The minirobot was built at Sandia National Laboratories to demonstrate that microminiaturized autonomous vehicles could handle jobs as diverse as locating land mines, detecting chemical or biological weapons, and prowling around buildings on surveillance missions.

"My main work is on sensor chips for Sandia's handheld chemistry lab," said researcher Doug Adkins. "But we needed some kind of autonomous vehicle that could carry sensors into otherwise inaccessible or hazardous locations, so we built the smallest robot we could." Adkins built the robot prototype with assistance from fellow Sandia researchers Ed Heller and Ray Byrne.

Sandia has been building tiny robots since the 1996 debut of the Mini Autonomous Robot Vehicle, or Marv. That machine maintained its autonomy by housing a microprocessor, battery and sensor in a robot that was less than 1 inch³ in volume. Further developments of rapid-prototyping techniques at Sandia enabled the project to grow the body for its newest minirobot, merging streamlined versions of components from Marv with the results of work done by the lab's Intelligent Systems Sensors & Controls Department.

Sandia's miniature robot houses bare dice for control functions, runs on watch batteries and uses tank-style tracks to reach speeds of 20 inches per minute.

The original Marv was constructed from printed-circuit boards that used standard microprocessors and similar chips to house an infrared "obstacle detector" sensor, a radio for transmitting its observations, a temperature sensor and batteries. But the smallest Marv still measured 1.6 x 0.75 x 0.71 inch.

"We needed a robot that was much smaller than Marv, so the sensor group collaborated with the robotics group to see how far we could push miniaturization while still using easy-to-acquire components," said Adkins.

As a result, Sandia's Sensor Technologies Department teamed with the Intelligent Systems and Robotics Center to explore new techniques for packaging electronics, wheel design and body material into a quarter-inch cube.

Swarming robots

Ultimately, Sandia hopes to mount radios on each mini-robot to allow the unit to transmit its findings back to human observers, as well as to get the robots talking among themselves for coordinated tasks.

"Eventually we hope to have them relaying information not only to human-manned stations but also to each other, so they can work together in swarms, like insects," said Adkins.

The first step to realizing the small robot began by taking the chip components out of their packages. For instance, the engineers found they needed a microcontroller chip that had integrated input/output and had at least 8 kbytes of read-only memory. But even surface-mounted chip packages housing commercial microcontrollers were too large, so they took the dice out of the package.

"The only way to shrink the robot further was to get rid of the printed-circuit board and all the packaging associated with it, so we found a microcontroller that we could buy in the raw-die form," said Adkins.

To mount the raw dice, the researchers turned to Sandia's Compound Semiconductor Research Laboratory, which donated a multichip module, allowing the chips to be mounted directly on a glass substrate. In that way, the microprocessor and the sensors, clock and associated I/O channels could be mounted on a single sliver of glass high atop the mini-robot.

Since there was no circuit board to form the robot's "body," the researchers turned to a new rapid prototyping technique developed at the lab called stereolithography — a 3-D material-building methodology that deposits very thin layers of polymer that are individually cured with a laser. Stereolithography enabled the minirobot's body to be "grown" layer by layer into a complex 3-D shape with cavities for the batteries, motors, axles, switches, sensors and glass substrate housing the electronic chips.

With the minirobot's smaller size, wheels could too easily become fouled with contaminants. That forced the researchers to replace Marv's wheels with tank-like tracks, providing extra traction because of their increased surface area. Now the minirobot can traverse smooth as well as rough surfaces at about 20 inches per minute.

Tough track

"We haven't put the new treads through a comprehensive set of tests yet, but fitting it with tracks instead of just wheels enables it to navigate a carpet — a surface that was too rough for its tiny wheels before," said Adkins.

For the future, the sensors and controls department plans to start mounting all the different types of sensors they have developed onto the minirobot platform. At the same time, the systems and robotics center plans to further streamline the minirobot as well as characterize its capabilities and shortcomings. In the immediate future, the labs will add wireless infrared or radio transceivers for two-way communication and will mount their already developed miniature infrared and video cameras, microphones and chemical microsensor arrays.