WKM IMU position on the vibration absorber setup

[fj_montilla]

Here's what I did, and I'm sure there will be other solutions, and suggestions. I mounted my IMU plate forward in the bipod, in front of my Zenmuse location. However, I moved my MC out from the usual slot and placed it on top of the center plate, where the cable from the IMU and GPS puck could easily be accessed. A strong double-sided piece of tape will keep it in place. All esc cables nicely tied will do the trick. Earlier entries in this thread a couple of us shared IMU positions for the assistant software, check them out. Hope this helps.

 

[ProPilotWannaBe]

ChrisViper has some nice picture's he has uploaded that helped me when I reconfigured mine with the anti-vibe kit:
http://www.multirotorforums.com/showthread.php?12396-S800-clean-build-tips-and-info
(post #11)

 

[ddikie]

Hi

On ChrisViper post I see you have a IMU V2 mounded in the nose of the aircraft presume you have it facing backwards in the confirgurator? I have a zenmuse which i will be fixing soon how much would that effect the x y z IMU settings?

There is no arrow on the V2 IMU presume the cable comes out of the font of the unit same as the old one, where did you calculate your measurements from too was it the front top edge of the IMU / front bottom of the IMU / its centre ?

I currently have it above the rear battery on the plate and have accounted for x -17 / y 0 / z -3 but that seems way off in comparison to what was posted by people..can anyone shed some light on this i had a crash earlier and hand my second flight to be better..

Where is the COG calculated from..with the Lipos & landing gear i think its slightly lower than the bottom of the hub plate? what is the consensus?


few pics attached..thats to chris for the suggestions for arial placement and the tube..wonderful idea..

View attachment 13513View attachment 13514View attachment 13515View attachment 13516

 

[ProPilotWannaBe]

On ChrisViper post I see you have a IMU V2 mounded in the nose of the aircraft presume you have it facing backwards in the confirgurator? I have a zenmuse which i will be fixing soon how much would that effect the x y z IMU settings?

When you install the Zenmuse, your center of gravity is going to move, so by definition, all your numbers will need to be re-figured out. Now, if in the process of installing the Zenmuse, you rearrange things so that the CG is still close to the center of the main hub, then your X and Y values shouldn't change. For example, if you currently have the battery tray right below the hub, and then move it to the back when you install the Zenmuse, if done correctly, your X/Y CG location could remain in the same spot. You should really do this because having the X/Y location of you CG as close to the center is HIGHLY recommended (improved performance, plus easier on the motors/ESCs). In the Z axis, there isn't much you can do. The Zenmuse is going to lower your CG position because of it's weight and located below the hub. And having a lower CG is actually a good thing.

There is no arrow on the V2 IMU presume the cable comes out of the font of the unit same as the old one, where did you calculate your measurements from too was it the front top edge of the IMU / front bottom of the IMU / its centre ?

I can't speak categorically on the IMU V2 direction, but your presumption of using the same orientation as the V1 makes sense. I measured my IMU position to the center of the cube.

I currently have it above the rear battery on the plate and have accounted for x -17 / y 0 / z -3 but that seems way off in comparison to what was posted by people..can anyone shed some light on this i had a crash earlier and hand my second flight to be better..

It all boils down to where your true Center of Gravity is. Your numbers don't seem too far fetched. I think my Z is at 0, and my X is around what yours is. I can check tonight when I get home.

Where is the COG calculated from..with the Lipos & landing gear i think its slightly lower than the bottom of the hub plate? what is the consensus?

My COG is about 1-2cm below the bottom plate and basically centered. That is with my LiPos, Zenmuse, and camera, all attached, and the landing gear in the down position.
That's why the Z of my IMU is zero, because of where the IMU is on the tray which places it slightly below the lower tray.

 

[fj_montilla]

Hi

On ChrisViper post I see you have a IMU V2 mounded in the nose of the aircraft presume you have it facing backwards in the confirgurator? I have a zenmuse which i will be fixing soon how much would that effect the x y z IMU settings?

