Alt-BEAM Archive
Message #03891
To: beam@sgiblab.sgi.com, zozzles@lanl.gov
From: Bruce Robinson Bruce_Robinson@bc.sympatico.ca
Date: Fri, 28 May 1999 14:45:48 -0700
Subject: [alt-beam] Re: Efficiency and Good Old Stryder
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).
AND, John A. deVries II wrote:
> I no longer have a clue what any of the readership of the BEAM emailing
> list means by the term "efficient" or "efficiency".
>
> 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.
Actually, Dave's comment is technically correct, at least in a
qualitative sense. Efficiency can be expressed in another way: (Total
Energy - Waste Energy)/(Total Energy). Lifting a leg (or the body of a
robot) consumes energy. If that energy is not doing anything useful and
can't be recovered, then it is waste. So the higher a robot lifts it's
legs, or it's body, to no useful purpose, then the less efficient it is.
However, I appreciate your point -- it would be nice to have some
quantitative measurements of efficiency. So how would you actually go
about doing that, Zoz? How DO you determine the amount of energy that is
required to move a robot of a given mass a given distance? In theory, it
should take NO energy to move a robot ANY distance (on a level surface).
A certain amount of energy is required to start it moving, but you can
recover that energy at the end of the journey when you bring the robot
to a stop.
Having the robot lift a weight is a little more like an "operational
definition". In other words, we don't say "This is the efficiency of
this robot", we say, "Following this specific procedure, this robot
performed as follows ...". This may not give you a precisely correct
efficiency measure, but it will give you a practical one. So how much
weight is the robot supposed to lift? And how far is it supposed to lift
it? And what if the lifting mechanism wastes energy -- does the robot
get penalized for that, even though the mechanism is simply there to
make the measurement?
That's the challenge, isn't it? To come up with a simple method that the
typical amateur can use and still get a useful measure.
Regards,
Bruce
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