Interesting Z axis settings..

Blacksails

Blacksails

Member
I'm flying a droidworx AD8 HLE with av200 and an all up flying weight of around 5.5 - 6kg

I've been flying for some time now with basic gains at 140-150% and the atitude gains set to around 130-140. I noticed that people have said there are major problems with the wkm in wind when flown on bigger ships. I found this odd, as my craft has been coping very well with wind (no erratic twitching, with good GPS hold etc).

I never really bothered too much with the IMU Z axis cog setting. I left it at 0cm and its been flying beautifully, but today I decided to set it as accurately as I could to try and improve even more on my copter. I figured that the Z axis cog is around 7-8cm below the IMU, inbetween the camera and the frame. I found this by hanging the copter from a string on a motor and following the line to the cross section, as well as simply balancing it on my finger tips from the landing gear.

The interesting thing is that with my IMU Z axis set correctly the bird is very VERY twitchy. Even the slightest disturbance and she'll start wobbling and over correcting like mad. Adjusting the basic and attitude gains imporved this but it just will not fly as well as it used to with the Z axis incorrectly set at 0cm. I set it back to its old paramaters and she flys beautifully again in to 10-12mph winds we have today.

Just thought i'd mention this for those people who have set everything up correctly but are still having problems with any kind of wind causing instability.
 

P

Picasso

New Member
i have the same detected. The CG from my Hexa is -4 , but when setting +4 cm (6-8 cm over the real CG) the Hexa is fly better.
 



R

rwilabee

Member
With it set to 0 does it do a return to home and auto land ok?

Rich

Blacksails said:
I'm flying a droidworx AD8 HLE with av200 and an all up flying weight of around 5.5 - 6kg

I've been flying for some time now with basic gains at 140-150% and the atitude gains set to around 130-140. I noticed that people have said there are major problems with the wkm in wind when flown on bigger ships. I found this odd, as my craft has been coping very well with wind (no erratic twitching, with good GPS hold etc).

I never really bothered too much with the IMU Z axis cog setting. I left it at 0cm and its been flying beautifully, but today I decided to set it as accurately as I could to try and improve even more on my copter. I figured that the Z axis cog is around 7-8cm below the IMU, inbetween the camera and the frame. I found this by hanging the copter from a string on a motor and following the line to the cross section, as well as simply balancing it on my finger tips from the landing gear.

The interesting thing is that with my IMU Z axis set correctly the bird is very VERY twitchy. Even the slightest disturbance and she'll start wobbling and over correcting like mad. Adjusting the basic and attitude gains imporved this but it just will not fly as well as it used to with the Z axis incorrectly set at 0cm. I set it back to its old paramaters and she flys beautifully again in to 10-12mph winds we have today.

Just thought i'd mention this for those people who have set everything up correctly but are still having problems with any kind of wind causing instability.
Click to expand...
 

FlyEYE

FlyEYE

Member
Picasso said:
i have the same detected. The CG from my Hexa is -4 , but when setting +4 cm (6-8 cm over the real CG) the Hexa is fly better.
Click to expand...

I always thought it was odd that down was positive. So are you saying you are using +4 to mean above your CG? Wouldn't that mean 4cm under you CG?

View attachment 3706
 

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Blacksails

Blacksails

Member
rwilabee said:
With it set to 0 does it do a return to home and auto land ok?

Rich
Click to expand...

I haven't tried as I still can't figure how to set fail safe to a switch on my jr11x. I expect it will perform as any other platform would though, as the z axis is only the measurement of the cog to the imu....the gps still works perfectly as all the axis settings are spot on for that. And for the auto landing I don't see how it would affect that as the z axis is to the cog, not the bottom of my extended landing gear so it still doesn't really know exactly when it's going to touch earth until it does
 

K

Kari

Member
Blacksails what props do you use? I actually tried today to put z-setting in my Cinestar 6 to zero but found it to be much more twitchy than with correct settings, i use graupner e-props 11x5. I have been quite happy it's wind behauvior but always could be better.

Kari
 
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Blacksails

Blacksails

Member
I use xoar 11x5's, so fairly similar to the graupners. I don't think it has to be set to zero, on some platforms it might benefit from being much higher or much lower than the actual COG....but I've only experienced the affects it has on my copter, it may be that for the majority out there having it set perfectly on the correct COG gives the best performance.
 

FlyEYE

FlyEYE

Member
I just change mine to 0 and.... smoother no doubt. Changed the GPS location by the same amount (not zero, 8cm less then it was).
Flying Rusty's UAP1 frame,Hex, 620KV motors with 12x6 props. It is however calm outside. I almost tipped it over on take off so it seems slightly less responsive.
 

