Alt-BEAM Archive

Message #03881



To: beam@corp.sgi.com
From: Wilf Rigter Wilf.Rigter@powertech.bc.ca
Date: Fri, 28 May 1999 12:40:30 -0700
Subject: [alt-beam] Re: What Tilden calls it.....


Hi John,

A dazzling display of Beam robological slight of hand you say?

As was discussed recently on the list by Wouter and myself, bicore bias
point switching thresholds have an effect on timing which is related to the
"structural permutation" issue..

It turns out that the two matched master bicore capacitors as well as the
two matched coupling resistors to the slave bicore will cancel asymmetry
caused by non-ideal thresholds (ie threshold which are not centered on
+V/2).

This is a problem in particular for 74HCT240 chips with offset logic
thresholds with the resulting timing cycle trigger alternately from the
lower threshold (~1V) of each inverter.

The effect of removing one coupling resistor of a HCT240 bicore will not
result in loss of "control lock" but will certainly "de-tune" the slave
bicore and in a walker would probably result in turning motion or tipping
over. The effect of this "de-tuning" would be less apparent in a wiggling
snakebot.

So in order to make a phase-slave bicore "robustly control-locked" in case
of "structural permutation" say caused by flying landmine shrapnel, you
better use a HC240 instead of a HCT240 chip.

enjoy

wilf

Wilf Rigter mailto:wilf.rigter@powertech.bc.ca
tel: (604)590-7493
fax: (604)590-3411

> -----Original Message-----
> From: John A. deVries II [SMTP:zozzles@lanl.gov]
> Sent: Friday, May 28, 1999 9:48 AM
> To: beam@corp.sgi.com
> Subject: Re: What Tilden calls it.....
>
> At 08:45 AM 5/28/99 , Jason - wrote:
> >Hie here is some tips i got over the years from mark T
>
> >>wut is the best materail for me to use as a leg for my walker
> >
> >Easy. Broken collapsable umbrellas are the best and cheapest form of
> high
> >reliablity leg.
>
> Of course, one can also get decent piano wire (or other stiff steel wire
> with a range of diameters) from hardware stores and hobby shops. This is
> particularly useful if you don't have a supply of broken umbrellas.
>
> >>and what is the main theory of the master and slave system
> >
> >A suspended bicore master will always robustly control-lock a phase-slave
> >bicore regardless of structural permutation.
>
> It seems to me that one permutation would involve breaking both
> connections
> between the master and the slave at which point there would be no
> synchronization ("control lock"). In fact, this is one of the things that
> I find bogus about the Snakebot demonstration -- Rigter showed that it
> only
> takes one of the two connections between the master and slave bicore to
> ensure synchronization. Snakebot consists of three bicores (one for each
> motor/segment) and has at least six connections (between bicores -- I'm
> not
> sure if there is one more pair between 'head' and 'tail'.)
>
> During his demonstration, Mark takes out a coupling resistor... and the
> robot continues to work. He takes out another, and then a third and the
> robot still functions. Finally, when he takes out a fourth, the robot
> becomes uncoordinated. Of course, he isn't taking out a parallel -pair-
> of
> coupling resistors at one time: in other words, I'm pretty sure that if
> you could disable the robot merely taking out two connections which would
> obviously seem less dramatic than four. . .
>
> Of course, I could be wrong -- I often am.
>
>
> Zoz
>
> ---------------------------------------------------------------
> John A. deVries II
> zozzles@lanl.gov

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