September 18, 2001 Meeting Notes
I wrote new graphing software that displays a lot more of
our telemetry data, and organizes it better.
We started looking at GPS outputs in our logs today. The positional data drifts too much to be
useful for any active control, but the lat / long velocity data seems to be stable
and precise enough for dynamic use coupled with an inertial system. Unfortunately, the altitude velocity doesnt
seem to work as well, because it didnt register much of any speed even on the
fast launch we did today.
Russ painted the big lander tank so we wont get carbon
fiber itches as much while handling it.
Russ finished the layout for new motor drive board, but we
dont have it built yet.
Welded on new mounting brackets for the seat belt at a lower
Built new braces for the throttle and joystick platforms.
Added top braces between the tank supports.
We have two ten foot long by two foot diameter filament
wound tubes on order for building our first streamlined (unmanned)
vehicle. The total vehicle will weigh
about 200 pounds, holding the same main propulsion system as the manned
lander. The second tube is just for
getting some experience machining filament wound structures. We will probably try and cut a hatch in it
as practice for the next larger vehicle.
The big lander still needs to have one of the support legs
re-tapped, so we werent able to fly it today.
Instead, we got the little lander back out to see how it worked with the
new asynchronous flight control logic.
We had to wait for a big thunderstorm to blow past us, so the air was at
100% humidity, making for pretty cloudy runs.
Initially, we just left the engines pointing straight down,
because we didnt want to mess with canting them by jamming spacers into the
engine mounts again (the big vehicle has smoothly turning roll adjustments),
but it wouldnt fly straight at all like that because it was trying hard to
make a roll correction happen that never would. The async control logic doesnt have an option to ignore roll
control, so we got out some spacers and properly set the engines up.
The next flight went perfectly, with a couple quick
maneuvers. The async control reacts
amazingly well, tracking the joystick position within a quarter second, and
that is only limited by the rate curve I set for adjustments. I suspect I could tighten that up
significantly more if we wanted even quicker response. The small lander has the engines in closer
to the centerline, which gives it less control authority, which reduces the
overshoots with the async control method.
The big lander should be much smoother when we try flying it in the
short form again.
We loaded three liters for the final flight. I intended to fly it up about thirty feet,
higher than we have taken any of the vehicles.
It popped right up there, and was easy to control coming back down. If I had known it was going to fly so well,
I would have hovered it at the top for a little while.
The async control is clearly superior on both vehicles, so I
am going to remove the old PWM support completely. The back and forth roughness is the only drawback, but the
perfect control more than makes up for it.
I can probably make a predictive software model for the vehicle response
and make it a lot smoother, but that would require some vehicle and load
specific tuning. Removing hardware
latency would make things better in every way, so we are looking at a couple
more things that can be done there. I
have inquired to KVH about getting gyros with greater than 100hz
bandwidth. Ideally, we would want 1khz
bandwidth, even if it was noisier. Russ
and I briefly talked about making attitude engines specifically to reduce
latency in thrust generation, even if they were less efficient or rougher. We could tap some extra holes and cut an O
ring groove in the bottom of a solenoid and create an engine that bolted
directly on the solenoid without a fitting in between, and it might be better
to have catalyst right at the exit of the fitting, without any kind of a
We have a few things we need to get before this Saturday:
Bob needs to fix the support bar that galled.
Russ or Phil needs to finish the new motor drive board.
Our new peroxide shipment needs to arrive, and Phil and I
need to go get ten gallons.
The plan is to do a ballasted hop with ten liters, then
immediately load it with another ten liters and have our first passenger climb
on. Each hop will only be about six
seconds. If everything has gone well,
we will probably load up a full five gallons for a longer manned flight.