[AR] Re: hovering rocket vertical position control
- From: "Monroe L. King Jr." <monroe@xxxxxxxxxxxxxxxxxx>
- To: arocket@xxxxxxxxxxxxx
- Date: Sat, 14 Mar 2015 18:58:04 -0700
Ardupilot can hover a rocket how are you gimbaling it?
Monty
> -------- Original Message --------
> Subject: [AR] Re: hovering rocket vertical position control
> From: Paul Breed <paul@xxxxxxxxxx>
> 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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