Fix Base Solution but fluctuating solution on rover

[Ali_Sahin]

Hi,

Goal: Im trying to accurately map and navigate an area using Emlid Reach integrated into a pixhawk build drone. I am using Reach RS as a base station.

Problem: I get fix solution on the Reach RS using NTRIP. However, My rover (drone) constantly goes back and forth between float, fix, and Dgps, when I monitor the solution on mission planner. Also, After mapping my ground control points are not accurate compared to the gps coordinates I get from Reach RS.

Drone and Base Set up:

My Drone is using a RFD900+ as the communication link.

Rover Settings:

Base Settings:

Here is what I did:

After setting all the parameters/ settings in the Rover and Base as the above images. I went out to a field placed control points (orange landing pads as seen on the pix4d image below). Placed the Reach RS as close to the middle of the X as possible. Turned it on and waited to get a low error float solution or fix solution. The Reach RS was getting its correction from NTRIP provider from a cellular phone gsm WiFi connections. I recorded three points with the Reach RS then turned on my drone.

From the Reach View app I chose average fix for the base mode of the Reach RS. Once the calculation were done. I opened mission planner and injected the correction to the drone. As soon as I inject the status goes from DGPS to rtkFLOAT. I waited some time for the error to reduce and got FIXED.

I set the mapping mission on mission planner and then executed the mission. As the drone started to fly the solution fluctuated between DGPS, FLOAT, and FIX.

When I mapped the images the error was from 20 cm to 1 m.

Example of the my results:

The point in the middle of the X is where I place the Reach RS and was able to get float solution with +/- 0.006 m in Lat., +/- 0.0015 m in Lon.
After mapping with the drone. The point on the left is where the GPS coordinates actually is. So, I have an error of almost 3 ft.

Pix4d link to the rest of the map and points:

PIX4Dcloud

Other Info:

ReachView v2.10.0

RTKPLOT image. it shows that i never had float or fixed

Base Plate under rover antenna is a copper plate with a 65mm in diameter.
The Reach RS is in Static positioning mode and the Rover is Kinematic.

Please help us in reducing the error. Right now the error is the same as a regular GPS.

Thanks,

Ali Sahin

[bide]

While your drone was flying, did you leave Reach RS on a GCP and logging both raw data and base corrections (with the NTRIP source connected)?

[Ali_Sahin]

Yes, The Reach RS was on a GCP and logging both raw data and base corrections with the NTRIP connected. I didn’t turn it off. When I chose Average Fix under the Base Mode tab it sets the reach rs coordinates and the rover uses those coordinates as its base with no changes in coordinates over time.

[bide]

OK, so that means you can run two post-processing jobs:

1. Use: Base raw data log and Rover raw data log
   • This should provide your best results
2. Use: Rover base correction log and Rover raw data log
   • In an ideal situation, this should look the same as your RTK position log
   • If it is substantially better than your RTK position log, then you probably had base to rover communication problems. (e.g. Radio interference or too much RTCM3 message data or not enough radio speed)

[bide]

Before you try the above, firstly I should have asked you this: Did you confirm that the rover was receiving base corrections before flying by opening ReachView and seeing grey bars in the status window and also seeing float or fix status?

[Ali_Sahin]

Yes, I did open ReachView and saw the grey bars also the status was float and fixed at one point. But, when I started to fly it started to fluctuate between the solutions.

I’ll try the post-processing. However, my goal is to achieve real time precise navigation with the drone using Reach.

Thanks for your reply.

[TB_RTK]

I just like to step on @bide toes a bit

I noticed your rovers antenna is like 5cm beside some device on your drone and the groundplate is only 5cm ish in radius. I havent checked the raw log but i would suspect your have some noice there.
Rising antenna and a bit bigger groundplate would help a lot.

[bide]

@TB_RTK

I just like to step on @bide toes a bit

please do…

[Ali_Sahin]

Ok, ill try again with a raise antenna and a bigger groundplate.

thanks

[TB_RTK]

[dshean (David Shean)]

Nice setup, and thorough descriptions of the issues. Looks like you are using copper PCB for antenna ground plane. I chose similar 6.5x10cm plates for some Reach antenna camera mounts, but left them as full rectangular size. Curious to hear if using a larger plate solves your problem.

Looks like the device on the ground near your base tripod is a wifi router for mobile hotspot? I’ve been using the TP-Link N300 (TL-WR802N) for local ReachRS/Reach setup and NTRIP feed. It works well, but range is limited to maybe ~50 m under optimal conditions. I’ve been looking at other portable wifi solutions for extended range, but haven’t seen anything like what you’re using. Can you share details? Thanks.

[Ali_Sahin]

@dshean

the device on the ground near your base tripod

Hi David,

I am using this device for my mobile hotspot MOFI4500-4GXeLTE-SIM4 4G/LTE Router AT&T T-Mobile Verizon Embedded SIM with Band 12. You can find it on Amazon. I haven’t test the range.

[Ali_Sahin]

Hi guys,

I increased the height of the emlid antenna and used a bigger aluminum plate (10 cm diameter). The results are the same my rovers RTK still fluctuates between DGPS, FLOAT, FIXED solutions?

I was wondering how sensitive is the Emlid RTK to the environment you are mapping? Can it only be used in rural areas? I am flying my missions in a suburban area where there is power lines and communication antennas. Does power lines affect the RTK solution of the drone at 100 meters or 120 m height?

Here are some pictures of my drones new set up.

Thanks

[egor.fedorov]

Would you mind sharing the logs from the flight? There are usually two things that cause this kind of behavior:

1. Bad sat reception. Usually from the copter interference. This is easily checked by taking a look at the raw logs from the flight.
2. Bad correction link. It is necessary for the rover to receive them on time to maintain good solution status. Rover’s position log includes age of differential which will show whether the link is reliable.

Also, a small tip. It’s easy to share your Reach’s settings by copying a “simple system report” from the settings tab.