Relying on high-amperage power to turn the motors on a multirotor means
incorporating large, heavy, expensive ESCs into its design. Using a higher-voltage
system can deliver similar performance in a much smaller package.
An electric motor’s Kv determines the number
of rpm it will deliver per volt of power applied.
These 1,180 Kv Cobra motors are mounted
on the Roswell Flight Test Crew’s flagship
hexacopter, RQCX- 3 Raven, which runs an 11.1-
volt battery providing 13,098 peak rpm.
for making your
If you’re interested in flying a multirotor aircraft, you have an easy choice to make. Which of the xcellent platforms that are currently available and
ready to go right out of the box do you choose? The
ubiquitous DJI Phantom 3 or the formidable Inspire
1? The feature-rich 3DR Solo, or my current favorite,
the Yuneec Typhoon Q500+? So many choices …
However, if you’re interested in building your
own multirotor—and as a reader of Model Aviation magazine,
I suspect that you are more inclined than most to follow this
route—you face a more complicated set of questions. What
components should I use, and how can I be sure that they will
come together to create a safe, reliable aircraft?
The Three Musketeers
There are many components that you’ll need to consider—
from the airframe, to the battery, to the flight management
system—but the three that create the most confusion among
new builders are the propellers, the motors, and the ESCs.
Choosing from among the options is made even more
complicated by the fact that any change you make to one of
them affects the other two.
What does each of these components contribute to aircraft
performance? The propeller moves the air, generating the
thrust that keeps the multirotor aloft and giving it the ability
to maneuver. The motor turns the propeller, and the ESC
takes input from the flight management system, speeding up
or slowing the motor as needed to maintain controlled, stable
If any link in this chain breaks, you immediately lose all
three components and your flight will likely end in an abrupt
and distinctly unsatisfactory manner. To make sure that
doesn’t happen, let’s start at the outside and work our way in,
beginning with the propellers.
According to the fundamental principles of aerodynamics,
the larger a propeller is, the more efficient it is. If you want
your multirotor to fly for a long time, use the largest propellers
that the airframe can physically accommodate (without hitting
each other or other components of the aircraft). The weakness
of propellers is that they are only able to generate so much
thrust before they experience structural
failure. In short, spin a propeller too
fast—ask it to generate too much
thrust—and it will break.
Quality manufacturers, such as
Advanced Precision Composites in
California, provide charts and tables
that will tell you how many rpm their
propellers can sustain before they are in
danger of failing.
Continuing our journey inboard from
the propellers, the next component
encountered is the motor. Motors come
89 Model Aviation SEP TEMBER 2015 www.ModelAviation.com
ADVANCED FLIGHT TECHNOLOGIES