Arducopter Issue using M+ and RS+

First off, I am new to using RTK GPS and I have just installed a M+ module on my PIxhawk 2.1 octocopter using a RS+ as a base unit and passing corrections through a RFD900x radio. I am using a Here2 as GPS 1 and the M+ as GPS2. I think I have everything working properly on the ground. I am getting a RTK fixed indication in Mission Planner so all seams to be working properly.

I just performed the first test flight of the octocopter while using the RTK system. I had a good RTK fixed position and started a simple waypoint grid mission. The first flight line seamed fine but then during the second line the drone violently rolled momentarily. This happened a few more times before I abandoned the Auto mission. There did not appear to be an issue flying in Pos Hold mode, only Auto mode. I see from the logs that there is a large skew of the POS parameter during the erratic movements. Any ideas?

Flight Log attached:

Check the GPS1 & 2 status in the df logs. Probably what happens is you have the two gps’ set to “usebest” and the status for the rtk drops and ardupilot switches to the other gps causing the abrupt change in your “roll”? Turn on the map while viewing the df log in mission planner and zoom to where it happened - then examine the GPS1/2 and POS tracks.

Mine did that a few times. I now use two Reach units as the GPS 1 and 2 and inject rtcm into both. I have my param set to “blend”. She flys quite well.


Thanks for the info. Yes, I am using the “Use Best” option and the logs show that it is failing over to GPS1 when the RTK drops out causing the erratic behavior.

Can you share a little more info about how you set up the two M+ units. Do they each need their own serial connection?

Can I use the “Blend” option when using the Here2 and Reach?

I don’t see why not. I suppose it depends on how accurate your use-case needs to be?

I have one reach connected through the uart port and another through a usb. I don’t recall all of the settings at the moment. But, they weren’t too bad!

Thanks for the info. I will try adding the second M+ and see if that helps.

Hi @AutoPilotOn,

May I ask you to share raw data and logs recorded during this flight from both RS+ and M+ units? Please also post here the solution log from M+ unit.

You can download them in the Logging tab of ReachView.

Just want to check why you could lose RTK fix.

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