[アイラ]

Hi, i tried INS13 on my Quad a few weeks ago and i didn't hat any chance to bring my mag (internal) to work (mag calibration was done), so i tried to arm it in the air, when the mag alarm was green.

--> The result
- Quad completely Freaked out
- 10 € Frame destroyed
- 1 Broken Prop.


Now after much research i found out that i could use an external mag (I2C).
I am on LP 16.09 Black Rhino and first i would like to ask if i could use every I2C mag or are there any exceptions? For example --> https://goo.gl/ZHttKa

And at last i'm worrying about the position of my CC3D in my Frame.
Here is a photo of my Quad --> https://goo.gl/Y9dU4o

Now i am flying in Basic Complementary and Attitude which works very good, but my CC3D is pretty much in the back of my frame, so wouldn't that effect my Accelerometer?
--> https://goo.gl/vorCdY Actually it doesn't

As written LP wiki the Complementary mode fuses gyro and accelerometer https://librepilot.atlassian.net/wiki/display/LPDOC/INS13+-+GPS+Navigation

So if i use an external I2C mag i shouldn't have problems with my accelerometer and GPS modes, is that right?


My GPS is working pretty good so far, i also have a OPLink ground station linked to my quad, with an OSD and also things like Ground Speed are shown correctly.

[Mateusz]

You get many things wrong. You can't fly GPS alone such flight mode does not exist. It's either gyro+accel or all sensors combined. GPS alone has error of ~4 meters and is only used to help other sensors. For autonomous flight Revo has absolute minimum of non redundant sensors measuring different physical things. That means all sensors are required to work perfectly for autonomous flights. None of sensors can be replaced as they measure different things. Only Magnetometer can determine heading for instance, no other sensor can measure that. When it comes to Mag, it's rare that internal mag works unless you would mount Revo above magnetic interference. Best is to use external mag and dial in correct orientation of external Mag it is described on wiki and many forum posts. Mag supported is HMC8853 if I remember correctly. Just check symbols on the mag chip on Revo , it should be the same Mag used as external. Symbols can be L8853 or something like that. You calibrated using both Magnetometer then you adjust orientation so on scopes both Magnetometers behave the same, that way you will know you type external mag orientation correctly. Then you can step towards checking other sensors. You should never try bypassing safety checks , if it's not arming then there is a reason, usually good one. Hope that helps.

[TheOtherCliff]

Every L883 compatible I2C mag (the kind you mentioned) I have tried has worked well, but some need additional pullup resistors.  If you are going to buy something anyway I would recommend a clone DJI GPS/compass for about USD $20 from eBay.

You mentioned CC3D several times.  CC3D does not do INS13, but Revo does.  You probably have a Revo.  The Chinese have attached the name CC3D to everything they sell, including toilets and clothespins, just to get you to look.

Building an autonomous quad from scratch is not as simple as buying a DJI Phantom.  You have to learn to do all the component selection and placement that DJI did, at least well enough to work.  You need to use testing procedures that take into account what might go wrong.  You already found out that compass selection and mounting must be done carefully.  There are other things too.  For instance, did you carefully twist all your power cables together?  Is your PDB designed to reduce magnetic fields?  Does your RC radio have a failsafe function?

It's almost like buying a car versus designing a car.  Just designing one that is safe enough to drive off road takes a lot of study.

Get it flying well in Attitude mode with Basic/Complementary, then in Attitude with INS13 before even trying to use GPS modes.

Good luck. 

[アイラ]

Okay thanks for your fast answers, so that means that the positioning of my Revo is not a Problem. Did I get that right?

[TheOtherCliff]

I believe that FC location is generally only a problem when you do fast pirouettes in a flight mode that depends on accel sensors (e.g. attitude or GPS modes), but it depends on how far from CG the FC is mounted and how fast you want to yaw in normal flight.

LP camera stabilization would also be affected.

[Mateusz]

If your FC senses that front of frame needs more thrust it will accelerate front motors. However your sensor on FC must be pointing that front so FC front is also motors front. If it points backwards and there it senses that more thrust is needed it will assume it's front and accelerate motors 1, 2 opposite side , and whole thing would flip. Arrow on FC must point front motors. If you installed FC incorrectly, you can always flip it in software by board orientation but it's easier to install it correctly from the beginning.