WTC teaches engineering lesson about rescue robot

If it's true that every cloud has a silver lining, a derivative of the Oklahoma City bombing may be that it prompted development of robotics in search-and-rescue missions.

So by Sept. 11, there were already several companies-Inuktun Services Ltd. (Nanaimo, BC, Canada), Foster-Miller, Inc. (Waltham, MA), iRobot (Somerville, MA)-working on search-and-rescue robots, whose engineers picked up whatever they had and headed to New York City in a hurry. Likewise, they learned many lessons at the World Trade Center (WTC) site, one of which is the importance of adaptability.

Remote inspection and observation are often the most difficult tasks for robots to perform. Most do not adapt to height variations, turning ratios, or traction requirements. The Micro Variable Geometry Tracked Vehicle (microVGTV) manufactured by Inuktun is an exception.

The microVGTV alters its shape during operation. The tracks, in their lowest configuration, are shaped like conventional crawler treads. When raised to their highest geometry, the tracks are shaped like a triangle, maintaining unit stability and ruggedness.

Controlled with a hand-held joystick for speed and direction, and separate controls for the raise/lower, camera tilt, focus, and light functions, the microVGTV remains fully operational throughout shape alterations. As a result, the unit continues to travel, maneuver, and collect data during configuration changes.

The microVGTV is unique based on its design, as well as its uses. The vehicle is not wireless, but gets its power and instructions through a 100-ft cable. The complete system is easily transported and managed by a single operator.

It runs at a maximum speed of 15+ ft/min, whether at its lowered configuration of 12.5-inch long x 6.5-inch wide x 2.5-inch high, or its raised configuration of 7.5-inch long x 6.5-inch wide x 10-inch high. On board the robot are a video camera, audio equipment, and heat detectors.

Making this equipment suitable for the application at Ground Zero required modification so that rescue workers could carry the controller, cable, and vehicle in their hands and on their backs while climbing over the wreckage during the search for bodies. That demanded special battery packs, additional equipment, and the cooperation of many people to rush the orders and shipments through.

An important feature of the microVGTV design is its five drive motors. Two motors drive the tracks, one raises and lowers the VGTV during geometric profile changes, and two perform camera tilt and focus control. Maxon motors were designed into the latest vehicle models.

"The motors provided almost twice the torque we spec'd in," says Paul Prunianu, a mechanical engineer at Inuktun. He indicates that the additional torque comes in handy when adding capabilities to the system such as lasers, increased track weight (for traction), and small load-carrying capabilities used with some third party sensors.

Independently controlled to provide increased turning capabilities, the A-max 22 mm motors and GP022A 690:1 gearbox drive the tracks. That makes them suitable for exploring the WTC as well as inspecting pipelines, nuclear power plants, and crawl spaces.

Although performance was Inuktun's primary reason for incorporating the Maxon motors, a close second was the "compact dimensions the motors offered for the corresponding power they packed," says Prunianu. The compact size of the A-max 12-mm motors used for the camera tilt and focus is a case in point. At 12 mm, these brushed motors provide a maximum continuous torque of 0.996 mNm.

Another challenge in the design was to keep the weight distribution properly controlled as vehicle geometry changed. Placing electrical and electronic components, including the raise/lower motor on a center-mounted chassis, was the key.

As the chassis raises and lowers, it shifts the system's center of gravity to keep weight distribution low, which prevents the robot from tipping when in a raised position, and stabilizes weight distribution over its tracks. A Maxon A-max 22, 22-mm motor is combined with a Maxon planetary gearhead model GP 22 A with 128:1 ratio to provide smooth, controlled operation of the geometric shape-changing function.

For track drive motors, the larger units incorporate Maxon's RE035, 90w motors and GP032 gearbox. The high-end RE motors are specially designed using rare earth, neodymium magnets. These magnets are the key elements in providing the motors with maximum power per volume.

When asked for additional equipment for use by the urban search-and-rescue units, Inuktun provided three additional systems assembled and appropriately modified to suit the needs of the teams, in 24 hours time. The equipment was instrumental in locating the bodies of at least five people.

For more information about motors from Maxon Precision Motors: Enter 533