There are three primary focus areas in Crusher's development:
- ruggedness to withstand extreme terrain without losing speed, even when carrying 8,000 pounds of cargo
- quiet motion on the battlefield to make it a viable reconnaissance asset
- autonomous operation to allow for scouting, reconnaissance and even combat roles without risking a single human life
Crusher's skeleton is made of aluminum and titanium. Its hull is an aluminum space frame (an open structure of connecting rods) with ultra-sturdy titanium nodes joining the rods for added strength in the likely event of collisions with large, hard objects. Immediately below the hull is a skid plate - basically a suspended, shock-mounted steel "bumper" that stands as a first-defense, protecting the hull from initial contact with the likes of boulders, tree stumps and steps.
To keep it moving over obstacles and generally unfriendly terrain, Crusher sports a six-wheel, all-wheel-drive system powered by a hybrid diesel-electric setup that allows for nearly silent operation - a handy characteristic in recon work. A 78-horsepower, turbo-diesel engine acts as a generator in the system, outputting a continuous 58 kilowatts (kW) of power to charge Crusher's 300-volt, 18.7-kW, lithium-ion battery pack. The batteries in turn run six 210-kW electric motors, one situated in each of the six wheel hubs. Each motor produces 282 horsepower. Like most hybrid-electric power systems, Crusher makes use of regenerative braking to return some power to the batteries each time it slows down (see How Hybrid Cars Work to learn about regenerative braking). The vehicle can run on silent battery power alone for 2 to 10 miles (3 to 16 km) depending on speed and cargo load.
Since each wheel is independently powered, if one or two die, Crusher can keep going. It needs only four of the six wheels to maintain its capabilities. And if it finds itself in sudden need of a turnaround -- say, surrounded on three sides by unpassable barriers - it can use its skid-steer ability, a turning radius of zero, to quickly about-face with no wiggle room at all.
To fit under low-hanging obstacles, face rocky terrain or better hide from the enemy, Crusher has a zero-to-30-inch (76-cm) adjustable ride height. In addition to height adjustment, Crusher's suspension can travel a full 30 inches to absorb shock, and it features adjustable stiffness for varying ground conditions. We were able to locate an under-the-hood view of Spinner, Crusher's predecessor - remember that Crusher is an upgraded version of Spinner 1.0:
Crusher's powerful frame, six-wheel-drive setup and extreme suspension capabilities enable the UGV to travel at high speeds, currently up to 26 mph (42 kph), over difficult terrain, facing obstacles like ditches, boulders, steep inclines and vertical barriers up to 4 feet, all without missing a beat.
Sturdiness, power and silence make Crusher an ideal scouting tool, but it's primarily the UGV's autonomy system that DARPA has so far shelled out $35 million to develop. The NREC hasn't released much detailed information about the UPI system, but says that "this technology spreads sensing abilities across the entire vehicle to help balance its perception and also support vehicle areas that may be less adept at sensing the environment. The [sensing] software will also let Crusher 'learn' and apply previously gathered information to new obstacles."
We do know that the perception hardware consists mainly of LADAR (laser detection and ranging) units and camera arrays. A LADAR unit sends out a laser beam to scan an area and measures how long it takes for the beam to be reflected back to the unit's laser sensor. Crusher has eight of these units - four scanning the environment horizontally and four scanning vertically. It uses six pairs of stereo-vision cameras for depth perception and four color cameras to apply a color pixel to each point of distance determined by the LADAR sensor.
The most recent incarnation of Crusher features an 18-foot telescoping mast for collecting data from a higher vantage point. The mast may incorporate parts of the LADAR and camera assembly seen above, or it may simply add an additional set of sensors to the perception system.
With all of the LADAR and camera data combined, Crusher's onboard CPU creates a 3-D picture of the landscape in which Crusher is traveling. The CPU is a 700-MHz Pentium 3 that controls Crusher's mechanical activities and runs the navigation software that handles sensor-data processing. An inertial measurement unit (IMU) detects Crusher's altitude, position and direction of movement using a combination of accelerometers (tilt sensors) and gyroscopes, so Crusher is always aware of its own motion and position relative to the landscape. The UGV also has a built-in GPS receiver and computer-based GPS database that includes pre-programmed terrain data.
So far, field experiments have shown that Crusher is well on its way to true autonomy. In testing, Crusher moved from GPS waypoint to GPS waypoint spaced more than 0.6 miles (1 km) apart without any outside control. Using its perception and navigation systems, Crusher can react to obstacles on the fly - it doesn't need an operator to tell it what to do when it hits something. It can climb an incline greater than 40 degrees, drive right over a 4-foot step and cross an 80-inch trench using its own decision-making capabilities. The trench-crossing ability is especially cool - Crusher's tires are mounted in such a way that they can drop down to support the vehicle while it's crossing a gap.
- empty vehicle weight: 13,200 lbs (5,990 kg)
- maximum payload: 8,000 lbs (3,600 kg)
- length: 201 inches (510 cm)
- width: 102 inches (260 cm)
- height (figuring 16-inch/41-cm ground clearance): 60 inches (152 cm)
- ground clearance: 0 to 30 inches (76 cm)
- tire diameter: 49.5 inches (125.7 cm)
- top speed: 26 mph (42 kph) in less than 7 seconds
- payload volume (in two internal bays): 57.7 cubic feet (1.6 cubic meters)
- possible control modes: remote control waypoint-based navigation full autonomy
The size and weight specifications mean that a single C-130H cargo plane can carry two Crushers into battle anywhere in the world. As of August 2006, Crusher has been fitted with a Rafael Mini Typhoon mount that holds a .50 caliber rifle, pointing to the possibility that combat roles may become an increasingly prominent focus in the development of autonomy technology for military vehicles. In the next section, we'll take a look at the future of the Crusher prototype and find out how it fits in with the overall trend in military research and development.