Types and Sizes
Multi-rotors are (for the most
part) broken down by size and type.
Sizes are measured in millimeters from
the motor centers. There really aren’t
any special rules when it comes to
size, and there is a lot of overlap.
• Nano: Less than 100 mm.
• Micro or Mini: 100 mm - 300 mm.
• Mid: 300 mm - 500 mm.
• Large: Greater than 500 mm.
a tricopter and has
more lift potential.
The tricopter is a
build. A hexcopter
is actually more
stable and has
more lift potential
than a quadcopter,
but the problem is
that the hexcopter
has more parts
and is therefore
harder to build
and costs more. A
quad gives you the best overall bang
for your buck. As for size, the smaller
the craft, the less damage it sustains
when you crash. Plus, you can usually
fly small craft indoors. The problem
with small craft is that they have very
little lift potential, but this just means
they make great general-purpose
Larger multi-rotor craft are very
stable and can lift more payload. They
also handle the wind much better
than their smaller counterparts. The
Types of Multi-rotors
• Tricopter: Three blades and one tail
• Quadcopter: Four blades in a +, X,
or H configuration.
• Hex: Six blades in a +, X, or Y
• Octoquad: Eight blades in various
Why not make the Kronos Flyer a
tricopter or a hexcopter? Well, a
quadcopter is a little more stable than
problem with larger craft is that you
need more space, money, and time to
fly them. They can also be quite
dangerous. The size of the Kronos
Flyer (Figure 2) is 17" from motor
center to motor center, or 430 mm.
This build seems to be the perfect size
for cost, complexity, and maintenance.
Its aluminum construction makes it
durable. I would not fly it around
indoors, but you may be able to
practice hovering it in a large
basement or garage.
Parts — the
1,000 Foot View
Here’s a brief overview of all
the components that make up a
multi-rotor. This will help later when
we order parts and assemble our
Kronos Flyer. This is by no means
the end-all in parts and accessories.
I will touch only lightly on each
The frame component — like the
ones shown in Figure 3 — can be
purchased or scratch-built. The frame
is made up of a series of booms that
connect to some sort of center
platform. The ends of the booms have
a means to mount to a motor.
Frames can be made from
aluminum, plastic, fiberglass, carbon
fiber, or wood. Most likely they are
made from a combination of these
materials. Each material type has its
advantages and disadvantages.
Most multi-rotors use brushless
motors. A few years back, brushless
motors were a rarity in R/C because
they were outrageously expensive.
Now they are the norm, and the
prices have come down.
They run smoother and quieter
SERVO 11.2012 37
than their counterparts. They have less
wear since you don't have rubbing
parts. They also produce less electrical
Brushless motors come in
inrunner and outrunner varieties. The
inrunner is much like your traditional
brushed motor with the shaft rotating
inside a housing. The outrunner
variety has the rotating portion of the
motor on the outside.
Outrunner brushless motors tend