Hello Mark.
The problem with the mobility of my set-up is that the vacuum pump is a couple
hundred pounds. Otherwise, I would like to bring it to a launch. Perhaps when
I get my utility trailer at the end of the year.
My head is kind of spinning right now, because this could be a complicated
conversation depending on what the objectives where. For example, if we were
interested in the accuracy of the barometric altimeters we are using for
rocketry, then we would need a precise instrument that was traceable to a
standard, or maybe check a few of them at the same time to see the variation.
Unfortunately, accurate instruments for low pressures (i.e. high vacuum) are
expensive. It would be nice to have something more accurate than a standard
vacuum gauge I’m currently using.
There have been some interesting discussions on this chat regarding altitude
determinations using barometric altimeters vs. gps units.
For me, the current objective is reassurance that barometric altimeters will
fire the drogue and main charges correctly, and if a side deployment bay will
not prematurely open on ascent. To have accurate altitude readings would be a
plus.
I’ll be installing 4 more electrical connections through the end of the vacuum
chamber for drogue and main charge connections.
I live in Temecula, and anyone that is interested in testing something using
the set-up I have is welcome to visit. Just contact me off chat.
From: Mark Woods<mailto:mark@xxxxxxxxx>
Sent: Monday, July 25, 2016 1:40 PM
To: roc-chat@xxxxxxxxxxxxx<mailto:roc-chat@xxxxxxxxxxxxx>
Subject: [roc-chat] Re: Vacuum Chamber for Ground Testing
Hi all,
I'm new to this community but an electronics engineer and would offer to help
if that's useful...
Thanks,
Mark
On Jul 25, 2016, at 12:43, James Dougherty <jafrado@xxxxxxxxx> wrote:
Hey Richard
Nice work! Would love to give it a shot with some calibrated altimeters ...
Maybe bring it to Roctober?
Thanks
-James
Sent from my iPhone
On Jul 23, 2016, at 4:27 PM, R Dierking <applerocketry@xxxxxxxxxxx> wrote:
This is a follow-up on an earlier post on creating a vacuum chamber for
testing altimeters and other rocket-related equipment. I’ve attached a
photo of the chamber that measures 3” square and 12” long.
Mike Kramer suggested that I make a smaller test version to work out
potential bugs, and it turned out that cutting the grooves in the 1 ¼”
polycarbonate ends for the o-ring seals was more difficult than imagined.
Also, it took a couple tries to create electrical connections through the
end to connect a switch. Unfortunately, the 2nd stage on the vacuum pump
isn’t getting as low as specification. I’m still working on that, but so
far achieved about 29 ½” of vacuum *. I tested a PerfectFlite SL-100 a
couple times and it recorded about 102,000’. So, I think that’s adequate
for awhile. 😊
The next chamber will be 6” square and about 40” long to accommodate the
upper half of a rocket I’m working on.
This vacuum chamber project has been kind of a distraction to my L-3
project, but I’m still glad for the time spent. Always fun building
something different and learning more about atmospheric pressure for amateur
rocketry.
Richard Dierking
* There are many different ways to denote atmospheric pressure such as PSIA,
Inches Hg, Torr, mbar, and microns. A Torr is 1/760 atmospheric pressure
and there’s about 1 Torr at 150,000’. I have an inexpensive (aka cheap)
vacuum gauge so it’s really only good for low vacuum.
<Test Chamber.JPG>
