Week of December 22, 2001 Meeting Notes
Russ Blink (Tuesday)
Bob Norwood (Saturday)
On Tuesday, we built new catalyst packs for the engines, and
tried to make new anti-channel rings.
Mark Henry had explained to us that the rings should be fairly thick,
and of the same material as the engine casing, so that they would expand at the
same rate and stay pressed against the walls at all times. I bought an assortment of different brass
sheet stock, but we broke a few end mills on Russs pc-board CNC mill trying to
cut the thicker sheets too fast. Russ
is going to work out a better process.
We also made a change to the way we are controlling the main
ball valve. When we first started
working with the ball valves, we had two motor drives burn out on us (complete
with smoke!), so when Russ built a custom board for us, I had the software
include significant delays between motor reversals to add some extra
We later found out that the likely source of our problems
was that the connector on the motor had been internally twisted up pretty
badly, likely causing an intermittent short circuit. I later lowered the
turnaround delay from 100 msec to 50 msec without any ill effects.
On Tuesday, I took the delay out completely, and everything
still seems to be fine.
This will help with the manual throttle control, because the
latency makes it harder to hover and land smoothly. It will also be
beneficial when I get an altimeter hooked up and have the computer running the
throttle in closed loop mode.
Our TZM moly bar stock is on the way. A 2.75 by 12 bar is 26 pounds, at $44 /
pound. That should be enough for at
least four test nozzles. If we get
lucky and have our first coating (probably going to try plain platinum first)
work, we can hang on to the rest for potential biprop tests at some point.
Russ was away for the holidays, so on Saturday, Phil and I
put the engines together with the old control rings, and prepared for some
normal flight testing.
The water test went fine, and after loading the peroxide,
the engines warmed quickly and ran perfectly clear. Then things went rather badly.
I started the guided run, and began throttling up. The engines were all firing, but it wouldnt
lift off. I was throttled all the way
up to maximum, about to shut down and reassess the situation, when it jumped
off the ground. It snapped off both
tethers like they werent even there, and flew up out of my field of vision
from inside the garage.
As soon as it left the ground, I throttled it back, but I
was thinking that the motor drive was stuck in some way due to our changes on
Tuesday. When I couldnt see it, I
completely killed the control. I was
gratified to hear the engines cut off, which I was a bit afraid wouldnt happen
if the motor drive was smoked. When I
could see it again, I reengaged the attitude engines, which straightened it
back out, but it still plowed into the ground pretty hard. This definitely looked like a better way to
crash than the one we had with the offset CG.
(our professional camera guy wasnt there yet, so it is
messier than usual
When I looked at the telemetry, it showed the throttle
ramping up to 25%, then staying there for several seconds and jumping all the
way to 100%. The motor drive was doing exactly
what it was told, but the entire throttle ramp up that I did was just
missing. I was almost positive that
that meant the flight computer wasnt receiving packets from the laptop over
the wireless link (even though the laptop was getting packets from the flight
computer). We have had some signal
quality problems (the 1000 mW Esteem 802.11b units just showed up on Friday,
but I hadnt integrated them yet), but the computer is supposed to just shut
everything down if it doesnt get any remote pilot packets for 200 msec.
I was considering that I might have broken that code when I
added the local pilot joystick control, but when I went back and looked at the
joystick sequence numbers in the telemetry (glad I saved those off!) I found
that the computer had been getting constant updates from the laptop just like
it should, but the joystick values just werent changing. Either there was a real hardware problem
with the joystick, or WindowsME was fucking up. Considering all the problems I have had with this laptop, I am
leaning towards WindowsME. I will
probably put XP on it soon, but I am giving some strong consideration to making
a stripped down linux laptop for the remote piloting. I dont trust X windows any more than ME for real time
applications (less, actually), but I might consider coding the remote pilot
application directly to fbdev for display purposes.
What went well:
The frame collapsed just about how you would want, absorbing
a whole lot of energy.
