Economies of the gait in robotics and animation

How a robot walks, runs and jumps is critical to how it moves through its environment. Beyond these instrumental questions, how a robot moves can’t help establishing a sense of its perceived character. We’ve faced these questions of movement, embodiment and identity before — in animation. The problems of designing the gait of robots recalls (and deviates from ) the technique of creating walk cycles in cel animation, which date back to the earliest days of cinema.

Both robotic and animated bodies use rhythms to generate economies in movement. For animators, walk cycles can continue indefinitely to fill any duration in the linear sequence of a final animation. The walk cycle helps establish character by communicating the urgency, competence and mood in the figure’s movements. Shape, style and frame-to-frame changes give the character an implied history by adding deliberate distortions: squashing and stretching the body, and manipulating the apparent forces of acceleration, inertia and gravity on head, torso and limbs.

For the roboticist, a well-designed gait is also economical, because it allows the robot to establish rhythms in movement that maximise its use of energy. A well-tuned gait takes advantage of the dynamics in between the points at which robotic motors activate. It uses the weight and intertia of the robot body to maintain balance and stability at speed. This is inevitably also read by observers as a creating kind of character. The aesthetic inevitably returns.

In designing movement, the animator seems to begin with an aesthetic problem, where the roboticist seems to start with instrumental problems. Of course, the animator must resolve the aesthetic through technical means: whether that is use of cameras and in-betweening, or 3D computer animation (quite similar to robot simulators). The roboticist, on the other hand, cannot escape the aesthetic, as the human eye inevitably reads movement as life and finds a face and character. See also Cholodenko 2007 and Sobchack 2009.

An example of an animated walk cycle.Todd Wheeler

A fast-walking robot built by a researcher in Thailand, Weerayut.

There are many other examples of roboticists using aesthetic / metaphorical framings to design robotic gait: walking on an incline ( and and from nature, pronking springboks).

Reference

Cholodenko, A., 2007. The Illusion of Life 2: More Essays on Animation, Power Publications.
Sobchack, V., 2009. Animation and automation, or, the incredible effortfulness of being. Screen, 50(4), pp.375 -391.
Van Breemen, A.J.N., 2004. Bringing robots to life: Applying principles of animation to robots. In Proceedings of Shapping Human-Robot Interaction workshop held at CHI.