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S-TEC 55X

Designing a stable autopilot is one of the hardest things. Need help?

Re: S-TEC 55X

Postby adnan » Mon Mar 29, 2021 5:16 pm

Hello,

I am new to FlightGear. I am trying to install S-TEC 55X autopilot on an MQ-9 Reaper aircraft. I have completed Step One and Two.

I could not complete Step Three because I did not find an "instruments" folder in the aircraft folder. It was an optional step. Therefore, it should not be a problem.

In Step Four, I added the 4 bindings in the -set.xml file between </nasal> and </PropertyList>. Is this the correct place for these bindings?

When I start FlightGear and try to activate the autopilot, it does not seem to work. Can somebody please help with the installation?
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Re: S-TEC 55X

Postby Octal450 » Mon Mar 29, 2021 11:46 pm

Hello. you can put the instrument wherever you want, just modify the path accordingly to load it.

Yes, it goes into there correct. Before you use the autopilot, you must turn the master on and wait for the self test to complete. This is all documented on the wiki, so please check the whole article.

Kind Regards,
Josh
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Re: S-TEC 55X

Postby wlbragg » Sat Aug 19, 2023 11:04 pm

Hi Josh,

Does the S-TEC 55X have a static port associated with it in any way? If so could you elaborate on it?
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Re: S-TEC 55X

Postby Octal450 » Sun Aug 20, 2023 6:00 am

Hi sir,
S-TEC 55X read from /systems/static[0]/pressure-inhg. Please let me know what other info you may need!

If you need this to be configurable, I can do that!

Kind Regards,
Josh
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Re: S-TEC 55X

Postby wlbragg » Sun Aug 20, 2023 9:23 am

Yes, I need it to read from /systems/static-pressure-inhg-selected
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Re: S-TEC 55X

Postby Octal450 » Mon Aug 21, 2023 12:42 am

S-TEC 55X have its own sensor as I understand it, where it computes pressure rate and altitude information. You should not tie into your switchable static system. Additionally if you don't follow my advice, and your static port not updates properly in sync, the autopilot will stop working, because it computes derivative of static pressure as part of the pitch control system.

Regardless, I'll add the ability to switch a couple numbers. But keep one static port for the S-TEC isolated.

Update pushed. You can choose between ports 0 thru 5. Should be enough. Set one dedicated one aside for 55X.

Kind Regards,
josh
Last edited by Octal450 on Mon Aug 21, 2023 2:42 am, edited 1 time in total.
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Re: S-TEC 55X

Postby wlbragg » Mon Aug 21, 2023 1:25 am

You should not tie into your switchable static system


So it has its own static port and is not normally tied to any exterior or alternate port?
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Re: S-TEC 55X

Postby wlbragg » Mon Aug 21, 2023 1:32 am

I get what your saying and that is not what I am trying to do. What I want is to allow the aircraft instruments to use the S=TEC's static port when the alt static port is engaged, such as the external port might be iced or malfunctioning. Then the instruments use the S-TECs port which is protected but maybe not as accurate as a working eternal port.

That should be OK. No reason to tie the S-TEC to the exterior static port.
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Re: S-TEC 55X

Postby wlbragg » Mon Aug 21, 2023 1:35 am

because it computes derivative of static pressure as part of the pitch control system


A derivative from what source, only its own sensors? If it uses its own source and the exterior port then ice potentially could cause issues with the AP. If it only uses its own sensors then it becomes the become the backup for the aircraft instruments. That is my understanding.
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Re: S-TEC 55X

Postby wlbragg » Mon Aug 21, 2023 1:46 am

S-TEC 55X read from /systems/static[0]/pressure-inhg.


Yes, I need it to read from /systems/static-pressure-inhg[0]-selected


I'm sorry I didn't read that closer. I don't need it to read from /systems/static-pressure-inhg-selected. I need /systems/static-pressure-inhg[0]-selected to be able to read the static-pressure-inhg[0] that is produced by the sensors in the S-TEC, if that is even possible.

But it sounds like the S-TEC is using the supplied /systems/static[0]/pressure-inhg from JSBSim or whereever that value is being produced. Is that right. You used the first static port configured under systems to feed the autopilot?
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Re: S-TEC 55X

Postby wlbragg » Mon Aug 21, 2023 2:01 am

OK, more thoughts on this. So what your adding then is the ability to use /systems/static[1]/pressure-inhg for the S-TEC instead of /systems/static[0]/pressure-inhg. Then I can use /systems/static[0]/pressure-inhg for my instruments and manipulate it with he icing system. The S-TEC using /systems/static[1]/pressure-inhg won't be a port of that system and so I can use its assigned static port of /systems/static[1]/pressure-inhg as the alt port when the alt static port is selected.

That is exactly what I am looking for. I wasn't understanding that all of these AP's are using /systems/static[X]/pressure-inhg as their own internal sensors.
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Re: S-TEC 55X

Postby wlbragg » Mon Aug 21, 2023 2:06 am

Thank you Josh, you did exactly what I requested even though I wasn't clear about it.
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Re: S-TEC 55X

Postby wlbragg » Mon Aug 21, 2023 2:45 am

Question, I was under the assumption that the interior AP sensors were not quite as accurate as the exterior sensor. So when configuring the simulated interior sensor we do something like below, where static n="1" is the interior AP sensor.

Does this make sense to you? Would this be a more accurate simulation.

Code: Select all
    <static>
        <name>static</name>
        <number>0</number>
        <tau>0.1</tau>
        <type>1</type>
        <error-factor>0.2</error-factor>
    </static>

    <static n="1">
        <name>static</name>
        <number>1</number>
        <tau>0.1</tau>
        <type>0</type>
        <error-factor>0.35</error-factor>
    </static>
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Re: S-TEC 55X

Postby Octal450 » Mon Aug 21, 2023 2:58 am

My pleasure. :)

I MADE AN ERROR in config.txt. Please make sure static-port-num is an int not a bool. Oops.

S-TEC 55X control loop uses static port for 2 things:
- Computing the profile used in ALT mode, for capturing the altitude
- Computing the climb/descend rate (via derivative of static pressure + smoothing) used in the master of the pitch control loop.

As for the error, that is fine. The system does not use any absolute since no QnH setting is there (only on the extended pre-select panel which I didn't model yet). It should "just work". If you run into issues let me know.

Hope this helps,

Kind Regards,
Josh
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Re: S-TEC 55X

Postby wlbragg » Mon Aug 21, 2023 4:38 am

Please make sure static-port-num is an int not a bool

Opps, good catch.

Do NOT tie into aircraft static system, requires its own dedicated port

You know, in most implementations I would be willing to bet that most people just use the first port, 0, and in as much, are tying into the same static port that is technically the external port that all the instruments are using. So long as there is nothing manipulating that port I guess it is not a real issue, but it certainly isn't simulating the S-TEC as a stand alone AP. Basically before you added the ability to change ports it was using 0 which is what all the instruments were using and the icing system is linked to. Developers need to be aware that when installing really any autopilot they need two static ports, one for the AP and one for the exterior default port.
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