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Old Aug 27, 2014, 09:15 AM
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theroots123's Avatar
United Kingdom, Thornbury
Joined May 2012
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Arduplane...RTL mode while GPS goes offline. What happens?

Howdy all,

I cant seem to find this information anywhere on the web. If i activate RTL and for some reason the GPS module goes offline. What mode will the plane go in to? iv tried activating RTL while gps is still warming up and the OSD just read mode:RETL still.

Am i correct in thinking it will go into 'circle' mode?? can anyone help?
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Old Aug 27, 2014, 12:16 PM
Just clumsy. Oh, forgetful too
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I can't tell you what it will do but "circle" must also rely on GPS ...I guess you'll find it downwind...
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Old Aug 27, 2014, 12:28 PM
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United States, CA, San Diego
Joined Jan 2005
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Quote:
Originally Posted by theroots123 View Post
I cant seem to find this information anywhere on the web. If i activate RTL and for some reason the GPS module goes offline. What mode will the plane go in to? iv tried activating RTL while gps is still warming up and the OSD just read mode:RETL still.

Am i correct in thinking it will go into 'circle' mode?? can anyone help?
Oh boy let's play theoreticals since this already happen to me and everyone in APM dev blew me off as crazy..

From my experience.. It will go into a form of FBW-A and keep on flying until the GPS comes online. The exciting part is WHEN your GPS comes online the spot where the GPS is 'locked' is now your new home location. This includes altitude as well. So let's say while your GPS was acquiring your plane climbed from 500' to 1000'. When the GPS locks it now thinks 1000' is zero and corrects the planes altitude to your RTH altitude.

They now have Rally points that may 'fix' this issue. However I've found the safest bet is to create a fallback autonomous route. Then let the whole system failsafe into this autonomous route. In the event of a GPS reacquisition, at least the plane knows how to fly back into a planned route.

http://plane.ardupilot.com/wiki/flyi..._To_Launch_RTL

Having lost a bird into an area where you do not want to lose a bird.. I'm over paranoid about RTH now. I was able to recover the bird.. However there was some serious questions as to why the system did what it did.
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Old Aug 27, 2014, 05:58 PM
I ask a lot of questions.
Canada, AB, Airdrie
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I'm not disputing your theory/experience on what happens when the GPS comes back online. But I would think that the "home" location was set on the APM when powered up (as it's designed to do), so I don't know if the GPS turning off then back on would even rewrite the "home" location....unless the APM lost all power as well.

It would be interesting to test it by adding some type of on/off relay and force the GPS to lose power with the flick of a switch. Then turn it back on and see where the plane flies to.

Anyone want to risk losing their plane in the attempts to replicate the issue?

Cheers
Stew
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Old Aug 27, 2014, 07:15 PM
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United States, CA, San Diego
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Originally Posted by Disco Stew View Post
It would be interesting to test it by adding some type of on/off relay and force the GPS to lose power with the flick of a switch. Then turn it back on and see where the plane flies to.

Anyone want to risk losing their plane in the attempts to replicate the issue?
You could be correct. I ground my stuff the second I notice anything funky is going on. This comes after some of the APM excitement I've had over the past two years. Personally I'd like a 'terminate flight' feature added to Mission Planner. Something that cuts the motor and spirals the plane in.
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Old Aug 28, 2014, 12:55 AM
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Greece, Attica, Athens
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Quote:
Originally Posted by typicalaimster View Post
Oh boy let's play theoreticals since this already happen to me and everyone in APM dev blew me off as crazy..

From my experience.. It will go into a form of FBW-A and keep on flying until the GPS comes online. The exciting part is WHEN your GPS comes online the spot where the GPS is 'locked' is now your new home location. This includes altitude as well. So let's say while your GPS was acquiring your plane climbed from 500' to 1000'. When the GPS locks it now thinks 1000' is zero and corrects the planes altitude to your RTH altitude.

They now have Rally points that may 'fix' this issue. However I've found the safest bet is to create a fallback autonomous route. Then let the whole system failsafe into this autonomous route. In the event of a GPS reacquisition, at least the plane knows how to fly back into a planned route.

http://plane.ardupilot.com/wiki/flyi..._To_Launch_RTL

Having lost a bird into an area where you do not want to lose a bird.. I'm over paranoid about RTH now. I was able to recover the bird.. However there was some serious questions as to why the system did what it did.

If that happened, then its most certainly a bug in the code.
Home is set upon the transition from 'UnArm' to 'Arm' and not from GPS power loss
(a plain GPS 'No-Fix', loss of 3DFix is not altering the home location, thats tested).
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Old Aug 28, 2014, 03:46 AM
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Originally Posted by MikeTheCrash View Post
I can't tell you what it will do but "circle" must also rely on GPS ...I guess you'll find it downwind...
No circle doesnt rely on gps or compass. loiter does. but circle just uses the gyros etc to maintain a constant bank and altitude. it will drift with the wind. This is why we have loiter as well. Loiter will circle above a point instead and compensate for winds. This is why circle is used as a failsafe, hence my asking
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Old Aug 28, 2014, 03:52 AM
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thanks for all ya posts guys. As with my quad while flying if i exceed 200meters i always make a point of trying RTL a few times while out on flight and all the while keeping an eye on GPS data. If GPS data ever glitches then i know not to use any GPS function for the remainder of the flight. Although it seems experience might outweigh actual knowledge of how its 'meant to work'. I think some experimenting is coming on. No need to test in the air, you can see the home point on the mission planner. I will try out a few tests at lunch on the ground and see if the home point changes when GPS is turned off and on again during power on simulating flight.

What i was more concerned about was if im in failsafe for any reason and at that time GPS goes offline what mode will it go into. Will it continue trying to fly back with duff data or will it switch to a different mode. My understanding was it will go into circle mode (not loiter, there is a difference)
Its this which i wanted to understand.
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