May 15, 2001 Meeting Notes
½ check valve
another small 12V polypropylene solenoid
More 1/4m to 1/8m fittings
Wire tie assortment
Hose clamp assortment
-6 hose ends
Various AN fittings
Two liter flasks
½ servo ball valve
New electronics box
Waterproof connectors and switches
Water hose reel
-10 hose, hose ends, and fittings for running the ½ valve
on the test stand
We made a few plumbing improvements today, putting the aluminum
6 hose ends on the test stand hardware, and converting to a 4 swivel fitting
on the fill cart from a 3.
We hopped the lander with three 800 ml peroxide loads, but
we didnt have as good of results today due to high winds.
Russ is going to be out of town, so next weeks meeting is
pushed to Wednesday unless someone needs it to be Thursday.
380 psi, which was only just enough to pick it up with
basically full throttle. Performance
seemed down a bit from the last runs.
You can see the strong wind blow away our leveling pads of
foam after liftoff.
Shows the need for active roll control.
Second run ended when the sensors saw a huge rate jerk right
as the last of the peroxide was expended.
Making max corrections, and not making much headway. Probably fighting the wind.
In the future, the camera operator should stand off to the
side so that all four engines are visible, and the fore/aft rotation can be
seen more clearly.
Raised pressure to our full 430 psi. The altitude is still easily
controllable. Now that the latencies
are down, throttle response really isnt all that much different than in the
It tips over a fair amount and comes down pretty fast, but
the landing gear works perfectly!
The second run is making its maximum correction at every
opportunity, but it cant get it to turn.
The third run displayed the same rate jerk as the last of
the peroxide was expended.
On the first hop I made some fairly strong manual input on
the joystick to try to correct for the wind, and while it probably helped, the
attitude correction couldnt force it all the way over to where I was
The second hop also leaned over fairly quickly.
We noticed a fair amount of leakage out of the engine top
The system did not have enough control authority to deal
with the winds. Most of the runs had it
doing as many attitude corrections as it was allowed in the same direction, and
still slowly tipping away.
On Saturday when it was calm, each attitude correction pulse
gave around 15 degrees / second of rate change. For today, I had added one more minimum frame of delay between
attitude corrections to account more for the low sensor bandwidth, which
reduced the maximum corrections to once every four frames from once every three
We had some leakage out of the top closures on most of the
engines, which may have been skewing the relative performance between pairs.
Engine zero (left side) also had a couple odd things happen. When we first started the water test, it
didnt fire. It turned out that the connector
had been bent a bit when we were connecting a manually switch to that solenoid
last test. We closed up the connector a
bit, and it worked after that. The
other odd thing is that the solid state relay driver board shows a faint light
in the activity LED even when there isnt a signal. There might be some kind of a voltage leak, which might make the
valve close slower than expected.
The large sensed rates at the time the peroxide runs out are
interesting. It seems to be a hard jerk
which is shocking the sensors, because it definitely isnt actually getting to
the rates that it indicates. Im not
clear why the final depletion of the peroxide, even if it was uneven between
engines, should be a stronger jerk than the normal attitude correction pulses.
While foam mounting the electronics box seems to have solved
the jerk behavior of the gyration gyros, the 10hz sensor bandwidth is proving
to be an even bigger issue than expected.
We really want a sensor that will show the full updated rate within 33
msec of the completion of an attitude adjustment pulse, which seems to
translate into a 60hz sensor bandwidth.
While looking for a distributor of BASE silicon gyros, I
came across this company:
I have requested information on their three-axis gyro that
has 70hz bandwidth and no listed G limit, as well as the BASE parts.
If nothing works out in the next couple weeks, I am going to
buy two of the $1500 KVH fiber optic gyros.
We have an electrically actuated ball valve on order from
We will need to drill the ball vent ourselves, but otherwise
it should suit our needs. It is a ½
valve, so it should be good for 600+ pounds of thrust as a central lifting
engine for the manned vehicle.
Control is by connecting 12VDC to two wires, reversing the
polarity to reverse the valve direction.
