Hexa WKM Wobble problems

[xavivo]

Hi Guys, I just finished building my DW Ad6 with the WKM.
All is working perfect but the only thing that I can not solve is when I hover it starts to wobble. I have played with the gains (from 100% to 140%.) and nothing happens.
Do I have to try under 100% of gains?
I'm flying without payload, my props are APC 12x3.8. Does this things affect?

Also I don't understand what's the difference between the roll/pitch from the basic gains and roll/pitch from attitude?

Hope you could help me.
Best Regards and sorry for my English.

Xavier


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[jetforce]

Hi Guys, I just finished building my DW Ad6 with the WKM.
All is working perfect but the only thing that I can not solve is when I hover it starts to wobble. I have played with the gains (from 100% to 140%.) and nothing happens.
Do I have to try under 100% of gains?
I'm flying without payload, my props are APC 12x3.8. Does this things affect?

Also I don't understand what's the difference between the roll/pitch from the basic gains and roll/pitch from attitude?

Hope you could help me.
Best Regards and sorry for my English.

Xavier


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Try to post a screenshot of your WKM assistent, what is your CG ?

The atti gains is how the atti is held, and the basic is the roll/pitch is how it is stabalized, in all modes nothing to do with the atti.

 

[Kari]

Hi Guys, I just finished building my DW Ad6 with the WKM.
All is working perfect but the only thing that I can not solve is when I hover it starts to wobble. I have played with the gains (from 100% to 140%.) and nothing happens.
Do I have to try under 100% of gains?
I'm flying without payload, my props are APC 12x3.8. Does this things affect?

Also I don't understand what's the difference between the roll/pitch from the basic gains and roll/pitch from attitude?

Hope you could help me.
Best Regards and sorry for my English.

Xavier


Sent from my SAMSUNG-SGH-I727 using Tapatalk 2

Hi Xavier,

I would try first with thinner and lighter props, APC slow flyers are wobbly combination with wookong. Graupner 11x5 e-props are yet best i've tried in my hexa. Also you might try to go higher to around 200% or more with P/R gains. Check CoG setting are correct and hexa is balanced when battery attached.

Kari

 

[xavivo]

Try to post a screenshot of your WKM assistent, what is your CG ?

The atti gains is how the atti is held, and the basic is the roll/pitch is how it is stabalized, in all modes nothing to do with the atti.

Lars, First of all thanks for your support I really appreciate it. Here is the screenshot of the IMU location but I notice that if I leave the Z axle to 0 it fly's better (only for the IMU) the real value should be -2. All others are with the right number. I mount the IMU the same place as you have in your pics.

Do I have to adjust firs the basic gains and then the atti? Or both the same time?
If I add more gain to the pitch and roll from basic gain does it suppose to be with more wobbly?

Thanks Again

Xavier
View attachment 3907

 

[xavivo]

Hi Xavier,

I would try first with thinner and lighter props, APC slow flyers are wobbly combination with wookong. Graupner 11x5 e-props are yet best i've tried in my hexa. Also you might try to go higher to around 200% or more with P/R gains. Check CoG setting are correct and hexa is balanced when battery attached.

Kari

Kari, thanks for your support, I really appreciate it. Today I ordered the graupner 11x5 pros. (will arrive next week). Im flying without weight, do you think this can be the problem or that should not affect?
Also I notice with higher pitch and roll basic gains the wobble is less than with lower gains, is this right?
Always before flying I check my CG and it is in the right place.

I have to mention that this is my firs multirotor and I have been flying helicopters for 8 years.

Thanks Again for your help

Xavier

 

[xavivo]

DJI WKM Confusing Meanings

Also what does in DJI means in the manual with the following:
"If the gain is to large, you will find the multirotor oscillating in the corresponding direction"
"Pleas increase basic gain slowly until vibration emerges after you release the stick"

Those phrases are from the autopilot section.

What does oscillating means? Or here what is the difference to vibration?
In the second phrase does the vibration is the same as Wobble?

Cheers
Xavier

 

[quadcopters]

Hi Xavier,
I fly a WKM Heavy Lift Droidworx Quad and I use 12x3.8 Carbon props and it flies like a dream ,, a nice dream .. I also have a Y6 Droidworx which flies with 11x5 Graupners and also flies really well so it is not just about prop size.
COG is most important , Size of prop is relevant to kv of motors and lipo cell count so without knowing motor specs its difficult to recommend ideal prop size , but you should get it flying well with both sizes.

