I’m struggling to get decent data rates out of MAVLink. I’m using RFD868ux_EU radios with the airborne radio connected to TELEM1 on a Pixhawk Mini 6C running ArduPlane. I am feeding separate 5V power into the radios. The ground station radio is connected via an FTDI USB cable to a laptop running a python program using pymavlink (from pymavlink.dialects.v20 import ardupilotmega). The data is being displayed in a mapping application.
I was originally trying to get the ATTITUDE, GLOBAL POSITION and HIGHRES_IMU mavlink messages at 25 Hz but that seemed to be too much data and I was getting big gaps between bursts. I now request ATTITUDE at 10Hz and GLOBAL_POSITION at 5 Hz, but I’m still seeing 1/2 sec gaps and the best data rate that I’m getting is 5Hz.
The EU version of the radio which I’m using is restricted to one channel; appears to always have Listen Before Talk (LBT) switched on, Error Correction is always off and the maximum duty cycle is limited to 10%. I’ve changed some of the radio settings to try to get better data rates, and this is the best that I’ve found:
Flow Control: Off, MAVLink: On, Air Speed: 200, Transmit Power: 27, Duty Cycle: 10, Listen Before Talk: 0, Max Window: 33, Air Frame Length: 240, Opportunistic Resend: Off
I tried to set LBT_RSSI to 95 but the radios wouldn’t connect unless it was 0.
My ideal would be to get messages at 25Hz. Is this possible? Am I being limited by the EU radio or have I got something wrong in my settings/programming?
your going to struggle with 868 datarates, if you dont need to use 868 then something like Mlrs in SIK replacement mode would get around all the bandwidth problems by using 2.4ghz. There is mLRS RC hardware from matek
Thanks for the reply. I went for 868Mhz radios because the RFD small ux devices seemed to be compact and I thought that 868 MHz would give me at least 5km range and I’d be able to get a good data rate. The 868 band is also unlicensed. However, I am struggling with the technology… Will this MLRS give me a 5+km range and a faster data rate? Do I just need two Mateksys boards and antennas? Can I operate this without extra licensing in the UK/EU? Sorry - so many questions…
Its 2.4ghz so unlicenced up to 100mw. But that will be more than enough for the range you want.
It’s very fast compared to 868.
You just need a pair of receivers and flash them with the correct firmware. There is a webflasher that does It in the browser so you don’t need to install anything. Just set your binding code when you flash them and it should just work.
The problem with 868 lora in europe is that its basically designed for things like power meters and weather stations that put out occasional bursts of data. it was never supposed to have enough bandwidth for live telemetry.
OK, thank you for the advice. I’m investigating 2.4MHz mLRS now. While I’ve got your attention, does the link have the same concept of a Network/Radio ID to allow me to connect to several different aircraft receivers (one at a time) and to stop clashes with other users?
Yes as long as it’s for a unique bind code then you won’t get interference from other mLRS radios.
Us you use it as a full RC + mavlink telemetry system rather than sik replacement then you can configure it to use the model match function of the radio handset so it will only connect to the aircraft selected. https://www.mateksys.com/?portfolio=mr24-30-tx
