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Old Jul 15, 2012, 10:16 AM
Im the eye In the sky
epedemi's Avatar
Denmark, Region Zealand, Jyderup
Joined Mar 2012
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Quote:
Originally Posted by tritan View Post
epedemi,
pls check your z-values for your IMU and correct me if I am wrong but you have a positive value for your IMU which place it below the CG.
Yes I have a positive Z for my IMU. Because I have heavy equiment on the buttom, like my lipo and my cam+gymbal.
That is how I understand the manual, and I get good stability in gps with allmost no drifting or movent, I would say 50cm in diameter in windy conditions... I find that good!
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Old Jul 15, 2012, 10:17 AM
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United Kingdom, England, Blackpool
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Originally Posted by nicnaimless View Post
Proof that X Y Z do not need to be changed based on distribution of weight ( CoG )
@3:30 we see the multi take a heavy load on one arm and no adjustments made. Gyros and Acc don't measure weight, only changes in space postition. CoG is often center of craft but not always.
http://www.youtube.com/watch?v=FeFEYTW7IXI
I agree, x and y are generally at centre, Y is not though, when batts and gimbals/cameras are added the Z can lower quite considerably.
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Old Jul 15, 2012, 10:19 AM
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Originally Posted by epedemi View Post
Yes I have a positive Z for my IMU. Because I have heavy equiment on the buttom, like my lipo and my cam+gymbal.
In that case your Z value should be negative...up from Cg is Negative.
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Old Jul 15, 2012, 10:19 AM
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Quote:
Originally Posted by Bengit View Post
All x,y and z references for the GPS and IMU are to the Cg of the craft (as stated in the manual). Anyone with RC experience (as you have done) would normally try and assemble the craft so that the Cg is at centre...hence by default, measuring the IMU/GPS to craft centre would be ok. As stated early, the only problem comes with the Z that can sometimes be hard to estimate when items are slung inder the craft. Just trying to help, A/C Weight and Cg is my job. Regards
Yea, i do understand that, ill do some estimates for Z,
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Old Jul 15, 2012, 10:21 AM
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Originally Posted by Bengit View Post
In that case your Z value sould be negative...up from Cg is Negative.

Yes, exactly, that's what I also would do.

If your IMU is above CG (green) then you should have a negative value, not positive.
It's where you place your IMU acording to CG , not the opposite.
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Last edited by tritan; Jul 15, 2012 at 10:40 AM.
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Old Jul 15, 2012, 10:21 AM
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United States, MI, Jenison
Joined Jun 2008
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Quote:
Originally Posted by nicnaimless View Post
Proof that X Y Z do not need to be changed based on distribution of weight ( CoG )
@3:30 we see the multi take a heavy load on one arm and no adjustments made. Gyros and Acc don't measure weight, only changes in space postition. CoG is often center of craft but not always.
http://www.youtube.com/watch?v=FeFEYTW7IXI
The CoG of a quad with a lipo hanging off ond arm would be very close to the end of that arm. I double-dog dare you guys to add the weight of a lipo on 1 arm then find the true CoG (which will be almost impossible) then busting out your trust ruler and tossing the distance from the true CoG to IMU in the assitant, write it and try flying. You'll be flipping faster than pancakes at IHOP on a Sunday afternoon.
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Old Jul 15, 2012, 10:22 AM
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Canada, QC, Greenfield Park
Joined Jun 2009
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I have found that the correct setting for the Z is quite important to get a nice hold. I was having a very slight wobble that I couldn't get out with gains so I tried changing my Z from I think -9 to -11 and it made a huge difference. Lots of folks are flying with their CG much lower than they think they have it and it makes a difference.
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Old Jul 15, 2012, 10:22 AM
Im the eye In the sky
epedemi's Avatar
Denmark, Region Zealand, Jyderup
Joined Mar 2012
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Quote:
Originally Posted by Bengit View Post
In that case your Z value sould be negative...up from Cg is Negative.
W.T.F ???

Then why am I getting good flights then?
Something I misunderstand?
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Old Jul 15, 2012, 10:24 AM
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Originally Posted by Bengit View Post
I agree, x and y are generally at centre, Y is not though, when batts and gimbals/cameras are added the Z can lower quite considerably.
Yes, and in that video the motor on this arm has to work harder to maintain level position - not good. Thats why you want the CG to be in the middle of the craft.

About 00:30 into that video you can see that they have placed the battery on top of the frames having a perfect relation between Center of gravity and the plane/height (z-value) of the props, cant' be any better than that.
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Old Jul 15, 2012, 10:25 AM
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Quote:
Originally Posted by Bengit View Post
I agree, x and y are generally at centre, Y is not though, when batts and gimbals/cameras are added the Z can lower quite considerably.
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.
The Hunting Trip Movie - OFFICIAL Behind the Scenes (4 min 56 sec)
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Old Jul 15, 2012, 10:26 AM
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Originally Posted by nicnaimless View Post
The CoG of a quad with a lipo hanging off ond arm would be very close to the end of that arm. I double-dog dare you guys to add the weight of a lipo on 1 arm then find the true CoG (which will be almost impossible) then busting out your trust ruler and tossing the distance from the true CoG to IMU in the assitant, write it and try flying. You'll be flipping faster than pancakes at IHOP on a Sunday afternoon.
the video only proves it can handle it, does not mean its correct to do it though.

all that means is its working far harder to maintain level flight.
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Old Jul 15, 2012, 10:27 AM
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.....
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Old Jul 15, 2012, 10:30 AM
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United States, MI, Jenison
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Originally Posted by Bengit View Post
What are you flying, a quad, hex, octo?
Currently I'm flying CineStar 8 with 2 axis gimbal.
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Old Jul 15, 2012, 10:31 AM
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Originally Posted by Davebbb View Post
the video only proves it can handle it, does not mean its correct to do it though.

all that means is its working far harder to maintain level flight.
Please explain why a gyro needs to know where weight is?
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Old Jul 15, 2012, 10:36 AM
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Quote:
Originally Posted by tritan View Post
Yes, and in that video the motor on this arm has to work harder to maintain level position - not good. Thats why you want the CG to be in the middle of the craft.

About 00:30 into that video you can see that they have placed the battery on top of the frames having a perfect relation between Center of gravity and the plane/height (z-value) of the props, cant' be any better than that.
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.
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