November 10, 2001 Meeting Notes
We are receiving some assistance from Dave Schaeffer in
working towards getting our FAA waiver approved. He is a commercial pilot, and was instrumental in getting the
local HPR waivers through. On his
suggestion, we have started flying large model rockets at the test site, with
the appropriate FAA notification filed.
Apparently it was a bit of a hassle to even file the notification, and
it took some explaining and reading of the regulations to them to show that
they werent allowed to deny it. We
will do this a couple more times, then file for a waiver again, stating that
our experimental rockets will be going over exactly the same airspace as the
large model rockets, they will just be larger and heavier. Well see how that works out. I will probably apply for both a one-shot
waiver and another standing waiver, so that if they deny the standing one again,
we will at least be able to get something in the air.
Russ, Phil, and Dave went out and flew a bunch of G motors
in the morning, but I was up until 5:30 in the morning working on the new
electronics box, so I missed out.
Electronics Box 3.0
We have a brand new electronics box built, with many key
The new Crossbow FOG IMU is used for gyros and
accelerometers. This is giving us twice
the angular and acceleration range, and more than twice the precision, even
inside the old range of the gyros we were using before, and it is calibrated
and compensated for all deterministic variables. This was an expensive part -- $8500.
The PC104 stack is securely restrained inside shock
rails. We believe that the last time we
lost the computer on a bounce was due to twisting the stack.
The PC104 stack now has a VGA controller in it, which allows
me to easily plug a keyboard and monitor into the computer without having to
take everything apart. It will also be
used for controlling a flat panel display in later high altitude manned
There is room for an additional four port serial board,
giving us a total of six serial ports.
I havent been able to get this working yet, though.
The wireless Ethernet has been moved from a PC104 PCMCIA
card to a separate standalone device, with the PC104 communicating to it with
Ethernet. For the time being, I just
took apart an Apple Air Port, but we plan on replacing that with a higher power
device before we fly any significant altitudes. Does anyone know of a wireless Ethernet bridge (it can be simply
point-to-point, it doesnt need to be an access point) that emits the full
allowed one watt with a dipole antenna?
It seems like most of the bridges use 100 mW or less, probably so they
can legally use the more highly directional antennas.
We are now set up so that the flight computer can have a USB
joystick plugged into it, which allows the local pilot to fly the vehicle, but
that joystick can always be overridden by the remote joystick on the laptop.
The new box has all the connectors on the box top, which
makes hooking it up and wiring things a lot easier.
One problem that I ran into (which kept me up until 5:30)
was that one of the solid state relay LEDs wasnt coming on. At first, I suspected I had botched the
custom ribbon cable I had made, then I suspected the PC104 utility connector,
but finally I found that the DB25 connector on our custom board was starting to
get flaky, and wiggling it could light the LED. Phil resoldered the connector before our flights, and it works
One annoyance of the Crossbow is that it takes 15-30 V
power, so we had to add a 12V to 15V converter in the box.
We still have a few more things to do on this box: I really want to get the motor drive
circuitry integrated onto the same board as the solid state relays, and get all
of our actuation outputs run through either very good connectors or ring
terminals, so we get rid of the bare wire elevator clamps we currently have on
there. We will also be combining our
current 5V and 15V power supplies onto a single board, which will also have
current monitoring capabilities.
We emptied out our drum of peroxide at LRS today, making
1000 pounds of peroxide we have consumed since we started. We will pick up another one next week.
The first hop was on the tether, just to make sure that
everything still worked with the new electronics box.
The second hop was our longest flight ever, with five
gallons of peroxide loaded. It spent 20
seconds in the air, and I was venting peroxide out the attitude engines for
quite a long time after it finally set down.
The throttled ball valve is a significant problem in trying
to set it down gently. Both the latency
and the shape of the power curve lead to over corrections. I am going to implement a re-mapping of the
throttle curve before our next flight, and we are going to get a Doppler speed
sensor fairly soon as well, which should allow computer control of the
throttle. At least the attitude control
keeps it steady during the bounces
Everything held together in the electronics box across all
those landing bounces, so the new computer container seems to be doing its
job. One standoff that didnt have
anything on top of it did rattle loose, but that I probably failed to tighten
it back up after I moved something off of it.
The electronics box battery did run down a while later. I monitor the voltage during our testing, so
there isnt any danger of it going away in the middle of a flight, but I am going
to get a bigger battery so we dont have to worry about powering it down
between tests. The VGA controller, 15V
power supply, and AirPort are all drawing more power than the old box did.