Bob,

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!!

Regards...Bill...N6GHz

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 KF4KSS