Sensor Fusion
The Scout sensor suite affords increased situational awareness over comparably
priced platforms1. Scout fuses long range sonar with short
range IR sensors and LED reflectance sensors to provide realtime feedback about the robots'
environment. Commercially available off-the-shelf components were used where possible,
selected based on range, accuracy, and repeatability characteristics.
learn more >>
Environment Mapping
Ultrasonic ranging sweeps 360 degrees around each Scout robot, providing up to 48
measurements per cycle. A compact stepper motor provides precise and rapid position control. The high resolution and
fast scanning speed are appropriate for 2D mapping and navigation.
The Maxbotix® EZ™ line of sonar rangefinders was chosen for their proven accuracy and
long term reliability2. The EZ4 provides the narrowest sensing
area of the EZ™ family, allowing higher precision maps to be produced, while still
providing wide coverage for obstacle detection.
Cliff Detection
A trio of short range Sharp® IR rangefinders provide early warning of sharp drop-offs that
could compromise the robot's mission.
Odometry & Vehicle Dynamics
Vehicle position is tracked by quadrature encoders on each wheel resulting in 3mm linear accuracy
3. A custom IMU (inertial measurement unit) consisting of a 3-axis accelerometer
and pitch+yaw-rate gyroscope provide detail of the vehicle's motion in three dimensions.
Complementary Sensing
The sonar rangefinders are optionally supplemented by short range LED reflectance sensors for close wall
following. Dual sensors on the front bumper provide resolved impact detection for escape manuevers or
when manipulating objects.
- Comparison with commercially available robots valued at <$500 USD.
- PDF: Maxbotix® EZ4™ Sensor Testing
- 48 clicks per revolution, 42mm diameter wheel. (42mm*pi)/48=2.7488mm
Communications
Scout communicates over several protocols, providing a robust interface
over long distances. Inter-robot communications and control commands are broadcast over a self organizing
high bandwidth mesh network. The robots also broadcast over IR (infrared light) for localization.
learn more >>
Bearing and Orientation Module (BOM)
The Scout BOM provides relative localization information between robots. Four IR transmitters
around the base broadcast the robot's identification code and the sensor position, allowing
relative orientation to be determined. The hardware is specially designed to reject environmental
interference such as noise from fluorescent lights and other source of stray IR.
The high refresh rate and robust communication permits tighter precision formation control over
distances up to 12 feet.
Wireless Network
Inter-robot communications are handled over a 2.4GHz Zigbee® network using the IPv6 protocol.
A transfer rate of up to 2Mbps can be achieved over a distance of nearly one mile line-of-sight
1. The system uses a true layer 3 mesh network, distributing data
packets intelligently amongst the robots. The nature of the mesh network is dynamically
robust, self healing after the loss of any communications node.
Wifi Bridge
An optional network bridge can link the 802.15 Zigbee® radio to standard internet
enabled devices (802.11b/g). When using this bridge each Scout can be accessed wirelessly over
the internet.