You will find that it will fly much better with some weight on , if you dont want to load your camera on until its flying right double up on lipos to add some weight and then work the gains .
Start off at 100 on pitch / roll then go up slightly and then keep going until you notice a oscillation it will look like a small shake or wag .. When this happens come back down around 10 -15 .
If gains are too low it will be difficult to control and will want to wander around .
Once your happy with pitch and roll gains , move onto ATTI gains and adjust to your liking .... Higher the Atti gains the faster the copter will autolevel and spring back the lower will make it more sedate and spongy feeling so depending on how you like it adjust as necessary .
Having the COG correct though and more weight on will make all the difference .

Hope you get her flying well .

Geoff

 

[Michael64]

xavivo
I agree with all the above and will one more the WKM does not like light disk loading so with no gimbal or extra weight you may be overproped you may try some 11x4.7 and see what happens.
The COG is very important as well but even if that right on the money with light disk load you will wobble you may try graupner props in 11x5 or APC thin electric which are stiffer and that may help to.
You also have no IMU settings you need to add those as well as the GPS sometimes and most time it make a difference as well.

Michael64

 

[xavivo]

Hi Xavier,
I fly a WKM Heavy Lift Droidworx Quad and I use 12x3.8 Carbon props and it flies like a dream ,, a nice dream .. I also have a Y6 Droidworx which flies with 11x5 Graupners and also flies really well so it is not just about prop size.
COG is most important , Size of prop is relevant to kv of motors and lipo cell count so without knowing motor specs its difficult to recommend ideal prop size , but you should get it flying well with both sizes.

You will find that it will fly much better with some weight on , if you dont want to load your camera on until its flying right double up on lipos to add some weight and then work the gains .
Start off at 100 on pitch / roll then go up slightly and then keep going until you notice a oscillation it will look like a small shake or wag .. When this happens come back down around 10 -15 .
If gains are too low it will be difficult to control and will want to wander around .
Once your happy with pitch and roll gains , move onto ATTI gains and adjust to your liking .... Higher the Atti gains the faster the copter will autolevel and spring back the lower will make it more sedate and spongy feeling so depending on how you like it adjust as necessary .
Having the COG correct though and more weight on will make all the difference .

Hope you get her flying well .

Geoff

Geoff, thanks for your input. Today I ordered the graupner 11x5 props and test them hopefully next week.
Thanks for your excellent explanation of how to adjust the gains, DJI should take this and write it on the manual.
What did you mean to check the CoG? To check it with the battery and balance the multirotor before flying it? Or the IMU/GPS X, Y, Z axis?
Are you using all the IMU/GPS X, Y, Z axis mesures with the real value? There is a post in this forum about the Z axis to be 0, how is yours?

Thanks for your input
Xavier

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[xavivo]

xavivo
I agree with all the above and will one more the WKM does not like light disk loading so with no gimbal or extra weight you may be overproped you may try some 11x4.7 and see what happens.
The COG is very important as well but even if that right on the money with light disk load you will wobble you may try graupner props in 11x5 or APC thin electric which are stiffer and that may help to.
You also have no IMU settings you need to add those as well as the GPS sometimes and most time it make a difference as well.

Michael64

Michael, thanks for your input. Next week I will try the graupner 11x5 props and see how it fly,also I will add some weight.
I also think that I'm overproped because if I set the gains to the default settings (all 100%) it wobble and there's no a big difference if I set higher gains.
Around which numbers should I have to be?
My IMU is located on the center plate so X = 0, Y=0 and for my Z axis should be -2 but I'm trying to set it back to 0 and see how it works.
There is a post in this forum about the Z axis to be 0 and they are getting great results.

Thanks for your support
Xavier

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[xavivo]

This is the link for the Z axis setting post:

http://www.multirotorforums.com/showthread.php?t=3118

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[Kari]

Xavier

Yes some of us has succeed setting z-value to zero or few cm off from right value, i have tried it also but found it more unstable with incorrect settings. I went through z-axis settings cm by cm, and it really is in my case flying best with correct settings. Difference is not huge if it's couple of cm off but you might find copter toilet bowling etc..

