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Old May 20, 2015, 04:20 PM
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Hi!
I'm using DOSD V2 with FY30A and GPS module. Trying to get RTH.
My DOSD in RTH mode (turned ON at ~ 50 m altitude) is doing crazy things - the plane is nicely turning to Home direction and then going down at 45 degrees in 30 - 40 m spiral, sometimes using throttle, sometimes not. Looks like RTH is not using IMU - there are no signs of leveling, even worse - the plane is going into spiral.
The plane itself is well balanced, hands-off IMU leveling is working nice, HomePosition and ArtificialHorizon are shown correctly all the time, but GPS height indicator is insane - at real 50 m it can show 10 m or even minus 1 m.
Most of settings are default.
GPS Passthrough - 0 (default)
Cruise altitude - 100 m
Cruise speed - 50 kmh (plane flies well at 40)
Descent mode - 0 (no descent)
Throttle mode - 2 (enabled).
Good SAT number - from 8 to11.
The day is nearly calm.

Is there problem with GPS height data? Would it work using barometric module?
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Old May 20, 2015, 08:42 PM
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Quote:
Originally Posted by Agades View Post
Hi!
I'm using DOSD V2 with FY30A and GPS module. Trying to get RTH.
My DOSD in RTH mode (turned ON at ~ 50 m altitude) is doing crazy things - the plane is nicely turning to Home direction and then going down at 45 degrees in 30 - 40 m spiral, sometimes using throttle, sometimes not. Looks like RTH is not using IMU - there are no signs of leveling, even worse - the plane is going into spiral.
The plane itself is well balanced, hands-off IMU leveling is working nice, HomePosition and ArtificialHorizon are shown correctly all the time, but GPS height indicator is insane - at real 50 m it can show 10 m or even minus 1 m.
Most of settings are default.
GPS Passthrough - 0 (default)
Cruise altitude - 100 m
Cruise speed - 50 kmh (plane flies well at 40)
Descent mode - 0 (no descent)
Throttle mode - 2 (enabled).
Good SAT number - from 8 to11.
The day is nearly calm.

Is there problem with GPS height data? Would it work using barometric module?
GPS altitude readings are variable at best...it's just not all that accurate. I use a baro on all my DOSDs for a far more reliable altitude reading. If your altitude is bouncing around that much in flight then I'd be suspect of the GPS itself.

As for you dive and spiral in RTH...that sounds like your AP controls may be reversed. Have you performed the Servo Direction Test in the main menu? If not, do not fly again until you do. Make sure you center your trims and sub-trims, and set your aileron and elevator throws to 100%. Go to the Servo Direction Test in the main menu and apply full right aileron. You should get up right aileron and up elevator. Don't worry if the surfaces jitter some during the test, this is common. If either your aileron and/or elevator move in the wrong direction you need to reverse the AP movements in the menu for the incorrect control surface and then repeat the Servo Direction Test to verify things are moving in the correct direction.

As for your
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Old May 20, 2015, 08:59 PM
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just got another DOSD

Figured it was the best choice for my ultralight setup

working on building the plane now... and going to modify the DOSD to be as clean as possible hope to fit it all in my 1/2"-3/4" flying wing body.
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Old May 21, 2015, 01:40 AM
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agades you might also try.lowering the turning gains, the plane will of course lose altitude in a turn as the wings provide less vertical lift. if the turn is tight and altitude is lost then dosd tries to pull up, which just tightens the turn and loses more altitude and so on.

as for stability, dosd will use it only if it is switched on by you. I believe that rth and stability can sometimes try to do opposite things - stab wants to fly straight and rth wants to turn. I think you should set up ap with stab on or off (off would be my preference for initial setup) but don't expect ap to work with stab on and off without changing some gains
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Old May 21, 2015, 04:03 PM
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I don't use trims and subtrims at all, servos are centered. Servo direction is checked and correct, all AP made turns and banks starting RTH are perfect. DOSD doesn't control altitude in RTH mode, it allows plane go down at some angle, circling at the same time. Spiral is not tight enough to lose speed or stall.
Sometimes at real altitude about 10 meters throttle turns on, but there is not time to continue observing - I have to recover plane manually.
Tried to change cruise altitude to 200 m to lift events higher to get DOSD more time, but result is the same - 30 to 40 m circling with pitch down at 30 degrees with throttle on, sometimes off. It even doesn't try to reach the cruise altitude or hold it, losing Home direction at the same time.
Looks like DOSD doesn't use altitude data, parameter on screen shows absurd currencies.
On another hand - IMU leveling and stabilization works fine, it holds direction nicely when hands off.

Hit distance is set to 5 m to avoid "the target is reached" behavior.

Can it really be GPS module altitude data fault, if coordinates and HomeDirection are shown correct?

Funny thing is - the plane doesn't lose altitude at turning to HomeDirection, looks like it releases all controls when Home is straight ahead and allows continue motion on it's own without any correction, turning throttle randomly.
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Last edited by Agades; May 21, 2015 at 04:35 PM.
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Old May 21, 2015, 06:45 PM
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Personally, I never liked using DOSD throttle control. I just felt to disconnected when, in AP mode, the throttle did not respond to my throttle movements. I'm not saying it didn't work, I'm just saying I didn't like the feel of it.
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Old May 22, 2015, 09:25 AM
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Quote:
Originally Posted by Agades View Post
I don't use trims and subtrims at all, servos are centered. Servo direction is checked and correct, all AP made turns and banks starting RTH are perfect. DOSD doesn't control altitude in RTH mode, it allows plane go down at some angle, circling at the same time. Spiral is not tight enough to lose speed or stall.
Sometimes at real altitude about 10 meters throttle turns on, but there is not time to continue observing - I have to recover plane manually.
Tried to change cruise altitude to 200 m to lift events higher to get DOSD more time, but result is the same - 30 to 40 m circling with pitch down at 30 degrees with throttle on, sometimes off. It even doesn't try to reach the cruise altitude or hold it, losing Home direction at the same time.
Looks like DOSD doesn't use altitude data, parameter on screen shows absurd currencies.
On another hand - IMU leveling and stabilization works fine, it holds direction nicely when hands off.

Hit distance is set to 5 m to avoid "the target is reached" behavior.

Can it really be GPS module altitude data fault, if coordinates and HomeDirection are shown correct?

Funny thing is - the plane doesn't lose altitude at turning to HomeDirection, looks like it releases all controls when Home is straight ahead and allows continue motion on it's own without any correction, turning throttle randomly.

if you are getting into a spiral of death, you have something tuned wrong. I have had a few airframes when the settings were off, it would get stuck in a spiral and with throttle control it will not pull out of it. once settings were changed, everything went back to normal. I cant say what "normal" is since 99% of my airframes are homebuilt and do not reflect anything similar to manufactured models.
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Old May 23, 2015, 08:31 AM
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Save throttle control for when you fit pitot tube - best to leave the the throttle at a cruise speed in AP IMO.

In a death spiral the GPS speed will be unreliable and will probably be controlling throttle badly
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Old May 27, 2015, 12:46 PM
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Dragon OSD saved my Skyhunter on Monday! I was on a mission to visit a distant hill and already 2Km out when the video went completely blank. Flicked RTH and waited 10 minutes and she came into view!

Video wire into the VTx plug was hanging on by a thread and finally gave up.
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