Only 1 GPS on SERIAL4/5 - No position telemetry

Stefan_Lofgren · September 26, 2015, 4:38am

I have a pixhawk. The GPS port was damaged in a crash and doesn’t work reliably now.

I connected the 3DR uBlox GPS to the SERIAL4/5 port. It works - kind of.

Good:
The ardupilot system passes the pre_arm check on the pixhawk.
It will follow planned waypoints in AUTO mode.

Bad:
In mission planner flight data, lat and lng is 0, but lat2 and lng2 shows a good positions.
I use a Teensy 3.0 to transmit Mavlink telemetry data to my Taranis FRsky Plus RC through my TELEM1 port. It still works, but it no longer passes any GPS information.

Question:

How can I get my pixhawk to use the SERIAL4/5 port the same as the GPS port (as the primary GPS)? It kind of does, but not fully.

Stefan_Lofgren · September 27, 2015, 7:41pm

Is there any way to set the APM code to look for the PRIMARY GPS sentences from SERIAL4 rather than SERIAL3?

I’m looking at the Github code postings, I think I see some promise there between the SERIAL and GPS folders.

Any ideas out there?

Stefan_Lofgren · October 30, 2015, 9:45pm

Well, OK, I think I solved this issue.

I spent a few days going through the APM Copter code and found the:

AP_SerialManager.cpp

file. Down about 1/2 way are some lines:

state[1].uart = hal.uartC; // serial1, uartC, normally telem1
state[2].uart=hal.uartD; // serial2, uartD, normally telem2
state[3].uart=hal.uartB; // serial3, uartB, normally 1st GPS
state[4].uart=hal.uartE; // serial4, uartE, normally 2nd GPS

All I did was swtch hal.uartB with hal.uartE so that uartB is the 2nd GPS and uartE is the 1st.

I think this whole cpp file is where the firmware sets what serial ports are doing what.

So, I saved that and compiled a new firmware and uploaded to the Pixhawk.

Success, so far.

The telemetry on my FrSky Taranis comes up with coordinates, now! The GPS (same 3DR/ublox GPS) now is more stable and wanders (dithers) less. Drone can fly in loiter mode now.

Solved…?

I know there are a number of people who are being told by 3DR to buy another Pixhawk, but this clearly works and is free. Granted, you’re not going to be using a 2nd GPS.

TCIII · October 30, 2015, 10:29pm

@Stefan Lofgren,
You can set up the Pixhawk serial ports’ baud rate and function using MP without having to mess with the code.
Regards,
TCIII AVD

Stefan_Lofgren · October 31, 2015, 5:47pm

Yes.

But I suppose I have failed to describe the problem well.

With a broken GPS (Serial 3) header, you can indeed connect your 3DR uBlox GPS to the Serial4/5 header. You can change the protocol and baud rate of Serial4 to match the GPS settings of Serial3 (this is indeed the default setting in the code for Serial4).

Good:
Your GPS will fire up, and the position will be reported through lat2,long2, etc… Yeah!!!
You can do ‘auto’ planned missions.

Bad:
However, in the Flight Data part of Mission Planner the GPS Fix indicator in the HSI with continue to indicate “No Fix”. And give no GPS Fix Data (numSats, 2D/3D, etc…).

Several flight modes don’t work well.

The position of the GPS dithers much more (I cannot understand why this happens).

If you are using a Teensy 3.1 to take the MavLink Data from Telem1/2 and transmit that to your Taranis, it won’t transmit any coordinates to your RC.

Altering the code in the way I did fixes the problem!

dsmoura777 · March 12, 2016, 4:40pm

[quote=“Stefan Lofgren”]Well, OK, I think I solved this issue.