Alt-BEAM Archive
Message #04226
To: beam@sgiblab.sgi.com
From: Jean auBois aubois@trail.com
Date: Thu, 03 Jun 1999 14:03:29 -0600
Subject: [alt-beam] Observations about Roswell
At 08:21 PM 6/2/99 , Tom Edwards wrote:
>The section on the PBS tape (if you've got the two hour version) is 1:36
>minutes in and lasts about 3 minutes.
>
>An observation of Roswell is that it takes a about 12 steps in twenty
>seconds and moves forward about 1 floor tile (which is just short of a
>foot) with each "step". A "step" consists of the motion of one diagonal pair
>of legs. The body describes an arc at about twice that rate (say, once per
>second.) As a result of that, it is going at the same average rate as that
>step (not twice -- it just wiggles more than it steps.) The net rate,
>therefore, is something like 0.4 miles per hour. My son, who graduated from
>high school this last Saturday, says that as an average track runner
>he has a mean speed on the mile of 11.25 mph or about 27 times as fast.
Even a 3mph walk would be nearly 9 times as fast...
>One could imaginably use the natural swing of the body to do scanning, at
>which point a separate head is superfluous. It reminds me of how well our
own
>entire skeletal system does at keeping our heads steady, and even then it
>takes a fair amount of visual processing to give the impression of a steady
>landscape. Perhaps the next challenge for head designers will be a gimbal
>design like the atlas and occiput: in effect, at least a ball-in-socket so
>that the Flat Head stays flat...
I suppose, if being stable with respect to the horizon makes a difference.
>The overall effect (towards the end of the segment) when looking at only the
>rear legs is a rather slight waddle. Take Groucho Marx' walk and tone it
>down about 2 orders of magnitude and you've got the right idea.
>The motion seems to depend on how the weight bears on a given leg -- when a
>foot is being pulled forward, less weight is being born (and, in fact, is
>pushing against the opposite diagonal pair). In the following diagram, x is
>one diagonal and y is the other:
>
> xy
> yx
>
>Ignoring the other foot in the same diagonal, say that . represents a foot
>being brought forward:
>
> .y
> yx
>
>then backward force is being applied against the y feet which slip with
>relatively more friction while . slips with less. Now, here is where the
>problem occurs: the feet slip on both the bracing and the power steps. As
>a result, it is obvious that energy is used without gaining forward motion
>as a result of dynamic friction which occurs at all times except when the
>cycle switches to the opposite diagonal.
It looks kind of like a four-legged ice skater.
>Although Hrynkiw is correct in stating that a forward-going foot is lifted,
>it is only by the merest amount. Even then, the amount of friction that
>occurs during forward motion compared to backward has to be carefully
>controlled: I don't know what the shafts of the legs are tippped with
>(essentially a resilient rubber-like surface?) but there was also packing
>foam wrapping each foot.
>
>One can't always count on walking on utterly flat linoleum & the feet as
>designed are far too fragile. Nonetheless, the latter makes a huge
>difference in the effectiveness of the walking.
One could imagine a comparable spring-and-dashpot arrangement (in other
words, when you squish the foam it acts like a spring but when you release
it it shows a linear component like a dashpot -- or "hydraulic suspension
cylinder" would give.) This is a hidden mechanical system with regard to
the walking mechanism -- one could imagine controlling the "springiness" of
something that won't wear out like plastic foam with a coil & one of those
powerful magnets we've being discussing and also the effective surface area
(variable valve) whatever viscous fluid is being used to tailor how the
feet deal with the surface. This is probably too complicated, though.
---------------------------------------------------------------
jab
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