Subject: [FlyRotary] Re: Digital Fuel Monitoring System

Hi Ed.

This of course all only applies to electronics in a vibration exposed environment.
Good practice, as I was taught it many years ago, is to have hole spacings to allow components to lie flat on the board.
Of course there are exceptions like power resistors that need airflow around them, but they should be mounted with "stand-offs" (small tubes on their legs). The rule used to be that components should not be held in place by the solder, but by their mechanical mounting. That's why the pins are typically bent 45 degrees where they stick through the PCB before being cut off and soldered. Heavy components are additionally secured with some kind of mechanical fastener or globs of goo (technical term). Now obviously the weight of the body of the component in relationship to number of pins/legs is a factor. An example would be an IC with oodles (another technical term) of pins.

I "grew up" in a company that secialized in sound and vibration. It was very educational to watch a PCB board mounted on a "shaker" (basically a loudspeaker where there membrame was replaced with a mounting place) lit with a strobe light synchronized to the frequency sweep. Components dancing around and finally falling off if not properly supported (mounted).

But that was then. Now we have surface mounted components which I know nothing about...


Finn (Looks like I've been kicked off the list again)


Geez, Finn, I was unaware that there was a "protocol" for resistor sizes on PC boards.  Seriously, is there some reason (vibration?) for forcing resistors all the way to the board or is it just "esthetics?".

 

Ed A

I still say your pc board looks good for a rotary engine. I couldn't tell from the pic  if the resistors are 1/4 or 1/2 watt.Those film resistors can take a lot of punishment.  Standing a resistor vertically on end allows more movement.  The yellow tantalum capacitor is the weakest component  I see, more easily damaged in soldering as over heating will damage the lead internally.  The resistor next to the pot might be put down to prevent it from bending over and touching the pot.

Is this a proto-type or to be put in aircraft?  If going in aircraft, I think sealed pots might be a good choice.

 

You should mount power resistors off the board so that the heat can dissipate without burning the pc board but you don't have any that I saw.  Many manufactures use little spacers to do this using water soluble spacers.  In my estimation, those little tubular spacers many use that are made of Teflon don't help rigidity much, but look cool.

 

If you want mil-spec board that is one thing but for our use I think Ed's board is OK except for above items. Anything large enough to move due to inertia forces should be glued down. I didn't see any large parts unless I didn't look close enough. Just don't put it in your space shuttle and pull 20g.  Personally I'd fly with it.  You fuse it like all avionics.

 

Wendell