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Old Jul 15, 2012, 11:36 AM
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Originally Posted by nicnaimless View Post
I've hung cameras 12" below multis without changing values. The gyros don't know the difference in the weight distribution. Here is a behing the scenes of a short film I did. I hung a GoPro very low to actually fly it into the river. Gyros were clueless of where weight was. All they wanted to do keep the craft level. http://www.youtube.com/watch?v=WDkfnxdDIxY&feature=plcp
12inches, you must be flying a big multi, i am flying an AD6HLE and cant get a camera that low below the centre plates. You may be right, all i am trying to do is explain what is in the manual.....you did ask!!!
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Old Jul 15, 2012, 11:36 AM
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Quote:
Originally Posted by nicnaimless View Post
I've hung cameras 12" below multis without changing values. The gyros don't know the difference in the weight distribution. Here is a behing the scenes of a short film I did. I hung a GoPro very low to actually fly it into the river. Gyros were clueless of where weight was. All they wanted to do keep the craft level. http://www.youtube.com/watch?v=WDkfnxdDIxY&feature=plcp

I think there is a "magic" formula consisting of motorsize/power/torque & prop/lenght/pitch/weight & arm lenght & weight of multi & CoG (all values) etc etc.

Some have found this formula and some haven't - I can just congratulate those who has.
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Last edited by tritan; Jul 15, 2012 at 11:55 AM.
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Old Jul 15, 2012, 11:40 AM
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Please correct me if I am wrong...
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Old Jul 15, 2012, 11:44 AM
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FW 5.12 octa - SAFETY ALERT

FW 5.12 for octa SAFETY ALERT

I have just upgraded WKM firmware from 5.08 to 5.12.
Octacopter "I", batt: 4S, ESC: CC Phoenix ICE 50 fw4.01 (set for MR, outrunner)
"Old" type WKM controller (december 2011)

After upgrading the fw I went through all tabs and reset /wrote the settings, new TX calibration included.

ISSUE, on ground, transmitter on, all motors should be at rest / disarmed / quiet:

Motors 7 & 8 periodically kick in . Very short bursts, but enough to turn props around a few turns (Youtube video upload in progress).

During this workshop session the octa was supplied by a power supply featuring adjustable current limit. The current limit was set to limit current to just a few amps, as a safety precaution should any surprise occur. It seems like sometimes during these power bursts the current limitation kicked in (Spectrum telemetry signalled low batt). Therefore I do not know how much power would have been employed into the props if it had been supplied by the regular high power drive batteries. And I feel reluctant to try that out, since I now strongly suspect a FW bug in 5.12 for octas.
With 5.08 this never occured (burst when all motors should be quiet).

I cannot rate the severity of this suspected bug, but any safety related bug should be treated with great caution, even if not 100% verified. And we all know that 5.10 had a bug that made octas not work at all. Maybe that bug was not completely resolved and 5.12 was not thoroughly tested on octa?

/ Tomas
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Old Jul 15, 2012, 11:45 AM
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Originally Posted by epedemi View Post
Please correct me if I am wrong...
This is how I have understand it:

your CG is below your multi right? Ok, lets say it is about on top of the red "Z" in your picture of assistant, about on the "roof" of the red "Z". So if you move everything , the CG white/black cirle, all red and green lines down so now the CG stands on the "roof" of the red "Z" your IMU is ABOVE the CG circle ok?
Green is negative.

Same for GPS, above which is green which is negative. I know of none who has a positive value for the GPS.
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Last edited by tritan; Jul 15, 2012 at 11:54 AM.
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Old Jul 15, 2012, 11:45 AM
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Originally Posted by nicnaimless View Post
Yes... for max efficiency you would have weight distributed evenly. But when you input changes in X Y Z values you are telling the WKM that the IMU has been placed that far away from the center of the craft which is USUALLY the CoG if you did a good job setting it up.
Thought you did not bother changing x, y and z?

I give in...
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Old Jul 15, 2012, 11:46 AM
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Originally Posted by nicnaimless View Post
Please explain why a gyro needs to know where weight is?

