78 SERVO 04.2014
years, but the earlier ones were
almost all gas-engine powered.
The reason for the popularity?
Enter the high power density LiPo
batteries for electric planes and flying
platforms. You don’t need a
screaming glow-plug gas engine
trailing smoke to allow your model to
leave the ground these days.
Figure 8 shows a $500 gas-powered Blackhawk 500 that is flying
inverted with the typical smoke trail.
An electric helicopter with a small
LiPo battery pack can get you 10 to
15 minutes of flight at a lower overall
cost for the whole system of less
than $100. The negative aspect: a
shorter flight time than the gas-powered models.
Model helicopter designs
improved very rapidly and costs
began to plummet. A little over a
year ago, I covered the multi-rotor
craze a bit from my exploits with a
helicopter and the ELEV- 8 from
Parallax. One of the most difficult
parts of my learning to fly a model
helicopter was the instability of early
Handling the collective, cyclic,
and tail rotor pitch was difficult for
beginners like me. Manufacturers
began to sell cheaper models that did
away with the complex tail rotor that
canceled rotor torque but allowed
easy steering. These designs used
two co-axial rotors to cancel the
torque of each rotor, plus they didn’t
require a tail rotor.
If you went into any county fair
booth or a Brookstone store in an
airport a few years ago, you would
have seen dozens of the small co-axial copters available to try out.
Purists wanted a better design and
opted for a single rotor and tail rotor,
but stability was still a problem.
Made Flying Easier
Aside from the LiPo battery
capacity, the onboard gyro/
accelerometer chips now cost just a
few dollars each as opposed to
thousands of dollars for spinning
gyros just a dozen years ago.
With the introduction of very
cheap and tiny gyros and
accelerometers built into
R/C systems, control
became a lot easier.
systems (or MEMS) are a
combination of an
integrated circuit and
technology that allows
outside forces such as
linear acceleration and rotational
force to be measured on a single
The outputs of these
measurements can be fed to a flyer’s
receiver to compensate for flying
instability and allow inexperienced
R/C flyers to keep helicopters and
multi-rotor flyers fairly stable in flight.
Go into the same Brookstone
store these days and you’ll see the
Parrott AR.Drone. It’s the $300
quadcopter shown in Figure 9 that
was one of the first smartphone app
controlled flyers with an HD camera.
There are still the standard co-axial
helicopters, but the ‘buzz’ these days
are the multi-rotor craft.
The MEMS and other sensors
such as GPS, magnetometer
compass, altitude hold, tilt and roll
control, data capture, and recording
are just a few of the capabilities of
the newer control boards. The
Parallax ELEV- 8 shown in Figure 10
uses a Hoverfly Sport control board
(shown in Figure 11) that allows for
easy control and stability of multi-rotor flight.
The Lockheed F-117 Nighthawk
stealth fighter would have been
impossible for a human pilot to fly
were it not for the onboard computer
systems that compensate for the
terrible aerodynamics of the plane
that are needed for stealth. The same
goes for the multi-rotor craft and
their MEMS chips.
The quadcopter brain shown in
Figure 12 is a project of Alan
FIgure 9. Parrott
FIgure 8. Blackhawk 500 gas