FEATURE
Build a drone
POWERING
IT ALL
Choosing a
battery
robably the most confusing part
of specifying components for a
multirotor comes in choosing a
battery. On the face of it, this should
be a straightforward component, but
unlike, for example, an alkaline cell
for a toy, there are a vast range of
different packs available.
All the batteries you should encounter for multirotors
share the same chemistry: they are formed from
lithium polymer cells, with a nominal voltage of 3.6 V
per cell. They are specified with figures as ‘S’ or ‘P’
by their configuration of cells in series or parallel,
but in the context of multirotors we are only likely to
encounter series packs. Thus, a 1S pack is a single
cell, a 2S has two cells, a 3S three, and so on. 1S and
2S packs are in the realm of toys and small craft, so
for our purposes we are most likely to find 3S and 4S
packs. The higher the voltage, the less current required
for a given power, so in our build we opted for a
4S pack.
The other figures on the battery are perhaps the
most confusing. There is a capacity rating in mAH, and
a mysterious ‘C’ rating. The former is simple enough,
a theoretical measure of the quantity of energy it can
deliver in terms of what current and for how long,
while the latter gives a guide to the peak current it can
deliver. Why they don’t simply quote the peak current
directly is something of a mystery, but the formula
peak current = C rating × capacity delivers the answer.
The peak current must be able to cover the
load from the whole machine, with all the motors
consuming their full capacity. So with our quadrotorP
Left
Our flight controller,
mounted upon part
of our frame