03 October 2001

Robotic explorer for all environments

by Bob Felton

Just plug in another set of wheels when you need more capability.

The technology developed for NASA’s extraterrestrial robots is now available to earthbound engineers who need to collect data from dangerous or hard-to-access areas, inspect remote equipment installations, or patrol a security perimeter.

"These or similar vehicles," said NASA’s Jet Propulsion Laboratory inventors, "could also be useful in such diverse terrestrial applications as exploration of volcanic craters or other hostile terrain, military reconnaissance, inspection of hazardous sites, or searching for victims of earthquakes, landslides, or avalanches. There might even be a market for simplified versions of these vehicles as toys."

Modular construction

The simplest robo-vehicle consists of two wheels joined by an axle, superficially resembling the rear axle and wheels of an automobile. In addition to the two main wheels, the assembly includes a caster wheel attached to the axle by an actuator link; the motion of the link controls the rotation of the axle, allowing sensors mounted on the axle to point in any desired direction. This mechanism permits the sensors to work in the forward or rearward direction. In the vertical position, the caster link serves as an antenna for wireless communication. Brushes mounted on either side of the caster link wipe dust off the solar cells.

The axle houses computer modules and three motors and their associated mechanisms for driving the wheels and the caster link. There are solar cells mounted on the outside of the axle. There are rechargeable batteries inside the wheel hubs; the effect is to increase traction and, hence, maneuverability. The rovers could weigh up to about 3 kilograms (6.5 pounds).

According to the inventors, users will build robots of any size "as an assembly of multiple units, plus one or more instrument modules connected to each other at the module interfaces. The module interfaces would contain standardized electrical and mechanical connections, including spring-loaded universal joints, about which the modules could comply to adapt to the terrain. Data would be communicated between modules via fast serial links."

Further, they said, "The symmetrical design of the modules would enable them to operate in any stable orientation, including upside down. This feature would contribute to robustness of operation in rough terrain, including the ability to recover after falling off a cliff. The simple and modular design of the assembly provides better maneuverability using fewer actuators and sensors and hence lower power requirements than traditional rovers. The system features scalable complexity. The motion control algorithms for the unit are very simple, and as the size of the train grows, the complexity of the algorithms increases."

Technical advances

The new robotic explorer represents an advance over previous robots because it can be reconfigured on the fly and is self-repairing and self-cleaning. Further, it uses low power. "We implement features such as low-power mobility, negotiation of difficult terrain, recovery from small drops, self-repair, and self-cleaning of solar cells. The robotic modules are rugged, agile, autonomous surface explorers that have a minimal mobility system. However, their symmetric design enables them to operate in any stable state and traverse rough terrain."

Comparing the new rovers with preexisting technology, the inventors said, "The former rover types often suffer from a phenomenon where the wheels are fighting each other when climbing over very rocky terrain, unless complex algorithms are used, which eventually would require more power."

The robot trains can also do more humble jobs. "In addition to carrying science instruments, the train can be used to carry loads from one location to another. This transport mechanism is more reliable than that performed by several disjointed rovers."

Additional information is available at www.nasatech.com/Briefs/July01/NPO20944.html. IT