If your CoG is central with everything else on as it should, then you add weight to the end of one arm, then the CoG is thrown, unless you alter other placements to compensate it, so no, the Gyros dont know about weight, but they know the craft is not level, so attempt to keep the craft level, as they know the CoG is off, which practically amounts to them knowing you just shoved a big lump on the end of your craft.
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Old Jul 15, 2012, 11:50 AM
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Originally Posted by Davebbb View Post
If your CoG is central with everything else on as it should, then you add weight to the end of one arm, then the CoG is thrown, unless you alter other placements to compensate it, so no, the Gyros dont know about weight, but they know the craft is not level, so attempt to keep the craft level, as they know the CoG is off, which practically amounts to them knowing you just shoved a big lump on the end of your craft.
I don't disagree with your statement here. But when you change the X Y Z values, you are telling the WKM that the IMU has been moved from the center of the craft by that much. You are not telling the IMU that you have uneven weight distribution. Like I said, DJI assumes you balanced your multi and they decided to call center of craft Center of Gravity. All the IMU understands is where is the center of your craft.
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Old Jul 15, 2012, 11:51 AM
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Originally Posted by epedemi View Post
Please correct me if I am wrong...
The circle is the CoG point , yes?

so therefore anything above that point is Negative value,

those lines are merely examples of direction, all you need look at is the CoG point being "THE" point to consider.
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Old Jul 15, 2012, 11:51 AM
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Originally Posted by nicnaimless View Post
Go take your WKM multi fly it, land and then hang a lipo or some other weight off the end of one arm. You will quickly learn that the Gyros and Accelerometers do not care about where weight is, which is CoG. They will make the necessary compensations to get the IMU backt to zero point. CoG and Center of craft are most often similar and I believe that DJI tried to write a manual for beginners that don't understand the data that gyros and accs. need to do the job. So in an attempt to follow the K.I.S.S. method they actual caused you guys to start chasing XYZ rabbits ever time you add an ounce to the multi. This isn't my first rodeo.

I'm not the one having flight performance issues. My rig has flown excellent from day one. I have added FPV gear, changed props, changed cameras, and numerous other devices added. I have never readjusted the the XYZ and only gain adjustments. So as you've said.... "I've gotten lucky" many times.
The xyz has NOTHING to do with atti or manual mode.. So you are right kind of. The senors dont care until you thorw the GPS / Compass in the Mix It's how DJI's fllight logic works.. If you want solid GPS(PH, RTH) you need these values to be close.

If it works for you then thats great but dont tell people they are reading the manual wrong. There are MANY videos showing how to get CoG for the WK-M
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Last edited by blade strike; Jul 15, 2012 at 11:57 AM.
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Old Jul 15, 2012, 11:56 AM
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Denmark, Region Zealand, Jyderup
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Quote:
Originally Posted by Davebbb View Post
The circle is the CoG point , yes?

so therefore anything above that point is Negative value,

those lines are merely examples of direction, all you need look at is the CoG point being "THE" point to consider.

Yes circle is COG.
I take that as I am right then ....
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Old Jul 15, 2012, 11:57 AM
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Originally Posted by epedemi View Post
Yes circle is COG.
I take that as I am right then ....

So your CG is exactly in the middel of your multi like in the picture and not below ???
Come on now ....

What happens if you turn your multi upside down - where is your CG now?

Grab the multi with one hand and turn it 90 degress, that is arms vertically , does your multi wants to turn either way or is it perfectally balanced in the middle?
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Old Jul 15, 2012, 11:57 AM
jab
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Quote:
Originally Posted by Davebbb View Post
If your CoG is central with everything else on as it should, then you add weight to the end of one arm, then the CoG is thrown, unless you alter other placements to compensate it, so no, the Gyros dont know about weight, but they know the craft is not level, so attempt to keep the craft level, as they know the CoG is off, which practically amounts to them knowing you just shoved a big lump on the end of your craft.
They what about stabilization when flying in wind gusts and such things? Does the WKM think about stabilization as weights moving around the frame while flying?

I agree with epedemi, and the math does to. A IMU does not care about weight distribution, it only sees rotation and acceleration and wants to know the center of the axes involved. The motor mix then has to compensate for any uneven weight distribution to keep the frame level, but the IMU could not care less about this.
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Old Jul 15, 2012, 11:58 AM
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Originally Posted by nicnaimless View Post
I don't disagree with your statement here. But when you change the X Y Z values, you are telling the WKM that the IMU has been moved from the center of the craft by that much. You are not telling the IMU that you have uneven weight distribution. Like I said, DJI assumes you balanced your multi and they decided to call center of craft Center of Gravity. All the IMU understands is where is the center of your craft.
Well ,i think the confusion is the fact, that to be fully efficient, you "need" a central point of gravity, and DJI are "assuming" that you have done that, so the placement options on the mounting section of the software are saying you can have the IMU in 4 positions, and each postion than has to be measure from the Centre of the craft, which if you have balanced correctly, should also be the centre of the craft.
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Old Jul 15, 2012, 11:59 AM
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Originally Posted by Bengit View Post
Thought you did not bother changing x, y and z?

I give in...
Yes, I adjust them accordingly to the center of the aircraft then I leave them alone unless I move the GPS mod or IMU. I do not change the values if I change the weight of the craft or add a piece of equipment such as different cameras.
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