Apr 10, 2001 Meeting Notes
Batteries and plugs for an Air Port power pack.
PC104 16 channel, 16 bit A/D board
Life jacket for pilot of manned ship
VOX headset for pilot of manned ship
Mil-Spec wiring, terminals, crimpers, etc
Several gallons of distilled water
Tide for washing tanks and plumbing
Dilute nitric acid
Neil: short section of hard line for pressure transducer,
1/8 NPT male on one side, ¼ NPT female on the other
Silicone break fluid for pressure transducer
We havent gotten a confirmed delivery date for our peroxide
yet, but we are hoping it will be before our next meeting.
ShowDataq.exe now takes parameters for sampling a single
channel at 240hz, or both channels at 120hz.
Output is in hex, decimal, and volts.
Gps.exe now accepts both radio modem input and UDP input, so
it should be usable by both rockets this weekend.
During testing, I did notice that my consumer Garmin GPS-III
was displaying noticeably different positions than the GPS-35 OEM module
connected to the flight computer. I am
still curious how much of the difference is due to firmware / hardware issues
versus fundamental issues. At some
point, I want to try comparing two absolutely identical GPS units. If the errors are exactly correlated, an
attitude sensing system could be built out of the GPS-35 modules with the
double precision floating point output.
It would only be once a second, but the timing pulse signal line could
be used to exactly mark the time, and the flight computer could adjust its
gyro integration based on the values at the pulse, even though the serial data
wouldnt be in for another quarter second or so. I dont have high hopes for this approach, but we are still
looking for an obvious winner in the absolute attitude sensing department.
Russ has the sensor board mostly working with the Gyration
ASICs now. The roll axis isnt working
right, but since we arent using that yet, we should be ok for a while. The precision is drastically better than
before it only has LSB noise with a full 12 bit range. I havent checked the integration error yet,
but I expect much better results now.
Assuming we dont wreck our electronics at the HPR launch this weekend,
we should be ready for another guided flight test next week.
The new Crossbow sensor catalog arrived yesterday, and they
have a few new fiber optic laser rate gyro packages. The prices arent listed, but the micromachined ones were in the
neighborhood of $3k - $5k, so I wouldnt be surprised to see the laser ones up
around $10k for the 6DOF inertial packages.
Another interesting point was that the laser products all require 15V
We got the GPS-35 mounted to a PC104 board, and the entire
stack put together with metal standoffs.
We added a tie wrap around the PCMCIA card, so it shouldnt pop
out. Neil still has to do a little more
work to get everything mounted correctly, so we are going to have a brief
meeting on Friday evening for final integration.
I finished the new flight computer software, but for some
reason, the new CPU boards serial ports dont seem to be working. I need to track that down in the next few
We should be launching two different electronics packages
Neils level 3 rocket will be carrying our full electronics
package, minus the solid state relay driver board. We will be getting GPS data, accelerometer data (although it will
be pegged at 4G during the initial boost), and rate gyro data. This will also let us test the range of the
IEEE 802.11b wireless network.
My level 2 certification rocket is a 4 diameter PML Tethys stretched
with a 2 electronics section. It has a
consumer Garmin GPS-III connected to a Tigertronics raw 1200 baud radio modem,
connected to a 200 mW radio. This will
give us another GPS trace, and let us compare the conventional radio modem with
We did a set of water flow tests tonight to compare the
effects of check valve size, solenoid size, and line size.
100 psi pressure, 500 msec pulse, three feet of line.
-6 line big solenoid no check : 64 ml
-6 line big solenoid ¼ check : 62 ml
-6 line big solenoid 1/8 check : 41 ml
-6 line small
solenoid ¼ check : 34 ml
-6 line small
solenoid 1/8 check : 31
-4 line big solenoid no check : 58 ml
-4 line big solenoid ¼ check : 56 ml
-4 line big solenoid 1/8 check : 40 ml
-4 line small
solenoid ¼ check : 33 ml
-4 line small
solenoid 1/8 check : 24
While back to back runs were very repeatable, we had some longer
term repeatability problems, where it seemed like the longer the tank sat
pressurized, the more volume seemed to flow.
There may be some effect going on with the pressurizing nitrogen dissolving
in or out of the water.
Our nov16_00 notes had the small solenoid flowing 70 ml/s,
which is roughly in line with what we saw today, because that was with a 1000
msec pulse, which should flow slightly more than twice a 500 msec pulse due to
Our nov21_00 notes had us testing the latching bottle valve
at 200 ml / s flow at 100 psi, with a longer 4 hose, which is quite a bit more
flow than we saw here.
We want 400 to 500 ml/s of flow to each engine for the
manned craft, which is a lot more than we were getting today. We could always increase the tank pressure
(even the 100 psi tested today is probably optimistic for total pressure drop
into the engine), but it would have a big impact on our 10-20 gallon pressure
vessel selection for the main tank on the manned craft.
It is clear that the small check valve was a major
restriction, but the ¼ check is not a significant restriction. The hose size did not seem to be a restriction,
so the likely bet is that even the big solenoid is the restricting point now.
The unscientific test of blowing through the valves a while
ago seemed to show the big solenoid flowing more freely than the latching
bottle valve, so we should retest that combination and see if it still shows
the 60% greater flow. The latching
valve (NOS remote bottle valve) is a non-momentary valve, but it doesnt switch
fast enough for pulsing. In fact, we
should test it at several different durations to make sure that it didnt get
the good flow rating by just taking longer to close.
There is only one size larger to go in the NOS solenoid
valves, and that is a slightly different configuration with a bottom discharge,
instead of an in-line in and out. They only
rate it for slightly more max horsepower, so I dont think it will cut it. I am getting back with Bob Fortune about
getting some custom pulsing solenoids made.
The other possibility is that the bottle manifold is the
restriction. The manual valves on the
nitrous tanks dont open up a whole lot, so there may be something to it. We can test that by running the same tests
with one of the tank manifolds that Russ made.
We can use the manifold from Spider, but it only has 1/8 ports on it,
and we probably dont want to drill on it.
Russ: when you get a chance, dig out that first manifold you
made with the single central 1/8 port, and tap it out to ¼.
It is possible that we wont be able to get a solenoid that
flows enough and can still pulse at 20hz, in which case we will have to
investigate actuating rotary valves of some sort, or move to multiple solenoids
per engine. Multiple solenoids would be
easy to implement with our current facilities, and they could be brought in
incrementally to avoid no-flow during pulsing, but would be obviously pushing a
technique past its sweet spot.