How do 2 or more GPS units work together?

Hello ,

Am about to install 2 here3 GPS units and one emlid reach m2,

How does that work internally? do all GPS units contribute to the efk? or the best solution wins ?

Thank you for your time,

Have a read through the documentation. You can set parameters to determine behavior.

Only 2 GPS modules are fully supported. Some of the source code is written broadly enough to be able to use more than 2, but I don’t think it’s a good idea to connect 3 or more in practice.

GPS/Compass (landing page) β€” Copter documentation (
GPS Blending (aka Dual GPS) β€” Copter documentation (
Extended Kalman Filter (EKF) β€” Copter documentation (
EKF3 Affinity and Lane Switching β€” Dev documentation (

Hello Yuri ,

Thank you for your reply i did read through the docs but missed that ,

Thanks for pointing that out :smiley: !

I recently had a crash with 1 here3 dying on the air , i wanted to put a second for redundancy. Then i need to have a proper RTK because the here3 rtk is super slow and out of 80 flights i never got a fix , so i wanted to add the emlid reach2 m2 .

If i had 1 here3 and 1 emlid, if the here3 dies i lose the compass it has and rely on the cube compass which is not advised either , right ?

Again thanks for your time,

Recommend simply disabling the internal compass and relying on sensor fusion.

If the Here3 compass is lost in flight and the internal one is disabled, heading will be determined via GSF, which is quite reliable, especially when groundspeed is greater than 0.

Compass-less Operation β€” Copter documentation (

Hi @Yuri_Rage ,

Thank you again for your reply!

So your proposed setup is to :

Thanks again for your explanation and links ! I also checked your youtube channel great stuff thank you for taking the time !!! havent wrote LUA since 2014 brought back some memories !


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