Alt-BEAM Archive
Message #04808
To: beam@sgiblab.sgi.com, Wilf Rigter Wilf.Rigter@powertech.bc.ca
From: Bruce Robinson Bruce_Robinson@bc.sympatico.ca
Date: Tue, 22 Jun 1999 23:36:34 -0700
Subject: [alt-beam] Re: Ah! Blessed Skepticism! (was: Feedback explained?)
Wilf Rigter wrote:
> To a standard suspended Bicore add a BG micro motor directly to the
> Bicore outputs. Observe the rotation and Bicore pulsewidth is about 90
> degree each way and 1 second pulsewidth duration. Now load the output
> shaft with some finger pressure (not a complete stall) and note the
> rotation is about 30 degree each way and the pulse width is 0.5 seconds.
> So there it is mechanical AND electronic feedback.
But you are driving the motor directly from the bicore, so there could
well be a direct influence on the circuit. I was taking exception to the
idea of a drop in supply voltage having a significant effect on the Nv
delay.
> If the Bicore output is buffered before connecting to the motor, the
> output pulse duration is actually slightly longer when the motor is
> loaded even if a small resistor is introduced in series with the
> powersupply to reduce supply voltage under load (so much for powersupply
> feedback).
Aha! A quantifiable, and hopefully reproducible, measurement. That ought
to make JotW happy. I like the Tilden checklist that Steve Bolt sent
along -- it pretty much matches my own observations: get the mechanics
right, then tune the Nv to suit the walker's physicla characteristics;
repeat; then go on to the frills; repeat.
> enjoy (although that's starting to sound like the Prisoner's "be seeing
> you")
Ha! If you hadn't told us your age a while back, that's a sure giveaway
(for some of us, anyway).
And I guess I just broke my promise about shutting up about feedback.
Sorry,
Bruce
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