There is no arrow on the V2 IMU presume the cable comes out of the font of the unit same as the old one, where did you calculate your measurements from too was it the front top edge of the IMU / front bottom of the IMU / its centre ?

I currently have it above the rear battery on the plate and have accounted for x -17 / y 0 / z -3 but that seems way off in comparison to what was posted by people..can anyone shed some light on this i had a crash earlier and hand my second flight to be better..

Where is the COG calculated from..with the Lipos & landing gear i think its slightly lower than the bottom of the hub plate? what is the consensus?


few pics attached..thats to chris for the suggestions for arial placement and the tube..wonderful idea..

View attachment 17084View attachment 17085View attachment 17086View attachment 17087

It really doesn't matter if your IMU is facing forward, backwards or on its side. You have an option to mount the IMU in any of these configurations as long as you select that config in the WKM Assistant Software, and your measurements are correct. I have the IMU mounted on it's plate in the rear, above the battery, same as yours, if you consider installing the Zenmuse.

Taking the Zenmuse into account, My IMU location is the following:
X -19cm
y 0 cm
z 5 cm

 

[ddikie]

Ok will measure it when i get the zenmuse on and the COG sorted.
But unless i misunderstand they way to calculate the +- of the red & green line any thing mounted above the green line should be minus figure & bellow the red line a positive figure..therefore your COG must be 5 cm bellow the COG..which is difficult for me to visualise at present until i try..I suppose it all depends on weight & location..we will see tomorrow..take care

 

[ddikie]

Ok thanks..and when your measuring the Z access of IMU are you measuring also to the centre of the IMU cube? or bottom or top mine is currently at 3cm to the top / 1.5cm to middle & 0 cm to the bottom of the IMU...does that make sense? also which flight mode do u take off is GPS / ATTI reading between the lines people get GPS lock first just to make sure failsafe would kick it..and then switch to ATTI for take off..and then back to GPS to position hold..

LAst question then i am going to bed..when I got my phantom 4 months ago the stock TX had a self centred throttle stick, if i let go it would spring to the middle and hover..when i upgraded the TX to Futaba i got this modified to act the same and am happy with the way it works..so in theory i should dbe able to fly the s800 -EVo in the same manner and adjust gains so it hovers at centre stick..i wonder with 8kgs if it could or what teh gain values would have to be to achieve that..

Take care

 

[ProPilotWannaBe]

But unless i misunderstand they way to calculate the +- of the red & green line any thing mounted above the green line should be minus figure & bellow the red line a positive figure..therefore your COG must be 5 cm bellow the COG..which is difficult for me to visualise at present until i try..I suppose it all depends on weight & location..we will see tomorrow..take care

You are correct, and I don't know exactly fj_montilla's setup, but yes, his settings would imply that his COG is a couple of cm above the top plate, which I also have difficultly seeing, especially if he has a Zenmuse mounted. Montilla, can you help us understand how/why you have a positive 5cm for your IMU?

Ok thanks..and when your measuring the Z access of IMU are you measuring also to the centre of the IMU cube? or bottom or top mine is currently at 3cm to the top / 1.5cm to middle & 0 cm to the bottom of the IMU...does that make sense? also which flight mode do u take off is GPS / ATTI reading between the lines people get GPS lock first just to make sure failsafe would kick it..and then switch to ATTI for take off..and then back to GPS to position hold..

I measure to the center of the cube.
Currently, I always take off in GPS mode, but that's just me.

LAst question then i am going to bed..when I got my phantom 4 months ago the stock TX had a self centred throttle stick, if i let go it would spring to the middle and hover..when i upgraded the TX to Futaba i got this modified to act the same and am happy with the way it works..so in theory i should dbe able to fly the s800 -EVo in the same manner and adjust gains so it hovers at centre stick..i wonder with 8kgs if it could or what teh gain values would have to be to achieve that..

The gains you will need is something only you can determine. I would recommend you use a dial on your TX and map it to X2 or X3, then setup the Wookong to use the input for controlling the gains. The WKM manual describes how to set the gains, and even provides a starting point for gains.