FIGURE 2
FIGURE 5
FIGURE 6
Obviously, some thought has to
go into your power needs! By far, the
most common method used in
combat robots is multi-cell packs of
Nickel Cadmium or Nickel Metal
Hydride batteries. You can purchase
ready made NiCd and NiMH packs
from a few different sources, but as
in most things, not all packs are
created equal.
Sometimes due to an unusual
shape needed to fit your design, or
an unusual voltage requirement, an
off-the-shelf pack may not fit your
FIGURE 3
needs. Whether it’s to fit an unusual
shape, or to save some money by
doing it yourself, you may want to
create your own packs.
The first requirement is to decide
on which particular cell you are
going to use. This is not as easy as
it sounds, as there are literally
hundreds of cells on the market, with
vast differences in performance.
Typically, you want a cell with at
least a 10C discharge rate. This
means that for a 3,000 mAh rated
cell, you should be able to draw at
least ten times that — 30 amps —
without causing damage.
Avoid cells that enthusiastically
claim “high discharge rates” without
supplying numbers to verify what
they mean by “high.” Also, there are
many cells on the market that were
designed to be used in power tools,
and come with tabs pre-welded to
one end (or both ends) of the cell.
Although the tabs may have
been adequate in making power tool
packs, they will not be adequate in a
combat pack. The tab itself is usually
very thin, and cannot handle the
amperage a combat pack has to
supply. And, they have a tendency to
pop off during combat, which is bad.
If you do come across cells that you
want to use that have tabs already
FIGURE 7
FIGURE 8
FIGURE 4
on them, you can carefully remove
them before assembly.
For this article, I am building
some packs from 3,500 mAh NiMH
sub-c cells. These are 10C discharge
rated cells, without tabs, and were
reasonably priced at about $50 for a
set of 20 cells. To be sure, there are
much better cells out there than
these, but for the price I felt they
would work well for my needs.
Other supplies needed for pack
construction are battery bars or braid
for making connections, some form
of high strength glue (I prefer the
glue used in tennis shoe repair,
although I have seen some builders
use two-sided tape), wire leads,
shrink wrap, and cell spacers, if
desired. Many of the specific pack
construction materials were purchased from www.battlepack.com.
You will need a fairly high wattage
soldering setup to solder quickly
without damaging the cells. Pictured
are a 260 watt gun, a 500 watt iron
for major work, and a heat gun for
shrinking the wrap on the pack.
Pack construction can be
completed with or without the
separation rings. These keep the cells
from contacting each other, and
allow air flow for cooling. Although I
normally prefer to use them, they do
FIGURE 9
28 SERVO 09.2007
