Sudden climbs/descents while in GPS mode (Wookong-M)

[Skysurf]

We recently finished building a large oktocopter that's using a Wookong-M.
It flies very well in atti mode, but in GPS mode it has made some sudden climbs and descents at a few occasions.
The climbs/descent are quite rapid, but can easily be stopped by making the appropriate correction with the throttle. Again, this has only occurred in GPS mode.

This is the 3rd platform that we built using the Wookong - have not had any similar issues before.

Has anyone experienced anything similar?

Thanks,

Jesper

 

[DucktileMedia]

I thought throttle was not compensated for at all in GPS mode?

Perhaps a side effect of yaw induced climb? Are you using heading hold as well?

 

[Skysurf]

This has happened when in GPS mode with the throttle at mid stick and the platform maintaining altitude automatically. Last time it happened it was wind calm and I did not input any yaw command. However, I do have a fairly high gain setting for yaw, I will reduce this to see if it makes any difference. Doubt it though considering the rate of clim/descent involved in these events.

Thanks for your input.

/Jesper

 

[BorisS]

Hi Jesper as far as i understood GPS is also used for altitude hold. May be reason is as simple as some GPS disturbance. At the same time though how do you climbs look like. Would this match you experience ?

Boris

 

[Skysurf]

Thanks for your input Boris.

I just figured it out, and it's a little embarrassing to tell you what was causing it. It seems that when setting up the different modes we managed to get the GPS set very close to Fail Safe. What has happened is that the platform has gone in to Fail Safe causing it to climb.

The strange thing is that most of the times when this has occurred, I have had it flying in GPS mode for a minute or so before it went to Fail Safe. Could this possibly have anything to do with temperatures?

Also, when checking the TX tab in the software, the GPS box turns blue, but at the bottom right corner of the window it says GPS and Atti (you can only see half of the GPS and Atti text). I never thought about this before. Can someone please confirm that this is normal.

Thanks,

Jesper

 

[plingboot]

i've experience this issue regularly too.

if i enable gps hold the quad sits there for a short while before slowly descending, it'll almost touch the ground, before slowly ascending again, it'll then repeat this behaviour. This is with no stick input at all and no red (gps) LED's

never got it totally 'locked', but i think this is to do with gains rather than anything else.

 

[Skysurf]

In my case I know it went into Fail Safe rather than GPS. I confirmed this by connecting it to the PC right after the flight. When I moved the switch from Atti to GPS, it only got to Fail Safe.

Jesper

 

[FlyEYE]

I've had this happen with mine, stable then slow descending.. No stick imput on my end as well. I also noticed that it seems very sensitive of the throttle at mid stick. If it's at all off from dead center it tends to climb or descent, a related issue?, I'll try a bit of expo. Because of these issues I actually checked the manual if it was suppose to hold altitude

i've experience this issue regularly too.

if i enable gps hold the quad sits there for a short while before slowly descending, it'll almost touch the ground, before slowly ascending again, it'll then repeat this behaviour. This is with no stick input at all and no red (gps) LED's

never got it totally 'locked', but i think this is to do with gains rather than anything else.

 

[lperagallo]

I've had this happen with mine, stable then slow descending.. No stick input on my end as well. I also noticed that it seems very sensitive of the throttle at mid stick. If it's at all off from dead center it tends to climb or descent, a related issue?, I'll try a bit of expo. Because of these issues I actually checked the manual if it was suppose to hold altitude

I am not sure that you can program expo into the throttle channel of a radio, at least not Futaba or JR. It wouldn't make any sense to do that. You can flatten out the throttle curve to get a larger center output, but you do that with a curve. Set a curve with an input range between 50% and 55% to output 50% and you get a 5% stick movement that actually will output mid stick. You can even program your idle up switch so when you turn to one position it always outputs 50% throttle. Problem solved. That way once you hit your desired output it stays there. I have not tried that, but it can be done. We do that when we are setting up pitch on a heli and need center stick with 50% output. Of course we use the pitch curve rather than the throttle curve. If you are not at center stick outputting 50% throttle than the quad will either drift up or down. Of course I am assuming that you have your altitude gain set up correctly.

Lou

 

[DennyR]

Also check that the small holes in the imu are not blocked.

 

[Skysurf]

I am not sure that you can program expo into the throttle channel of a radio, at least not Futaba or JR. It wouldn't make any sense to do that. You can flatten out the throttle curve to get a larger center output, but you do that with a curve. Set a curve with an input range between 50% and 55% to output 50% and you get a 5% stick movement that actually will output mid stick. You can even program your idle up switch so when you turn to one position it always outputs 50% throttle. Problem solved. That way once you hit your desired output it stays there. I have not tried that, but it can be done. We do that when we are setting up pitch on a heli and need center stick with 50% output. Of course we use the pitch curve rather than the throttle curve. If you are not at center stick outputting 50% throttle than the quad will either drift up or down. Of course I am assuming that you have your altitude gain set up correctly.

You can get an Expo effect by flattening the center of the throttle curve, this works fine, we have tried it. I have also been thinking about setting the throttle hold to 50% to get it to hold altitude by the flip of a switch. This is a really good idea, will give it a try soon.

Jesper

 

[lperagallo]

I am not sure that you can program expo into the throttle channel of a radio, at least not Futaba or JR. It wouldn't make any sense to do that. You can flatten out the throttle curve to get a larger center output, but you do that with a curve. Set a curve with an input range between 50% and 55% to output 50% and you get a 5% stick movement that actually will output mid stick. You can even program your idle up switch so when you turn to one position it always outputs 50% throttle. Problem solved. That way once you hit your desired output it stays there. I have not tried that, but it can be done. We do that when we are setting up pitch on a heli and need center stick with 50% output. Of course we use the pitch curve rather than the throttle curve. If you are not at center stick outputting 50% throttle than the quad will either drift up or down. Of course I am assuming that you have your altitude gain set up correctly.


Lou

If you don't want to be that radical and program a throttle curve at a straight 50% across the board you can make a curve with a flat 50% from say 50 to 65% input. That way you can still descend and climb but you will need to give more stick input then you would with a linear throttle curve.

Lou

 

[FlyEYE]

I've using a modded Turnigy 9x (with er9x software). I believe it gives me full control over everything, adding a little expo on throttle should work, however I'm still figuring it out. Looks like I have a couple options, thanks. Hopefully I'll get some time this weekend to figure it out.

 

[FlyEYE]

Adding Expo appears to have helped the slow rise or descent (no problem with the er9x) not perfect but better. Might be a quality issue with the centering of the 9X but appears to be good when connected to the PC
With any minor wind gust the WKM tends to do a sudden climb. Would adjusting the vertical gain be the right thing to play around with. I was adjusting it today and thought it had it nailed but the weather was calm at the time, next time out with just a little wind I same issue. Would too high a gain cause this or too low? What about the advanced parameters (a little nervous messing with those), Vertical I and V.Damping? Thanks.