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Feb 8, 2001 meeting notes

Feb 8, 2001 meeting notes:

Location: Long Range Systems

In attendance:

John Carmack
Phil Eaton
Russ Blink
Bob Norwood

Next meeting at Long Range on Thursday at 6:00, which should give us time to get things ready for the next flight test.

New supplies:

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

On order:

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 weren’t strong enough to open all four solenoids at the same time.  The new batteries worked perfectly.

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 didn’t 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 time.

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 tube sleeves.

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 problem.


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 don’t 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 purposes. 

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 the tethers.

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 updates.

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.


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