4 and 8, 2003 Notes
Big vehicle work
We installed a new crush cone this week, and this time we drilled
two 2 diameter air vents to release pressure as it is crushing. Making a rupture disk for only a couple
PSI is fairly difficult, as even a little strip of tape can often resist for
force than that. When we make a version
2.0 of the vehicle assembly, we will probably move the nutserts up a little
bit, shorten the crush cone by about six inches (which will allow it to be made
from two standard sized pieces of sheet metal, without welding two extra
corners of metal in), and put reinforced vent ports into the cabin section, so the
disposable crush cones dont require the extra fabrication steps. The vents can probably be covered over with
down-facing vents, and just left open.
The hatch is nearly completed:
It is made up of several parts: the cabin skin (0.125),
hatch reinforcement (0.25), hatch sealing lip (0.25), hatch (0.25) with
gasket, and four hatch dogs. The hatch
dogs have T handles on the inside, and will have a sealed bushing on the
outside that can be rotated with an allen wrench. The hatch has a handle on the inside, but we are probably going
to have to have a removable external handle to pull it into place while the
dogs are tightened.
We will be doing a rough fit-up test on a real tank in the
next few weeks, but we dont intend to actually permanently bond it to the tank
and pressure test it until we have absolutely everything done in the cabin,
because working on it with an 8 long, 800 pound tank attached will be quite a
bit more cumbersome.
Phil closed himself up in the cabin for a while to see what
it was like. After 30 minutes, the air
was damp and stale, but he didnt have any real problem with it. Our plan is to have an air bottle that
maintains cabin pressure, but have an adjustable vent valve that is always
leaking air out of the cabin. This should
control temperature and humidity sufficiently.
The launch-to-landing time for
our X-Prize flights will be right at 15 minutes, but there will be a healthy
margin in the air supply to hopefully make up for any unintentional leaks.
We bought a new welder on Ebay to help with our larger fabrication
work. This is the third welder we have
at the shop we bought the last one larger than we thought we would need, but
welding thick aluminum was a lot harder on it than we expected.
Also on the topic of used equipment, I spent several hours
working on duplicating the floppy boot disk for our CNC mill, because it is
giving occasional errors on bootup, and I dont want a useless 4000 pound ornament
in my garage if the disk dies completely.
It was one of those annoying discovery processes, where I learned far
more about floppy formats than I really wanted to know. The mill drive is a double density drive,
but the disk is a high density floppy, which causes some problems until the
density hole is covered up. More of an
issue is that it numbers sectors from 0 instead of 1, making most utilities
unable to deal with it. I finally got
all the data pulled off with low level linux utilities, but I still have to do
a custom format before I can write it out to another disk. Someone please tell me where I can find a
nice little utility (windows or linux) that does all this crap automatically
I looked for a while, but gave up early to
try pulling the data myself with the linux tools. I probably should have kept looking.
Small vehicle work
Here is a shot of the engine bulkhead after the
Fastblock-800 coating, also showing the paintball tank and large solenoid we are
using for drogue ejection now:
Installed in the vehicle, showing the releasable chain that
holds the main parachute, and the fill ports for both the drogue nitrogen tank,
and the main tank:
The electronics bulkhead has gone through some changes. Russ finished the next rev of our driver
board, which incorporates four motor drives with very large transistors, and eight
solid state relays. We ran the engines
in buzzing-back-and-forth mode for several minutes, and they barely got warm,
so this design seems solid. We did have
one odd flaky problem that went away after Russ touched up the soldering, but
this is still considered a prototype board for us. Because the monster solenoid we are using for the drogue ejection
system draws 30 amps, we have to include a separate 40 amp solid state relay
for it, since the board relays are only good for 10 amps. Since we havent built our next-gen power
supply board (and probably dont have room for it on this layout anyway), we
pulled the dual small batteries, and just moved to a single large battery for
the main system. We also upgraded the
actuator battery, but that probably wasnt necessary. The old actuator systems drew almost no current when they werent
switched, so I just left the battery permanently wired to the board. The way the new motor drives are set up, the
current draw is high enough that I now switch both batteries with a DPST main
Having a dedicated connector port for a dual battery charger
makes recharging the system much nicer.
On all the old systems, I was always clipping a charger to the batteries
with alligator clips, then moving it to the other battery later. Now we just plug it in. One thing that we are already missing from
this system is a nice, bright power light.
We learned the usefulness of that on earlier systems, but we forgot to
add it to this one. Well get that in
We are having a pretty distressing issue with our wireless
communications when the flight computer starts sending UDP telemetry packets,
the TCP telnet connection and ICMP pings start getting dropped. I had seen signs somewhat like this before,
but it has managed to degenerate to a serious issue, and Im not sure why. We may have messed up the Esteem on the
flight electronics by pulling it from the case and building a custom shield for
it, but it is such a reproducible problem that it seems like a software
issue. We have a spare Esteem on order,
so we will be able to do a swapout test soon.
Resolving this is top priority, but we can do our hover test even in the