Norman Yarvin & Ivan Vuletich
Thank you guys for helping me out! Thanks, Ivan for tieing the 2 posts
together like that. This is going to be a long post so if you're not
interested you can stop here the rest of you.
I have not worked on the Ardupilot code for something like 2 years so I
need to pick it back up again. You may even wonder why I would want to
use that code? Well, I can tell you it's because I have a long
relationship with it I've done so much with it and I just want to keep
using it. I like how it works and I like the ground station and the
tracking and how it works with simulators like X-Plane, Flightgear and
Gazebo. I like mavlink and I like that I can network with it and share
or even control it remotely over the internet.
I like the framework that it has. I like open source.
We need to strip it down and build it back up. I've got reaction wheel
and RCS thruster code I want to put into it. I want to add back the IR
attitude control (this was removed some time ago after the mems sensors
became so cheap) and I want to add the Startracker. I want to keep the
communications framework and all the functionality I mentioned
previously.
I need you guys and anyone else that will keep helping SatNogs and keep
them alive because I want to use them for tracking and data retrieval.
I'll get back to helping them soon I hope. I want to give away about
150-250 tracking units (Just the tracking mount) Which soon I can CNC
the parts for.
I'm finishing up the 5-Axis machine I designed specifically to make
turbopump impellers and we plan to show it off in April at the 2019
Space Access conference. Right now I'm hand scraping and getting the
machine into as near perfect tolerance as I can (which is extremely
tedious work) I have to render the 4th and 5th Axis in steal because
right now they are mostly aluminum.
So I have to keep on this right now to make sure we are ready to unveil
the machine in April. I have a lot riding on that machine because the
funding for it means my partner wants to sell the machines. He wants to
back the turbopump project beyond that so that's what I'm doing.
The turbopump is the heart of any good engine so once that project gets
underway well, you can see how busy that is.
We paved the way with the FAA getting NOTAMS and Waivers for high
altitude balloon launches and rocket launches and they know the plan.
I've also done the work with the FCC, DOT, ATF, DOD, Fire Marshal, The
county and the state.
Some of that has to be gone back over because some laws have changed but
at least I know how to that kind of thing.
I think I have time right now to play with the Startracker while working
on the machine but I can't pick up the ball with ardupilot because it's
just too intense.
All I can do is keep plugging. The machine took 2 years. If things keep
going like they are perhaps in another 2 years I'll have a turbopump.
You guys are welcome to any data I have.
The original ardupilot and the thermopiles makes a great straight up
guidance for model rocketry. That would be so easy and all that
functionality I mentioned goes with it. (Ground station, tracking,
simulation) I think that much is useful to everyone and there is very
little modification needed to complete that.
I can help someone wanting to do that after I finish playing with the
Startracker (because that's about the same load of work) The real deal
though is a project that will have to wait until after an engine is
developed. So it's another 2 years if things keep going the way they
have been. Then 2 years of legal clean up in the end game.
I'm 56 so if I can make it to 66 I might have a shot at this. I think I
can do it. So it may be 20 years total work.
I get help from time to time someone gets interested and we make a leap
here and there. I'm always ready for a leap guys so if your willing I'm
willing.
Meanwhile, I keep making nozzles and parts for people on the side and
helping however I can so if you've got a need for something like that do
ask! And most of all keep looking up!
Monroe
-------- Original Message --------
Subject: [AR] Re: Star Trackers, was Re: Re: Spin stabilized rocket
From: Ivan Vuletich <ivan.vuletich@xxxxxxxxxxxx>
Date: Sat, December 29, 2018 12:50 am
To: arocket@xxxxxxxxxxxxx
The other wrinkle to consider is that Ardupilot probably uses a flat
Earth coordinate system, with constant gravity acceleration and the
ground at z=0. Assumptions which are pretty good enough for a UAV.
A good coordinate system for a sub-orbital or orbital rocket would be
Earth Centered Inertial, which is Cartesian (x,y,z) with the origin at
the Earth's center. At the very minimum you will need spherical Earth
altitude and gravity functions, but WGS-84 altitude and gravity would be
better and match up with your GPS. On top of that, the Earth's surface
is spinning wrt to the coordinate system as Norman has pointed out.
On 28/12/2018 9:55, Norman Yarvin wrote:
On Wed, Dec 26, 2018 at 11:07:55PM -0700, Monroe L. King Jr. wrote:
That all makes sense. The problem I have is we have code with an earthPart of what might be puzzling is that there's a very good chance that
frame and we need to go to an inertial frame and I don't know how to do
that. I don't even know where to start to rewrite the code.
the code already implicitly assumes an inertial frame (as in not
having any corrections for Coriolis force and such) and the existing
users are just accepting the resulting inaccuracy. In that case it's
mainly the initial values that need changing: instead of starting at
zero m/s, you'll be starting out moving with the rotation of the
earth. Code alterations might then be needed so that the atmosphere,
too, can be modeled as moving at the same velocity.
By the way, with Ardupilot, the software assumes that it will
constantly be making corrections as a result of feedback. Coriolis
force errors are infinitesimal at first, so when flying a plane the
software doesn't have any difficulty correcting them out just as it
would correct any other random perturbation. But when going for
orbit, the assumption that minor corrections can constantly be made
doesn't apply: you may be doing one burn, waiting, then doing another.
During the wait period it's impossible (or at least much harder) to
correct the flight path.