Investment Fosters Future Motor & Control Technology

Electric motors and motor controllers play an important role in the future of space exploration, military operations, and environmental conservation. Consequently, federal agencies continue to invest in these technologies by funding projects that improve their performance and efficiency. This work will not only shape the future of these specific application areas, but will also have significant crossover into the commercial marketplace.

Space Exploration

Autonomous robots are expected to free astronauts of routine and repetitive tasks (e.g., simple inspections, maintenance, scouting terrain, and gathering field samples) during future space exploration missions. Today's Earth-bound technologies play a key role in the development and enhancement of these robots. One recent example is Thibodeaux (see Figure 1), a four-wheeled autonomous mobile robot being developed at NASA's Johnson Space Center in Houston, Texas, for use in lunar and Mars missions.

Roughly the size of an all-terrain vehicle, Thibodeaux is designed to pre-scout areas for astronaut missions, and to carry heavier payloads for construction and in situ science tasks. The robot is directed by astronaut voice commands, and can be driven remotely using wireless communications and onboard video cameras. Four onboard, sealed lead-acid batteries provide power.

Currently reaching speeds of only 3 miles per hour (mph), one 1.8-kW electric motor (the patented 2x motor from WaveCrest Laboratories of Dulles, Virginia) is being outfitted into each wheel to enable speeds up to 30 mph. Originally designed for electric scooters, cargo scooters, and motorcycles with top speeds up to 37 mph, each motor will be current limited to produce 180 Newton-meters (Nm) of peak torque for the NASA project.

The permanent magnet, DC brushless motor (see Figure 2) has an inverted architecture - meaning the rotor surrounds and rotates around the center-mounted stator. The stator consists of a series of independently controlled electromagnets driven by a proprietary power electronics module. Conventional steel laminations are used as the stator core material. The rotor has rare earth-based permanent magnets and housings that are arranged in a proprietary design. Connected to the power electronics, a digital signal processor activates the electromagnets by analyzing motor position, desired torque, and the electrical characteristics of the energy management system powering the motor. Patented adaptive algorithms adjust the current and excitation sequence of each electrical phase.

"One of the key things about our technology is the patented software used in the integrated motor and control. It allows the motor to reconfigure itself within nanoseconds," said Tim Hassett, vice president and general manger of motors and operations for WaveCrest Laboratories. "The software senses load such that it reconfigures the motor and allows it to run at an optimal performance while properly dissipating heat." Integrating the motor and control also eliminates electric and magnetic field (EMF) issues and shortens cable lengths to reduce line chatter.

Additional customization is necessary for the NASA project mainly because Thibodeaux will be an all-wheel drive robot requiring communication among four-wheels, whereas the scooter only had a single wheel on the back drive. While specifics cannot be provided due to the nature of the work, software will be altered so that it works with the robot's existing vehicle control and some of the components on the power board will be changed to better suit the application. According to Hassett, alterations to the housing or anything mechanical will not be necessary.

Military Operations

The U.S. military invests heavily in the development of technology aimed at reducing the number of causalities on the battlefield. Consequently, unmanned ground, air, and underwater vehicles receive ample attention and funding. In 2004, for instance, the Defense Advanced Research Projects Agency (DARPA) kicked-off its annual Grand Challenge in response to a Congressional and U.S. Department of Defense (DoD) mandate. The Grand Challenge aims to accelerate the research and development of autonomous ground vehicles (AGVs). More discrete projects have been taking place all over the country with assistance from programs like the DARPA Small Business Innovation Research (SBIR) program for years.

Under a DARPA contract ThinGap Corporation of Ventura, California, has developed an 8.3-inch diameter brushless ring motor (the TG8250 motor) based on their patented electromotive coil design that replaces an iron core and wire windings with a free-standing, precision-machined copper sheet coil, see Figure 3. A version of this motor powers a ducted fan that has already successfully lifted an unmanned air vehicle (UAV) in initial tests. The unique feature of this lightweight thin ring motor (7.5'' ID) is that the propeller is mounted inside of it.

Based on a Phase II SBIR contract granted by DARPA in October 2004, the company will be taking the technology a step further, adapting it into a larger, 14-inch model (see Figure 4) for use as a potential electric-drive in a six-wheel, unmanned ground vehicle (UGV). The UGV could be used for a variety of missions, including hauling equipment, detecting land mines, and land assault. Application requirements include high torque at start up - 1,200 ft-lbs at 28 rpm for 500 seconds (8.33 minutes) and high speed at 260 rpm with efficient heat dissipation. The application requires 6.5 hp constant power output throughout the power curve.