The Crab Crawl maneuver of sideways propulsion.

An industrial-class excavator was developed for use on the Moon and perhaps on Mars. The model mobility platform uses Ackerman Steering with active drives on all six wheels, and steering on the corners. A faulty sequence of wheel steering and driving commands resulted in undocumented behaviors in a simulation and rendering program that appear to have actual applicability to surface operations. Quite by accident, it was discovered that by applying power and steering to the wheels in a complex pattern, the excavator could move laterally, hard to starboard. The intended command was “reverse,” and the execution was a seemingly random turning and driving of all of the simulated six wheels. The faulty behavior was employed to remove the robotic platform when it was stuck on rocks, and enabled the platform to “scoot” side-ways, successfully disentangling from the rocks. The method drove the wheels in the direction of the intended motion, while steering them in a sweeping motion, and the apparent motion resembles swimming.

In the figure, the green arrows depict the robotic vehicle's direction of motion, while the red arrows depict the direction of driving wheels at the surface, and the sweep or steering motion applied to the steering motors. This alternating steerage of the driving wheels clears the vehicle of protruding obstacles. Ultimately, the long-term solution was to increase the torque available to the drive wheels.

This may not be practical with a platform deployed at a distant location, so the Crab Crawl maneuver may be worth further investigation as a hardware feature.

This work was done by a team lead by Gary Rodriguez of sysRAND Corporation for Johnson Space Center. NASA is seeking partners to further develop this technology through joint cooperative research and development. For more information about this technology and to explore opportunities, please contact This email address is being protected from spambots. You need JavaScript enabled to view it.. MSC-25012-1