Mecha-scarab walk cycles

Now that our mecha is rigged, it’s time to test it out. But how does a six-legged vehicle get around, anyway? Animator Mark Medrano assembled this collection of walk-cycle tests, to help answer that question.

Tripodal, sequential and bipedal animations by Mark Medrano; gallop animation by Kyle Bernard
High-res video: HexaWalkComparison-HD.mp4 (30MB)

Upper left: tripodal gait

This is a very common gait in both insects and robotics as it is statically stable, meaning that the machine can stop at any point during the step cycle and not fall over. As long as its center of mass remains within the triangle formed by the feet on the ground, the machine can maintain some margin of static stability, even at fast speeds. A cockroach can travel nearly ten times its own body length per second before its gait becomes unstable.

Upper right: sequential gait

This is also a statically stable gait, even more so than the tripodal one, since only one foot at a time is ever off the ground. This gait also occurs in nature but tends to shift from one side of the body to the other, sometimes lifting legs at random rather than the specific pattern displayed in the render. However, the increase in stability of this gait comes at a great cost of speed. Since the forward leg must travel much faster than the legs pushing back, actuator limits will kick in long before the machine can get up to its top speed.

Lower left: tetrapodal gait

This gait can be seen on insects whose legs have been hurt. Despite it being an unnatural walk, their nervous system automatically adapts. For our purposes, the legs don’t have to be damaged for this gait to be useful. If mecha-scarab needs to carry a heavy object, we can fall back on the same leg sequencing that a quadruped uses. This gait is referred to as dynamically stable: the two feet left on the ground don’t provide a solid base, so the machine needs to constantly adjust to keep from tipping over while it’s walking.

Lower right: gallop

We’re comfortably certain that no real-world insect walks this way. Pretty adorable, though!