AC-3X is a synonym for Acro Control 3-Axis, a state of the art flight control stabilization for
radio controlled helicopters. The goal of the development of AC-3X was to create a flight
control stabilization for flybarless helicopters which ensures a flight performance far beyond a
normal Bell Hiller rotor head, reachable with a minimum of adjustment effort. Beside this, the
flight stability and neutrality of a good conventional rotor head should have been kept. The
system should be small an light enough to be installed in small electric helicopters and the
setup of the system should be possible without any other  equipment but helicopter and
transmitter.
 
AC-3X is using intelligent PI-control algorithms on all three axis which are fed by the signals
of three SMM-Gyros and an three axis linear acceleration sensor to control the helicopter
motion. During the design of the control algorithms special focus was set on the stopping
behavior from fast rotations. Without knowledge of the Eigenfrequencies of the helicopter the
AC-3X algorithms are able to stop the helicopter from rotation without any oscillation
tendency. The integrated tail gyro has an intelligent feed forward control to reduce torque
effects.
 
A highlight of AC-3X is the calibrated and uncoupled sensor unit. Every individual AC-3X
runs through a calibration process which ensures that the three axis (elevator, aileron and tail)
are perfectly uncoupled and thus e.g. rolling figures are in line without any corrective steering
inputs on elevator. The same is with pirouettes, the rotor disc stays very stable while
pirouetting. Beside this the sensors are also temperature compensated so that even at very
high temperature changes no drift effects are noticeable during flights.
 
As a result the AC-3X user obtains a high agility and a neutral and also very stable flight with
one single setup. Thus an AC-3X controlled helicopter can be used for 3D aerobatics and
smooth F3C-like flying without any modification on the helicopter.
 
AC-3X includes an universal 3-servo swash plate mixer so that no additional mixing in the
transmitter is needed. As swash plate servos any servo with 1.5 ms neutral pulse length can be
used. The swash plate servo framerate can be varied in a wide range from 50Hz to 200Hz.  
The tail gyro supports all of the state of the art servos with 1.5ms neutral pulse width
(standard digital servos), 960µs pulse length (Logitech) and 760µs (Futaba S9251/S9256 or
BLS 251). The framerate for the gyro servo can be selected to be 165Hz or 330 Hz. The
power concept of AC-3X ensures a save function even under low voltage conditions below
3V. AC-3X was developed with special regard on low electromagnetic emissivity so that AC-
3X can be combined with any kind of RC-equipment without any influencing.
 
Sensors and controller of AC-3X are integrated in one single aluminum housing, no extra
volume is needed for a processor unit. The user interface of AC-3X is realized with a blue
OLED-display and three pushbuttons. The brightness of the display assures sufficient contrast
even under bright daylight conditions. Via the integrated diplay the user can overview many
important status informations like stick positions or the rc-battery voltage with a single look.

Weight app. 20g without wiring
Size  (LxWxH ) 31mmx26mmx15,5mm
Supply voltage 3-9 Volt (including  2S Lipo)
current ( typ.) 60 mA
Resolution of ADC for sensors 12 Bit
CPU 32 Bit 72MHz RISC