Hello all, after losing my radio signal today, i'm wondering what this "circle" mode is.  it doesn't actually execute a circle as in loiter, but it does have a slight aileron offset.  there seems to be very little mention of this mode (and generally no information on its characteristics) anywhere.  

I also didn't find a way to disable/shorten the 20 seconds of signal lost before kicking into RTL.  when i lost signal earlier today i watched the FPV footage as the plane skimmed over treetops and barely skimming/missing/passing between buildings before RTL kicked in and got the plane to 100m altitude heading back home.  I mean... it takes a 2-second signal loss to kick into circle, and then 20 seconds from circle to RTL.  I'm pretty sure that by 5 seconds of signal loss I'd rather have it go RTL than into a mode which i can't seem to find what it does...

so does anyone know the supposed characteristics of "Circle" mode, and whether it's possible to disable this or change the duration of signal loss before RTL kicks in?  preferrably within mission planner? 


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Hi Aleck

The Failsafe behaviour is well described here http://plane.ardupilot.com/wiki/arduplane-setup/apms-failsafe-funct...

Tridge pointed out your post to me and he is going to add 2 parameters:

FS_LONG_TIMEOUT and FS_SHORT_TIMEOUT, to make the two time thresholds settable.

Thank you, I have read that page before and more than once, and yes i do have it set up right or else my plane would've been lost today.  however that page still doesn't help with explaining what "Circle" mode actually is since my plane didn't seem to "circle" the point at which it lost RC signal (note that i do have loiter mode set up correctly and that in loiter mode my plane does indeed loiter).  it did however go into a slight bank and held altitude.  the short and long time out will definitely be a nice feature, but i do want to know more about this "Circle" mode and what the plane is supposed to do in this mode (as it doesn't seem to actually circle anything).  the same behavior has been reported in https://code.google.com/p/ardupilot-mega/wiki/FlightModes

Comment by project member garyrmccray@gmail.comOct 8, 2011

I would really like to know about "CIRCLE" mode as opposed to loiter as a switch selectable mode.

I thought it was the same as Loiter but without throttle control.

CIRCLE is selectable in the APM set up portion of the planner, but doesn't actually seem to execute a circle at the current point (or a circle of any kind for that matter) even though statically it does very slightly offset the ailerons.

I also find no reference to "CIRCLE" in the GCS info???

I have attached the .kml file of the flight.  the yellow segment wandering off beyond the trees and into/between the buildings is the "Circle" segment i was talking about.  (i do notice that this flight the ardupilot switched into "circle" intermittently rather often, noting a high RF interference in the area today, i will be more careful/do range check next time).


Circle mode is described here


Circle mode is similar to loiter, but doesn’t attempt to hold position. This is primarily meant as a failsafe mode and is the mode that the aircraft will enter by default for 20 seconds when a failsafe event occurs, before switching to RTL.

Circle mode is deliberately a very conservative mode, and doesn’t rely on GPS positioning as it is used when GPS fails. It will do a large circle, The bank angle is set to the LIM_ROLL_CD divided by 3, to try to ensure the plane remains stable even without GPS velocity data for accelerometer correction. That is why the circle radius is so large.

Circle mode uses throttle and pitch control to maintain altitude at the altitude where it started circling.

ahh thank you so much, i don't know how i missed that page (there does seem to be more than one "complete" reference/manual for the arduplane and copter), makes a lot more sense now!

Hi Aleck,

The CIRCLE mode is explained in the flight modes documentation (you may have missed it as it was only updated recently).

I agree that the timeouts should be settable, so I've added FS_SHORT_TIMEOUT and FS_LONG_TIMEOUT parameters for the upcoming 2.74 release. See the new parameters here

Thanks for the suggestion!

Cheers, Tridge

My experience is a bit different.
I fly on a low altitude (20-50m), and the things that I wish to see in the filesave is:
1. Ability to set timeout (from 0 to ...) to go to the first fs action.
2. Ability to set as many fs actions as user want.
3. Ability to set the duration of each action.
4. Ability to set any mode on any action.
IMHO these things can make the APM filesave function very flexible.
In my case against of the CIRCLE mode I need the LOITER mode on the specified altitude which triggers immediately after the RX looses the signal and then after some time it should go to the RTL. The key thing I need is to climb up immediately after the RX looses the signal, otherwise the model can easily go to the planet because of the low altitude)
So I hope to see the changes in the feature.
Regards to the developers.

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