Alt-BEAM Archive

Message #06208



To: beam@sgiblab.sgi.com
From: "George Rix" rix.g@bmts.com
Date: Mon, 27 Sep 1999 20:02:26 -0400
Subject: [alt-beam] Re: master/slave bicore walker problems


> What is happening in the circuit when you do that? I'm still trying to
> understand the basic pathways it's going through...
What happens is that you're speeding up the pulse when it goes to the
motors, so they aren't on as long, making them avoid turning so far.
Signing off,
Rob Rix

___________________________________________________________________________
'I guess I picked the wrong week to stop sniffing glue' - from Airplane



6209 Mon, 27 Sep 1999 18:00:18 -0700 [alt-beam] Re: master/slave bicore walker problems "'beam@sgiblab.sgi.com'" Wilf Rigter (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


> -----Original Message-----
> From: Richard Weait [SMTP:crs0274@inforamp.net]
> Sent: Monday, September 27, 1999 3:52 PM
> To: beam@sgiblab.sgi.com
> Subject: RE: master/slave bicore walker problems
>
> At 10:59 AM 9/27/99 -0500, "Phillip A. Ryals" wrote:
> >I haven't tried springs OR pots. I thought about springs, but wasn't
> sure
> >how to implement them. What's the general idea there?
> >
> >Curious... when I hold the bot in the air, the motors seem to be just
> fine.
> >It's just when I put it on a surface when it starts freaking out. I
> assumed
> >that meant it was getting feedback. Is there something else going on?
>
> You may be asking too much from the '245. Sounds like all is
> well until the motors (servos) are loaded. They draw more
> current when loaded, and that may be over heating the '245. A
> quick test is to put another '245 in parallel with the existing
> one, and see if that helps. You can do this by stacking, without
> solder, for a temporary test. (Make sure the power is off when
> you line them up :-))



6210 Mon, 27 Sep 1999 18:15:13 -0700 [alt-beam] Newbie/European source for parts alt-beam@eGroups.com mhenriks@vip.cybercity.dk Hi Guys

I'm new to the list and the world of BEAM. I'm currently in the process
of stocking up to build my first BEAM robot which will be a
Photopopper. I just received some nice pager motors from BG MICRO. I
even managed to find a supplier of Sunceram cells here in Denmark. But
now the trouble start: I can't seem to find any supplier of 1381's
within the EU. I have nothing against buying from USA/Canada if it
wasn't for the fact that the goods have doubled in cost by the time I
get them (shipping, duty, VAT). Can anyone point me in the direction of
some European stockists?

Best regards

Michael

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