Alt-BEAM Archive
Message #08719
To: beam@sgiblab.sgi.com
From: Bob Shannon bshannon@tiac.net
Date: Fri, 31 Dec 1999 09:53:27 -0500
Subject: [alt-beam] Re: tilden-class walker
Dave Hrynkiw wrote:
> At 05:16 PM 12/29/99 , Mike Kulesza wrote:
> >So i have those sleek LEGO gearmotors (tiny - 1cm x 1cm x 1cm, efficeint,
> >high torque)
>
> Finally got to play with one of these not long ago - veeery nice motors!
>
> >What should i use for the driver? to SMT transistor deliver as much
> >current as normal ones for H-Bridge?
>
> As a rule, SMT offer similar specs EXCEPT in regard to max current
> deliverable. Because they're smaller, they have a harder time dissipating
> heat, therefore the decrease in ability.
I gotta agree with Dave here.
This is especially important if your building a 'classis' SE (1381 or FLED)
with surface mount parts, and your motor is slightly more inductive than
others.
P-sub-d (power dissapation) is lower for the SAME transistor (like a 3904/6)
in a SMT package than it is for the ~same~ type of transistor in a standard
TO-92
package.
This nearly drive me nuts a while back when I was testing some suspension
ideas.
I needed to build a 'duplicate' of an existing bot, only lighter and with a
different
set of spring constants. Some people insisted that a 3904 was a 3904, and the
fact
that it was a SMT part made no difference (I'd originally thought is was the
SMT
version of the 1381 causing the problems).
Not so. Even the published spec sheets show the difference. If your driving a
motor
don't use a SOT-23 package, look for something in a SOT-223 or SOT-143 package.
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