GPS flight control modes and stabilization for fixed wing
« on: December 11, 2016, 01:22:05 pm »
Hi !

I have a Revo with M8N GPS and an Aux mag installed and configured in a fixed wing (FPVraptor 2000).
Stablization is configured and running without Mag or GPS alarms. INS13 attitude algorithm is in use.

I have been looking for information about the GPS support for fixed wing, both in the wiki and in the forum.
I have not been able to conclude much since there is a lot of multirotor talk and that raises confusion.
So let me ask a couple of questions.

Which of the GPS flight modes work for fixed wing ? https://librepilot.atlassian.net/wiki/display/LPDOC/GPS+Flight+modes
- position hold
- return to base
- course lock
- home leash
- velocity roam
All ? Any ?

Is the GPS assist option (in GCS shows in "Assisted control" option) only for multirotor ? https://librepilot.atlassian.net/wiki/display/LPDOC/Gps+assist
In my fixed wing config I get a "Config error" alarm if I use GPS assist in any flight mode.

Final questions concerning stabilization - which stabilization modes work for fixed wing ?
- manual, rate, attitude, axis lock. I guess so.
- what about cruise control, altitude vario, altitude hold ?

Which stabilization can be used for thrust other than manual ? I have no airspeed sensor.

thank you!

f5soh

  • *****
  • 4052
    • LibrePilot
Re: GPS flight control modes and stabilization for fixed wing
« Reply #1 on: December 11, 2016, 01:46:14 pm »
Which of the GPS flight modes work for fixed wing ? https://librepilot.atlassian.net/wiki/display/LPDOC/GPS+Flight+modes
- position hold
- return to base
- course lock
- home leash
- velocity roam
All ? Any ?

Should be all


Quote
Is the GPS assist option (in GCS shows in "Assisted control" option) only for multirotor ? https://librepilot.atlassian.net/wiki/display/LPDOC/Gps+assist
In my fixed wing config I get a "Config error" alarm if I use GPS assist in any flight mode.

Only Multirotor, the config alarm lock and prevent GpsAssist for others vehicles.

Quote
Final questions concerning stabilization - which stabilization modes work for fixed wing ?
- manual, rate, attitude, axis lock. I guess so.

Ok, all stabilization modes that can be applied to Roll/Pitch/Yaw.
Acro+ or Rattitude are also fine for fixedwing.


Quote
- what about cruise control, altitude vario, altitude hold ?
Which stabilization can be used for thrust other than manual ? I have no airspeed sensor.

No.
The warning in Rcinput talk about those choices.

The normal Thrust mode for fixedwing is Manual.

Re: GPS flight control modes and stabilization for fixed wing
« Reply #2 on: December 16, 2016, 06:56:35 am »
It would be interesting to play with getting Altitude Hold and Altitude Vario working with for fixed wing.  A simple, nose heavy fixed wing with up trim so it climbs when you add power could be set up to work with these but would definitely require tuning the vertical PID.  The issue that would keep you from playing with it is that it uses CruiseControl internally to get the quad power in the ballpark so the baro code doesn't have to track such large excursions (like a 45 degree bank causing an altitude drop due to loss of vertical component of thrust.

CruiseControl would require code changes, but could work to apply the correct amount of elevator for the current bank angle.

Re: GPS flight control modes and stabilization for fixed wing
« Reply #3 on: March 19, 2017, 09:16:59 pm »
I would like to use a minirevo (with GPS) on a little powered glider : is the PositionHold flight mode tested and reliable for fixed wing ? Does this mode consist in flying in circles arround the GPS position (like Loiter in Arduplane) ?  If it does, is it possible to affect value for the radius of circles ?
Thanks

f5soh

  • *****
  • 4052
    • LibrePilot
Re: GPS flight control modes and stabilization for fixed wing
« Reply #4 on: March 19, 2017, 09:49:10 pm »
There is no radius settings while doing PositionHold on fixedwing, he try to maintain position with a turn (right or left) based on bank angle after he exceeded the position and do a loop.

Gaijin

  • *
  • 1
Re: GPS flight control modes and stabilization for fixed wing
« Reply #5 on: March 29, 2017, 09:19:28 am »
Can someone explain clearly how to setup and use tps on a fixed wing, for example my flying wing works well when stabilised at low speed but as it accelerates the surfaces flutter as it overcompensates, until I tame that I cant test GPS function.

I've searched and searched but can't find any guidance that doesn't relate to multirotors not fw

Re: GPS flight control modes and stabilization for fixed wing
« Reply #6 on: April 04, 2017, 08:32:39 pm »
On fixed wing, the oscillation is proportional to aircraft speed, not motor speed.  You can have the motors off but going very fast in a dive.  So TPS based on throttle (like for quads) doesn't work for fixed wing.  To get it to work on FW, you need some form of airspeed sensor, and I am pretty sure it is only available on Revo class FCs.

The standard way to set it up is to turn down the PIDs till it stops oscillating at maximum speed.  This is not optimal because then it is less effective at slowest speed.

Re: GPS flight control modes and stabilization for fixed wing
« Reply #7 on: April 04, 2017, 08:48:02 pm »
If you have an airspeed sensor configured and working, you can set StabilizationSettings ScaleToAirspeedLimits and set ScaleToAirspeed to the airspeed where you tuned it and it will decrease PIDs when above ScaleToAirspeed and increase PIDs when below.