The robots in H.G. Wells' War of the Worlds may have been terrifying, but they also had a feature notably lacking in a lot of today's robots: the inherent stability of a tripod. But film realizations of the tripod robots have always suggested they moved in a sort of inefficient shuffle: if you were a tripod creature, how would you walk? Three-legged locomotion doesn't make sense.
But researchers at Virginia Tech have begun development on a robot that looks like a tripod but has a simple and elegant gait. Check out this short movie clip showing how it works:
Clever, no? An article in New Scientist has the details:
To take a step forwards, the robot shifts its weight onto two of its legs, allowing itself to fall forwards away from the third leg. Its body then flips upside-down and the third leg swings up between the other two just in time to catch the ground and return STriDER to a stable tripod stance. To change direction, the robot simply switches its choice of swinging leg.
The body-flipping is the key to the whole thing: without flipping over, the robot's legs would get tangled up faster than a kitten in a knitting basket. This arrangement has some disadvantages. You probably wouldn't want to use a STriDER to transport loads, for example. The Virginia Tech researchers suggest using it to deploy sensors -- its high vantage point makes it a great camera platform (imagine what Survivorman could do with a couple of these!).
Here's a more extended video:
The only thing that seems odd to me is the way the robot in the animation is shown traveling through dense undergrowth. With lots of obstacles underfoot, wouldn't it make more sense for the third leg to flip over the top of its body, rather than under the bottom?
Cute. Some problems, though.... There's not much room for batteries or solar power panels or whatever in that little body. And what happens if it catches that foot as it swings forward and does a "face"-plant? Can it pick itself up again? And that's an awful lot of repetitive motion and physical stress on those joints. I'm guessing it will have a pretty short MTBF...
Maybe this time, global warming will kill off our would-be Martian Overlords.
It can't swing the third leg over the top. It uses gravity to initiate the swing of the rear leg through to the front.
On the other hand, the walking motion will be quite robust to things like uneven ground and such like and since the body has no up or down orientation it can't get turtled if it does fall over and a relatively simple procedure should get it up right again.
The key is not to stop it from falling over (its a robot, it isn't going to graze its knee). The key is to make sure that it can stand itself up again easily.
(Disclaimer: I'm not an engineer)
But if the leg was spring-loaded, that could give it the propulsion to flip the leg over the top. But that would be very inefficient, and make it easier to get tangled up.
Swinging from underneath would be better, especially if the leg were more jointed. That way, if it ran up against low obstacles, the leg joints would just fold until it finally overcame the obstacle. Of course, this is based on 10sec of video, so I don't know. I'm just sayin...