Step Motor Helps Robot Capture Images in 3D

Michael Comberiate, who manages the Special Projects Initiatives at the NASA/Goddard Space Flight Center, and his team of graduate and undergraduate engineering students build robotic vehicles that are used to test flight avionics, instruments, communications protocols, and approaches for planetary exploration. One project involves developing new communication protocols suitable for the delays encountered in space travel. This research involves the transmission of commands and images between the flight center on Earth and exploratory vehicles roaming various planets. The team works with a robot named Nanook that is outfitted with an imaging system that uses a step motor to help it collect data for 3D images. If Comberiate’s research proves successful, the communication protocols will be used in projects like the Mars Rover explorations, but they could also help solve communication problems here on Earth.

The robotic mothership undergoes testing in Anartica and Alaska while being operational from Maryland. The current test system runs around $30,000 while the final rover that will be sent to Mars can exceed $100 million.

The Internet, for example, is not suited to a transmission delay of more than 3 seconds. When sending data from say Mars, line of sight transmission can still experience delays of five to ten minutes. Without line of sight, the delay is even longer, often hours.

When a communication protocol experiences a transmission delay, the usual procedure is to try to send the transmission again, from the beginning. This process is not suitable for planetary exploration, thus, the need for a new communication protocol that can handle long delays.

In their research, Comberiate and his team developed a robot that is being tested at the arctic and that could wind up in the Mars Rover mission. Communicating between their offices in Maryland and the robot at the South Pole is similar to communicating to a roving robot on Mars. The engineers experience satellite synchronization issues with volumes of data as the robot takes digital dot-matrix pictures of objects it finds, similar to what they will experience when transmitting with equipment on another planet. The images are sent to the engineers, who then decide what objects require a closer look. Dot matrix is used because it will transmit faster than a digital camera image.

The robot uses laser-based guidance known as LADAR (Laser Detection and Ranging) to find and take images of objects. It is semi-autonomous and has 3D scanning capability with image stitching.

The laser has a spinning mirror inside that sweeps the beam from left to right, measuring the time it takes to return a pulsed beam of infrared light from an object. The mirror spins four times on each horizontal line and then a step motor raises it up ¼ of a degree in the vertical axis. The laser spins again along the horizontal line, building the image one line at a time. “We scan with a ¼ degree of accuracy left and right, and ¼ degree of accuracy up and down,” noted Comberiate, “which gives us a 3D image. The colors show a low resolution of the distance to every point in the scan, but the computer onboard has about 1000 times more data than shown in the images. These images convey the critical information to the operators on Earth, but take 1000 times less time to send than a typical photograph.”

The 3D scanning provided by the mothership brings back images that show depth of field plus azimuth plus elevation. The different colors shown in the images depict varying distances from the mothership.

Previous imaging systems could not deliver the needed resolution and the pictures displayed considerable distortion. “We chose the Lin Engineering step motor because it could handle the arctic conditions of -40 below 0 and still deliver smooth motion and hold position,” said Comberiate. “It gives us excellent remote control over the size of each step.”

In the rugged environments, the robot must operate off batteries. “We direct the heat from the electronics to where it is needed throughout the robot and to the batteries to keep them warm. Any motor we choose must be able to handle such environmental conditions.” Comberiate and his team will be continuing their research at the arctic in January 2010.

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