Alt-BEAM Archive

Message #03885



To: beam@sgiblab.sgi.com
From: "John A. deVries II" zozzles@lanl.gov
Date: Fri, 28 May 1999 13:52:15 -0600
Subject: [alt-beam] Efficiency and Good Old Stryder


At 11:49 AM 5/25/99 , Dave Hrynkiw wrote:
>I look at Stryder and see a working example of
>something I thought wasn't possible - a 4 legged, fixed motor position
>walker capable of very efficient walking gait (not lifting legs very high
>saves power).

I no longer have a clue what any of the readership of the BEAM emailing
list means by the term "efficient" or "efficiency". I had always been led
to believe that "efficiency" was a ratio of what you got out of something
for how much you put into it. In other words, if one was talking about
useful work efficiency, you'd want to look at W(useful)/W(total).

I've read about the "efficiency" of motors and of circuits and of walking
gaits and the like, but in so many different ways and so loosely and so
without any measurement or evidence that I can hardly believe that those
meanings have much to do with the most commonly accepted version. I mean,
nobody seems to figure out how much energy is being put into a system and
how much energy generates useful work (after all, work and energy use the
same units: it is just that "useful" work is less than "total" work or
else we'd be violating one of the laws of thermodynamics.) No one ever
_measures_ anything, ever calculates the ratio, ever compares the ratios
(i.e. efficiency) of one system with another. It seems to me that the word
"efficient" is used as a synonym for "good" and the word is used for hype
like "new" and "improved" in ads.


I wish that people would measure the useful work produced by these robots
and compare it to the amount of energy that was put in. In other words,
determine the amount of energy that is required to move a robot of a given
mass a given distance (or use Watt's method and have the robot lift a
weight) and compare that to the total amount of electrical energy it
consumed doing so. Then you'd have a meaningful "efficiency" you could
compare to another robot's in a meaningful way.

Until then, "efficiency" and "efficient" are meaningless buzzwords.

Zoz

p.s. anyone want to bet whether or not the Beamant 6.x is more efficient
than Stryder???



---------------------------------------------------------------
John A. deVries II
zozzles@lanl.gov

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