Aeronavics / Droidworx Skyjib X4. GPS position hold problems when fully laden

[Dependabletv]

Hi All,
I have an issue with GPS position hold on a Skyjib X4. It has an AV200 gimbal with Radian stabilisation. Wookong M flight control. It seems to fly reasonably with no payload. However, when we add our maximum payload of 2.5kg it exhibits toilet bowling and really quite significant GPS position hold drifting. I've done all the compass calibaration and GPS RX direction tweeking that's described in the manual.

I need to diagnose and fix the problem but am at a bit of a loss to know where to start. (I was in a similar state with our gimbal recenetly but thankfully found the utterly brilliant John Cunningham) We got the helicopter RTF (or not I fear!) and have been on a very steep learning curve ever since. It has no flight data recording on it at the moment. Things I am wondering are whether the position of the GPS RX might be an issue. It's currently on a boom a little lower than the IMU and below the batteries. It's also under the path of a prop. I've read on the FF forums that the GPS RX should be above the batteries??? As problems can occur with larger power draws that would be required for heavier lifts. Would we be better to mount it on the top of the crash cage? (We're using 2 * 10 amp 6S batteries) We have lipo alarms on the batteries set to 3.2v. They alarm pretty much from take-off but settle down after a few seconds. We then get around 6-7 minutes fully laden. The battery alarm on the remote is set to 21.5v. This also alarms from early in flight but each time we check the batteries with a % checker they seem fine for 6 mins or so.

What I really want some advice on is how to diagnose the fault. Is there a way of recording and interpreting the GPS data in flight? Why might there be a difference in GPS performance when fully loaded? All help very gratefully received,
Regards
Richard

 

[nickwad]

Do you have any pictures showing the GPS location? I have almost the same x8 , AV 200, Wookong . I am having a big problem to get stable video with the tarot stabilization on the av 200 !

 

[iceman]

Hi Richard, if your GPS antenna is under a prop I'd say it's too close to the motor (magnetic field) but without a picture of your set up its hard to say for sure. Just curious who John Cunningham is? I also use AV200 and would like better results from it.

 

[Dependabletv]

View attachment 14687The GPS RX is on the left hand rear boom as you look at this photo. It's just under the tip of the props but the cables run next to the power feeds for the motors. My first plan is to move it to on top of the crash cage to see what that does. John Cunningham is the chap that invented the Radian which he then licensed to Freefly. They don't like talking about Joh but boy does he know his stuff compared to the FF Radian forums.

 

[jackwrangham]

Hi Richard

A quick thought... since you got the machine ready to fly was the CofG calibrated with no payload? If you have since added a payload the CofG will have changed quite significantly (especially on the Z axis) - this could easily be causing the issues you have.

 

[Dependabletv]

Hi Jack,
We adjust the COG to the payload. That was an issue when we first got it as RTF is one thing, but being that we needed to adjust it would have been a great help! (Yes that's tinged with bitterness and resentment!) But we got there the hard way! So, it's a good shout but I'm pretty sure that's not the issue,
Regards
Richard

 

[Dependabletv]

Hi Richard, if your GPS antenna is under a prop I'd say it's too close to the motor (magnetic field) but without a picture of your set up its hard to say for sure. Just curious who John Cunningham is? I also use AV200 and would like better results from it.

The crucial thing John helped me with is to get the servo out down to 0% in idle. We needed to replace the fixed resistors with pots (£4 from Maplin) and tuned the Servo Out and 0%. It all came good at that point. Not sure if that's your issue but it helped me enormously.

 

[iceman]

A

The crucial thing John helped me with is to get the servo out down to 0% in idle. We needed to replace the fixed resistors with pots (£4 from Maplin) and tuned the Servo Out and 0%. It all came good at that point. Not sure if that's your issue but it helped me enormously.

I've spent quite some time setting up my gimbal but using RSGS has been a challenge, it stabilises really well holding the horizon every time and tilt but I still have some occasional jitters I would like to eliminate if possible. Looking at you rig I would move the GPS as you have planned and make sure it is orientated in relation to forward direction. RTF are always going to be a challenge to set up compared to self build as you won't have the benefit of knowing how each component in the build has been installed and setup. Hope you get it sorted.

 

[Quinton]

The GPS RX is on the left hand rear boom as you look at this photo. It's just under the tip of the props but the cables run next to the power feeds for the motors. My first plan is to move it to on top of the crash cage to see what that does. John Cunningham is the chap that invented the Radian which he then licensed to Freefly. They don't like talking about Joh but boy does he know his stuff compared to the FF Radian forums.

So you know I just built my first DW Skyjib 6 ti and I put the GPS/Compass on top of the crash cage.
Everything is flying really well at the moment with the latest Wookong firmware.

I took the aluminium GPS holder that came with the wookong, and tapped the hole in it so you can screw it though the hole at the top using a bolt.
That way there is no need to have it stuck to the top, and you can turn it to whatever angle you like at any time.

 

[jackwrangham]

Hi Jack,
We adjust the COG to the payload. That was an issue when we first got it as RTF is one thing, but being that we needed to adjust it would have been a great help! (Yes that's tinged with bitterness and resentment!) But we got there the hard way! So, it's a good shout but I'm pretty sure that's not the issue,
Regards
Richard

Cool, well in that case I would try mounting the GPS on top of the crash cage as suggested by some others here - we havent had problems mounting it on the boom on flat octos, but maybe with the shorter booms on the X8 its too close to the motors. We have it mounted on top on our X8, and also some copper tape on the underside, which may help. Good luck!