All up weight configuration and mounting location

J

jotto

Member
1) The manual on the DJI Naza says that "You must re-configure if the ALL-UP-WEIGHT had been changed on your multi-rotor" under "Mounting location". I can't find any AUW setting in the software. Where do I define this?

2) Why does the software need to know about the location of the GPS relative to the CG? A GPS isn't that accurate anyway. Or am I supposed to enter the location of the Naza control unit?
 

ChrisViperM

ChrisViperM

Active Member
Hello

1) If you change the weight (ALL_UP_WEIGHT) of your copter by using different LiPo's, different camera, additional FPV equipment, than your center of gravity (COG)will change...sometimes more and sometimes less. To set the correct center of gravity is pretty important and will affect the performance of your copter. The settings are a bit irritating, but with a little bit of logical thinking it should not be a problem.

2) I tried to mount the GPS in different positions without changing the settings in the Assistent Software...and did not see any difference in performance. The important thing is to have the arrow on the GPS in a straight line with the IMU....if you have it a few degrees to the left or right will influence the copters performance. Although the mounting position doesn't seem to have an affect on the copters behaviour, I still make the settings according to the manual....you never know.


Chris
 

jforkner

jforkner

Member
jotto said:
1) The manual on the DJI Naza says that "You must re-configure if the ALL-UP-WEIGHT had been changed on your multi-rotor" under "Mounting location". I can't find any AUW setting in the software. Where do I define this?
Click to expand...

That's a good question. I have no idea what parameter you would modify by simply changing the weight of the MC. Changing the X, Y or Z parameters on the Mounting screen could be necessary if you changed the CG, but that's not AUW. Based on the poor language used in the manual, I would not be surprised if their ALL-UP-WEIGHT term really means something else---what, I have no idea.

Using the process of elimination, I cannot figure out what they would have you change based on weight alone:
  • Mounting - NO
  • Motor Mixer - NO
  • Tx Cali - NO
  • AutoPilot - Maybe???
  • Gimbal - NO
  • Voltage - NO

From my experience, there is no need to change the gains (AutoPilot) if the AUW changes. I fly my non-GPS Naza-based quad & hexa with & without a camera, which obviously changes the AUW, and never alter a configuration parameter (of which there aren't many). So who knows what they're talking about.

Jack
 

ChrisViperM

ChrisViperM

Active Member
jforkner said:
That's a good question. I have no idea what parameter you would modify by simply changing the weight of the MC. Changing the X, Y or Z parameters on the Mounting screen could be necessary if you changed the CG, but that's not AUW.


Jack
Click to expand...

The center of gravity will change if you change the weight of your copter, therefore you have to re-adjust x-y-z values of COG


Chris
 

kloner

kloner

Aerial DP
i think the sensitivity of the module helps the magnetometer and gps react with the gyros and acceleromters. When you nail it, they hover awesome. When them numbers are wrong, the position hold sucks.
 

OneStopRC

OneStopRC

Dirty Little Hucker
So what you guys are saying, if I am right, if not please let me know. The place where you set the X Y Z is where the CG is? I thought that was where you tell it the GPS antenna is?
 


OneStopRC

OneStopRC

Dirty Little Hucker
ohh, I will need to pay more attention to that. Mine is not flight ready as yet, waiting on a couple of parts.

Thanks for the heads up.
 

P

PeterLester

Member
If I understand it correctly, the 9DOF IMU inside of the MC must be at absolute Center of Gravity on all 3 planes. Even when the batteries and/or payloads are stacked at dead center horizontally, any change in the weights will require an adjustment to the "z" or vertical parameter. The NAZA software probably takes into account both the weight and the height of the GPS antenna which is supposed to be mounted up and way from everything else on the end of the carbon fiber rod. As far as inherent mechnical stability of the airframe, a CG located below the thrust plane of the motors would likely be more stable. In the case of the S800, for additional stability, they have actually moved the thrust plane to angle inward at the top much like dihedral on an conventional top winged aircraft as far as I can determine.
 


