WKM S800 Mounting X-Y-Z

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ksrimoungchanh

Member
Wondering if anyone can share their mounting numbers in the assistants: Seems that I cannot get rid of my isolating hover.


I have standard DJI S800/props
WKM mounted with the GPS mount in the middle of the top bracket.

I have the Zen15 with NEX7
I use 2 6000mah batteries.

My CG is now moved down to right above the ZenMuse yaw motors... My numbers are below:

IMU:
X : -7cm
Y : 0cm
Z : -7cm

GPS:
X : 0cm
Y : 0cm
Z : -22cm

Still get the toilet bowl..

I also turned my GPS but it does not seem to be doing anything.. untill it really gets off. The little adjustments are does not do much, till it is to far.

Thanks all.

KS
 

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Chris98

Member
Well your numbers are off how can your z axis on GPS be -22 and your z axis on your imu be -7 the easiest way to understand this is forward and rt of your center of gravity is positive and rear and left negative pu your hex on the y axis first to see where it goes if it goes back where it bends is the location of center of gravity on the x axis hold the x axis to find the y then virtually put the imu and the GPS on that point coordinate wise in the same spot so if your imu is in the rear facing forward its that number - and how far - cm to get there then do the z and y so my coordinates on mines are -18 on x because. I have vibration absorber kit and my y axis is 0 because its not to the rt or to the left of it and my z axis is -22 cm because my imu is -22 cm from my center of gravity measuring starting from half the imu and bottom of center of gravity you are essentially flying your center of gravity with your gps and imu on top in the same spot ps check your magnetic north make sure that your gps is facing the rt way
 
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ProPilotWannaBe

Member
Chris, I agree your comment about ksr numbers... They don't add up with what he is describing.
However, with regards to your setup, I trust your measuring from the z-axis CG, and not just measuring from the IMU position. In my case, with landing gear, camera, battery, etc., my CG is about 2cm below the bottom plate which coincidently lined lined it up pretty close with the center of the IMU on the vibe kit.
 

Benjamin Kenobi

Benjamin Kenobi

Easy? You call that easy?
I'm not sure what you mean by CG being on the zen. CG should be the very centre of the S800 when balanced. The Zen is just a payload.
 

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Chris98

Member
Well the center of gravity is not a object it's invisible the point where it breaks in space so if your wt is pulling slightly back or aggressively back the point where its bending is center of gravity the equipment is esoteric I.e batt landing gear etc its just the wt your looking for and how does it act out on the performance of the motors meaning if my -x axis is to high it will pitch forward stronger rear motor and if my positive axis is to high it will slope back stronger forward motors and the same with the y and z although z is pretty much all motors because of newton or Einsteins general theory of gravity
 

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Chris98

Member
Well while you have it cg 2cm pass your bottom plate that does not put your Imu on your center of gravity you have your x accounted for putting it there on center but how does it get to the cg let's take take the earth it goes on a axis lets say you are in Sc can you go to Cuba by just going south you will hit something southern but it will not be Cuba you need correct coordinates
 

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Chris98

Member
@ ks send a picture of your hub so I can see where your gps is at your imu should be x -6 if all of your cg is on the middle screw
 

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ProPilotWannaBe

Member
The CG is the z axis would be how far down is the tipping point. Is the aircraft top heave or bottom heavy. It becomes the point around which the rotation occurs. For example, without the Zen, the CG is higher. If I were to take off without landing gear, it's even higher. If I were to put weights at the bottom of the landing gear, it would be lower.
There are several threads on this forum and on RCG that discuss how to find the z-axis CG. All that said, I have seen a few comment that the vertical center of gravity isn't as critical as the other two.
 


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Chris98

Member
That is correct the heavier it is the cg will change because the axis will change and those numbers needs to be represented and yes all the numbers count but its true if you just leave the y axis 0 it will not make that much of a differance you can correct in your gains if its not to out of wack example if y needs to be on positive axis 10 you will be up for some serious oscillation
 


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Chris98

Member
@ pro. I don't find it that strange to share what you have learned by trail and error on a open forum so you will not have to go though the same problems that the next person has gone through it can be very costly to make mistakes on the s800 trust me I know I wish someone had help me 7 months ago ps if I'm writing on here you can take what i say to the bank because I had a issue with it at one time and I learned how to fix it but if I need help I would ask too
 

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ProPilotWannaBe

Member
Chris, I totally agree with you. I just through it was humorous. It was for that same reason that I felt it was good to explain the z-axis CG as well. Thanks for sharing, and let's keep the info flowing.
 

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