, mankind has
struggled to keep them from coming
undone. In the past 100 years, many
advances have been made, yet
screws still loosen and no single
solution works universally. This
article will examine what is available
and what solutions work best in
combat bots.
How Threads Loosen
Nuts and screws rely on friction
between the threads to prevent
loosening. We create the friction by
tightening the parts until they are
under tension. Thread loosening has
several causes:
• Temperature changes cause the
expansion and contraction of
fasteners and the bot’s frame,
which reduces bolt tension and
clamping force in the assembly.
30 SERVO 04.2010
