Military Communications and Information Technology: A Trusted ...

Chapter 3: Information Technology for Interoperability and Decision...
311
The UAVs have high precision position stabilization as well as a location estimation
system. As in most localization systems a GPS receiver provides information
about the absolute position which is fused with measurements from accelerometers,
gyroscopes, a magnetometer, and a barometer. For communication, a special chip
running a specialized embedded Linux distribution is added. It supports both
the communication channel with the base station and with the other robots, as well
as autonomous flight control. Our control module utilizes the position and attitude
estimations from the UAV, as provided by the manufacturer, and generates signals
that are fed back into the proprietary control software of the drone. The interface
we use is identical to the original radio control connection. This allows us to make
use of all position stabilization functionalities provided by the manufacturer, as we
electronically simulate a human operator. By the flick of a switch a real operator
can obtain control over the UAVs at any given time.
Communication from and to the UAV is realized with two wireless connections.
The original radio control device is connected over a bi-directional low-bandwidth,
but high distance 2.4 GHz channel. It sends control commands to the UAV and receives
information about the height, attitude and the state of the battery. The second
channel is a 5 GHz Wireless LAN connection used to transmit data with high bit rates.
Since the project is mainly focused on reconnaissance, each UAV is equipped
each with a 14.7 MP zoom camera. However, as the UAVs have to alter their attitude
to make changes in movement, a fixed mounting of the cameras would result
in blurry images. To prevent this, the cameras are mounted within a moveable frame,
which is deflected by two servos. The angle control input is taken from the attitude
estimation made by Microdrones. Pictures are accessible in two versions. One
is the live video preview used on the camera display as default. Respective pictures
have a resolution of 320 x 240 pixels, an average file size of 9 kB, and are available at
25 Hz. The second is the single picture mode by which high resolution pictures
can be taken. High resolution pictures have a resolution of up to 4416 x 3312 pixels
and an average file size of 4 MB.
IV. Challenges using ROS
The requirements of robot control software for MRS are a) the control
of the MRS as one unit, and b) the separate control of specific robots. This demands
self-sufficient control software on each robot but also communication between
the robots. To be able to use the communication interface of ROS it must be
compiled for the specific processor structure and operating systems of the robots.
We used one ROSCore for all robots, which allows communication over
ROS topics. For each robot there is a ROS node which listens to specific topics
and controls the robots according to the given commands. Those commands are
defined in BML. The robots communicate not only with the C2 system over BML
but also with each other. This means an intelligent node, handling the commands