Feedback is by a potentiometer on the motor shaft. We should be able to run this with two
solid-state relays and some diodes, and read it with one single ended A/D
I had been looking for a valve that just took a signal level
and opened to that level, but now that I think about it, having binary
directional control with feedback is actually a lot better, because it removes
a level of black-box computer control in the valve, and lets us actually measure
operating response instead of trying to infer it. It is also nice to be able to avoid having a D/A control signal.
With this resolved, the propulsion system for the manned
vehicle is now clear: a central lifting engine run by the ½ servo valve, with
four outrigger engines run by the medium sized (10 amp, not 30 amp) NOS
solenoids. I propose that the outside engines be positioned exactly the way
they are on the demonstrator, so that they provide lift as well as attitude
correction, which will make motion of the CG (the pilot) a lot less
critical. Those solenoids will flow
around 50 pounds of thrust at 400 psi, so the platform should be able to lift
off and hover without the central engine firing at all, when there is no
pilot. The central engine should
probably be sized around 600 pounds of thrust.
This basic engine configuration, with higher and higher
performing central lift engines, should take us all the way through the
vertical dragster and to the space shot vehicle.
The propellant tank is now the number one question for the
manned vehicle. One path would have us
use 150 psi tanks slightly over spec, starting at around 200 psi. If we target this pressure instead of the
400-450 psi we have been doing all of our work at, we would need to more than
double the engine dimensions. Isp would
also suffer a fair amount, but that isnt a critical issue.
I inquired at Lincoln composites about using their NGV
division tanks. They would be massively
over-built for our needs (3000+ psi operating pressure), but they are built to
survive car wrecks, so they would be very safe to use. The response I got was probably not a qood
idea, but they were vague about potential contaminants. If the materials are all good, I may get one
for us to work with anyway.
I have a couple other inquiries out for tankage for the
manned vehicle. Our desired pressure
(500 psi) is in sort of a no-mans land for commercial tanks. There are lots of good 150 psi composite
tanks for water processing, and there are lots of 3000 psi tanks for NGV,
scuba, compressed gas, etc, but not much in between.
Neil: at one of the very first meetings we had, you had dug
out a big NGV tank. At the time, it was
far larger than what we wanted, but it might be exactly what we need now. Fifty pounds of tank isnt that big of a
deal when we have a pilot dominating the dry mass.
Our ideal tank has pipe fittings on both ends made of
aluminum or stainless, holds between 10 and 20 gallons, has a working pressure
above 500 psi, and has a polyethylene liner, or a stainless / aluminum core.
Stuff To Do
Sensor board microcontroller rework: 60 hz synchronous, read
axis in reverse order, read accelerometer
(After reviewing all the data again, I dont think we will gain anything
by going to 120 hz, because none of our problems are related to integration)
Drill out the engine nozzles to 0.275 from 0.25
Make another small engine retainer plate so we can run the
test stand without stealing it from the VTVL.
Test drill ball vent on our old valve
Make a new custom tank manifold for ½ plumbing (might want
to wait on seeing the big tank)
Pick up the rest of our plated foam
Pick up tables
Tool chest and organizing bins
Follow up on the NPT blow off valves
1000 psi nitrogen regulator
6 of steel hard line for pressure transducer isolation (we
can probably just chain some fittings together if
you dont find anything handy)
Update 3D simulator to use the new control laws, tank blow
down, and the measured angular rates
Investigate the dim signal light on the driver board
Investigate the strange warmup behavior with manual joystick
Investigate the improper angle exit with joystick input
before I commented that check out
Investigate the lost pilot packet exit
Follow up on gyros and tanks.
Gyro integration initialization by accelerometer gravity
Instant graphing software for guidance logs
Test stand runs:
Log tank pressure blow down with water, just use the small
solenoid with no engine attached.
Run the small engine for 30+ seconds
Run the small engine with the insulated chamber pressure
Run the small engine with different PWM attitude correction
trains to watch recovery times
Run the small engine with the plastic solenoid at 125 psi (I
have seen mixed data on the peroxide compatibility of polypropylene)
Run Juans engine at 150 psi with the big piloted solenoid
Run Juans engine with the super big shot solenoid and 6