ArduPilot Mega IMU board

For Scout to auto-stabilize, it needs sensors to find its orientation in space.  No one sensor can do this on its own.  It takes several different sensors working together to calculate Scout’s orientation.  The sensors used to calculate orientation are gyroscopes and accelerometers.  More recently, magnetometers are being incorporated to calculate direction.

Conveniently, there are boards that incorporate all of these sensors together.  These boards are called inertial measurement unit, or IMU.  An IMU uses accelerometers and gyroscopes to measure and report the aircrafts velocity, orientation and gravitational forces on multiples axis.

Scout uses the ArduPilot Mega IMU shield.  I chose this board because it was developed to work with the ArduPilot Mega board.

Wireless Communication

XBee 1mW Wire Antenna Series 1 Modules

The ArduPilot Mega supports serial communication between the quadcopter and a computer.  This serial communication is used to upload the software, change tuning settings and to update the flight path.  The ideal wireless solution is XBee.  XBee modules are available at different frequencies and power outputs.  I am using the XBee 2.4GHz 1mW with the wire antenna modules.  The XBee 2.4GHz modules are more than sufficient for initial setup, tuning and short range use.  The XBee 2.4GHz modules operate at the same frequency as microwave ovens, WiFi routers and just about any other wireless consumer device.  These modules have to contend with radio interference and this why they are not ideal as a robust long range solution.  For applications requiring longer range and robust communication, using the XBee Pro modules is a better solution.   The XBee Pro’s operates at 900MHz the lower frequency allowing for a longer transmission range for the same power output as the 2.4GHz modules and are less susceptible to interference.  The XBee Pro’s are offered in different power outputs. The higher the power output, the longer the transmission range.


Futaba 7C 2.4 GHz Radio

The R/C radio controls the throttle and the direction that the quadcopter travels.  When choosing an R/C radio, the most important feature is how many channels the radio supports.  One channel independently controls one servo or ESC.  The more channels, the more devices that can be independently controlled.  The minimum number of channels for a quadcopter is 5.  Four of those channels are for the four motors and the other channel for switching between flight modes.   These flight modes could be switching from stable or acrobat mode or to enable or disable autonomous flying.  A radio with more than 5 channels will allow auxiliary devices to be controlled.  Some devices that could be controlled are lights, robotic cameras or landing gear.

The Brain

ArduPilot Mega board with soldered header pins

The brain of Scout is the ArduPilot Mega.  This board is based off of the Arduino Mega processor and uses the Arduino IDE (integrated development environment) for programing the board.   This board is capable of auto-stabilizing and navigating Scout.  If a GPS unit is connected to this board, it can then auto-navigate the aircraft to user programmed locations.