Feb 8, 2001 meeting notes
Feb 8, 2001 meeting notes:
Location: Long Range Systems
Next meeting at Long Range on Thursday at 6:00, which should give us time to get
things ready for the next flight test.
AN 3 and 4 thread taps
Teflon O-ring assortment
Level and plumb bob
Extra safety goggles
More 1/8 check valves
Two 7v RC car batteries and charger
Clip connectors for solenoids and batteries
More washers and screws for solenoid plate spacers
Oxidizer hazmat labels
PC104 PCMCIA card interface
Two wireless Ethernet PCMCIA cards
Small innertube for VTVL base
Still to get:
Project box for flight computer / batteries / sensors
More wiring terminals and crimp connectors
The major problem last week was that the batteries werent strong enough to
open all four solenoids at the same time. The new batteries worked
We had some leakage at the top of the engines last time, so we were planning on
pipe taping all the top closure threads, but one of the new Teflon O-rings fit
right in, and worked great.
We made all new catalyst packs so we could guarantee that all four engines were
the same. We tried a small number of very compressed disks, and they
worked fine. We used one inch of catalyst disks (15 disks) compressed to
one half inch, supported by a length of copper tube inside the engine.
This is a significant pressure loss, but it runs smoothly. We could make
much shorter engine tubes if we wanted to, but the extra chamber volume is good
for smoothing out the pulse width modulation.
We replaced the one fixed 90 degree fitting with a swivel so that all the sides
had identical plumbing.
We adjusted all the engine mountings with a plumb bob so that they were all
pointing close to straight. This was a little bit troublesome because the
legs didnt hold the platform in a completely definite position, so pushing
down on it would move things around. We are going to build four small
plumb bobs that will fit inside the engines and come out the nozzles, so we can
align all four engines at once.
We flow tested the entire setup by loading it with water and holding four cups
underneath the engines, then running through a range of throttle positions.
Everything came out nice and even.
We had cinder blocks for the chains this time, so we gave it a bit more slack.
The blocks work perfectly for our purposes.
The initial engine puffs were very cloudy because there was still lots of water
in the system from the flow tests, but the liftoff was nice and straight this
On the second hop, it pulled one of the tethers taut, which caused it to rotate
quite a bit. It came down on its side again, and cracked one of the leg
The tethers definitely cause a serious attitude change when they come taut.
If we had more slack, we could have taken it up and down without a serious
Bob is going to add bolted cross
members between the lander legs to replace the tension wires. The wires
worked fine when we just picked it up and dropped it, but dont provide any
support when it comes down at an angle. The bendable legs also make
aligning the platform more difficult. I want to see about mounting a plate
under the tank manifold and placing that on top of an innertube for the primary
weight support, and just use the surrounding legs (with the cross ties) to
rotate the platform when it comes down at an angle.
This test satisfied us that the engines produce even enough thrust for our
We are going to try to run with an attitude sensor next week. Initially it
will just be the guts of a GyroMouse, which will only give us pitch and yaw, but
it should be sufficient for stabilization. We will double the length of
We may try to put together our first 3DOF attitude sensor with the rate gyros if
we have time. Output will just be a constant ascii serial stream with
three 16 bit hex numbers per line, one for each ADC from the rate gyros.
Other stuff to do:
Build a solid box for the solid state relay driver board, batteries, and rate
sensor, and bolt it to the platform. We will probably do this before we
get the full flight computer going.
Tap out one of the 1/8 NPT ports on the VTVL manifold to 4 so we can get rid of
the adapters to the fill connector.
Take our original test engine and drill a chamber pressure port.
Turn down the larger copper pipe to make better pack supports.
Russ took lots of pictures during the construction of the VTVL engines, so I
need to get a real web page together for all of them and all of our past
I am going to try and have the flight computer booting on battery power from
compact flash sometime soon.
Finish four of the engine alignment tools.