The legs are lean relative to its body for the same reason horse, deer, and other quadruped mammals have lean legs. The relatively short proximal hindlimb has a shorter range of motion but is driven by extremely powerful muscle groups and large tendons. The lean distal hindlimb translates the short movement of the proximal hindlimb into a large movement at the hoof, so is mostly bone, requiring far less muscle. The same is mostly true for the forelimb. The light distal limb requires less energy to move, resulting in very efficient locomotion.
I'm impressed by several features in this demonstration. First, the robot "gets up" from a "reclining" position, secondly it manages to move at a variety of speeds, and finally it manages to recover from a "fall". A great demonstration. Next I'd be interested to see how well it can maneuver around obstacles, how well it manages on rough terrain, and how it climbs stairs. Finally, an aesthetic consideration ... when that "insect buzz engine" is muffled and the pitch dropped, it will become much more welcome in human company. In that regards, animals have it beat many times over as they quietly graze or scamper in a field.
I have seen the videos of the big dog and I thouht it was quite impressive, but this Wildca package is even more impressive. I thought that I saw a number of different gaits, so it may be able to handle a lot of different situations. But it would never be battery powered at that speed. I can see quite a few applications for a "beast" like it, both law enforcement and military. Just picture this beast charging at the bad guys in a standoff situation. It could easily have armor added and travel on a path making it hard to target. And it could simply bash into somebody and allow the humans to follow, sort of like a blocker in football. In fact, can you imagine teams of these playing football? THAT would be quite a game, and probably cheaper than the pro football players today. How is that for an unaticipated application? They would need to look a bit nicer, though. It could be the first real "Iron Man" football game.
Re. the gasoline-fired engine: Energy Density. And the need to drive a hydraulic (or pneumatic) pump directly.
These sort of machines got their start in the MIT Walking Machines lab decades ago (I know--I applied). But back then, they were tethered for both mechanical power AND computational power. Most people then couldn't comprehend that a gas-powered engine would solve the mechanical limitations, and time would solve the computational bottleneck. (I could--but I wasn't hired!)
But, they've grown into some pretty amazing devices! I'd hate to get on their bad side, though....
Insect legs? I wouldn't worry too much about size, when comparing the power of mechanical legs vs the legs of a mammal, for example. And as to worrying about the speed? Man has created any number of "creatures" which can move faster than their creator. Not to mention that there are any number of four-legged creatures which can do so anyway.
Great demo. Seems to me that expecting this device to move as fast in rough terrain as it does over flat terrain is not essential. After all, the same laws of physics apply to it as to living creatures. You wouldn't expect a cheetah to run as fast over rought terrain either. Rough terrain creates faster accelerating movements in different directions, at any given horizontal speed, compared with flat terrain, so you'd expect some tradeoff there.
What makes this a great demo is that obviously the designers studied the physics of horses walking, trotting, and galloping. The physics have actually been well known for some time now, by equestrians if no one else. And the designers applied these same techniques to a machine. The result is something that to a human appears "familiar" for a living creature, but not familiar movement from a machine. Hence the wonder.
You might be right Caleb...but looking at bison, deer or a goat I get the impression that they do have more powerful legs although I didn't make any measurements ;-)...artificial legs I guess are made from stronger material so that is why they probably be so thin...still wildcat looks obese and not esthetically pleasing! (not that it matters to the application)