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NTRIP without base, only rover. Is it possible?

Hello.

I’m new in dealing with RTK receivers, and need your help.

I’d like to check whether the configuration below works.

What I’m trying to do is:
(1) Install NTRIP client on Raspberry Pi 3, and receive RTCM message via LTE
(using NTRIP caster provided by national organization)
(2) Connect Raspberry Pi 3 to Drotek RTK receiver through USB, to inject RTCM message into the RTK receiver.
(3) Connect Pixhawk to Drotek RTK to receive corrected GNSS data.
(Pixhawk port: I2C, GPS // Drotek RTK receiver: Rover)

Has anyone have done this configuration before? Did it work?
(or, does anyone know whether it works?)

If you say yes, am I right to use port as configuration above?
(Raspberry Pi 3 USB - Drotek RTK micro USB ==> to transmit RTCM
Pixhawk I2C and GPS - Drotek RTK “Rover” port ==> to transmit NMEA)
Does it need soldering right above the Telemetry port on Drotek RTK receiver?

Thanks for your help in advance.

Hello Quuone_J,

RTCM3 & NMEA data are sent in both ways using the same UART on the Rover PORT.
Therefore, the USB cable is only required to power the XL RTK receiver up. Alternatively, you may use the Pixhawk 5V output to power supply the XL RTK board. Thus it means no USB cable needed anymore.

Actually, I do think you should provide more details regarding the interface between the Pixhawk and the Raspberry Pi 3. You will certainly have to forward NMEA & RTCM data, again, in both ways using a UART interface between those two.

Hope you are going to find your way out. Please keep us informed if you got it sorted. :slightly_smiling_face:

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Hello Paul_T

Thanks for your reply.

I thought I have to explain more about what I’m trying to do.

As shown in the figure above, I want to change the red-box part into the blue-box part.

In the red-box, there occurs a process of sending correction data (RTCM) to the RTK receiver.
Though it can be done as using a stationary base with radio transmission, I want to convert that part into blue-box, which uses NTRIP caster - NTRIP client and do the same work (i.e., sending correction data to the RTK receiver). The NTRIP client on Raspberry Pi will choose the nearest mount (base station) from the rover, and request the correction data to NTRIP caster.

During this process, Pixhawk already uses “Rover” port of Drotek RTK receiver, so I thought that I have to use either USB port or “Telem” port of the RTK receiver to send the correction data. This is why I connected Raspberry Pi to micro USB port of the RTK receiver in the first question.

With this explanation about what I’m trying,

(1) Which port of Drotek RTK receiver should I use to send correction data from Raspberry Pi to the RTK receiver?
(2) What is the role of “Telem” port on the RTK receiver?
(3) If I can use only “Rover” port, how can I send(forward) correction data from Raspberry Pi to RTK receiver? In this case, it seems that the correction data flow would be Raspberry Pi --> Pixhawk --> RTK receiver.

Thank you. Any other comments are always welcome!!

Hi,

Actually the TELEM port is supposed to be used directly with a standalone telemetry kit such as 433MHz/900MHz/LoRa modules without any autopilot needed, this is not the case here.

I understood very well what you were trying to explain in the first place by using a Rasperry Pi acting as an NTRIP client.

The solution could be to forward raw RTCM data out of the raspberry (NTRIP client) to the Pixhawk, so that the Pixhawk is aware there is incoming RTCM data and then let it start doing its own stuff with the GPS.

As you can see, there is no straightforward solution, as you will need to develop some code to gather RTCM data and send them back to the Pixhawk.

Hope I have been quite helpful here. :slightly_smiling_face:

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Thanks Paul_T!

Seems I should use MAVLink protocol to forward RTCM data to RTK receiver, through Pixhawk.
Well… it becomes more difficult than I expected :cry:

I think it is not difficult as you thought.
If you are JUST using Raspberry Pi as NTRIP Client , and Pixhwak as Wireless bridge (send RTCM from Raspberry Pi to Drotek-Rover), I think ESPrtk can be your choise. ESPrtk just ESP32 module, it’s cheap, small and support WIFI + NTRIP Client +Ublox Configure also.

You dont need Raspberry Pi any more , just connect as this image to use.

Thank you ESPrtk for your very detailed reply.

However, Quuone_J is not using the new Drotek RTK F9P module, but he is using the previous XL RTK M8P version. (https://store.drotek.com/xl-rtk-gnss-m8p)

Furthermore, if using the last Drotek RTK F9P module, there is a little mistake in your wiring schematic above. Indeed at Drotek we are using an electronic system to enable SPI over CON1 port (see schematic below), therefore disabling Rx/Tx on CON1 port when you provide a 5V power supply on the ‘5V in’ CON3 input. So in order to keep using UART over CON1 move your 5V power supply connection to the CON1 or CON2 or by using a USB chord.

(The schematic below is taking into account the corrections I just said above)

Many thanks again ESPrtk for the drawings :blush:

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Paul_T: Great, thank you for helping me, I don’t know it. I also have drawings on M8P + ESPrtk. Does this diagram have errors?



All the pictures seem ok, except the 5V designators on the first one. You could check here to see how we did it.

https://drotek.gitbook.io/rtk-f9p-positioning-solutions/rtk-f9p-drotek-modules/rtk-zed-f9p-gnss/hardware/pinouts

Our doc is pretty new, feel free to send me PM or email (paul.thelu@drotek.com) to let me know if you find out something unclear.

Back to topic, perhaps OP wants to use its RTK solution within an autopilot environnement such as a drone or any rover, therefore the use of a Pixhawk is necessary. If you have the possibility to forward raw RTCM data from the Raspberry Pi to the Pixhawk, I think it can do the job. :slight_smile:

Thank you again, I have updated the diagram on my page. I certainly have many questions about Drotek in the future.
Back to the topic of Quuone_J:
He said “Any other comments are always welcome !!” I hope my comments will be low cost and low weight solutions for Drone.

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Drotek documentation have been updated, find all infos about RTK F9P solutions here (https://drotek.gitbook.io/rtk-f9p-positioning-solutions/)