Nov 21 meeting notes
Nov 21 meeting notes:
Location: Long Range Systems
In attendance:
John Carmack
Phil Eaton
Russ Blink
Next meeting: next Tuesday at LRS
We just had a short session today due to the holidays.
We have a delivery date for our 90% peroxide: Dec 6
I finally got a USB joystick for the laptop.
I am going to see some commercial property this week that I may get for us to
work in. It apparently has enough land that we could do tethered flight
tests right outside the shop.
Today we tested the water flow rate of the latching bottle valve over a range
of pressure.
Manual bottle valve to latching valve to 8' of 4 hose, 200ms pulse:
50psi 100ml/s
100psi 200ml/s
150psi 257ml/s
200psi 295ml/s
250psi 325ml/s
300psi 350ml/s
350psi 360ml/s
400psi 385ml/s
This was obviously tailing off pretty fast. We then removed the long
hose and crammed our collection bottle right up to the launch valve, and it
flowed 660ml/s. That was a pretty surprising amount of loss in the hose.
We need to test with a one foot section of hose to determine if it is the
actual diameter or just the length that caused the loss.
Still, it did show that we can get >500ml/s through the launch valve,
although depending on the engine chamber pressure, we may need >500psi of
tank pressure.
We will only need about one foot of flexible hose in the dumb rocket, but we
may need to go to 6 hose for it. We still have the option of rigidly
assembling the tank, fill junction, launch valve, and engine if we use Russ's
straight out manifold, but that might put too much stress on the fittings.
I have ordered a bunch more fittings to restock us from www.anplumbing.com:
1/8 to 3, 1/8 to 1/8, 1/4 to 4, 1/4 to 6 fittings, and a few 6 hose ends, but
I need to find some 6 teflon hose.
Phil finished the six channel driver board for the lander (four differentially
modulated main engines and two roll control engines):
After getting over the minor mishap of trying to use a null modem cable
instead of a straight through parallel cable, and adjusting some code for the
fact that he wired D1-D6 instead of D0-D5, the board worked fine.
Russ finished the distribution manifold for the lander and we plumbed and
wired everything together for testing. We don't have a frame for the
lander yet, so all the solenoids were just tied down in a row.
When we connected it to the tank and opened the launch valve, we had water
leaking out of almost every connection (we were still at 400psi). We
tightened everything down, but there was still leakage from the hose ends we
assembled last week.
We went ahead and played with it while it was leaking. My pwmdialog.exe
program wasn't set up for the shifted control bits, but we were still able to
throttle and differentially modulate the flow with the joystick.
We still won't have peroxide next week, so the major goal will be to get all
of our lander plumbing leak free. We can probably also do some more flow
testing of different large motor configurations.
I should have a telemetry based PWM driver done by then.
Question: what type of batteries should we be considering for the lander?
Will standard radio control toy battery packs work out ok? I am hoping
that we can run all circuitry off of a single 12V power bus, instead of having
separate batteries in the transceivers, microcontrollers, and solenoid
drivers. We will probably need some switching regulators to do that.
We should consider meeting at Norwood Autocraft again to get Bob to help us
with the lander frame.
Week after next, we will probably delay the meeting until Thursday when the
peroxide gets in (hopefully), and then we can get back to serious engine
testing.
We should try and get some of the different injector plates we discussed made
by then.
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