Jun 12, 2001 Meeting Notes
1500 psi regulator
Pressure relief valve
½ quick connects
Etched sheet steel
AMP multimate crimper
AMP CPC connectors for new electronics box
The fiber optic gyros from KVH finally arrived, but
unfortunately, the demo kit only included 10hz digital output, which isnt fast
enough for us. They have agreed to swap
the units for analog output ones, but I dont have a firm delivery date.
I did learn something important playing with one of the
One of the things that I had been disappointed about with
our previous gyros was that the highly scientific test of wiggling the sensor
board around by hand would usually result in a significant drift in the
integrated positions when it was set back down in its original position.
I had been assuming that the problem was due to the low bandwidth
of the gyration gyros causing it to integrate poorly as the rate was changing.
I was surprised to see the same thing happen with the FOG. If you leave it on a flat surface and rotate
it back and forth, the integration performs very nicely. However, if you pick it up and wiggle it
around, then set it back down in the original spot, there will usually be a
significant error in the integration.
I should have realized this at the beginning, but it turns
out that you cant integrate the axis independently. The extreme example is this: with the gyro flat on a surface,
rotate it clockwise until the integrator reads 90 degrees. Then tip it up towards you, not changing the
integrator at all, because it is an orthogonal axis. Then tip it to the left, again on the orthogonal axis. Then lay it back down in its original
position. The integrator still reads 90
degrees, even though it is back in its original position.
At small angle changes the effect is much less significant,
which is how we have gotten away with it so far, but once we start wanting to
tip it aggressively for translational maneuvers, we are going to need to deal
with it correctly.
The right way to deal with it is to maintain a full
coordinate system, and rotate it each sensor sample, instead of
integrating. I will also have to give
some thought to the engine controls, given that the joystick angles are going
to be in absolute world angles, which will have to be transformed into the
local coordinate system.
The FOGs are also limited to 100 degrees / second, down
somewhat from the 150 degrees / second of the gyration units. 100 d/s is not all that fast, but should
suffice for us. We wont ever intend to
rotate even half that speed, but once we start flying faster, the aero loads
may push it around more. I think the
trick will be to be correcting very rapidly, so that even if a strong force
starts rotating the vehicle, it wont have much chance to build up rotational
Bob has one quarter of the frame tacked together, and should
finish it up in a week or so. It is 13
in diameter, but the legs disassemble so it can be moved in a normal truck.
It seems to be a truism that things always weigh more than
you expected. Once everything is all
put together, the vehicle is probably going to be 150 pounds dry. With a light pilot, five gallons of peroxide
should give 15 seconds of flight.
Our second motorized valve for the master cutoff switch is
on the way, and Russ is about to start machining the custom manifolds we need,
so we should be able to get the complete plumbing together in a couple weeks,
with Juans motor standing in until we build our big one. I am probably going to need to order some
more 6 hose
We are still discussing pilot facing tank versus pilot
facing away from tank.
We are still discussing what the pilot will use for throttle
We are going to leave the bottom frame cross brace off on
the pilot corner, so a bailing pilot wont have anything to hit. The platform is plenty stiff to not be
impacted by removing it, and it will still have the pilots standing platform
by the tank providing some bracing.
The term servo valve is a little bit ill-defined. It is sometimes used to refer to any DC
motor valve, but seems to be more properly used to refer to a valve that has an
internal closed loop control system, like model airplane servo motors.
The kzco valves we are using are probably better referred to
as dc motor valves, because all they have is two power wires, which you can
put current through either way, and a potentiometer for feedback. This involves somewhat more work on the
flight computer, but is probably better in the long run, because your telemetry
stream can have where the motor actually is, and what you are trying to do
about it, instead of where you are telling the servo is should be.
If you just apply power to the motor, it gets up to speed
very rapidly, but if you remove current, it takes a considerable time (quarter
second or so) to coast to a stop. If
instead of just removing power, you short the leads together, the motor acts as
its own brake and stops as rapidly as it starts.
I burned out four solid state relays and two motor driver
boards working with the motor, due to a lack of respect for the inductive
The driver board has instructions like for maximum life,
slowly increase the motor speed over several seconds, and wait several seconds
before changing directions. Well, when
trying to match a valve position to a moving joystick throttle, you wind up
running full blast all the time and making a few reverses a second. I fried some things (reminding me why I like
I eventually got it all working reliably by using
electromechanical relays, but Phil is going to try building a proper
transistorized driver that can do what we need.
RemotePilot.exe now has starts making a loud beep after a
certain amount of time has gone by, as a crude propellant warning.
An updated Lander3D.exe is available at: media.armadilloaerospace.com/misc/Lander3d.exe
GraphLog is updated for three-axis display.
We talked a bit about where we are going after the first
manned vehicle. The basic goals will
Mass ratio of two or better. This will be the first time we are actively trying to build
Supine pilot. It
will pull several Gs.
It wont be going to space, but it will be going high enough to want pressure.
One question is if we are going to make another small
vehicle, or if all future vehicles will be capable of holding a pilot (they
will all still be flown by remote control during testing, of course). Small vehicles would be easier to transport
and would use less peroxide, but they wont really be much easier to build, and
even if they are built, they wont answer all the questions that manned
versions will need to address.
The plumbing will probably be identical to the current
manned vehicle, it will just be different tankage, structure, and a somewhat
larger lifting engine.
The FAA issues will have to be addressed.
Master To Do List
Slightly drill out demonstrator engines to
account for the extra weight of the new electronics box.
Experiment with slower pulse rates on the VTVL,
because the bigger valves may need to be slowed down.
Finish new electronics box
Make a milled mounting corner for FOGs?
PC104 SSR board
Better 5V power regulation?
Manned vehicle issues
Closed cell foam for base
Motorcycle throttle potentiometer
Three custom manifolds
Tank cleaning and passivation
35% peroxide locally
Pump for peroxide loading instead of vacuum
Buckle the pilot in?
Pilot communication headset
50lb thrust engines
Better O-ring seals?
Long burn tests.
Pack wear tests.
Good attack/decay tests for pulses.
High pressure tests
NPT burst discs, both 1/4" and
1/2". We may want both 600 psi
burst and 1500 psi burst.
are we ok with the relief valve?
Gyro angle initialization by accelerometer
Metal line for test stand chamber pressure tap
Pack transducer with brake fluid?
Cooling vests for hazmat suits
Continue pushing Porvair about pure metal foams
Follow up with FAA if no response after 30 days
Tank level measurement by pressure / temperature
600lb thrust engine
Drill ball valve vents
Drill out Juan's engine for 150 lb thrust?
Flash a light on vehicle every second for
telemetry video sync
Lifting motor valve driver
Make a PCB for it.
Master cutoff valve driver
Basic stamp and flightcom development
Make a PCB for it.
Vertical test stand
Clean out Neil's tank, or get another big one
from Bob for the test stand
Integrate test stand electronics into a single
box and cable.
55 gallon plastic drums for water at new site
Ballistic demonstrator flight
Ultrasonic / radar altimeter testing
GPS / accelerometer altimeter testing
802.11 range extending devices
Hybrid / biprop development
Investigate separate pressurization tanks
Pressurized cockpit capsule
Really fat tanks
Satellite phone telemetry systems