[simpits-tech] Using real instruments

Sat, 25 Jan 2003 16:49:16 -0500

Success!

Following up on my thinking that the pneumatic instruments could be driven
by compressed air, I did this:

I took the face cover off, removed the hands and dial faces, remove a
retaining ring (circle clip) and extracted the barometer assembly.  I
drilled a small hole in each of the two bellows inside.  The bellows were
under vacuum and the bellows expanded and drove the linkage to their full
range (~ 60,000').

This is great!  Sometimes things work out. :D

I resealed the bellows by soldering the holes.  I reassembled the Altimeter
and set the dials to 5,3000' (room pressure).  I can now apply
0.1-7.75(approx.) psi pressure and the Altimeter spins from 50,000'
to -1,000'.  That was pretty easy.  The hardest part of the whole mod was
taking it apart and reassembling it without damaging the works.

Unfortunatly, I didn't expect it to work the first time and didn't take any
pics.

Craig R.

-----Original Message-----
From: simpits-tech-admin@simpits.org
[mailto:simpits-tech-admin@simpits.org]On Behalf Of Craig Rochester
Sent: Friday, January 24, 2003 9:34 PM
To: simpits-tech@simpits.org
Subject: RE: [simpits-tech] Using real instruments

Ok, I bought the Altimeter.  I took it apart(a delicate task).  It could
definitely be driven by vacuum, but I'm going to try to modify it to be
driven by pressure.  The ASTEK meter I have works by the expansion of two
sealed metal bellows expanding as the atmospheric pressure decreases at
higher altitudes.  I'm going to drill a hole in each bellows, port them, and
try pressurizing the bellows.  In theory this will be equivalent to applying
a vacuum to the outside.  If it works I'll post pics of the results.
Otherwise...anyone interested in a ruined Altimeter? :)

Craig R.

-----Original Message-----
From: simpits-tech-admin@simpits.org
[mailto:simpits-tech-admin@simpits.org]On Behalf Of Craig Rochester
Sent: Wednesday, January 08, 2003 8:39 PM
To: simpits-tech@simpits.org
Subject: RE: [simpits-tech] Using real instruments

I'm thinking driving the real instruments from two(2) electronic regulators
would be simpler than modifying each instrument.  Particularly if you were
doing a dual pit.  I don't know what the leak rate is on the VSI, but the
rest could be run from a tiny compressor(and vacuum pump if required).
Barometric pressure varies from 14.7 psia(0 gage pressure) @ sea-level and
decreases to about 1.1 psia @ 60,000 feet.  If you could modify or adjust
the Air Speed Indicator and Altimeter to be off-set down by about 15 psi,
you could use pressure instead of vacuum.

I know the pneumatic altimeters uses a sealed metal bellows that expands as
the barometric pressure falls with altitude.  The movement of the bellows is
converted to dial rotation with gears and levers. Maybe there is enough
adjustment in the works to have the instrument read 60,000 feet with no
applied pressure and then output 1-15 psi from the regulator.  Or maybe a
fitting could be fashioned to the bellows and connected to the regulator.

I see electronic pressure regulators on eBay pretty often:
http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&category=26210&item=3105137770
They're called an I/P transducer(eye-to-pee) current to pressure or
V/P(vee-to-pee) voltage to pressure transducer.

Craig R.

-----Original Message-----
From:	simpits-tech-admin@simpits.org [mailto:simpits-tech-admin@simpits.org]
On Behalf Of Matt Bailey
Sent:	Wednesday, January 08, 2003 5:04 PM
To:	simpits-tech@simpits.org
Subject:	Re: [simpits-tech] Using real instruments

I remember talking about using an air compressor to control real gauges
several months ago. Sounds like a GREAT idea to me, a little more complex
than just using servos but the extra realism in gauge movement would
probably
be worth it. Not to mention the utter coolness of being able to drop a REAL,
UNMODIFIED instrument directly into your sim. The instruments themselves are
pricey though, unless you found an old junk instrument but that would defeat
the purpose of making your sim accept real instruments since the instrument
would not work. :)

Driving gyro instruments like the turn coordinator I suppose could be done
with servos driving the gyro cages (although the ball is just a ball in a
glass tube, it's not driven by any mechanical device in real life so it
would
probably have to be totally reworked) or just removing the gyros completely
and hooking a servo directly to the small aircraft representation. Anyone
done this?

	-Matt Bailey
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