Oct 13 and 14, 2001 Meeting Notes
Joseph LaGrave (sat)
Bob Norwood (sat)
Our 2 diameter filament wound fiberglass tubes
arrived. We are intending to use the
10 section for the next vehicle, and we have 14 extra feet in case we crash it
or decide we need more length to hold a longer tank.
We now have a containment palette, so we are keeping a drum
of peroxide at our workshop, which is important now that we can start going
through ten gallons in a test day on the big lander. I have the rest of our stock stored at Rinchem, a chemical warehouse
Repairing the broken fiber optic gyros was quoted at almost
$1000 and two weeks time, but KVH had the proper model in stock, so I just
ordered a brand new one for $1500 and got it the next day. It took six weeks to get when I first
ordered new ones, so if anyone is thinking about buying some KVH FOGs, you
might want to get them while they are in stock.
Russ picked up a tig welder and started practicing with it,
so we can make cleaner welds and deal with other materials at Long Range,
instead of having to get everything over to Bobs shop. We have some better brackets on the fill
cart and on the big lander computer strap down now.
We had everything ready to fly on Saturday, and we had an
ambulance standing by in case we got to a point we were going to try flying a
person on the vehicle. Ambulance
standby cost $300 for the evening.
We sunk a couple concrete anchors with eye bolts into the
curbs out back so we could tether the big vehicle down with heavy chain until
we are quite comfortable with its behavior.
We had two major changes in the vehicle from the last time
it was flown:
The throttling is now completely done by the central engine,
and the attitude engines just control attitude. Previously, the central engine had a fixed jet in it to lift most
of the vehicle, and the four attitude engines handled both attitude and lift,
just like the little vehicle. The old
way was convenient, because the software didnt change much from the little
vehicle, but a mis-jetting led to the last crash. We had to start throttling the main engine for higher G vehicles
in any case, so it was about time to move that way. An expected problem was that the 1/2" ball valve gets almost
its entire control range between 25% and 50% open, and is very non-linear. A 3/8 ball valve would work a lot better
for this size, but we couldnt find a motorized one with the right
The electronics box, with the gyros and accelerometers, was
rotated 45 degrees out of line with the engines so it could be securely
strapped down, instead of held by brackets.
If we had had it like that before the crash, it wouldnt have come free
and bounced across the parking lot, which almost certainly caused a lot of the
damage inside. This required software
changes to move the angles from the box space to the frame space.
There were also several minor changes on the vehicle, like
new hoses and the addition of pilot counterbalance weights for better abort
behavior. When we have it fully
ballasted up to include the weight of our upcoming pilot, the entire vehicle
weighs 330 pounds dry. We can only load
about 50 pounds of peroxide into the current tank before the pressure drop
becomes too much, so our flight times are severely limited. We are nearly 100 pounds heavier than we
originally intended to be. We are
probably going to get a taller tank so we can load more peroxide for longer
flights, although we will probably accomplish our goals for this vehicle in the
next month or two and move on to the next one.
We didnt have any luck at all on Saturday. All the tests went fine, and it throttled up
smoothly, but it would just pick up two legs and prepare to tip itself
over. It was easy to set back down, but
the behavior was completely repeatable.
My first thought was that the inclinometer initialization of
the starting angles was wrong for the rotated box, which was making the vehicle
think it was angled a different direction (there is a pretty good slope at our
tether point). I changed that and we
tested again, but it still wasnt working right. Later that night after testing, I realized that the inclinometer
init was correct the way it originally was, so I put it back.
The last thing we tried was angling the engine roll angles
more, because we had the small lander once not fly right when we didnt cant
the engines, because it was putting all of its effort into correcting a roll
that was never going to change. Still
I was sure it was something with the rotated box, so Joseph
put together a quick wooden frame for me to lay the box on so I could more
easily make test rotations at home.
I finally figured out what it was while I had the angular
positions rotated into the vehicle frame coordinate system, I was still using
angular rates from the box coordinate system, which of course hopelessly
confused things. This was clearly
evident in the telemetry once I thought about it it had angles changing in
different directions than the indicated rates.
We got back together on Sunday to have another go at it.
We did three brief hops, and the attitude control worked
perfectly, even when the vehicle pulled taut against one of the tethers.
The throttle control is extremely touchy with the response
curve of the ball valve. The first two
hops had me bouncing it off the ground a couple times as I overcorrected. You can deal with it by making very small
changes, but I am probably going to add an option to map 0% to 100% joystick
throttle to 20% to 70% ball valve position, which will give a little more
The big engine is having some channeling problems, leaving a
lot of peroxide fumes during firing. We
had just added some new discs on top on Saturday, but we didnt replace
everything, and we didnt have a good enough press to properly compress
them. We opened it back up and changed
a few more discs and packed a strip of catalyst around the outside. The thermal crunching is pretty significant
on the big motor it started out requiring a press fit, but after the dozen or
so firings we have done on it, the pack rattles around freely inside, with
nearly an eighth of an inch clearance all the way around.
Russ has a cool automated printed circuit board mill at LRS
which we used to cut some anti-channel rings for putting in between some of the
catalyst discs. We only had micro-etch
perforated metal to try it with today, so it isnt a great barrier, but the
process worked great, so next time we are going to have various gauges of solid
sheet metal to try it out on.
The third hop worked fine, but it was pretty short, and the
engine was still running a bit wet at the end.
Here is the telemetry graphs (GPS and temperature not connected):
And the video:
When it was clear that the attitude control was working
fine, Russ offered to jump on the lander for a last flight, but with the main
engine channeling again, and no ambulance, prudence won out and we just started
cleaning up. The next tasks will be
really fixing the engine channeling, and hopefully improving their life span. We expect our pure silver foam for the small
engines any day now.
We are all loaded up for the Space Frontier Foundation
conference in LA, so we wont be doing any new work next week:
We will be there Thursday through Saturday with both the big
and small lander and some other gear.
We arent going to fire or fly anything, but we will be happy to talk
about any aspect of the projects.