[eagle] Re: Revised Module Suggestion

Dick Jansson-rr rjansson at cfl.rr.com
Tue Oct 16 08:02:47 PDT 2007


Juan:
 
There is another issue that comes to mind regarding "specialized" modules.
In a program such as Eagle we will need to create an acceptable module
design that is useful for many applications in the mission and then turn on
the fabrication machinery for producing these long before the electronic
forces are ready to populate them for flight. On P3D in 1992-3 we gambled
and manufactured a very many module parts, expecting that we would have some
spares left over - wrong! Even with this quite large quantity of parts (and
at that time there was criticism that we were making too many) we ran out
before flight and had to make some more.
 
Fabricating module parts for this program is a guessing game, with some
estimates of needing to construct up to 80 sets of parts, and that may not
be enough. You can do the detailed program mathematics and come up with some
number and I will be willing to bet that you end up on the wrong side of
that guess. It's a dicey game.
 
The lesson in this is that we must create a generic module design and
hardware that can be adapted for many different assignments in the
spacecraft. Save for your specialized need, we have no indication of any
other specialized module needs. This is why I prefer to adapt a generic
module to your needs with the added heat sinks, rather than make just a
specially machined device just for your needs. And if we do, we will
probably not have enough of them. This is why I prefer to have a generic
module design and then carefully adapt it as required for specialized module
needs. We will be flying more than just the U receiver!.
 
'73,
Dick Jansson, KD1K
 <mailto:kd1k at amsat.org> kd1k at amsat.org 
 <mailto:kd1k at arrl.net> kd1k at arrl.net 
 
From: wa6htp at gmail.com [mailto:wa6htp at gmail.com] On Behalf Of Juan Rivera
Sent: Monday, 15 October, 2007 15.38
To: Dick Jansson-rr
Cc: Bob Davis; AMSAT Eagle
Subject: Re: [eagle] Revised Module Suggestion
 
Dick,
 
That looks nice!  It appears to solve the issue of getting that front panel
at exactly 90 degrees to the baseplate and also increases the stiffness of
the baseplate.  Increasing the useful front panel space also eases the
problem of working around the CAN-Do PCB with all of the necessary I/O
connectors. 
 
Would it be possible to customize the baseplate for the few modules that
draw high power?  It would be nice to machine the baseplate and heat sinks
as one chunk of metal instead of the existing method of having several
individual heat sink pieces.  I would like to see the PCB laying flat on top
of the baseplate with milled cutouts to accommodate any devices attached to
the bottom side.  In a perfect world there would be no components on the
bottom and the PCB would make contact with the baseplate across the entire
surface.  Another possibility that might be worth considering would be the
ability to include "U" shaped heat sinks that would bridge over the top side
of hot components and attach to the baseplate through holes cut into the PCB
on either side of the component.  Thermal gap filler could allow room for
CTE mismatches so that the device isn't crushed. 
 
73,   Juan - WA6HTP



 
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