Fly By Wire-2012/04

While I was browsing the
HeliFreak online forum,
I stumbled across the
prediction that RC helicopter pilots
would one day reminisce that “there
once was a time of frequency pins,
nitro, and flybars.”
It is true that no one can blame a
“dumb-thumb” crash on frequency
interference, thanks to the 2.4 GHz
era; however, the sound of a welltuned
nitro engine and the sense of
raw power are exhilarating and I do
not plan to forego this pleasure! But
what about conventional rotor heads
with flybars (FBs)? Throughout the
last few years, the interest in flybarless
(FBL) rotor control systems has really
taken the RC heli world by storm.
Not wanting to miss out on this new
technology, I decided to try to convert
my T-Rex 450 Sport to a FBL control
system. One advantage of the 450-size
heli is that you need less area in which
to fly it. Nevertheless, I have always
found smaller helis more difficult to
fly than larger ones.
40 Model Aviation April 2012 www.ModelAviation.com
head on my 450 Sport with one made by
RJX Hobby.
Performing the conversion on the
T-Rex was simple. I only needed to
remove the old head and main shaft,
transfer the new head to the existing
main rotor shaft, place it back onto the
helicopter, and make two new links.
A word of warning is in order, though.
Many modelers have tried using existing
blade grips or modifying existing main
rotor hubs, etc. Some of these work, but
many can be troublesome. Dedicated
FBL heads have different design
parameters that are optimized for FBL
controllers. A safer bet, which ensures
a successful FBL conversion, is to use
replacement heads or conversion parts
specifically designed for FBL applications.
After installing the new head, I
proceeded to install and program
the MICROBEAST. The controller
is housed in a small box that allows
it to be mounted on the bottom of
the helicopter. It can be placed on a
horizontal or vertical surface, but must
be mounted on a solid surface because
vibrations can degrade performance.
and mixing arms that a conventional
helicopter uses for stabilizing and
controlling the main rotor blades. The
blades go through changes during
rotation that provide lift and directional
control. A FBL controller takes the
place of the FB and provides electronic
stabilization, input for the cyclic
functions of roll and pitch, and tail
control.
A tail gyro contains a single gyro. A
FBL controller has three gyros arranged
to provide stability and control in all
three axes—roll, pitch, and yaw. As a
result, a FBL head is considerably less
complicated than one with a flybar. FBL
heads do not have a flybar, flybar carrier,
or mixing arms. Instead of a washout
hub and washout arms, a separate
swash “follower” and washout arms are
utilized. Some newer heads actually
integrate the washout arms onto the
main rotor hub.
To convert an existing FB rotor head,
order specially designed conversion
parts or choose to replace the entire
head with one that is dedicated to FBL.
I decided to replace the existing rotor
One possible solution is to add
weight onto the FB; however, that
reduces maneuverability and fun. Would
FBL technology allow me to fly my
T-Rex 450 Sport as confidently as I
do my larger helicopters? Would FBL
technology facilitate learning more
complicated maneuvers? And finally,
as someone who has limited computer
skills and is not a “techie,” could I
successfully set up a FBL heli?
To answer these questions I
purchased a MICROBEAST threeaxes
microelectromechanical system
(MEMS) gyro system from German
manufacturer BEASTX. This small unit
replaces not only the FB, but the tail
gyro as well.
Although there are several
manufacturers now producing highquality
FBL systems, I chose the
MICROBEAST because it was priced
only slightly higher than a quality
heading-hold tail gyro. An added bonus
was that the MICROBEAST does not
require a computer to use.
A FBL controller replaces the FB
and paddles as well as the FB carrier
The T-Rex 450 Sport with the FBL head has nice, clean lines.
Photos by the author
During Step J of the setup, it is important to
obtain a blue light at the same time 6° of
cyclic pitch is reached.
I decided to mount the MICROBEAST
on the bottom of the helicopter, where
it fit nicely.
Avoid using the existing gyro
mount on the T-Rex 450; it
tends to amplify vibrations.
By following the enclosed
instruction manual, I
completed the mounting,
electronic connections, and
setup procedures without
difficulty. The manual is well
thought out, but to ensure
success, follow and complete
the programming steps
sequentially.
Programming is done
through a button on the
MICROBEAST, allowing
access to two menu levels.
The Setup menu is for basic
programming or bench setup.
The Parameter level is used in
conjunction with three dials
on the faceplate for adjusting
flight characteristics. At each
menu step, transmitter input
through the rudder stick
is used to choose available
options similar to the fashion
in which some ESCs are programmed.
