passive walking animals?

[brunonery]

Hello,

I'm studying robotics and I stumbled upon "passive dynamic walking": robots designed to walk with almost zero energy, where its mechanical parts interact in order to move the body. An example may be seen on this YouTube video:

http://www.youtube.com/watch?v=CK8IFEGmiKY

I would like to ask if any of you know about animals that can behave like this, i.e., have physical characteristics that allow them to "walk passively" - not necessarily walk, that's for sure - crawl, fly, swim, etc. In other words, do you know any animals that can "move passively"?

[mith]

the ramp is angled, so it's more like gliding.

[mcar]

How about the sloth?

[brunonery]

I didn't mean strictly zero-energy, but animals that might use the environment to save energy while moving. I read that some apes brachiate using almost no muscular energy, and I was thinking if some other forms of life (specially simpler ones - worms?) have this kind of capability.

BTW, how does a sloth moves?

[mcar]

Well, I remember from a prime time program here that they are so slow and may only move when it's feeding time. http://en.wikipedia.org/wiki/Sloth
http://encarta.msn.com/encyclopedia_761562271/Sloth.html