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The BEAM Bestiary is a BEAM Reference Library site.

3 motor walkers -- hexapods
Getting around with an alternating tripod gait


Hexapods are interesting little 6-legged 'bots that move along using what's called an "alternating tripod gait." This gait isn't the fastest, but is very stable; hexapods are probably the simplest 'bots that can create it.

Hexapods work very simply -- the front and rear legs on a given side are connected, and are driven together by one motor (per side). The middle legs are used to shift the 'bot's weight from side to side (thus selecting the leg pair in use at a given time). This is easiest to visualize with a quick animation -- if your browser supports JavaScript (and if it's enabled), you can use the animation panel to the right to step through the geometry (or just hit "play" and watch it walk).

Here, the right side front / back legs (along with the left middle leg) are drawn in green; the left front / back legs (along with the right middle leg) are in red. The 'bot body is denoted by the black outlined rectangle, the feet are solid if they are load bearing (i.e., are touching the ground), and unfilled if they are not supporting any load.

Turning is accomplished by changing the angle through which the legs on a given side "reach" forward in a given cycle.


For more information...

Rich Piotter's hexapod page is here.

Lynxmotion sells hexapod robot kits ('though they're not cheap)-- see here.

Robodyssey also sells (very pricey) hexapods -- at the very least, they have some very good pictures for you to get some mechanical ideas from. They're hexapod is called the "Roach."

Meanwhile, Henry Arnold has an interesting set of pages on "Cricket," a 3-motor / 6-leg walker (mechanically very similar to Rich Piotter's hexapod, but CPU-controlled) here.

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Page author: Eric Seale
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