Fuel Cell Powered Mobile Robots

Sandia National Laboratories' Intelligent Systems and Robotics Center (ISRC) has developed the RATLER™ ("Robotic All Terrain Lunar Exploration Rover") vehicles to fulfill a wide variety of functions. A RATLER™ was originally developed as a prototype vehicle for a lunar exploration mission; however, RATLERs™ are now used for tasks such as surveillance, perimeter control, localization of chemical sources, and search and rescue missions. RATLER™ vehicles come in a range of sizes, from 8 inches up to 3 feet long; are lightweight, maneuverable; and must be able to navigate over long distances. Because of their wide usage, RATLERs™ have unique power requirements.

RATLERs™ traditionally have carried batteries for onboard power; however, batteries are typically large, heavy, and have limited capacity. ISRC was interested in a power / propulsion system that would fit the same space requirements as the battery system, have extended standby reliability, a low thermal signature, safe intuitive operation, similar or better power available for mobility, and affordable life cycle costs. When looking for a viable alternative to battery power in robotic vehicles, ISRC believed that fuel cells could offer a practicable solution. Fuel cells offer a way to improve Sandia's electric robotic vehicle performance, to extend operating range and life, and to reduce observable signatures so that robotic vehicles can be used more effectively in a variety of demanding applications.

Fuel cells constitute the most efficient energy transducers known to man; they are twice as efficient as batteries. Fuel cells are electrochemical devices that convert a fuel's energy directly to electrical energy, operating much like continuous batteries when supplied with fuel to the anode (negative electrode) and oxidant (e.g., air) to the cathode (positive electrode). Instead of following the traditional extraction of energy in the form of combustion heat, conversion of heat energy to mechanical energy, and finally turning mechanical energy into electricity, fuel cells chemically combine the molecules of a fuel and oxidizer without burning, dispensing with the inefficiencies and pollution of traditional combustion.

Sandia is a member of the Fuel Cell Propulsion Institute, an organization that consists of about 60 members, including universities, mining companies, fuel cell manufacturers, and related research companies. In 1998, a contract was written between Sandia and the Fuel Cell Propulsion Institute to coordinate the design, procurement, and fabrication of a prototype fuel cell for the RATLER™.

A pair of hydrogen fuel cell systems, complete with a safe storage method for the gas and all required support systems, designed specifically for a small RATLER-style robotic vehicle was produced, bench-tested, and delivered to the Mobile Robotics Department at Sandia National Laboratories in August 1999. The integration of the fuel cell with a small tracked RATLER-style chassis is expected to be complete by mid-November 1999. This will be among the first fuel cell-powered mobile robotic vehicles.

There are many types of fuel cell chemistry. The type used in the RATLER™ is a PEM, or Proton Exchange Membrane. It combines hydrogen and oxygen to produce electron flow or current, without appreciable heat, using a platinumcatalyst on the surface of the membrane. It is at this interface that hydrogen and oxygen combine to form water and electrical energy.

The prototype has the potential to triple the operating range of the RATLER™, which will be verified in field tests scheduled to begin fall 1999. The next step is to certify the units, transfer safe systems to ISRC, have the fuel cell RATLER™ tested alongside a battery-powered unit, and analyze the data to determine actual performance of the system in field conditions.

Because power and energy density are limiting factors when deploying robots in field applications, fuel cell technology can help address these issues.