But remember if it doesn't work for me it doesn't mean it wouldn't work for you. Even if you had an exactly similar setup. And also there is lot of great props you might find working good, i just based my comment about slow flyer props with DJI to my tests and what i have read from forums. It's still possible but unlikely to get it flying well with slow flyers too

Kari

 

[xavivo]

Xavier

Yes some of us has succeed setting z-value to zero or few cm off from right value, i have tried it also but found it more unstable with incorrect settings. I went through z-axis settings cm by cm, and it really is in my case flying best with correct settings. Difference is not huge if it's couple of cm off but you might find copter toilet bowling etc..

But remember if it doesn't work for me it doesn't mean it wouldn't work for you. Even if you had an exactly similar setup. And also there is lot of great props you might find working good, i just based my comment about slow flyer props with DJI to my tests and what i have read from forums. It's still possible but unlikely to get it flying well with slow flyers too

Kari

Kari, thanks for the input. I will try the graupner 11x5 props and see the difference, but I'm sure that is the problem because I'm flying without weight (to much propo for no weight) and if I go with very low gains (90%) still wobbly, it's like having to much gain.
I will start working with the Z axis setting and find the right one.

Just curious what are your IMU/GPS X, Y, Z axis mesures?
And your basic gains?

Cheers
Xavier

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[xavivo]

Here are some pictures of my setup:



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[xavivo]

Hi Guys, another question. Do you fly in manual mode? Do you adjust gains in manual mode or Atti? I know that vertical gain does not apply to manual.

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[DLien]

Hi Guys,

I have been lurking and learning for the past few months. I noticed that I wasn’t the only guy who had trouble figuring out the COG on my 550 that I have been flying. Here is what I have done.

Being a private pilot, I know how to find the CG of the Cessna that fly so I adapted that process a bit. In the Cessna, the firewall serves as the datum or the zero point. Every item in the plane has a “station”, the number of inches forward or aft of the firewall that it is mounted in the plane.

Here is how the math works (in a nut shell). The attached file is a spreadsheet that will do the work for you.

1. multiply the weight of the item by its station to get its “Moment”
2. add the Moments together and the total weight of each of the items
3. divide the total moment by the total weight to get the CG.

With the 550, I used the bottom edge of the props as the zero point and measure the stations vertically, up and down along the Z axis. I am using stock DJI motors on my 550 so that puts my zero point 2.5 cm above the top plate. You can use any point as your zero point as long as you use it constantly.

DonView attachment 4919

 

[snurre]

Hi guys.
I am striving to tune a WKM on a 100cm octa and I have made some progress, but I am not done with it yet.
First, I agree with the guy who said that SF props are not a good friend of WKM. True! I started out with APC 14*4,7 SF and found it impossible to find a sweet spot in WKM auto pilot settings. I noticed that the SF props are very flexible in their nature and on big props that kind of ruins the rigid function between motor power and lifting force. The propeller disks flexing diminishes control authority. So I bought Xoar 14x5 wooden props. They are much more rigid and when using them instead of the SF props the performance increased significantly!

Now, for me it still remains to attach the camera under carriage and a camera equivalent weight, to increase the disc load and achieve true working conditions CG , AND to tune the WKM Z axis CG setting. I really hope I can get it good without sacrificing the prop size, because the 14x5 gives good flight time, reasonable hover throttle and huge peak power capacity (AXI 2814/22 at 4S).

Now (finally) to my point: The Lift Center. Should it not be part of the equation? The WKM setup interface only adresses the position of IMU unit relative to the Center of Gravity of the assembly. But isn´t the Lift Center (on Z axis) an equally significant parameter for the control algorithms?
On our multicopters, the Lift Center Z position is in the plane defined by our propeller discs.
Now imagine three different MR designs (hypothetic):
1. Extremely high motor mounts - propeller disc plane 1 meter above CG
2. Centered propeller disc plane - aligned with CG
3. Extremely low motor mounts - propeller disc plane 1 meter below CG

Obviously these three designs would provide very different control characteristics;
Number 1 would have too much static stability and pendulum effect.
Number 2 would have no inherent static stability (or instability), it´s neutral, and no significant pendulum effect.
Number 3 would have a static instability, and depending on the motor arms length probably be mostly unflyable.

If you agree with this reasoning, you agree that the Lift Center matters. Then the question is - why doesn´t DJI provide a parameter input for the Lift Center Z axis value, to include it in the flight control calculations?
I suggest this might be the missing link for consistent results in Z axis CG tuning.

Your thoughts on this most welcome.
/ Tomas