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Re: [Paparazzi-devel] Suggestions: Auto-tuning of gains and upload via

From: Christophe De Wagter
Subject: Re: [Paparazzi-devel] Suggestions: Auto-tuning of gains and upload via modems
Date: Mon, 21 Jun 2010 08:42:57 +0200

Uploading used to be over the serial link in the past (2005). Do not underestimate the time this took to upload new code. 

On Sun, Jun 20, 2010 at 3:39 AM, Eric Parsonage <address@hidden> wrote:
Hi Florin, Maik,
I am sure that ZN would definitely work, but its just how well it works! I am pretty sure ZN is the only option if you cant derive the Transfer Function of the system analytically, so for most people who use paparazzi and haven't learnt that much about classical or modern control, or for airframes that may have weird Dynamics (like a flying wing), it is definitely the way to go. ZN based tuning also results in a controller that is very good at rejecting disturbance, which for level flight is great, I just worry about the step response of that sort of controller in regards to setpoint changes, like rolling into or out of a heavy bank, I fear that it may be very oscillatory. It does of course depend on your aircraft, and whether or not you are constantly changing its attitude.
However, Maik does make a very interesting point. the community could probably develop a little script, or even a simple spreadsheet, that assumed you had a straight winged monoplane platform, and took inputs about its geometry, moments of inertia etc. then approximated the  transfer function of the system based on that, with that it could then analytically calculate, using at least a couple of PID tuning methods, the appropriate gains for your system which you could then program in. This could be done without you even having to leave the ground! of course, you would need to do a little bit of manual tuning once you got up in the air, but at least you could have some trust in your controller to begin with. Of course, someone would need to derive the state-space model for a generic aircraft in terms of variable regarding its dimensions. Any of you control gurus wish to comment on this suggestion (I know you are reading)?

On 19 June 2010 18:15, Florin Mingireanu <address@hidden> wrote:
Hi Eric,

I've used succesfully ZN on flying wings.
I haven't used it on other planes.


On Sat, Jun 19, 2010 at 11:34 AM, Eric Parsonage <address@hidden> wrote:
Hi Maik, Florin,

I would suggest that ZN tuning would not be that effective, This is due to the fact that the ZN algorithms were empirically derived from work with process systems which all exhibited a particular response (time delay, big phase lag, integrator racking up error to a step input). Perhaps a more sensitivity driven algorithm, like kappa-tau, or pole placement, would be more effective since aircraft tend to act a lot more like a servomotor-style system than a phase-laggy process one.


On 19 June 2010 17:54, Florin Mingireanu <address@hidden> wrote:
Hi Maik,

The method I tried to describe is called Ziegler-Nichols.

On Sat, Jun 19, 2010 at 11:20 AM, Florin Mingireanu <address@hidden> wrote:
Hi Maik,

As far as I know, tuning P and I-gains is like:

increase P value until you detect instability (oscillation as you said) and then decrease P to half and start to increase I until sufficient stability is obtained.

If, additionally, you have a D term (d-gain) then you apply recursively this algorithm for subsequent I and D.

So tuning gains for a new aircraft is more like a cascaded algorithm.


On Sat, Jun 19, 2010 at 10:12 AM, Maik Höpfel <address@hidden> wrote:
Hello dear community,

I recently added two features I would like to see to the Software
Wishlist in the Wiki, but did not get any feedback. So I'd like to
present them on the list as well:

1) Auto-tuning of gains: as far as I see it, the rules for setting the
P-gains on a new aircraft are pretty easy: "turn it up till it
oscillates, turn down a little". Now given sufficient height and a bit
of trust in the airframe, this should easily be doable by an algorithm
instead of the crew on the ground, shouldn't it? Oscillation can be
detected via the IR sensors/IMU... I imagine it like a special flight
plan block that then sets the correct gains.

2) Flashing via modems: Couldn't the boot loader wait for a special
sequence from the modems before starting up the Paparazzi code? And
then the GCS just sends that special message and the firmware that is
to be flashed? Should be error-checked, of course. But it's possible,

I'm really looking forward to your thoughts! I think both things would
make Paparazzi even easier to use for beginners.


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Florin Mingireanu
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