[eagle] Re: CAN-Do Suggestions from Juan

Lee McLamb ku4os at cfl.rr.com
Wed Jul 18 18:56:44 PDT 2007


As we consider flex stresses we also need to ensure we've considered the 
launch adapter specs for G-forces and are providing adequate support for the 
boards.

For ESPA:  10.6 G on all axis 
For ASAP5:
X  +/- 6 g
Y  +/- 6 g
Z  -7.5 g / +5.5 g

Lee-KU4OS

On Wednesday 18 July 2007 08:41:23 Robert Davis wrote:
> Jim, Juan, and all,
> I'm sorry for not being active in this conversation earlier. I'm absolutely
> creamed at work. I forecast being at my maximum at work for about another
> week or two. I'll spare you the details.
> I am sure that we can redesign a module that is at least partially milled,
> that will maintain the flatness that Juan quotes from a vendor of .008" per
> 1". It really isn't that hard, but absolutely throws out the sheetmetal
> baseplate we've had until now. In my mind, for this one issue it's only a
> decision as to whether the entire module height is milled (and then there's
> just a simple flat cover) or whether the milled portion is part of the
> height of a module and a shorter "bent cover" is used. I think I'm favoring
> a milled module with simple flat cover.
> For the issue of the isolation of the CAN-DO in a separate compartment,
> this can be done and I guess I've seen it frequently with milled modules.
> I'd like to avoid it because it moves farther towards having truly
> customized modules, instead of a generic with minor connector or heatsink
> mods. For the issue of the RF connectors exiting the side of the module,
> this is potentially a larger issue. In our current arrangement, we have
> identified a connector face on the modules because all the modules are
> (potentially) packed side-by-side to consume a dimension of the spacecraft.
> If we had an accurate accounting of how many modules, and what sizes they
> are, then we might be able to say with confidence what gap is present
> between modules available for RF connections. I've attached a spreadsheet
> with the only accounting of modules that we've attempted and it's pretty
> old.
> The flip side of this would be: impose a requirement on mechanical to
> provide room for RF connectors on specific (or all) modules, and specify
> what the module sizes are and we can see where we stand. Maybe it would
> help to have an idea of what kind of protrusion from the side of a module
> we're talking about. 20mm?
> So, comments on the list of modules & sizes can get us started with
> determining what is available next to a module for RF.
> bob
> Robert Davis
> KF4KSS
>
> On 7/17/07, Jim Sanford <wb4gcs at amsat.org> wrote:
> > Team:
> > Some comments on this thread, as I indicated earlier.
> >
> > In no particular order:
> >
> > " . . working in a vacuum."  To not do so is why we have EaglePedia, and
> > why I have been pushing for requirements and sharing of lessons learned.
> > The harsh reality is that Juan and his team have been testing some of our
> > stuff in new ways, and we're learning things.  Perhaps we could/should
> > have learned some of these things in the past, I don't know.  We didn't,
> > but we know them now, so let's press ahead.
> >
> > Regarding the board flexing issue:  Juan, please add this to your lessons
> > learned.  It would be a welcome addition to the component selection talk
> > that Lyle gave at Pittsburgh.  In the mean time, please extract all the
> > things that you've learned we should do differently into a text document
> > that I can add to the lessons learned sub page from my project management
> > page.  I'll get Dave to post, this is all good stuff.
> >
> > Milled enclosure:  Bob Davis is looking into that.  I've asked Dick
> > Jansson to locate an unmodified sheet metal enclosure to get into Juan's
> > hands for evaluation.  Many considerations here, let's make decisions
> > based on EVALUATION.
> >
> > EMI:  We need requirements, but nobody has stepped up to write or
> > extract.  My threat (grin) to dig out the MIL-SPEC was properly
> > incinerated.  So, we still have no requirements.  I offer the following
> > "top level" EMI requirements, based on my earlier post regarding the 3
> > things it takes to have EMI:
> >     1.  Every potential EMI source (like switching power supplies) should
> > be as quiet and well shielded as reasonably posible.
> >     2.  Every potential EMI victim should be as immune to conducted and
> > radiated (other than on-channel thru the antenna) as reasonably possible
> > I'll leave it to guys like Tom Clark to tell me what exponent we should
> > attach to the value of this in the aggregate of many sources and victims,
> > I just know that attention to the basics on a per module basis will make
> > our lives much easier at integration/testing time.
> >
> > We also need to standardize on IF output levels from RX modules and input
> > levels from SDX to TX modules.  Volunteers?
> >
> > I think the above provides all the guidance we need to proceed with an
> > electrical redesign of the U RX based on what we've learned so far. 
> > We'll need Bob's input on housing studies and we'll need to assess what
> > the CAN-Do! team is up to before committing to PCboard layout and
> > construction. Juan thinks we should wait until some top-level specs are
> > better refined; we'll come through this discussion.
> >
> > Regarding the CAN-Do widgets:  The team has offered to do a redesign. 
> > I'm reluctant to get too carried away on this.  We've learned some things
> > that we'd like to change regarding the power supply, but the rest of it
> > works, and we should not toss that.  So, this is an area where I very
