How Crusher Works

By: Julia Layton  | 
Crusher Unmanned Ground Vehicle
Photo courtesy Carnegie Mellon, National Robotics Engineering Center

Crusher made its debut in true monster-truck style: The two prototypes entered a Carnegie Mellon University building to blaring music and flashing lights. One Crusher stood by while its counterpart proceeded to roll over and crush piles of cars that would have most monster trucks backing up with their tails between their legs. Crusher is no typical truck. It can drive right over a 4-foot vertical wall while carrying 8,000 pounds of cargo.

Crusher is an unmanned ground vehicle (UGV) funded by DARPA and designed by Carnegie Mellon's National Robotics Engineering Center (NREC). The thrust of the Crusher project – which builds on another NREC-designed UGV called Spinner (Crusher is sometimes called Spinner version 2.0) – is pretty much the thrust of all of the military-funded research and development in the UGV world right now: increased perception capabilities, autonomy and ruggedness. The U.S. Army would like few things more than an unmanned, silent tank that can carry limitless payload, defend itself against the enemy and speed unfettered across terrain that would have the Hummer curled up in fetal position.


The Crusher probably will never see mass production. The cost would be too high (the designers don't even quote a number). It's designed as a functioning prototype to test various technologies the NREC is developing as part of a program called UPI.

UPI stands for Unmanned Ground Combat Vehicle PerceptOR (off-road) Integration, a DARPA-funded mouthful that encompasses experiments to "assess the capabilities of large scale, unmanned ground vehicles (UGV) operating autonomously in a wide range of complex, off-road terrains" [ref]. The 6.5-ton Crusher weighs nearly 30 percent less than Spinner and can carry more cargo. The only thing the NREC left out of Spinner's upgrade is the ability to keep on truckin' if it's flipped upside down. No word on why that cool function disappeared, although logic would suggest it was either to make some of Crusher's other upgraded functions possible or to cut a high-cost capability that may not be crucial to UPI's main mission.

So, what can Crusher do?

  • It's an unmanned vehicle designed primarily for reconnaissance and support roles, and the lack of a human crew allows for new approaches to creating a rugged, flexible vehicle that can carry huge payloads. For instance, Crusher can forego armor under certain circumstances so it can carry more supplies.
  • Ultimately, Crusher will be able to navigate autonomously over extreme terrain complete with ditches, rock barriers and man-made obstacles.
Photo courtesy Carnegie Mellon, National Robotics Engineering Center
  • Crusher can run on battery power alone, allowing for nearly silent operation.
  • Crusher can carry weapons, so it can take on combat roles down the line.

According to the NREC, Crusher's technology is six to 10 years from real-world implementation. While smaller, human-controlled robots have made it onto the battlefield already (see How Military Robots Work), massive, unmanned robots like Crusher are still in laboratories. The complexity of the perception and control systems necessary for a large-scale robot to handle unknown terrain and conditions are still in the research-and-development stage. Crusher's perception and navigation systems are prototypes intended as test platforms for increasingly innovative approaches to ground combat vehicles that require no human input to carry out their mission.

In the next section, we'll take a look at some of those systems. Since Crusher is first and foremost a military project, complete details aren't available for the general public, but HowStuffWorks has managed nonetheless to find out some interesting information.


Crusher Technology

Crusher prototypes
Photo courtesy Carnegie Mellon, National Robotics Engineering Center

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.


Photo courtesy Carnegie Mellon, National Robotics Engineering Center

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 features upgrades in ride-height adjustment, suspension travel, vehicle weight and cargo capacity.

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.

Early version of Crusher's perception system

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.

Photo courtesy Carnegie Mellon, National Robotics Engineering Center

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.

Photo courtesy Carnegie Mellon, National Robotics Engineering Center

Crusher Specs:

  • 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.


The Future of Crusher

Photo courtesy Carnegie Mellon, National Robotics Engineering Center

As of 2006, the U.S. military has deployed approximately 4,000 battle robots for active duty. The military uses these robots primarily to "sniff out" bombs and clear buildings and other enclosed structures. The Army's Future Combat Systems (FCS) program is looking to spend about $300 million to fund updates to expand the roles of battlefield robots. The FCS seeks robotic mules that can carry cargo alongside troops over uneven terrain and much larger unmanned vehicles that can operate with no human input to scout areas and patrol borders, sending crucial data back to troops. If these large, autonomous vehicles can also carry huge payloads over difficult terrain without losing speed, that'd be an added bonus. Crusher or something like it would be ideal in the latter roles.

Crusher itself will probably not see deployment. It's mostly a research project and will be in testing and experimentation until 2008. At that time, the NREC will turn the Crusher technology over to DARPA so it can be applied to related projects, most of which fall under the domain of the Future Combat System. The FCS is running development programs like the Armed Reconnaissance Vehicle (ARV), which aims to realize a fully autonomous, battle-ready vehicle for reconnaissance missions; and the Autonomous Navigation System (ANS), an overarching program to develop common-platform autonomy capabilities for a wide range of military robots. The overall goal of FCS is seamless integration of both manned and unmanned vehicles, ground and air, into a structure that can be managed via a single, web-like control system.


By way of FCS, we may see Crusher-like vehicles supporting troops in battle operations in five to 10 years. They'll most likely start out in reconnaissance roles and then transition into combat, supporting troops as opposed to replacing them. But Crusher's cutting-edge autonomy technology is not military specific. The NREC envisions – and has in the works – research projects that utilize the systems developed for Crusher in civilian applications. In a decade, we could see autonomous vehicles performing risky tasks in areas like farming, mining and construction, ultimately transferring some of the danger faced by humans in these fields onto replaceable robotic counterparts that feel no pain.

For more information on Crusher, UGVs and related topics, check out the links on the next page.


Frequently Answered Questions

What does crusher work for?
A crusher is a machine designed to reduce large rocks into smaller rocks, gravel, or rock dust. Crushers may be used to reduce the size, or change the form, of waste materials so they can be more easily disposed of or recycled, or to reduce the size of a solid mix of raw materials (as in rock ore), so that pieces of different composition can be differentiated.

Lots More Information

Related HowStuffWorks Articles

More Great Links


  • Boyle, Alan. "Robotic Crusher has its coming-out party." April 28, 2006.
  • "Carnegie Mellon’s National Robotics Engineering Center Unveils Futuristic Unmanned Ground Combat Vehicles." Carnegie Mellon University. April 28, 2006.
  • "Crusher." National Robotics Engineering Center, Carnegie Mellon University.
  • Crusher Brochure. Carnegie Mellon: The Robotics Institute.
  • "Crusher Unmanned Ground Combat Vehicle Unveiled." Army News Service. May 4, 2006.
  • "DARPA's Smart, Mean, Off-road Drone." Defense Tech.
  • Erwin, Sandra I. "Next-generation robots: bigger and better?" National Defense. July 2006.
  • "FCS Unmanned Ground Vehicles."
  • Gawel, Richard. "Crusher Charges On To The Battlefield—All By Itself." Electronic Design.
  • Jackel, Larry. "DARPA's LAGR and UPI Programs." DARPA.
  • Piquepaille, Roland. "Emerging Technology Trends." ZDNet Blogs.
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