Discussions

Using USB and 3DR radio at the same time with APM 2.5

Posted by Daniel Frenzel on February 8, 2014 at 8:20am

Hi,

I wonder currently about how to use the 3DR radio with the serial USB simultaneously. 

I have an APM 2.5. In the wiki is written, that a hardware muxer is preferring uart0 over uart2 at the uart0/2 port if usb cable is inserted (if I understood correctly). 

So if I want that uart0/2 is always uart2, shall i simply do like described here: https://code.google.com/p/ardupilot-mega/wiki/APM2Wireless under point "(Optional) Changing your telemetry to use UART2 (aka Serial3)" and USB will work together with radio on uart0/2?

Greetings, Daniel

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Replies

  • Jesus May 7, 2015 at 7:14am

    Hello,

      We are trying to connect a device to the usb and the telemetry to uart2. To do this I tryid this:

      http://copter.ardupilot.com/wiki/common-appendix/common-archived-to...

      But I can´t connect, any other modifications are necessary?

      Thanks in adavance!!! :-)

  • Daniel Frenzel February 8, 2014 at 9:33am

    I made the mod, wrote a firmware and it is working perfectly. Just if someone is interested. 

    All three serial channels can work independently. I have no clue why a mux was implemented.

    • Jakob M. L. Hansen > Daniel Frenzel May 14, 2014 at 1:53am

      So you are the guy to ask if i wanted to have redundant telemetry on my 2.5board?

      apm usb <=> android(3g)

      apm telemetry port <=> 3dr radio

      • Developer
        Bill Bonney > Jakob M. L. Hansen May 14, 2014 at 7:43am
        See http://diydrones.com/forum/topics/using-usb-and-3dr-radio-at-the-sa...
        • Daniel Frenzel > Bill Bonney May 15, 2014 at 6:43am

          I have the problem, that if I read the radio I get only crap if I use heavily the CPU. If the load is low I read correct values. Why is that so. Happens on AM 2.5 and 2.6. Also using UartC. On uartA I can always read correctly independent on the CPU usage. 

          • Developer
            Bill Bonney > Daniel Frenzel May 15, 2014 at 6:52am
            The APM will drop packets if the buffers fill up, or cpu is high to favour flight control over telemtry. Its better on newer FW. Which version are you using, and have you up the data sending rates?
            • Daniel Frenzel > Bill Bonney May 15, 2014 at 7:39am

              I wrote my own flight control firmware and I was wondering about this behavior. 

              One day I had the idea that I want to control my quad over smartphone or laptop. 

              So commands go over uartA. Since I recognized that radio would be nice too, I bought a 3Dr radio kit and wondered.

              ATM. I use the telemetry port only if Wifi is not available. However then I limit the loop rate to 50 Hz to ensure, correct read outs. 

              Sending rates of the radio are very small, because I compressed the control signal to 8bytes. 

              However I wonder whether I can switch this package drop off somehow?

              • Developer
                Bill Bonney > Daniel Frenzel May 15, 2014 at 7:57am
                Have you used any of the APM code?

                If you are not using MAVLink, turn of the MAV link feature in the radio as well. Turning off ECC gives you more bandwidth as well.
                • Daniel Frenzel > Bill Bonney May 15, 2014 at 8:14am

                  I use the complete ArduPilot library for handling the sensors and motors (AHRS, InertialNav, GPS, ..) but wrote some alternatives for filtering and sensor fusion, frame and network code as well as scheduler. My firmware is in contrast fully OOP. My network communication is different (no Mavlink) at all. I disabled ECC and all the features of the radio already. The only thing what is helping so far was to give the CPU all the time necessary to read on uartC and then do other calculations. The problem is, that there is no general rule.

                  Theoretically I could achieve with my firmware ~166 Hz on the APM 2.5 (no readout of the radio possible). However with 100 Hz loop frequncy there is already a 50-75% package drop rate. at 75 Hz maybe just 5-15% and on 50 Hz nearly no with 8 bytes command string. Drop rate is dependent on the complexity of the other calculations. 

                  I just would like to know how this drop mechanism works.

                   

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