> > strongly feel that incremental improvement is in order, not a wholesale
> > redesign.  My sense is that the power supply noise issues we've
> > discovered IN TESTING were not anticipated by design folks who are not
> > necessarily power supply experts.  (Bdale just confirmed this on the
> > phone.)  Now that we have them, we're seeking such experts.  We may get
> > some input soon from someone who is such an expert who knows somebody who
> > knows somebody who is on the team.  If any of the rest of you have such
> > expertise or know somebody who has it, please step up to the plate.  I'm
> > gratified at the willingness of the CAN-Do! team to do whatever it takes,
> > but DO NOT want to toss the baby with the bath water -- we then start
> > over, and cannot afford that in time, intellectual effort, or $$  Part of
> > this discussion is the recent conversation regarding high density
> > connectors.  If we need them and they're acceptable, so be it.  Some seem
> > to think this is a big deal, I do not -- it's a technical issue to be
> > evaluated and dealt with.
> >
> > One commentor expressed disappointment about silence regarding these
> > changes and lack of direction from "management".  I have been following
> > this conversation closely, but have not weighed in since I had no new
> > thoughts or extraordinary value to add.  Rest assured, I follow these
> > issues closely, and try not to weigh in unless I have something
> > significant to say.  My silence to this point should be interpreted as
> > satisfaction with the conversation and apparent direction.  If ever you
> > think I should weigh in and am not, ask the explicit question.
> >
> > Chuck asked if someone would pursue alternative inductor components to
> > reduce radiated noise.  I have asked Juan to see of Project Oscar would
> > take this on.  I think there is tremendous value in testing with
> > substitues of this single component.
> >
> > Finally:  SYMPOSIUM
> > It is CRITICALLY important that we demonstrate something this year.  We
> > need it to dispel doubts and we need it to encourage fund-raising.  Our
> > hosts, the Wireless Association fo the South Hills (WASH) have committed
> > to helping us do this.  They will provide a 30+ foot tower on a trailer,
> > antennas, coax, and I'll provide a power supply.  We have a working
> > U-band RX, and may have a better one.  Bob McGwier assures me that we'll
> > have a working SDX to demonstrate.  I'll get a 2m TX for it to drive at
> > significant power.  This will allow us to demonstrate Eagle in the hotel
> > and in the surrounding area -- vital for publicity and fundraising.  We
> > also need to show IHU and CAN-Do!, ifthey're working and sending
> > telemetry on the "downlink", so much the better!
> >
> > We have much to do in a few short months.  Let's get on with it.
> >
> > Thanks & 73,
> > Jim
> > wb4gcs at amsat.org
> >
> >
> >
> >
> >
> > Juan Rivera wrote:
> >
> >  Chuck,
> >
> > Forgive this long email...
> >
> > SInce everything is interrelated the only way to deal with it is from a
> > system engineering perspective (in my opinion).  You can't design the
> > various subsystems with each group working in a vacuum.  If you do, this
> > is what happens.
> >
> > For example:  I've researched the maximum amount of bending that should
> > be allowed on a SMT circuit board.  AVX, the capacitor manufacturer,
> > suggests a maximum bend radius spec for SMT circuit boards of 60 inches. 
> > That works out to 0.0084" maximum deflection over any 1" segment.  That's
> > about the thickness of three sheets of paper.   The tolerances of the
> > existing sheet metal enclosure with separate heat sinks and multiple
> > swaged-on stand-offs is way too loose, by at least an order of magnitude.
> >  The enclosure I have is also warped and flexes.  To me that means we
> > need a milled enclosure...
> >
> > If we're going to do that we might as well do it right and make it into
> > two separate cells with noisy digital circuits in the front and analog in
> > the back...
> >
> > If we do that then you probably don't have to worry too much about
> > radiated emissions or changing the PCB form factor or connector...
> >
> > Filtering conducted EMI would rise to the top of the list of concerns.
> > Moving the switching frequecies of all the supplies up as high as
> > possible would ease the filtering burden on everything on the satellite
> > and tend to push any spurs out of the passband.  And so forth and so
> > on...
> >
> > Once we had some hard data on the amount and characteristics of the
> > conducted EMI from the power distribution point, then John could start
> > designing in the necessary EMI filtering and CPB layout to fit into the
> > box and meet the yet to be determined EMI susceptability requirement for
> > the receiver.  If his design didn't look like it would be able to meet
> > the requiement then there would be some push-back to the power
> > distrubution subsystem to clean up their radiated EMI, etc.
> >
> > I guess the bottom line would be that since you can't know the radiated
> > and conducted EMI susceptability of everything that may end up connected
> > to the CAN-Do module, all you can do is try to make it as clean as you
> > can and get the switching frequency as high as possible.  By the way, I
> > just looked up the Maxim converter you're using and it looks like it's
> > very lightly loaded which would explain wny its running at 5 kHz instead
> > of the 200 kHz they spec.  I spent some time looking for a better choice
> > and couldn't find anything, but I don't know what you requirements are.
> >
> > 73,
> >
> > Juan
> >


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