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Cratos-Tracked Test Rover Designed and Built at NASA Glenn

Photograph
Cratos tracked rover.

In Greek mythology Cratos was the personification of strength and power. His character typified the goals of the researchers at the NASA Glenn Research Center when they were designing a tracked test rover called Cratos (shown in the preceding photograph). A heavy-duty aluminum frame, two powerful direct-current motors, and a versatile sensor-laden control system made this an ideal test vehicle for studying various track designs and control algorithms. Cratos will be tested in various terrains and with different track designs to help determine the feasibility of using tracks to descend into a crater on the Moon.

Cratos was a multi-divisional effort led by the Flight Electronics Lab within Glenn’s Instrumentation and Controls Division. It was funded under the Exploration Science Mission Directorate at Glenn and was part of a rover codevelopment program with the Carnegie Mellon University (CMU) Robotics Institute. CMU developed Highlander, a tracked rover to develop and test methods for lunar crater wall descent. As part of this effort, engineers at Glenn built and used Cratos to specify, develop, and test inertial measurement, tilt and odometry instruments, control algorithms with sensor fusion, and communications protocols for the CMU Highlander. As needs were determined at CMU, Glenn responded by developing and integrating new capabilities into Cratos. Once ready for use, these new components, techniques, and software downloads were delivered to CMU and were integrated into Highlander.

Photograph
Glenn controller.

Because of cost and time constraints, off-the-shelf hardware and software components are often incorporated into test rigs such as Cratos. But in this case, many of the vehicle control components had to be customized to meet the design criteria. It proved to be more expedient to design a unique control system to implement Glenn’s customized data packet structure for telemetering the sensor data. This new Glenn design includes a flexible controller with 16 pulse-width-modulated output ports, six relay output ports, two external interrupts, a RS232 serial port, a radio-link serial port, and 16 analog-to-digital input/output lines (see the preceding photograph). The radio link utilizes Maxstream’s 900-MHz Extend-Radio with a maximum 40-mi range when its full 1 W of power is used. Data and control packets are telemetered between the controller and either a hand-held remote or a personal computer with a LabView program that emulates the remote and records the sensor data (see the following photograph and screen capture).

Photograph and screen capture
Hand-held remote.

Screen capture
LabView remote and data logger.

In its current configuration Cratos has an electronic gyro, a two-axis accelerometer configured as tilt sensors, current sensors, and optical encoders for both track motors and a battery voltage/ampere-hour monitor (see the final photograph). Also included in Glenn’s design is a Global Positioning System (GPS) unit that will interface to the controller through the RS232 serial line.

Photograph
Gyro, tilt sensors, and current monitors.

At the heart of the controller are two 8051 core processors from Silicon Laboratories. These processors use a pipelined architecture allowing the execution of 25 million instructions per second. One processor controls all of the communication, motor control, and battery monitoring, whereas the other controller is used to read the digital-to-analog and interrupt input as well as to implement the user code. All the code is written in C and includes modules for easy input/output setup, motor control, and radio network (RNET) communication between the controller and host. The Joint Test Action Group interface between the personal computer and microcontrollers allows for quick troubleshooting during debugging sessions. Furthermore, status indicators for program fault, RNET fault, and low battery power give users a quick indication of the controller status. We hope to use this test rover to validate and/or improve various track designs as well as to test a variety of control algorithms for locomotion and navigation.

Glenn contacts: Lawrence Greer, 216-433-8770, Lawrence.C.Greer@nasa.gov
Mike Krasowski, 216-433-3729, Michael.J.Krasowski@nasa.gov
John Caruso, 216-433-3324, John.J.Caruso@nasa.gov
Authors: Lawrence C. Greer and Michael J. Krasowski
Headquarters program office: Exploration Systems Mission Directorate
Programs/projects: Surface Mobility

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Last updated: December 14, 2007

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