BorisS

BorisS

Drone Enthusiast
dji actually has a tutorial video on that, Its for the ace one but i doubt that they switched the logic for WKM.


boris
 
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BorisS

BorisS

Drone Enthusiast
If the CG is under the IMU you have to give it a negative number. If the IMU is under the CG its a positive. In the Diagram the little back circle were the axis meet indicates the actual components from which you are measuring to the CG. So in the case of the IMU being over the CG you fall into the green line thus negative measurement.

Boris
 


P

Picasso

New Member
homer911
yes, over the copper plate is the GPS antenna. Signal is good, not better or worse then my first test with the original beam.
 

homer911

homer911

Member
What do you mean original beam? What thickness plate is it? Is it pure copper? That must be very heavy. I'm looking for a different material than copper for my craft. Any suggestions on what material prevents the propagation of electro magnetic interference?


---
I am here: http://tapatalk.com/map.php?ksqxdy
Sent from my iPhone using Tapatalk
 


V

Vortex Aerial

Member
The ways of the Wookong are in deed mysterious.
Been using the Z number at "0" with great results for some time now as well. (perhaps this is the magic PID adjustment)

Loved the fortune cookie comment. ;)

Intend to learn ALOT at the NAB show
 

DucktileMedia

DucktileMedia

Drone Enthusiast
Just had this thought. Is it possible, just a question, that DJI's z measurement is completely meaningless and not even part of a formula for helping with stabilization? I think it may be possible that this parameter is a placebo of sorts and just sits in it's field with no links to other parts of the software. When changing my system from 3s to dual 4s, i noticed the heli flew like crap because I now had a lot of weight up top. Spinning a smaller prop faster made for smoother flight but it jitters like crazy in the air no matter what. Before I only used 1 3s battery and it flew without the oscillations in the air. I adjusted the Z for what seemed like the right CG for both batteries. I have tried so many different settings I have almost given up on making it fly the way it used to. As a test I will lower my batteries below the frame plate and leave the Zat 0 just to see for myself.
 

R

RTRyder

Merlin of Multirotors
IrisAerial said:
Just had this thought. Is it possible, just a question, that DJI's z measurement is completely meaningless and not even part of a formula for helping with stabilization? I think it may be possible that this parameter is a placebo of sorts and just sits in it's field with no links to other parts of the software. When changing my system from 3s to dual 4s, i noticed the heli flew like crap because I now had a lot of weight up top. Spinning a smaller prop faster made for smoother flight but it jitters like crazy in the air no matter what. Before I only used 1 3s battery and it flew without the oscillations in the air. I adjusted the Z for what seemed like the right CG for both batteries. I have tried so many different settings I have almost given up on making it fly the way it used to. As a test I will lower my batteries below the frame plate and leave the Zat 0 just to see for myself.
Click to expand...

The WKM is VERY sensitive to disc loading and flight weight and though I have yet to figure out exactly how they interact with each other there is definitely a relationship as well as with the axis measurements. In your case it sounds like the gain settings need to be tweaked for the weight difference which has a bigger effect than the axis measurements in my experience. I have one of my WKM on a large quad frame with Avroto motors, Graupner 11 x 5 props, a single 4S 5000 pack and an RTF weight of roughly 2800 grams, this seems to be the ideal setup as far as all around stability and GPS hold. When I installed a set of Droidworx landing gear and an AV130 the increase in weight sent it off the cliff as far as stability went, I could not find the sweet spot for gain settings until I ADDED more weight and went to a larger prop to get back to the proper disc loading. It either was far too soft and wobbly or would oscillate badly in anything other than a steady hover until I made the changes then I was able to dial in the gains so it flew acceptably well but not as nice as it did before I added the landing gear and camera mount. Eventually I put it all back the way it was and it's back to the smooth stable flyer it was at the start.

Today I reflashed a new set of ESCs for the CS6 WKM and in the process of testing them out noticed that it flew quite differently without the weight of the Nex 5n on the AV130 so I strapped a second 4S 8000 pack to the camera platform not wanting to risk the 5n if things went wrong. The pack being substantially heavier than the 5n the additional weight changed the Z axis CoG measurement enough that the effect was immediately noticeable. A tweak of 2 CM on the Z axis as a SWAG at the change seemed to put things back to close to normal so I have to say that it depends a lot on the setup if you will see a difference with the correct axis measurements or not, it was noticeable to me on the 825mm Cinestar frame but I don't see as much difference when I make a change to the same setting on the much lighter 550mm WKM quad with Avroto motors.

Ken
 

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