[AR] Re: hovering rocket vertical position control
- From: rsteinke@xxxxxxxxxxx
- To: arocket@xxxxxxxxxxxxx
- Date: Mon, 16 Mar 2015 19:14:20 -0600
Thrust vectoring is with jet vanes.
How does Ardupilot do vertical position control?
----- Original Message -----
From: "Monroe L. King Jr."
To:
Cc:
Sent:Sat, 14 Mar 2015 18:58:04 -0700
Subject:[AR] Re: hovering rocket vertical position control
Ardupilot can hover a rocket how are you gimbaling it?
Monty
-------- Original Message --------
Subject: [AR] Re: hovering rocket vertical position control
From: Paul Breed
Date: Sat, March 14, 2015 4:33 pm
To: arocket@xxxxxxxxxxxxx
I made a simple PID loop with vertical acceleration as desired input
variable...
and later had to scale the PID constants by measured tank pressure
(IE
blowdown pressure decay)
My valve was a butterfly not a ball.
It was rated for 100psi I hydroed it to 800 and it leaked.
I ran at 400 psi or less and at 400 psi it leaked just enough to keep
the
cat pack warm.
Paul
On Tue, Feb 17, 2015 at 7:41 PM, Henry Vanderbilt
hvanderbilt@xxxxxxxxxxxxxx wrote:
Leaving aside the algorithm, if you want a dirt-simple rig for
initial
testing of purely your vertical position control, here's an
(untested)
thought: A simple compressed-air rocket, sliding on a vertical rod,
fed by
a long loop of flex-hose, might let you work out the initial control
bugs
cheaply.
Henry
On 2/16/2015 4:18 PM, rsteinke@xxxxxxxxxxx wrote:
I have a question about vertical position control for a hovering
rocket. One option is to do a PID control loop where the manipulated
variable is vertical acceleration and the controlled variable is
vertical position. The thing is, you aren't really manipulating
vertical acceleration. You are manipulating the throttle valve.
You've
got a few confounding factors in the mapping from throttle valve
position to thrust, and net thrust needs the vehicle's weight
subtracted
out and weight is always changing as propellant is consumed. I've
thought of a few ideas to deal with this:
1) Do a lot of testing and analysis and get a really good educated
guess
of thrust mapping and propellant usage. Any errors in those get
handled
by integral gain in the vertical acceleration to vertical position
controller.
2) Have another controller where the manipulated variable is throttle
position and the controlled variable is vertical acceleration.
3) Cut out the middle man and have a single controller from throttle
position to vertical position. I don't even know what the gains on
such
a controller would look like without knowing where the "zero point"
is
of zero net vertical thrust.
What have other people done? Are there other ideas?
Thanks
Bob
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