[AR] hovering rocket vertical position control
- From: rsteinke@xxxxxxxxxxx
- To: arocket@xxxxxxxxxxxxx
- Date: Mon, 16 Feb 2015 16:18:32 -0700
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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