Jan 16, 2001 meeting notes
Jan 16 meeting notes:
Location: Long Range Systems
Next meeting on Tuesday at LRS for VTVL system checkout with water and more
We now have more than sufficient thrust out of the small engines for the VTVL.
Russ is going to start cutting four engines (we should probably keep the current
one as a spare test mule) this week. Russ: you might want to think about
leaving space for a pressure port if you can.
We made new catalyst packs out of our batch of newly silver plated foam.
This foam was plated for longer, and was noticeably more brittle. We tried
making the packs this time by just rolling it up instead of cutting out
individual disks. It still catalyzed fine, but we believe that the rolled
packs contributed to the more ragged results today. We will be going back
to cut disks.
All runs after the first were with
200ml of propellant.
1: new rolled catalyst pack with a couple disks at the top, slightly compressed.
100ml run. This is more thrust than last time, due to the less compressed
pack letting more peroxide in.
2: increased pressure to 450psi, 200ml run. A little more thrust, holding
5kg, but a bit ragged.
3: new rolled catalyst pack with no disks and no compression, slightly better
flowing, increased the peroxide concentration to a bit over 90%. The run
made a bit more power, but was more ragged. The nozzle did show a little
bit of silver deposited on the inside, so this is probably pushing it too much
on the concentration.
4: drilled the nozzle throat out from 0.20 to 0.25. Averaged 7.5 kg
5: verification run with the same parameters as five. Similar good
6: Our first attempt at a pulse width modulated hot fire, 20 hz, 50% duty cycle
It was pretty ragged (20% variation), and gave about two thirds the power of the
100% duty cycle.
We didnt touch the engine between runs four, five, and six, so there was
still a little residual tension in the test stand, giving a bit higher starting
values. It was pretty cool to just be able to suck more peroxide in and
run the engine over and over.
The later runs with the drilled out nozzle are still making a fair amount of
thrust just from the nitrogen blowing through the hot catalyst pack after the
peroxide runs out.
The 7.5kg of thrust we are getting is more than sufficient for our needs, so to
try and smooth things out a bit, we are going to go back to fairly tightly
compressed disk packs like we had last week. Our pressure drop seems to be
very large, but our tank is designed for 1100 psi use, so we arent going to
sweat it right now. When we build an optimized system, we will need to
The nozzle isnt very optimal right now, because Russ couldnt cut a narrow
diverging cone at the time, and we dont have anything resembling a radius on
the throat, so I expect we will get another five or ten percent when we make
We have a few directions to go with developing the PWM. We will do another
run with a compressed disk pack, and we will try some different frequency
ranges. I am also interested in experimenting with a small pressure
accumulator between the solenoid and the engine.
One issue that may be significant is that our current load cell meter only reads
at 12hz, and we arent sure how much averaging it does over that period.
We may have a huge aliasing problem. We will try a 24 hz cycle time and
see if the runs look smoother. If they do, we are probably aliasing, and
the returned values would be in an unknown part of the pressure cycle. I
may need to break down and buy the high frequency sampling meter that I wish I
had seen in the first place.
We did some clothing peroxide safety tests today so we could see for ourselves
exactly what is likely to happen if there is an accident.
Cotton shirt and denim jeans were
basically unaffected in the five minutes or so that we left it on before dunking
it in water. It was only 45 degrees out, so results may be worse in the
middle of summer, but this concurs with the advice we had heard before: cotton
is good, because it will soak through and give you peroxide itch long before it
90% Nylon / 10% lycra and 50% cotton / 50% polyester had minimal effect.
Pure polyester and silk melted into goo, but did not combust.
Leather fizzed a little bit, then no-shit burst into flames quite violently
after it had been sitting there for about a minute.
The lessons are simple wear cotton, and make sure you dont have any
leather shoes, belts, or jackets.
Russ finished the new bottle manifold for the VTVL, and it is going to work
The bottom four ports go to the
engines, and we are going to use the top ports for the fill cart quick connect,
a pressure gauge, and dual blow off valves. We can save a fitting chain if
we tap one of the 1/8 NPT ports out to 4 AN for the quick connect. Bob
has a tap for that if Russ or Phil want to run by there some evening with the
I got new, all-metal check valves from McMaster-Carr. They are just
machined pipe fittings, which means that we can replace the male/male pipe union
we had between the solenoid and the engine with the check valve and simplify our
It turns out that the nice swivel 90 degree fittings I got wont clear the
solenoid mounting bracket, so we are either going to have to add a spacer, or
use the non-adjustable 90 degree fittings and wrap with Teflon until they clock
to the right angle.
Russ/Phil: when you find an allen wrench, take the screws out of the solenoid
mounts and go buy us a box of them. If we go the spacer plate route, we
are going to need longer ones as well.
My wife had her graphic artist make us an Armadillo Aerospace mylar sticker for
the dumb rocket airfame.
Phil dug up some candidate battery packs for the VTVL. We will be tying
three 4.4V (is that correct?) packs together for the unregulated supply to drive
the solenoids and serve as input to the 5V regulated power supply on the flight
computer. We are apparently going to need to remove the current limiter to
get enough power out of them for our needs. We should build and test a
couple packs with appropriate mounting hardware and charging stations soon.
Terry Parks has gotten a quote from Murata for the rate gyros, but they have a
minimum order of 100 parts. Prices are:
ENV-05D 100pcs $29.90ea
ENC-03JA 100pcs $13.00ea
ENC-03JB 100pcs $13.00ea
Russ also found a Delphi auto part rate gyro:
I just got a Delphi distributor
number from Bob, so I am going to check into getting some of these. If
that doesnt work out, I will probably buy 100 of the Murata gyros and just
give them out to any experimenter that wants some.
The magnetometer gives nice clean data, but the inclinometer is useless on a
moving platform. We will probably run the magnetometer just to collect the
data, but without another axis, we cant use it for attitude control.
John Dom sent me a link to a supplier of pure silver foam, which I have
requested a quote from:
I have been working with the single
board computer a bit. I installed linux on the dev system drive, and I
have booted dos off of the onboard flash Disk On Chip, but I havent
configured a linux system on the DOC yet. I did a little bit of work
making sure I know how to talk to our sensors over the serial ports, but I
havent built a real architecture yet.
I am still fretting about the exact system choices. The current dev system
has a power supply, HDD, floppy, and CD in a nice metal enclosure, and the SBC
(EBX form factor) sits on top, with power and two ribbon cables connecting it.
The SBC has video and Ethernet on it, which could have been part of the
development system, and might have then let me use a completely PC104 form
I need to get some more experience one way or the other, in any case. I
ordered a couple grab bags of standoffs and connectors for us to use in putting
various boards together.
Russ and I discussed possibly putting the solid state relays on PC104 boards,
either just for mounting purposes, or actually having it decode an IO port so we
dont need to ribbon cable from the parallel port to that board.
Stuff to get:
Refilled nitrogen tanks (get two)
A new vacuum pump for when this one dies
Light chain for tethering the VTVL.
Female 4 to male 1/8 NPT if we dont tap the manifold for the quick connect
At least 2 more 1/8 to 3 90 degree fittings if we dont make spacers for the
Pressure gauge for the VTVL manifold
Blow off valves for the VTVL manifold
Change the PWM program to allow it to vent the engine for 30 seconds without
logging the data.
Long parallel port cable for the tethered VTVL testing
Polycarbonate safety glass
Still need to find hazmat stickers