Alt-BEAM Archive

Message #06225



To: "'beam@sgiblab.sgi.com'" beam@sgiblab.sgi.com
From: Wilf Rigter Wilf.Rigter@powertech.bc.ca
Date: Tue, 28 Sep 1999 13:07:06 -0700
Subject: [alt-beam] Re: master/slave bicore walker problems




Hi Phillip,

74HCT240 are fine perhaps you can check the yellow pages for a surplus
electronics or computer store. Older broken laptop motherboards are a good
source of surplus 74ACxx parts. Adding Leeds should have no effect on the
operation of the bicore. From your comments of strange behaviour when adding
the Leeds, it appears that you may not have used a current limiting resistor
in series with the Leeds. The Leeds are usually placed across the bicore
outputs but may also be connected across the motor. Try again connecting the
Leeds as shown.

regards

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

<>

> -----Original Message-----
> From: Phillip A. Ryals [SMTP:phillip@ryals.com]
> Sent: Tuesday, September 28, 1999 8:17 AM
> To: beam@sgiblab.sgi.com
> Subject: RE: master/slave bicore walker problems
>
> OK, I'm at work now, so I can't try the suggestions just yet. I'll tell
> you what I tried last night though...
>
> First of all, In response to the questions below.. I'm powering the whole
> thing with 6V. The bicore is a 74HCT240. And I did set up LED's to
> monitor
> the thing. I'm completely lost there, though. When I hooked up the
> LED's,
> it immediately changed the whole behavior. (Should that happen?) It
> seemed
> to me that I couldn't get a definite feel for what it would eventually do
> unless I took them off. I was connecting the LED's at the motor leads
> from
> the bicore. (Before the HCT245, obviously :)) Should they go somewhere
> else?
>
> As far as the servos go, the brand is Hitec. They were cheap. I can't
> recall what the loaded and unloaded voltages are though.
>
> btw, I've been using HCT's because they're all I can find. I know Radio
> Shack doesn't have anything different... are there any other "chain"
> stores
> that carry the others? I'm in Tulsa, if that makes a difference.
>
> Phillip
> mailto:Phillip@Ryals.com
>
>
> -----Original Message-----
> From: owner-beam@sgiblab.sgi.com [mailto:owner-beam@sgiblab.sgi.com]On
> Behalf Of Wilf Rigter
> Sent: Monday, September 27, 1999 8:00 PM
> To: 'beam@sgiblab.sgi.com'
> Subject: RE: master/slave bicore walker problems
>
>
> (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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