A standard frame-walker moves by extending a structure forward, placing it on the floor, and moving the body forward along the structure. The body is then set on the floor and the process repeats. This is a simple, reliable method of locomotion, but it is very inefficient: the entire mass of the robot comes to a stop during each step.

One solution to this inefficiency is to use two frames that can be moved independently with respect to the body. This allows the body to move along one frame, which is planted on the ground, while another frame moves forward to take the place of the ground frame before the machine reaches the end of its stride. This permits the body of the robot to move forward at a constant velocity, which conserves momentum and thus conserves energy.

The Carnegie Mellon University Robotics Club built Jim, a prototype double frame-walker, during the 1997-1998 school year. The prototype was unable to walk, due to several design flaws, so the Robotics Club began work on a new double frame-walker. After two years of development, Jim 2 successfully demonstrates the viability of continuous-motion frame-walking.

The first significant test of Jim 2’s abilities occured at the Society of Automotive Engineers’ Walking Machine Decathlon in April 2000. The robot took first place, autonomously completing 8 of the 10 competition events.

The Jim 2 double frame-walker.