One step in the Setup menu is critical
and unique to the MICROBEAST. I
will elaborate on Step J or “teaching the
cyclic-pitch geometry.” To achieve good
success with the MICROBEAST, this
step must be correctly performed.
A blue light on the unit must be
achieved at the moment that 6° cyclic
pitch is reached. If the blue light
cannot be obtained, you must go back
and determine whether or not the
mechanical setup is correct. Do not
be satisfied with anything less than
obtaining that blue light at 6° of cyclic
pitch.
Remember my warning about
modifying an existing head without
using parts specifically designed for
FBL? Here is where it comes into
play. FBL heads often have different
geometry with pitch arms of different
length than its FB equivalent. This
difference can make or break a
successful setup.
After completing the setup steps, the
parameter menu level is accessed to
set the flight characteristics. Although
you can set the MICROBEAST to
allow transmitter adjustment of aileron,
elevator and rudder exponential, and
www.ModelAviation.com April 2012 Model Aviation 41
tail gain, I chose to use one of the
preprogrammed settings instead. For
Parameter menu, step B, I opted to be
conservative and chose the default Sport
setting for the initial test flights.
Upon completing the setup, I rebound
my JR 9303 2.4 GHz transmitter
to ensure a correct fail-safe setting. It
is always a good idea at this point to
recheck the correct response of the
controls, especially in a situation such
as this where a major modification
has taken place. (See my article about
preflight inspections, “Ready for Liftoff,”
on page 49 of the March 2011 MA.)
I was now ready for the all-important
first test flight. Finally, a chance to see
for myself what all the excitement was
about FBL! The day of the test flight
was not ideal for a 450 helicopter. The
sky was overcast with a gusty wind
averaging 15 mph. Not easily deterred, I
decided to go ahead and give it a try.
On the first flight, the helicopter
settled into a stable hover 15 feet off
the ground. Despite the gusty wind,
my little 450 stayed in one place with
hardly any control input. What a
difference from previous flights with
the FB head in place! As the wind
gusted, my 450’s MICROBEAST gyros
42 Model Aviation April 2012 www.ModelAviation.com
responded and held the helicopter at a
constant attitude.
After flying a few circuits to
accustom myself to the way the heli
flew, it was time to try some tricks.
During rapid Tic-Tocks, the rotor head
began to shake. I cautiously landed the
heli and entered the Parameters menu
and changed control behavior from
Sport to Pro. This provided a quicker
response and eliminated the shaking.
After a few initial test flights, I
decided to wait for better conditions.
The next time I flew the 450 it was a
calm, sunny day. On my first flight, I
flipped the little helicopter and found
it would hover inverted, hands off!
Even my larger, more stable helicopters
will not do that. Funnels and inverted
backward hurricanes came next and
were almost as easy to perform as with
larger aircraft.
Of all the differences between FB
and FBL, the most noticeable was the
stability during flight maneuvers. I
had been struggling to learn inverted
backward flight with my FB helis for
some time. The FBL system stabilizes
the heli after you are settled into the
maneuver, so continuous corrections are
not required. This makes learning new
maneuvers easier.
The MICROBEAST is not an
autopilot, though. You still need to
make correct stick inputs to accomplish
the maneuver.
I am now a FBL convert. Since
my initial experience of using the
MICROBEAST on my T-Rex 450 Sport,
I have converted three other helicopters
to FBL, all with the same improvement
in handling. The only downside I have
experienced so far with FBL helis is that
servo gears are more likely to strip in a
crash because of their direct connection
with the rotor head.
How about FBL for beginners?
The answer is a tentative “yes.” An
absolute beginner should probably
stay away from FBL until he or she is
more experienced because it would be
difficult to sort out problems that can
arise during setup; however, the stability
FBL offers would make learning to fly
easier and would be an excellent choice
if experienced help is available.
Give FBL at try. There are many
good systems available with excellent
online support through the various
manufacturers’ websites and online
forums. It is fun to try something new,
and like me, you might not long for the
days of those pesky frequency pins and
clumsy flybars.
Sources:
BEASTX
[email protected]
www.beastx.com
Align RC USA
(562) 598-4700
www.alignrcusa.com
Horizon Hobby
(800) 338-4639
www.horizonhobby.com
RJX Hobby
www.rjx-hobby.co.uk
HeliFreak Online Forum
www.helifreak.com
Tatiana, the author’s
daughter, displays the FBL
T-Rex 450 Sport.