P

PeterLester

Member
In a system that has 9 degrees of freedom, such as the typical IMU used for these devices the components will be:
3 degrees of freedom for the Magnetometer
3 degrees of freedom for the GPS position
3 degrees of freedom representing the Altimeter (guessing here)
Above are all based on a single center of gravity for the entire system.
The Kalman equation performs complex concurrent calculations such that any significant distance between the GPS location and the center of the IMU will introduce significant errors.
While minor errors will go unnoticed, there may be situations where rapid spinning and or simultaneous rotations on two or more planes could result in the IMU losing control of it's own 3D position relative o the actual 3D space GPS position....

http://www.jayconsystems.com/forum/viewtopic.php?f=22&t=40&start=50
 


P

PeterLester

Member
Oops.... some mistakes in my previous post. If I understand IMUs correctly there are:
for each of the 3 axes, i.e., x,y,z coordinates. The most critical are....
3 magnetometers, 3 accelerometers, 3 gyros for a total of......
9 degrees of freedom.
Some advertise 12 degrees of freedom now but I don't fully understand that.

Additional functionality is then added such as GPS 3D positioning and altimeter for tighter altitude control close to the ground.

In my opinion, if you can rapidly rotate your MC 360 degrees continuously and have it spin on its center, you have a very well calibrated/balanced system.
If it rotates off center then there are errors in the Kalman calculations attributed to manual data input related to Center of Gravity and/or unequal motor thrust issues.
 

ChrisViperM

ChrisViperM

Active Member
jotto said:
Sorry, I didn't understand that. Are you saying there are two different settings? I can only find one GPS relative to COG setting.
Click to expand...

ooops....since I only use WooKong-M (where there is 2 different settings) I thought that in the Naza assistent it will be the same....now I checked the manual and saw that in the Naza assistent there is only x-y-z for the GPS....but the settings still will change if you add some (significant) weight and your COG is changing. Maybe in the Naza COG + GPS position are somehow combined into one setting. But if you set your values as described, you should be on the save side....

Chris
 

FerdinandK

FerdinandK

Member
You have to change (e.g. raise the baisc ) gains if you copter is getting heavier. Typically for IMU and GPS mounting position only the z-value changes (a bit). If you are flying the copter with different loads, setup your gains for the most light-weight setup.

best regards

Ferdinand
 

C

cpmboy

Member
FerdinandK said:
You have to change (e.g. raise the baisc ) gains if you copter is getting heavier. Typically for IMU and GPS mounting position only the z-value changes (a bit). If you are flying the copter with different loads, setup your gains for the most light-weight setup.

best regards

Ferdinand
Click to expand...
so, is it...
heavy loads....higher gains and vice versa?.....or
the other way around?..
 

FerdinandK

FerdinandK

Member
If the "load" is mounted "rigid" to the frame, the gains are getting higher with the load (the more the load is placed off-center as the moment of inertia raises).

best regards

Ferdinand
 

B

Bob. just Bob

New Member
Gotta insert another newbie question here, regarding the XYZ axis measurements. I am interpreting the (haha) manual to read that the GPS antenna is a MINUS number in the vertical plane (green line) when it is above the MC?
 

P

PeterLester

Member
Yes.... the point of reference becomes the GPS module such that the controller, i.e., Naza or WKM is below the GPS and therefore the z value is negative.
Bob said:
Gotta insert another newbie question here, regarding the XYZ axis measurements. I am interpreting the (haha) manual to read that the GPS antenna is a MINUS number in the vertical plane (green line) when it is above the MC?
Click to expand...
 

EastCoastJib

EastCoastJib

Member
Out of curiosity.. is there a calculation for determining COG? I have yet to enter any of the x,y,z values.. and my bird flys straight and holds position fine. But I'd love to make it even more of a sure thing if possible.
 

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