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From: rstevew@armory.com (Richard Steven Walz)
Subject: Re: Two-legged robots
Organization: The Armory
Date: Sat, 3 Dec 1994 09:03:08 GMT
Message-ID: <D08959.FBs@armory.com>
References: <hallumdCyz6GG.Io3@netcom.com> <3aihsg$au2@seralph9.essex.ac.uk> <3aog72$lme@handler.Eng.Sun.COM> <3aq8nv$o36@mojo.eng.umd.edu>
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In article <3aq8nv$o36@mojo.eng.umd.edu>,
Vadim Polyakov <polyakov@eng.umd.edu> wrote:
>
>In article <3aog72$lme@handler.Eng.Sun.COM>, cmcmanis@Sun.COM (Chuck McManis) writes:
>>K J Withers (kjwith@essex.ac.uk) wrote:
>>: This however is where the problems start, to enable such a system to balance
>>: you need three different routines a) one to move the foot from one position
>>: to another ( this routine has already been written as it has formed the basis 
>>: of mobile robotic routines for years), b) one to balance the body by moving
>>: the center of gravity using laws of moments, and c) one to place the center of
>>: gravity onto one or two legs.  
>>
>>: I am working on the second routine at the moment using greatly simplified 
>>: structures to enable me to understand the basic principles before I start
>>: adding things like limbs, hips, necks, backbones and tail structures.
>>
>>I'm quite interested in Biped robots and believe that problem 'b' can be
>>solved using a subsumption approach. If you build the system so that the
>>foot returns a balance indication (that is, given weight sensors in the
>>toes, are all toes seeing the same weight) and tying that to a body
>>positioning subsystem whose behaviour is to simply move the center of
>>gravity such that the toes are always reading 'in balance', then you've
>>basically saved the problem without having to compute any kinematics.
>>
>>In such a system, lifting one leg would cause the robot to automatically
>>balance on the one 'down' foot. Then push the robot over (add an input 
>>to lean forward) and when the other foot hits, it takes over and recovers
>>the balance. 
>>
>>--
>>--Chuck McManis			     All opinions in this message/article are
>>Sun Microsystems Inc.                those of the author, who may or may not
>>Internet: cmcmanis@Eng.sun.COM       be who you think it is.
>
>One has to be clear by what is meant by "balance" above. When we walk at a normal
>pace there intervals of time when the body is not statically balanced and we "fall". 
>This results in continuous interchange of kinetic energy (which increases as we bacome 
>unbalanced and "fall") and potintial energy (which increases as the swing leg catches the
>fall and the body is raised ). It's hard to describe in words.
>
>What, I think, we mean by balance here is that the body is executing a stable periodic
>motion of walking, i.e. it will not fall.  This is a question of dynamics. Though 
>I am believer in the power of subsumption, in this case we need to consider physics, IMHO.
>
>For those of you interested in legged locomotion there is a special issue of International
>Journal of Robotics Research V3 No2 Summer 1984 (I think). Very nice article of mechanics of
>legged locomotion in humans - it has nice pictures describing the determinants of human walk.
>
>-vadim

------------------------
God! Vadim, fix your editor to stop at 70 per line, eh!?
-Steve Walz   rstevew@armory.com

