Use a 'tough' material for the standoffs - often pc-104 standoffs are
aluminum or plated brass or plated steel, but are available in nylon... I
suspect other materials can also be had. Some pc-104 systems use nylon edge
channels in tube enclosures (kinda like a rocket body? ) instead of the
standoffs. Not sure what is already planned, but using non-conductive
standoffs might be desirable in case of an early shear-off as it increases
survivability with no conductive particle loose and floating around in that
event. If you will be FEA'ing the standoffs anyway, suggest just running a
few additional materials to compare against.
Using *no* standoffs and, instead, clamping at connector points might also
work, as long as there are appropriately machined non-conductive spacers in
areas where the interboard connectors are not carried all the way through
the pc-104 stack. This might save weight (wishful) or not, but could be
cleverly designed to improve shear-force shedding/spreading.
-Doug
On Fri, Dec 23, 2011 at 10:36 AM, Dave Camarillo
wrote:
> On Wed, Dec 21, 2011 at 2:57 PM, Andrew Greenberg
> wrote:
> >> Hello Airframe Team, attached are a few snapshots of the first
> >> proposed mounting technique for the new PC-104 flight computer
> >> stack...
> >
> > Sweet! I love it!
> >
> >> Constraints:
> >
> > It doesn't look like there's room for a fourth PCB on that stack. Is
> > that true? If not, could we add that possibility? It might turn out to
> > be very, very convenient to have a FC "breakout" board as a fourth board.
> >
>
> There's barely enough room... it will be tight, but I think it's
> doable... see attached images...
>
> > Also, how far apart is the heatsink from the C channel? Can we arrange
> > for it to be exactly one thickness of thermal interface material (TIM)?
>
> Maybe, depends on the thickness of the TIM... there are a few parts
> that will interfere if we move the heat sink any closer to the
> channel... It's currently 0.125" from the channel. How thick is the
> TIM?
>
>
> >
> >> -There is no support on the top edges of the PCB. We could add foam
> >> or other material to help handle upward loads (i.e. during recovery
> >> and hitting the ground. However, this also means that if the battery
> >> box pushes downward, those forces will be passed thru the PCB's, not
> >> desirable.
> >
> > .. which is why I wouldn't put anything up there. I bet we're OK, unless
> > we lawn dart, but we shouldn't design for that.
> >
> >> There's also the question of how much of a moment can we apply to
> >> those 0.6" standoffs, noting that they are 4-40 threaded.
> >
> > Can we directly answer this question using SolidWorks coolness?
>
> Yes, we can FEA it
>
> >
> > Andrew
> >
> > --
> > ---
> > Andrew Greenberg
> >
> > Portland State Aerospace Society (http://psas.pdx.edu/)
> > and...@psas.pdx.edu C: 503.708.7711
> > ---
>
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