Alt-BEAM Archive
Message #12032
To: beam@sgiblab.sgi.com
From: "Timothy Flytch" flytch@hotmail.com
Date: Fri, 17 Mar 2000 13:23:00 PST
Subject: [alt-beam] Re: *A little irrelevant.....list within a list???
How about this: just put an star * in the subject line for your advanced
posters... then when you receive more than you want to read just read the
*'s ??? everyone takes a brake once in a wile...
* will be reserved for advanced use only... and you can just slap us when we
use it for other...LOL...
Rules...
1) you can only post an * if you have build at least five working BEAM
bots...
2) you can only answer a * if you have real experience with the problem at
hand...
Timothy...
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12033 Fri, 17 Mar 2000 16:42:43 -0500 (EST) [alt-beam] Re: scoutwalker2 details beam@sgiblab.sgi.com jester96beam@iname.com > also, does one 74AC240 chip have enough power to drive one of those tower
> servos?
I have a 2 motor walker which uses 1 74AC240 to drive BOTH motors.
Chris
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12034 Fri, 17 Mar 2000 15:29:02 -0600 [alt-beam] Re: power filter caps question beam@sgiblab.sgi.com SG
How fast is it?
how many feet per second?
(For referance reasons)
-Sparky
At 01:39 PM 3/17/00 -0800, you wrote:
>I really appreciate this reply. Thanks Dilip!
>
>As far as the race walking goes, my bot seemed to lose a lot of motivation
>when it went on a diet of batteries. I had been using a computer 5V power
>supply before. Also, I *may* have fallen victim to "Gushing New Father
>Syndrome" and percieved the thing as going faster than it was. Anyhow, it
>plods along just fine now, and the mechanics are going to be used as a test
>platform. My next (baby) step will be to power it from a master/slave
>bicore. From there I'll start adding sensors to both the microre and the
>bicore circuits, and keep finding what works and what doesn't....
>
>
>Thanks again!
>
>Jeff
>
>----- Original Message -----
>From: Sathe Dilip
>To:
>Sent: Thursday, March 16, 2000 11:56 AM
>Subject: Re: power filter caps question
>
>
>
>
>> "Jeffrey B. Williams" wrote:
>
>> 1) Does the cap, in parralell to the power pins of the IC filter all
>> the variations (AC current) through it to the ground rail so that they
>> do not influence the chip? (In other words, I'm clueless and would
>> like an idea on why it works..)
>
>More or less. The value of the capacitor decides what frequencies will
>be sent to the ground. Smaller the capacitor, higher is the cut off
>frequency beyond which it will be effective in sending the
>variations/spikes/noise to ground. The type of the capacitor also
>matters. An electrolytic capacitor will not do as good a job as a
>ceramic in this situation
>
>> 2. Can a put a single capacitor in parralell to a series of chips,
>> cores, ....whatever to stabilize them, instead of a cap per chip.
>
>No. Distributed is the word. One cap per chip (particularly the ones
>that contribute to the spikes/noise and the ones that are susceptible to
>the spikes/noise. The reason is, the cap has to be as close to the
>source/target (of noise) as possible to be effective. Even the lead
>length matters in severe cases. (PCB track/wire inductance and to a
>lesser extent resistance helps noise in its dirty work)
>
>> 3. What's a good size for these beasts. To be honest a single .22uf
>> worked to stabilize my walker, but I still don't have that warm fuzzy
>> feeling that tells me its not just waiting to go up in flames. I
>> have the impression that they should be larger, but what is too large?
>
>One 10kpF to 100kpF ceramic (monolithic chip ceramic - MLC is also fine)
>capacitor per chip is generally good enough.
>
>> Now that it's tamed, I don't know why its called a walker.... The
>> thing runs and scampers pretty darn quick...
>
>May be its practicing race walking? :-)
>
>Dilip
>--
>----------------------------------------------------------------------
>The early bird may get the worm, but the second mouse gets the cheese.
>----------------------------------------------------------------------
>
>
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