Mobility
Ground Contact
The TerraHawk Vehicle (THV) is propelled by force generated from contact between its six tires and the ground. Figure 1 shows the general layout of the vehicle. The six wheeled vehicle is made up of three segments. The segments are articulated in one degree of freedom relative to each other to allow limited steering. Each segment contains the drive and suspension for two wheels. The front and back segment each contain a generator and the middle segment houses the core computer systems.
Locomotion, Steering and Braking
The THV generates torque with six 10 hp electric motors. Each motor is coupled to one wheel through a gear reduction, an external belt drive and a final gear drive within the wheel hub. Four of the six wheels have pneumatic/hydraulic brakes. Steering is generated in a progressive manner. Inter segment articulation provides a turning radius as small as 30 feet for higher speed turning. Low speed turning down to zero radius is accomplished with differential drive to the motors.
Actuation
All components that require physical motion use either pneumatic or slow electric actuators. This includes the suspension, steering, isolator platform and brakes. Reserve volume for the pneumatic actuators is kept within each segment.

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Power
Source
The THV generates torque with six 10 hp electric motors. Each motor is coupled to one wheel through a gear reduction, an external belt drive and a final gear drive within the wheel hub. Four of the six wheels have pneumatic/hydraulic brakes. Steering is generated in a progressive manner. Inter segment articulation provides a turning radius as small as 30 feet for higher speed turning. Low speed turning down to zero radius is accomplished with differential drive to the motors.The THV generates power using two 14kW DC diesel generators. Temporary additional demand is met with 18 packs of NiCad batteries capable of sourcing up to 54 kW of power.
Peak Power
The peak power required by the vehicle is dominated by the very short startup transient of the DC motors. All six motors can consume a total of ~99 kW of power for about a second.
Fuel
The peak power required by the vehicle is dominated by the very short startup transient of the DC motors. All six motors can consume a total of ~99 kW of power for about a second.

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Processing

The peak power required by the vehicle is dominated by the very short startup transient of the DC motors. All six motors can consume a total of ~99 kW of power for about a second.

The primary functions for each processor type are listed below:

PC 104

Motor Control
Generator Control
Pneumatic Control
Vehicle Control
IMU data Processing
LIDAR Data Processing
Core Processors

Sensor Fusion
Road ID algorithms
Radar Processing
Solid Model Construction
Mode Determination
IMU data Processing
LIDAR Data Processing
Kalman Filter Processing

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Environmental Sensors
The sensors are used in one of three ways. The first is to derive state data for the vehicle. The second is to gather data for the solid model generation. The third is to gather focused data as directed by the navigation system.
GPS
The Navcom GPS provides position data in Earth Centered Earth Fixed (ECEF) coordinates when the appropriate signals are present. When all signals are present in sufficient strength, the GPS can provide location information to 10 cm accuracy.
IMU
The Northrop Grumman LN-200 IMU provides 6 DOF worth of data at high rates to propagate the vehicle state when the GPS signal is not available. The IMU data is combined with the GPS data within a 15 state Extended Kalman Filter (EKF) when both are present.
Coarse Heading Sensor
The coarse heading sensor contains three magnetometers, three gyros and three accelerometers of moderate quality. The sensor provides near instantaneous heading information with a resolution of less than 1 degree and an accuracy of 5 degrees.
Boundary ID Cameras
The Boundary ID cameras are low resolution video sensors primarily used to identify artificial boundaries installed by the DAPRA Grand Challenge staff. Road ID Camera The road ID cameras use texture ID algorithms to identify roads/trails along with associated confidence levels.
Binocular Vision
The matched set of machine vision cameras are the first of three sensors used to construct a near real time solid model for low to moderate speed navigation.
Radar
The Eaton VORAD radar provides tracking data on up to 20 objects. This data includes azimuth, distance and closing speed. It is the second sensor used in the solid model construction.
Lidar
The Lidar sensor is the final sensor used for solid model construction. It is the primary obstacle avoidance sensor.

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Localization
Geolocation
Geolocation of the sensor platform is accomplished with the Navcom GPS and LN-200 inertial reference unit. A 15 state extended Kalman filter is used to combine input from all available sensors.
GPS Outages
If the GPS signal drops out or becomes unfavorable, the Kalman filter will automatically shift gains and de-weight that input.
Challenge Route Boundaries
When the boundary cameras detect artificial boundaries or the lateral boundaries become very small, the narrow passage navigation mode will be entered and speed will be reduced to minimum.

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