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? <g>) 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 <dave.camari...@gmail.com>wrote: > On Wed, Dec 21, 2011 at 2:57 PM, Andrew Greenberg <and...@psas.pdx.edu> > 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 > > ------------------------------------------------------- > > _______________________________________________ > psas-airframe mailing list > psas-airframe@lists.psas.pdx.edu > http://lists.psas.pdx.edu/mailman/listinfo/psas-airframe > >
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