Subject:
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Re: I was thinking about bipedal walkers this morning and....
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Newsgroups:
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lugnet.technic, lugnet.robotics
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Date:
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Fri, 19 Dec 2003 01:08:23 GMT
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Viewed:
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1913 times
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Now, think about what physically goes into making yourself walk. How much
energy and control is involved? Try walking on a flat, level surface (or
better, one at a slight decline, like a very long handicap ramp). Walk with
your natural gait, at the most comfortable speed.
Now, as you walk, take specific notice of what muscles you feel being used
(not what you *think* needs to be involved, but what muscles you can
actually feel working). With how much force do you pull your leg forward at
your hip? Is your quadracep contracting to bend your knee at the end of
your step as you bring your foot forward?
Now compare this to how much effort it takes to make similar motions while
not walking (i.e. with one foot on a platform, so the other one isn't
standing on anything, let your leg hang straight down, then lift your leg
forward at about the same speed it moves forward while walking, bring it
down to vertical, then bring it back the same way - do the same with bending
your knee.)
If you notice a discrepancy between how much energy it seems to take to lift
your leg from rest versus the same motion while walking, it isn't because of
"invoulintary control". How many such leg lifts does it take to fatigue
your leg muscles, compared to how many strides while walking does it take to
become similarily fatigued? It's the same muscles involved, so they get
tired at the same rate, no matter what's controlling them, so something else
must be involved.
So what is this exercise all about? Am I leading you somewhere with this?
Think simple harmonic motion. Your legs are pendulums, walking is what our
legs naturally do, even without muscle control. If you're lucky enough to
find a ramp with just the right decline angle, you'll find that you need to
do practically no work at all to keep walking at a continuous pace
http://tam.cornell.edu/~ruina/hplab/downloads/WM_models/McGeer_at_Cornell.mov
This is a simulation of a completely passive walker - absolutely no
electronics or control loops of any kind, it's all physics. The only trick
here is that gravity is directed slightly to the right, in other words,
exactly the same effect as having the flat surface slope downward slightly
from left to right. The only major function our muscles perform is to add
that little boost of energy walking on a flat surface that gravity provides
on a slope.
Here's an entire lab dedicated to the study of such passive walkers, they've
even built working physical models of the animated walker above.
http://tam.cornell.edu/~ruina/hplab/pdw.html
Dan Lauber
"Mark Tarrabain" <markt@lynx.SPAMBLOCK.net> wrote in message
news:Hq3zBJ.tL0@lugnet.com...
> Consider the way we walk... we start by effectively starting to lean
> slightly forward, and we swing a leg some distance in front of ourselves
> to stop from falling. We then start to bring the other leg forward as
> we reupright ourselves and repeat the process, each time stopping
> ourselves from falling with a leg that we bring forward. If we
> alternate legs, it is called walking and if we use the same leg each
> time, it is called limping.
>
> Has anyone ever tried to build or design a bipedal walker that imitates
> this form of motion? I'm thinking that it probably wouldn't even be
> possible to do without flexible knees. Is this level of sophistication
> even implementable in LEGO to the point that it's genuinely useful and
> not just a proof-of-concept?
>
> > > Mark
>
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