Alt-BEAM Archive
Message #08350
To: beam@sgiblab.sgi.com
From: Darrell Johnson beamtastic@yahoo.com
Date: Fri, 17 Dec 1999 22:35:29 -0800 (PST)
Subject: [alt-beam] Re: Bi ped
yeah, you are going to need *at least* 10 motors to
make a biped walker that can actually walk. each motor
= 1 degree of freedom. You are going to need:
3 DOF for each hip/thigh
1 DOF for each knee
1 DOF at least for each ankle/foot
the mechanics are going to be by far the easiest part.
Getting the thing to actually walk is going to be
*extremely* difficult to accomplish. I'm a character
animator by profession, and I have spent a great deal
of time studying the mechanics/dynamics of walking,
and believe me, walking isn't easy.. Any of you that
have built a 4 legged 2 motor BEAM walker know how
much tweaking it takes just to get a fairly efficient
walk out of just that little bit of bot.
Say you want the bot to lift one leg while standing.
You are going to have to shift the center of gravity
'COG' over the foot that is still planted on the
ground. This is where your original pic that you
posted fails. you have no DOF to accomplish this
shift.
Now you want it to take a step forward. You have to
start shifting the COG forward while bringing the leg
that's raised in the air forward, while keeping the
weight shifted over to the side of the planted foot.
Now as the foot is about to touch the ground, you need
to shift the weight over to that foot, while still
keeping enough forward momentum to keep walking, but
not too much or it's going to fall on it's face.. You
are also going to need an impact cusioning motion at
the knees for the leg as it plants, or your bots steps
are going to be so sudden and jarring that it's going
to bounce itself right onto it's back.
Now in order to stop it has to be able to shift the
COG slightly back in order to slow down and counteract
the forward momentum.. all while still shifting side
to side and taking steps.
Now all this has to be done while dynamically keeping
track of the balance of the bot, or it's going to fall
over all the time. And you plan on doing this with a
*Basic Stamp*???
I dunno.. I don't want to rant about this too much..
Honda has done an amazing thing with thier humanoid
bot, in that it walks fairly closely to how a human
walks..
The MIT little dinosaur bot can't even walk yet as far
as I know.. all it can do is stand itself up from a
crouch and then go back to a crouch. And they seemed
pretty ecstatic about it..
IMHO, you'd be better off spending your energy
elsewhere.. There are plenty of exciting things to do
in hobbyist robotics research.. Let the big
orginazitions throw money at making bipedal walkers..
Not trying to rain on your parade or anything.. just
being realistic. If you think you can do it, go for
it.. just be prepared for lots and lots and lots and
lots of frustration.
-darrell
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8351 Sat, 18 Dec 1999 00:00:13 -0700 [alt-beam] Re: Bi ped Ian Hey, About the design idea I had about keeping the foot strait seems to be
employed in this walker....
http://www.aist.go.jp/MEL/soshiki/robot/undo/kajita/biped-e.html
More on my idea is in an earlier email.
Laterz
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