fight was temporarily stopped and
this left me and the event organizers
with a problem. Should we let a
wrangler enter the arena to put out
the fire and unstick the robot while
the entire arena was filled with thick
white smoke? We eventually did
allow a wrangler to enter the smoke
filled arena and hit Taxes with a
blast from a CO2 fire extinguisher. A
couple of minutes later, I also briefly
entered the arena and unstuck the
robot, and the fight resumed for
another 30 seconds or so. However,
Taxes couldn’t move at this point.
After the match was ended, we
opened the arena doors to help vent
the smoke into the building. (It
should be noted that both the arena
and the building had ventilation
fans.) After several minutes, the
robots were powered down and
Taxes was removed from the
building to an area where we had
two buckets of dry sand to smother
the batteries once they were
removed from the robot. The
batteries kept smoking and still were
a fire hazard for almost an hour. This
also stopped the event for over 30
minutes while the smoke cleared.
In a discussion with the
builders of Taxes, it was determined
that probably the physical damage
to the first pack caused the battery
failure and its open flames
eventually burned away the added
fire resistant foam protecting the
pack, and then the one next to it.
This caused the second pack’s
packaging to fail and it ignited and
burned, as well. It was also
mentioned that the robot was not
designed for use with Li-poly
batteries but they were added for
this event. This started some
discussion on the Robot Fighting
League forum about better ways of
building with Lithium Polymer or
even Lithium-Ion battery types.
Some Ideas and Tips
from the Builders of
Death and Taxes
(This information was graciously
provided by Billy Moon and Dick
• Always use LipoSacks in the pits
and for shipping batteries when
they are not in a Ti container.
• Always use battery boxes for the
Lithium Polymer packs. When
building those boxes, use overlapping sides (no butt seams).
Allow for a ‘chimney’ through the
middle of the packs and plan for
the fire/smoke to exit there.
Anything above/below that
chimney will get damaged.
• Always shock-mount the battery
box rather than hard-mounting it.
If you have a multi-cell pack, then
make sure to orient the packs so
that the most likely impact blows
are along the ‘length’ of the pack.
• Tape down and insulate open
terminals on the balance plugs so
that they don’t get cut or shorted.
• Use fairly stiff foam to keep the
packs from shifting around in
• Design so as not to draw more
than 50% of the capacity of the
batteries and to never exceed the
continuous draw capacity of the
packs. For example, in Taxes, there
were two 5,000 mAh packs, 125
amps continuous, 250 amps burst.
The speed controller was set for
80 amps per channel, so its
maximum continuous draw was
160 amps. This required two
packs so that the continuous draw
capability was 250 amps. Don’t be
tempted to violate this rule.
LiPoly’s are small and light so you
can give them enough juice. In
Death, there were four of those
packs. There were also four speed
controllers: two sets for a
maximum of 80 amps and two
sets for a maximum of 160 amps.
The robot needed 480 amps
continuous, so four packs were
put in to give 500 amps
• The packs never come out of
battle more than 30% discharged
and are barely warm. For a long
battle, it typically takes 1.5-1.8 Ah
to recharge the packs. Fan-cool
the batteries before charging.
Fighting the Fires
and then Dealing
with the Batteries
Li-poly fires are a bit different
than other battery fires. For the
most part, the open flame can be
extinguished with a CO2 or dry
chemical ABC extinguisher, although
is is possible and likely that the pack
may re-ignite because of its internal
energy. There are commercial fire
extinguishers available just for this
type of battery available using Ansul
Lith-X. There is also a copper
powder. It’s been proven that just
covering the batteries in plain dry
sand works really well.
It is not recommended to
pour water on the batteries if the
case has been breached. This
actually varies for different
battery chemistries but as a rule of
thumb, water is not the best option.
Water coming in contact with the
battery electrolyte can produce
hydrofluoric acid. Water coming in
contact with the battery anode
material can produce flammable
The smoke produced from these
batteries is a health hazard. The
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