Alt-BEAM Archive

Message #07193



To: beam@sgiblab.sgi.com
From: "Ben Hitchcock" beh01@uow.edu.au
Date: Sun, 31 Oct 1999 11:33:37 +0000
Subject: [alt-beam] Re: Time Capsules


Hi,

----------
>From: "Mike Kulesza"


>>...tantalum capacitors are renowned
>>for not lasting a long time, as are the electrolytic caps normally used as
>>storage caps.
>
>This fact scares me a bit: does that mean that my walker, using a bicore
>euiped with tantalum caps will not last very long? How much time is "not
>long" anyway?

I base this on the time I spent in a service/repair area of BHP, where I
work. During that time, I noticed (And was told on numerous occasions) that
when tantalum caps were used, they would start to leak after a few years.
This was especially noticeable if they got a reverse-charge on them
occasionally.

There was one particular brand of TV that came into the workshop on a number
of occasions. Peter (the resident guru) turned it on, looked at the
picture, and told me to replace capacitor C32 with a ceramic version. I
opened it up, spent ages looking for that capacitor, found it, pulled it
out, and tested it. Sure enough, the leakage current was way too high. I
replaced it with a ceramic cap, and all was fine.

Peter explained to me that tantalum capacitors will only last for a couple
of years (ie. 2 - 5 years), and less if they get reverse voltage on them.
Of course, reverse voltage won't matter in a SE robot because you can't ever
get reverse voltage on the storage cap.

In a bicore (As I understand it, anyway, thanks to that animated gif Wilf!)
the caps WILL become reverse biased half the time. So I guess you might
find the timing change after a couple of YEARS of continuous operation. I
should be so lucky!

I would expect - in my household anyway - that the walker is far more likely
to get stepped on, or commit suicide over the balcony than die a slow death
due to bad tantalums.
If you're worried then replace them with ceramic caps. They're bigger than
tantalums but then again they won't give you that problem.

Ben



7194 Sat, 30 Oct 1999 19:02:01 -0700 (PDT) [alt-beam] HemiCore beam@sgiblab.sgi.com BotDoc
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content-disposition: inline


Attached is the schematic of a circuit that I call a
hemicore, with a monocore slave. It functions as a
tri-state bicore and is divided up into 2 asymetrical
hemispheres that are coupled together. Each
hemisphere is itself an off duty bicore (i.e. 45/55
and 55/45 duty cycles)and on an opposite sides of a
240. When both of the enable pins are low, the
asymetrical hemispheres create a stable 50/50
bicore... this is the normal walking gate. The duty
pulse length is determined by treating the 2 off sized
resistors as they are parallel. When one of the
enable pins is bought to v+ (with a power smart head,
touch sensor, or any logic output) it turns off one of
the hemisperes, leaving only one oscillating at an off
center duty cycle (45/55). This results in turning.
How long the motor turns one way with respect to the
other way is set by the difference between the 2
different resistors on the same bicore. If you want
it to turn the other way, just raise the other enable
pin. and drop the first one.
justin

=====
http://www.geocities.com/ResearchTriangle/Node/3904/
__________________________________________________
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Bid and sell for free at http://auctions.yahoo.com

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7195 Sat, 30 Oct 1999 15:31:27 -0500 [alt-beam] Re: Time Capsules Timothy Flytcher
| my r/c friends magnetize their competition motors
| on a regular basis...
| I have seen gains of 10%-30%
| by disassembly of the motor
| and remagnetizing the magnets
| and demagnetizing the armature.

Tim,
How is that done, exactly?

jlz

You are in a maze of twisty little passages, all alike.


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