August 11, 2001 Meeting Notes
I made several reliability modifications to the electronics
box that were tested today.
The small battery that ran the electronics was replaced with
another 3.3Ah battery identical to the solenoid driving battery. This lets the computer stay on for almost
three hours without a problem. The
electronics draws about 1.2 amps constantly, while the solenoids draw up to 35
amps during operation, but that is only during the variable duty cycle of a 10
second or less hop. The electronics
battery always needs more charging.
I installed a better main power switch. The previous one was a little light for my
tastes, and might have caused a voltage drop during operation. Since we moved to dual batteries, we have
had the solenoid battery wired directly to the solid state relays without a
power switch, but there doesnt seem to be any measurable current leakage. One effect I do need to watch for is that
this means that the SSR board has live current unless I disconnect the
battery. I once got some sparks when I
accidentally let the board rest against a metal standoff.
When we wired in the second battery, one of the wires was
crimped to an improper connector gauge.
I replaced this with an appropriate one.
The bare wire screw terminals powering the PC104 stack were
rather loose. On inspection, several
screw terminals needed tightening. In
the future, I am going to insist on ring terminals for all of our boards, and
we will probably replace some of the connectors on the commercial boards we
We didnt experience any electronics anomalies, so I hope
all the issues are addressed. I also
got some copper bar stock that I will probably use for main power and ground
distribution in the future, replacing the jumpered terminal strips I am
currently using. I have found some
cases where moving a power or ground lead from one terminal to another has
effected A/D values noticeably, so I am going to give everything a big, fat
hunk of copper to move through.
Phil outfitted the test stand with a metal spring to keep
the slide against the load cell. After
we broke two load cells with bounces on the 70 pound thrust engines after the
warm up pulse, we had taken to using rubber bands to make sure it stayed
Bob fabricated a lever handle to help us pop the fill cart
quick connect off under pressure. It is
certainly an improvement, but we could still use something better.
We built all new catalyst packs for all four engines, with
15 discs compressed into the 13 disc sized spacer.
It started sprinkling before we got the first motor fired,
but we went ahead with it. It performed
as expected, still slightly rough, but with good enough characteristics. Oddly, there was what looked like a thin
stream of liquid in the center of the otherwise transparent exhaust jet. It wasnt a typical cloudy run, so we had
never seen an effect like that. We meant
to take the motor apart and see if it was tunneling all the way through the
pack, but we didnt get around to it.
It started raining hard by the second motor test. This one was also odd. It was a very cloudy exhaust, but the thrust
was extremely smooth. Performance was
down from about 70 pounds to 65 pounds.
We dont know what to make of these results yet. It may be weather related. Our previous tests have been in nearly 100 degree
weather and very dry conditions, while it was down to 80 or so and 100% (and
then some) humidity for todays tests.
We may just go back to completely filled cat packs, and live
with the roughness, or try compressing even more in to keep a lot of pack but
smooth it out a bit.
Small Lander Hops
We did a couple tests to see if the electronics were holding
On the first hop, something was clearly wrong it rapidly
started to flip over. I was able to set
it down before it could, but when I throttled up again, it started to flip the
other way. It turned out that two of
the engines had been connected backwards
I have just finished changing the electronics box and our
venting electronics over to a single eight pin connector, instead of four two
pin connectors, so this problem wont be possible in the future.
The second hop worked fine, with five seconds of flight on a
liter of peroxide.
The third hop was a test with a lower PWM frequency. We have been using 30 hz with the small
solenoids, but I am leery about trying to run the larger solenoids that
fast. We did this run at 10hz, and it
still flew fine for five seconds, but the pulses were now clearly audible, and
the control gain probably needed to be adjusted down, because the one push I
made on the joystick resulted in a very fast turn.
We decided to use 20 hz for the big lander. We may make this the default for future
flights of the small lander as well.
Big Lander Work
Bob brought the big frame back with its fresh powder coat,
and, somewhat to my surprise, we managed to get it completely assembled for a
We configured it in its short form, with the engines
directly connected to the main frame, instead of out on braced extensions. This makes it look almost exactly like an
upscaled version of the small lander.
We will probably want to use the long form that will be much harder to
tip over, and has the longer attitude lever arms when we put a pilot on it, but
the short form is probably seventy pounds lighter. We will still try flying it in short form with appropriate
ballast to simulate a pilot, and see how things go.
I ordered four assembled stainless braided Teflon hoses for
the vehicle, but they werent scheduled to arrive until next week, so we made
our own 6 assemblies. In hindsight, we
should have remembered to thread all the hose ends onto the hose before we cut
it into four parts. Stainless braided
hose is a pain to assemble (often literally, due to the sharp little barbs),
because you need to fit a hose end around the outside of the braid, then a
ferrule on the inside of the braid, then screw everything together. I did the first one, then Phils friend
Joseph took over and finished the other seven hose ends. We have been a little spotty with our
success rates on hose ends, but Joseph seemed to have the nack for it, because
none of them leaked a bit.
We bolted the electronics box to the pilots foot plate, and
got all the engine solenoids hooked up to CPC connectors.
Bob had steam cleaned the carbon fiber NGV tank we are using
as the peroxide tank, and we tested it with some 30% peroxide without any
We did a water test with a gallon of distilled water
first. It took quite a while to draw
the vacuum (five minutes?), and about five minutes to load a gallon of
water. We will be moving towards
loading the peroxide in the top eventually, but for now we are just using the
same manifold as the small lander. On
Tuesday, we will probably upsize the main fill cart hose, which will get us
some improvement in load times.
We need to weigh the big lander in this form, but we
estimated that it is at least three times the mass of the small lander. We prepared four liters of peroxide (almost
completely running us dry at Long Range), which should be good for five to ten
seconds of flight, depending on the total mass. The engines are over four times the thrust of the engines on the
small lander, so we were planning on starting at 300 psi instead of the 550 or
so we have been using on the small lander.
Unfortunately, our nitrogen bottle ran out with less than
240 psi in the lander. A 32 liter tank
goes through nitrogen really fast. We
are going to move to larger bottles, and have a company start delivering
nitrogen to us directly.
I throttled it up slowly, because we werent sure what the
thrust to weight ratio was going to be like.
Huge, billowing white clouds came from all the engines. It wound up completely covering the lander,
and it hadnt lifted off. I let the
clouds clear, then gave it full throttle, but it still didnt have enough to
We need to get more nitrogen and more peroxide, then figure
out why all of our engines are cloudy.
We will probably try to fly it again on Tuesday.