How will inaccurate values for mounting affect the MR?

[europe]

Hi, it says in my manual that I have to change the values (X,Y,Z) offset from center of gravity, each time a change the all upp weight (eg add/remove a camera).

How will these numbers affect the behavior of the bird? To me it seems that it flies equally good even when I add a Nex-5 (about 450g) without changing anything. However I did have a very hard landing using fail-safe. I'm curious how DJI use these values in their algorithms. My guess is that they only affect flight characteristics such as stability or what? Anybody got a clue?

Also could someone link to a good Youtube video that explains a method of finding the exact COG on a complex multirotor with attached gimbal and camera, I would be most grateful. I searched but could only find people who more or less guessed.

Cheers!

 

[Benjamin Kenobi]

You'll come to an understanding of COG over time. In the beginning you can simply think of it as the middle of the craft. With gimbals and legs underneath the COG will be a little lower. And yes, it affects stabilisation and flight characteristics.

 

[PeterLester]

COG x,y,z

It is imperative that you keep the center of gravity with respect to x and y values at the center of your Multirotor.... or some of your motors will be working harder and burn out faster etc. You can shift the z value up and down in accordance with the weight and position of your payload. To ensure the payload does not shift the x,y c of g.... move the batteries so that they counterbalance correctly. Suspend your MR using one or two strong strings/cords..... when it suspends level you have determined the CofG on the x and/or y plane. Do the same for z plane by suspending the MR via a single cord from any perpendicular side.

Hi, it says in my manual that I have to change the values (X,Y,Z) offset from center of gravity, each time a change the all upp weight (eg add/remove a camera).

How will these numbers affect the behavior of the bird? To me it seems that it flies equally good even when I add a Nex-5 (about 450g) without changing anything. However I did have a very hard landing using fail-safe. I'm curious how DJI use these values in their algorithms. My guess is that they only affect flight characteristics such as stability or what? Anybody got a clue?

Also could someone link to a good Youtube video that explains a method of finding the exact COG on a complex multirotor with attached gimbal and camera, I would be most grateful. I searched but could only find people who more or less guessed.

Cheers!

 

[europe]

Thanks for your input. Slowly beginning to get a grip. But the accelerometers are located in the main unit I guess?

Still puzzled by the fact that you have to enter offsets in cm for a sensor that collects GPS data? And how can a faulty Z-value by a few centimeters affect the ability to land smoothly?

Please share your knowledge and experiences fellow MR-pilots.

Regards,

 

[Benjamin Kenobi]

Remember Die Hard 2 where they set ground level lower? The plane smashed into the ground. That kind of thing.

If you think of the craft as a disc (think spinning plate) the angles of manoeuvre are different depending where you are on that disc. If you're at the edge there will be big movements, near the middle not so much.

Something like that. Cool?

 

[europe]

Heureka! Got it! Thanks
With this in mind I guess z- position is totally irrelevant for the craft to calculate necessary thrust in order to slow down descending velocity? I have my very hard fail-safe landing in mind...

 

[bruce365]

Hi Europe, If you are putting a NEX-5 on your gimbal your copter will probably be very heavy (I can not see that you have told us what you have Naza? or what copter). I usually leave my XYZ settings at Zero it does not seem to make a big difference.

""I did have a very hard landing using fail-safe"" What form of failsafe Low battery or RTH or landing? what are your assistant settings? with a lot of weight on your copter and fail safe due to low battery it will land very quickly and hard.

Regards - bruce

 

[europe]

Hi Bruce and thanks for your input

Most of the fact regarding my hard fail-safe landing is to be found here http://www.multirotorforums.com/showthread.php?12444-Tested-failsafe-with-a-not-so-good-result

As you can see, it was a fail-safe verification test which didn´t turn out as I was hoping for.:black_eyed:

I really would like to do some changes to the craft prior the next test, but I am struggling with what really caused the problem. It is quite heavy yes, but with the new motors and props It really is designed to cope with the extra weight of the camera/link equipment.

It´s a little bit too expensive to use trial-and-error so I´m still looking to find what caused this (in my opinion) malfunction hence this thread about the function/algorithms of DJI´s system.

Regards!