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3.2 The ERSP Software
Player/Stage
3 THE SCORPION ROBOTS AND ERSP
The part of the initialization related to obtaining an interface requires explicit naming of
the sensor, actuator or other hardware. E.g. it must be done for each sensor used or every
driving system. The unique names of the hardware is described in the next section.
The sensors, actuators and other robotic hardware is now accessible in the main part of
the program.
Before termination of the program the initialized interfaces should be shut down. This
is done by using a release function on the Resource Containers and finally deallocate the
Resource Manager itself. [20] [21].
The unique names of sensors available on the Scorpion robot in ERSP is described in
Figure 5. These names are used when issuing a request on the Resource Container for an
interface.
In ERSP the hardware details is also described in configuration files. The resource configuration file (resource-config.xml) specifies physical aspect of every piece of hardware
on the robot. The file is used often for reference as well as the figure shown. In the file all
devices are mentioned and we find it relevant to mention:
Motor devices The two motors on the robot has device ID’s Drive_left and Drive_right.
(Hardware) Avoidance device Device ID is avoidance and this device implements, possible in hardware, an default enabled avoidance system using bumper and IR sensors.
Joystick A joystick for Linux is available as device ID joystick.
odometry There is a odometry device that report wheel odometry for the differential drive
system. Device group ID is odometry with members Drive_right and Drive_left.
3.2.4
Coordinate Systems
ERSP uses either the robot coordinate system or the global coordinate system to describe the
robot’s incremental motion and sensor and actuator positions. The robots sensors and actuators position and orientation are described in the documentation with respect to the robot
coordinate system. [19]
The robot coordinate system is 3D and has the origo of the system at the floor level, directly
below the center of the drive wheels’ wheelbase. The positive X-axis of the robot extends
forward in the direction the robot is facing and this is also defined as North. When the robot
is on a flat surface the positive Y-axis extends West and the positive Z-axis is straight up. The
robot’s coordinate system is depicted in figure 6.
The world coordinate system is centered where the robot is turned and coincident with the
robot’s coordinate system at that time. The world coordinate system is fixed to the robot’s
starting position on the floor, while the robot’s coordinate system moves with the robot.
Angles in both coordinate systems is measured from the X-axis and are positive counted
counter-clockwise.
The robot’s orientation is defined from a single angle with respect to the world coordinate
system. Beside this it takes three angles to fully specify an object’s orientation in 3D:
• Roll: The rotation angle around the X-axis
• Pitch: The rotation angle around the Y-axis
Bue Petersen & Jonas Fonseca
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