LENSnce a choice has been made
over the number of rotors,
there are a number of styles,
depending upon the desired
characteristics of the final
craft. Which style you opt for
will have an impact across many
of the components that you will need to source
for your build, but the most fundamental of those
components is the one most closely associated with
your style. The frame provides a platform to support
the motors, batteries, and electronics, and must
be rigid enough to permit the aircraft to fly without
vibration or distortion.
We will look at two styles here: a 450 mm frame
which will form the basis of the machine we’ll be
building, and a smaller frame designed for racing.
If you need an analogy to help understand their
different characteristics, in this context the 450 mm
frame is like a large estate car, while the racing
frame is like a racing motorbike. The former is a
capable all-rounder that can carry anything a family
can throw at it, while the latter is a fast and nimble
machine designed for fun and thrills, but lacking
significant carrying capacity. Multirotor styles seem
to follow fashion – for instance, a few years ago the
larger frame was king, while it’s fair to say that the
racing frame is a far more popular choice today. Yet
we’re building a 450 mm craft today, so why is this?
The answer comes on several levels. The larger
machine is a much easier one to fly than its smaller
sibling, and its enhanced carrying capacity means
that it is a far more versatile platform for future
expansions and upgrades.START IN THE MIDDLE
At the centre of a multirotor frame is always a
platform for the electronics and battery, from which
radiate the arms that carry the motors. We’re looking
at a quadcopter here, so in our case there are four
arms. The electronics platform is frequently made
into an enclosure in the space between two plates,
this provides extra rigidity, as well as protection
for the fragile components. A very popular choice
for racing frames, due to its high strength and low
weight, is a carbon fibre frame.
When choosing a frame, you will find a
bewildering array of models to choose from in
supplier catalogues and websites. Many of them
are very similar, and among them will be many
good choices but, as with so many things, there
will be pitfalls to avoid. Fortunately the onlinemultirotor community has produced a huge array of
information and component reviews, and you should
always check the experiences of other builds with a
component before committing your money to it.
The frame we are using for our build is a generic
450 mm frame, with glass reinforced plastic (GRP)
arms, and a central platform made using GRP-printedcircuit board material, that doubles as a power
distribution system. Almost identical frames can be
found from multiple suppliers. As is often the case
with multirotor frames, there is a means of denoting
which is the front of the craft – two of the arms are
red in colour and we have assembled them in the
forward position.O
AT THE CENTRE OF A MULTIROTOR
FRAME IS ALWAYS A PLATFORM FOR
THE ELECTRONICS AND BATTERY,
FROM WHICH RADIATE THE ARMS
THAT CARRY THE MOTORS
OTHER KINDS OF DRONES
The first military drones were used in the Yom Kippur War
(1973), as Israel flew unmanned aircraft to force Egypt to
exhaust its supply of anti-aircraft missiles, ahead of manned
missions. Since then, militaries around the world have
been extensively using drones for reconnaissance and
launching attacks.
Multirotors are now used in a wide variety of industrial
roles, including building inspection, firefighting, filming,
agriculture. There have been several widely publicised
attempts to deliver food by drone, but none have been
released commercially ... yet.