I just noticed tonight that the X, Y, and Z offests for the IMU and GPS mounts can only take-on values between -128 and +128.  If you enter a number like 160, you actually get it's 8-bit two's compliment value.

I don't know that it's a show-stopper, but it does mean that the GPS mount needs to be one of the shorter posts.  I suspect my GPS is around 135-145 mm above (so negative) from my COG, but I'm using a value of -128.

Comments?  Am I missing something here?

Thanks in advance.

I am having the same issue ,i type in the value and disconnect from PC,once i reconnect a lower value shows up for the 2- added pro GPS modules .How can we make sure the values for XYZ are set since there is only a reset button ?Also only the mount screen shows under basic settings no way to update individual  components within the M600.I had to downgrade to previous firmware version then re-upgrade to update the 2 additional IMU's.

brich12003.yaho Posted at 2016-6-24 07:09
I am having the same issue ,i type in the value and disconnect from PC,once i reconnect a lower valu ...

I originally thought it was an issue with the values not being stored properly.  As it turns-out, they're being set exactly as intended -- they're just stored as 8-bit 2's compliment values.

Try entering values between +/- 128.  They will store perfectly every time.

What I believe you are observing (and I apologize in advance if I am incorrect) is the effect of entering values that can't be stored as 8-bit two's compliment values.  So a 160 might show-up as a -32 once you enter it.

I cheated.  I switched to the shorter GPS mounting posts and settled for -128 values on all three GPS z-values.  That at least reflected the measurement from the GPS to the top plate of my S1000+.

But I don't believe my COG is at the top of the S1000+.  It's probably about 50 mm below the top of the upper plate.  I mounted the IMUs on that top plate and declared their z-values around -50.  I did a test "hover" earlier today and it seemed to work well.  Wish me luck!  

How did you determine your COG?  I have not experienced those high of values on either a S1000 0r S900.

Tahoe_Ed Posted at 2016-6-25 20:34
How did you determine your COG?  I have not experienced those high of values on either a S1000 0r S9 ...

The motors, ESCs, arms, and props were above the top plate (hence above the IMUs), but below the top plate (and IMUs) I have:

- Z15 Gimbal
- Sony A7
- FPV camera
- DJI Lightbridge II receiver
- 2.5 kg of 22,000 mAH battery
- Retractable landing gear
- Bottom Plate

But I'll admit it was a guess.  While the center of thrust was probably 20 mm above the flight controller (since the arms tilt upward), the COG was probably about 50mm below it.

I'll be the first to admit that I've done something wrong though.  Am I missing something?

And as always, thanks for the help!

Here's a picture of my setup along with my values:

Internal IMU x = 0; y = 0; z= -50 (internal IMU is centered on the top plate)
Internal GPS x= 120; y = 0; z = -128 (GPS is centered in front of the IMU, but up on a mount)

The external IMUs are behind and to the left and right of the primary IMU.  They're all in the same Z-plane, located on the top plate.

The second and third GPS are in the standard locations for an S1000 (not a lot of choice there), and they are all at the same height as the "internal" GPS.

IMU1 x = -48; y = 37; z = -50
GPS1 x = -45; y = 110; z = -128

IMU2 x - -48; y = -37; z = -50
GPs2 x = -45; y = -110; z = -128

Are those plausible based on this photo?  All the IMUs are mounted on the top plate of the S1000+ and the GPS are mounted on short posts above the top plate.

The XYZ values for the internal IMU/A3 on the M600 are preset(Z-36) based on the center of frame/batteries i used that to then add GPS value making Z axis -230 using the longer post in which the machine flew and held its position very well!When I try to add additional GPS values it will not let me go above -128

brich12003.yaho Posted at 2016-6-26 09:11
The XYZ values for the internal IMU/A3 on the M600 are preset(Z-36) based on the center of frame/bat ...

So when you reconnect to your flight controller using the assistant, are the z-values for your GPS -128 or -230?

I'd bet it will let you enter -230, but then when you reconnect it will be something like +102 (or so).

What does it read?

When I reconnect to the assistant they both(GPS modules) come back at +56 not the -200 i type in.The -230 for the  original GPS included with the M600 stays set along with internal IMU settings only having this issue with the  two added pro kits.

brich12003.yaho Posted at 2016-6-26 21:34
When I reconnect to the assistant they both(GPS modules) come back at +56 not the -200 i type in.The ...

I never checked the primary GPS.  Good catch.

I sense an update coming.  They are truncating the #2 and #3 imu/GPS values at +/- 128.

bcdebusk Posted at 2016-6-27 05:59
I never checked the primary GPS.  Good catch.

I sense an update coming.  They are truncating the  ...

Would be nice with a quote from one of the DJI Guys here on the forum. Should we wait with installing the A3 Pro upgrade kit we have purchased or?

I pulled the the pro kits off until i here something official from DJI.I noticed on last update to the assistant 2 they mentioned added support for A3 pro but all it did for me was to help recognize the 2 added IMU's.

https://dl.djicdn.com/downloads/ ... ote_en_20160613.pdf

Tahoe_Ed Posted at 2016-6-26 09:34
How did you determine your COG?  I have not experienced those high of values on either a S1000 0r S9 ...

Check out this post for help on finding the Center of Gravity.  It's for an S900 but the same rules apply for all copters.

Nic video.  Better than the one that I found many months ago.

As stated above finding the center of gravity is not the issue as the M600 batteries are within the frame and internal IMU values are pre-set.I wish someone from DJI would chime in to answer why Z values on 2 pro kits GPS modules will not go and set at -200???

I received the below from DJI support ,apparently they are aware of the problem and will send an update hopefully soon.



It is a bug of the assistant 2. We will soon release a new version of this software to solve this problem. Please wait with patience.

We apologize for the inconvenience it may cause to you.

Regards

Andrew

New DJI assistant

Seems to have fixed mounting value bug installed yesterday and we can now enter correct values

http://www.dji.com/product/a3/info#downloads

brich12003.yaho Posted at 2016-7-19 22:42
New DJI assistant

Seems to have fixed mounting value bug installed yesterday and we can now enter ...

I'm glad to hear that you are finally able to get yourself up and running,

I have installed the A3 pro on the S1000+ and mounted the imu's on the centre plate, GPS on top so my Z values on GPS1,2,3 were -290 from the assumed centre of mass to the GPS pucks and it allowed them fine. It flew superb without the gimbal and camera but when I was satisfied it was flying OK I put them back on but did not do a recalibration and it drifted horribly. I have reduced the figures to -210 and will do a new compass calibration and see what it does.

Its not easy finding the centre of mass of such a big bird unless anyone has an easy way of doing it especially with gimbal and camera attached ??

HI,
I bought A3 Pro and I want to set offsets but I don't know how measure distance. Is it from center of IMU to center another IMU? Same problem with Z offset. Is it center of IMU to COG?

Thanks