The attitude engine restart while airborne worked
perfectly. After our last crash, I
added code to let the computer continue tracking the gyros even when it isnt
active, and when it is reactivated, if it determines it is airborne by seeing
that the gravity vector isnt (roughly) unity, it leaves the axis where they
are instead of reinitializing them.
We had added a manual ball valve to the fill plumbing on the
vehicle, which allowed us to vent most of the pressure out of the tank before
firing the remainder through the engines.
Our fill-cart based switchbox for manually firing the engines also
worked well. We might want to add
another valve to the vehicle to allow us to vent peroxide without going through
Nothing broke loose in the electronics box.
What went poorly:
We lost the computer on impact again, and it wouldnt come
back on a power cycle. When I got it
home and pulled everything apart, I found that a couple pins on the bottom
PC104 connector had been bent together.
After I straightened them out, everything came back to life. Im still not exactly sure how the could
have been bent, because there were standoffs on the bottom that should have
prevented them from hitting anything.
There was probably sufficient flex in the box at the time of impact to
do it, so I have swapped the standoffs out for taller ones.
The utter failure of the tethers was a rude shock. The chains are pretty heavy, but this was a
classic case of the weakest link. One
side ripped off the thin bar of 4130 on the landing leg that we had it attached
to, and the other side broke the aluminum quick link that we had the chain
connected back to itself with. We will
add reinforced mounting loops directly to the frame on the rebuild, and if we
continue to use chains, use only steel quick links. We may move to nylon rope for the tethers, which would let them
take up the shock much more gently. We
couldnt do that on the previous vehicle because the engines were right next to
the attach points, but with them in the current locations it would probably be
ok. There is still a worry about flying
back over them on the ground.
The main motor bell hit the ground hard enough to break the
bolts securing it to the frame, which pushed all the plumbing up high enough to
crunch the burst disk holder through the bottom of the seat by an inch or
so. We plan on modifying our main
distribution manifold so we can get rid of a cross fitting and a union fitting
above the manifold, which will clear up enough room so that it cant hit the
seat even if the frame is sitting completely on the ground.
The rest of the damage was more or less as expected. A few tubes broke on the frame. One attitude engine hit hard enough to break
the expansion cone off. One solenoid
had a wire ripped off. The ball valve
motor broke off the valve. A couple
connectors in the electronics box were bent.
The basic vehicle design seems pretty sound, and wont
change much. Bob wants to upsize two of
the crossmembers, and we will add really good tether points and shorten the
plumbing under the seat, but mostly it is going to come back together the same
way it was. I have ordered some
replacement valves and solenoids, and Bob thinks he can have the frame re-built
within a week or two. We may wind up
having the altimeter and computer control of the throttle before we fly again,
which would allow the flight computer to auto-land if the remote pilot computer
loses its mind in some way.
Master To-Do list (created before the crash
visible strobe on
vehicle for syncing telemetry to video
side seating drop
More shelves for
New catalyst pack
Get new small engine
retaining plate material and water jet cut to size
plate / gaskets for motors
Combined solid state
relay / motor drive board
Combined 5v / 12v /
15v power supply board with current sense output
1000 mW 802.11b integration
altitude computer simulation
Logging of all
New real-time graphs
of all flight parameters
graph average duty
cycle for each async engine
Optional real time
smoothing of any data channels
Flight sequencer for
convert GPS lat/long
to meters from start point
dead band at 0.5 on linux joystick driver
investigate using a
large disk-on-chip instead of the IDE-flash board
Get four port serial
expansion board working on linux
Rotary rocket stuff:
Tap other end of
Ball bearing mount
on old vehicle for initial spin tests
sensor for computer logging
bearing housings for prop
Rotating hub seal
Hybrid motor testing
aluminum nozzle for
moly nozzle coatings
test range stuff:
trench / berm
order more 5 gallon
electric or air pump
tank bladder testing
ballistic parachute stuff:
shipping from CA
conversion to HPR