[eagle] Re: We need to step back and reorganize

Bill Ress bill at hsmicrowave.com
Sat May 26 19:04:27 PDT 2007


I hear what you say about machined housings and the concerns that Juan 
has about sheet metal. Personally I prefer a machined housing to help 
(not cure) many of the issues that Juan raises regarding CTEs.

Consider this.....

I have been using eMachineshop ( www.emachineshop.com) with great 
success and with very nice pricing for rather simple machined housings 
for my microwave widgets. I have a small prototype mill and lathe to 
build the first one and when I'm happy, the drawing is converted to 
their software, the quote is done online, you place your order and the 
parts come in the mail. So we don't need a team member with CNC 
capability. Since our housings are somewhat "universal", a "basic" 
housing can be machined (in quantity) with modifications tailored to the 
specific circuit variations required. Seems like we have to do that with 
the sheet metal housing anyway.

Just a thought!!


Robert Davis wrote:
> Juan,
> You bring up things that should be discussed. I hope you're not as 
> frustrated as your email sounds. If you are, then I fear that our 
> communication shortcomings are worse than the technical problems you 
> refer to.
> I can comment on a couple of your points.
> Here's the history of the module development as I heard it. From AO-40 
> there was the desire for greater access to components on the PCBs, by 
> removing the side walls. As a reaction, Dick created a lightweight 
> module where the PCB mounts to the baseplate, then a cover is added. 
> This was his solution for the "requirement" he was given or at least 
> interpreted.
> I absolutely recognize the problem of having a baseplate that can be 
> flexed or even bent, to which a geometrically sensitive circuit board 
> is screwed, and then this is contorted to fit a potentially imperfect 
> cover. It seems to me that machining a module (base & walls) would 
> contradict the requirement Dick had to begin with. It's also possible 
> that the requirement for greater access is just plain at odds with 
> SMDs. Maybe this can be improved with a thicker baseplate. This is 
> absolutely an open issue right now.
> The CAN-DO is another topic. You're right. You can trade internal area 
> for the connector face. I do regret that this was not a specific 
> conversation earlier, as you have the PCB area to do almost anything.
> As for the unused area inside the module, I personally have no 
> interest in pursuing module dimensions that react to the PCB 
> dimensions in both planform directions. We already have 3 module 
> variants where we vary one planform direction. I think this is enough. 
> The spacecraft module mounting real estate is not valuable enough to 
> make modules based on each PCB delivered. We've essentially bloated 
> the exterior of Eagle to generate more power, and the innards haven't 
> changed much.
> You also bring up machined chassis. On AO-40, AMSAT paid for *a lot* 
> of machining, because AMSAT has no specific CNC capabilities. 
> Volunteers offer what they have, and whatever volunteers we have this 
> year has entered into our decisions on what to make. And certainly 
> this is the case for machined modules versus bent sheetmetal. Using 
> jigs, it was seen as a good thing that modules could be replicated by 
> someone with perhaps fewer fabrication capabilities. The bent 
> sheetmetal chassis have alignment issues that in the 3 or 4 prototypes 
> we made, we were unable to demonstrate reliable tolerances. This 
> didn't bother me so much, as the alignment jigs for bending were built 
> during this process. You certainly imply here that sheetmetal modules 
> are not compatible with SMD PCBs. I hope that's not true, as then 
> that's a driving requirement for us mechanically.
> Anyway, there's my comments for the day. I suspect the issues you 
> bring up are major enough that we'll be addressing them for a while, 
> not simply a weekend of emailing.
> Best regards,
> bob
> Robert Davis

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