Aug 21 and Aug 25, 2001 Meeting Notes
Russ got a new tank manifold cut with a half inch straight
through port. He originally tried it in
stainless, but couldnt cut the 1/2" thread with a tap, so we went back to
aluminum. We now have aluminum manifolds
on the little lander, the big lander, and the test stand, with no more NOS
bottle manifolds in service.
Each manifold has a fill port quick connect, a 1000 psi
pressure gauge, a pressure transducer for the computers, and a burst disc or
relief valve. We are still waiting for
our larger burst discs, so we are moving the small NOS ones around right now.
We made a length of 10 AN Teflon hose for the test stand. It has a slight leak at low pressure, so we
should probably cut that end off and try again, or just get a pre-assembled one
I have ordered a 3 gpm DC powered Teflon diaphragm pump from
PEP-Plastics. This can pump into 30 psi
of pressure, so we wont need to draw vacuums in the tanks, and will generally
make things a lot faster now that we are doing tests with over a gallon at a
time. It was $2500.
I have put down the deposit for 5000 pounds of peroxide from
X-L. We are getting it at 90% instead
of 98%, so we will be able to skip the dilution stage in the future.
Large motor testing
On Tuesday, we first tested with an existing solenoid, and
it didnt make any more power than the smaller motors, clearly showing they are
the limiting factor. It probably flowed more peroxide into a lower chamber
pressure, but the additional over expansion more than compensated.
We then hooked up the big motorized half inch ball valve and
made a run at 400 psi. We got a bit of
The data collection turned out to be clamping at half scale,
so we just saw it maxing out at > 300 pounds thrust for most of the burn.
On Saturday, we installed concrete anchors for the test
stand, moved up to the 3000 pound load cell, and ran it again at 400 psi, then
at 600 psi.
This is a lot rougher than we would like, and somewhat below
our estimated thrust. Now that we are
out of the micro-motor range, Russ is going to try and cut some cavitating
venturiis and see how they work for us.
They will be designed to slip into a 1/2" union fitting, and we
will probably start out with a 1/4" throat, which should still be good for
400 pounds of thrust.
New Data Acquisition
I finally have everything weaned off of AC power, so we can
move everything to the test range when needed.
I have a Dataq DI-195B with a load cell signal conditioning module, and (on
order) another straight voltage module for the pressure transducer mounted in a
box with our solid state relay that starts the test runs.
I have run into some difficulties with this setup. On my laptop, I get jittering values in the
three least significant bits, but when hooked up to my desktop, it only has LSB
noise. The laptop only puts 5v on the
serial port, vs 10v for the desktop, but it is odd that it works at all, and
just degrades the values. Phil is going
to make an RS232 buffer and see if that fixes the problem.
One really nice feature of the new setup is that I wired it
up so I can control the test stand solenoid with the serial DTR line, instead
of having to run a separate parallel port cable from the computer.
Big Frame Hop
We securely glued the foam pads on, so we dont have to rely
on duct-tape any more, and Bob cleaned up a lot of the wire and hose routing,
so it is starting to look really good.
I changed the electronics box so that it can control a
single engine in the center with a solenoid signal. We will eventually be putting the throttled ball valve in the
center, but this allowed us to stick a 70 pound thrust motor in the center to
effectively just lighten the lander mass for the attitude engines. We might wind up doing this for the early
manned flights as well jet the big motor so that it makes enough power to
almost lift the vehicle without a pilot, and just treat it as an on-off motor,
letting the fast acting attitude engines do all the throttling just like on the
small vehicle. That lets me dodge the
motor-response time control law issue for a while.
Bob is going to be building mounting plates for the big
motor and adding a shelf for the computer next week (the computer is currently
bolted where the pilot is supposed to stand), at which point we will be just
about ready to strap in our first pilot a heavy punching bag donated by
We loaded up six liters of peroxide and pressurized to 500
psi, which should be good for around six seconds of flight. Gain was set at 0.010.
The central lifting engine worked fine, allowing it to lift
off with a lot less throttle than with just the side engines. I jostled it off the ground a bit, then let
it fly up to a reasonable height. I let
it come down a bit harder than I wanted, and the computer died. Resetting did bring it back, so it was a
transient effect. From the
accelerometer logs I was able to tell that the computer was ok when it hit the
ground, but there was a fairly severe +/- 4G acceleration at impact. The closed cell foam isnt nearly as soft as
the open cell foam on the small lander, so things dont get quite as soft of a
We have video of this, but it will be a few days before I
can get it on the web.
We opened the electronics box up and checked things out,
looking for something that could have caused a temporary reset. Twisting the PC104 stack is a possibility,
but one of the power leads to the CPU board screw terminals was relatively loose
again, so that is our leading candidate.
Russ pulled the little terminal block off the CPU board and directly
soldered wires to the board, and I have it all back together in that form
now. I tried to move our relay driver
board off of the top of the PC104 stack and onto the box lid to reduce twisting
on the stack, but things didnt quite work out, so it will probably have to
wait for electronics box 3.0 and a major reorganization.
If I had been a little more delicate with the throttle, this
would have been flyable for the proper amount of time. However, we are still planning on testing my
new asynchronous flight control code next week, which will hopefully make it
smoother and more responsive.
The back-and-forth roughness is proportional to the sensor
latency plus the propulsion system latency times the engine control authority. The small landers engine arrangement lets
it fly smoother, because the engines have less of a lever arm, and the landing
gear is extended out past them. We may
want to consider moving the engines on the big platform, or testing again with
the short form after we work out all the control system issues.