Trouble communicating with Pixhawk


What is the best way to troubleshoot why the Drotek M8P RTK is not being recognize by the Pixhawk?

Also, is there a diagram that illustrates where the various solder bridges are and which ones are required to communicate with the Pixhawk?

I’m using Rover port with a JST cable that was split and spliced into two DF 13 cables for the GPS and Compass.

I soldered the bridge at the location shown in the diagram as well.

I tried allowing the Pixhawk to auto-configure the GPS and also manually setting all the values using these instructions:
Rover Setup

I did manage to get the GPS working for awhile, but then it stopped being detected and I haven’t been able to get it detected again. The GPS appears to be functioning since u-center is communicating fine with it.



Here are how my cables are wired:

(The forum software would not let me post two images in my post.)

If you do not use the 3.5 firmware of Ardupilot it will not work.

Use also the latest version of Mission Planner

Check that in Mission Planner , Gps tree parameters, Autoconfig is set to 1 and Gps 0 is enabled.

If you use one single telemetry on your system you have to solder the pcb.

3.4.6 should work. It supports RTK and other 3.4.5 systems have worked. Why do you say that 3.5 is required? (I know 3.5 supports multiple GPSes better and fixed the status flags to report the GPS state correctly.)

No you are wrong , 3.4.6 might support rtk but it does not support the M8P .

It is not an opinion it is a fact written in the change log of the 3.5

The problem with 3.4.6 is that it do not recognize and initailise the M8P correctly.

3.4.5 might be broken for automatic configuration, but it can be used if the GPS is manually configured with U center. My colleagues have done it successfully for a couple of copters, but I’m having troubles with my particular setup. I likely have something misconfigured, but just haven’t figured it out yet. Like I said, it was working at one point and then something changed to break it again.

Using the 3.4.5 and the 3.4.6 I had success getting finally a rtk fix (using manual GPS config and disabling MP autoconfig ) but after some weeks when I tried again there was no way to make it function as you can read in several post of last days.

With 3.5 I solved all problems and you do not have to use Ucenter to configure anything even if it is better to use it to load the last M8P firmware

I do not understand why you do not want to use the 3.5

If you do not solder the pads on the rover it will never work

I’ll look at 3.5, but it in beta now, which makes me reticent to use it on expensive copters.

I use it with a 3500 $ camera and a quite expensive copter with no fear , it is not the first release of beta.

I tried the latest 3.5 and used all the default parameters, but the Pixhawk still does recognize the GPS. I’m using a baud rate on Serial 3 of 38 kbs and the GPS protocol. Is that what you’re using?

Do not understand what you mean when you talk of serial 3

Just connect the rover N8P with the provided cable to the Pixhawk Gps port .
The baud rate is automatically configured by the Pixhawk firmware at boot.

Did you solder the pads on the rover M8P ?

Serial3_BAUD and Serial3_PROTOCOL, which is used for the GPS port. The provided cables had the wrong connector type so I had to create a new cable by splicing the two other cables from my original GPS and compass into the cable for the Drotek GPS (see wiring diagram above.) I did solder the pad shown in my diagram to no avail. I also reverted all the settings on my GPS to defaults just to ensure that I hadn’t done anything to prevent communication, but that didn’t impact the communication problem either.

I tried out the other JST cable and jammed it into the Pixhawk and that worked so I must have a bad solder joint in my cable. It worked at one point so I think its wired correctly.

In Mission Planner parameters tree under “GPS” do the GPS_AUTO_CONFIG is set to 1 ?

So the pad in your first picture is soldered ?

Are you sure that tx on the gps is conected to rx on the Pixhawk ?

In mission planner do you have "No gps " label on the HUD ?

I performed a continuity tests on the 4 connections to the GPS port and it looks like all the connections are good. I have TX going to RX and RX going to TX. May go ahead and resolder just to make sure.

Check that the connector is on the Rover port , seems obvious but I connected to the wrong port one time.

Yeah, I’ve checked that a few times. It must be some type of problem with my cable, but its not obvious what is wrong with it yet since the continuity tests passed and it appears that I have it wired correctly.

Just realized that I must have the Rx and Tx wires switched since the bundled cable does not cross the Rx and Tx wires and it works fine on the Pixhawk.

Switching Rx and Tx in my wiring harness worked!

I told you !

Happy you did it .