Alt-BEAM Archive

Message #06218



To: beam@sgiblab.sgi.com
From: Evan Dudzik evandude@yahoo.com
Date: Tue, 28 Sep 1999 03:51:43 -0700 (PDT)
Subject: [alt-beam] motors and cells, cheap


i think i may just auction off my entire BEAM parts
bin, which inludes 15+ pager motors and 10+ solar
cells, as well as all sorts of capacitors,
transistors, and resistors, as well as an entire
photopopper! all my stuff cost me over $150, and i
might possibly sell it to the highest bidder, starting
at $40, email me with offers. trust me, its worth it!

__________________________________________________
Do You Yahoo!?
Bid and sell for free at http://auctions.yahoo.com



6219 Tue, 28 Sep 1999 10:16:54 -0500 RE: master/slave bicore walker problems 'beam@sgiblab.sgi.com' owner-beam@sgiblab.sgi.com [mailto:owner-beam@sgiblab.sgi.com]On
(Words of wisdom from Richard worth repeating!)

Hi Phillip,

You can use HC or HCT245s interchangeably as drivers. The 74AC/ACT245 is the
best choice for this application since it supplies 3x-4x (75mA) as much
current as the HC/HCT. BTW You can also use 74xx240s as motor drivers but
with a different pin layout of course. Some questions: What servos are you
using? Any idea what the loaded and unloaded motor current is. What is your
supply voltage? Are you using 74HC240s for the bicore? Do you have LEDs for
monitoring the bicore states?

Once you have LEDs try a simple feedback test: hold the walker up in the
air, with legs moving. note the speed and "phase" relationship of master and
slave bicores, then slow the front legs by hand: any change in bicore speed?
How about the rear legs? Bicores using HC240s are more sensitive to feedback
than HCT240 and loading the motor will generally shorten the pulse of a
master or slave bicore because noise and voltage fluctuations on the power
supply tend to reverse the state of the bicore before it's "normal" time
out. That is good when using stops, since the hitting the stops towards the
end of the time out cycle occurs when the bicore is most sensitive to
feedback. It may help prevent a gear box from stripping itself. For more
details on feedback also read Walter Brock's paper.

regards

Wilf Rigter mailto:wilf.rigter@powertech.bc.ca

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