Telemetry transmission speed

Ground Control Software Mission Planner
1

Hi, maybe this is a stupid question, but I didn’t find an answer in this forum… Maybe I was searching for the wrong terms…:

I noticed that the rate at which data is sent wirelessly to Mission Planner differs a lot between using a USB cable and a (cheap Banggood - nothing else was on stock at that time) wireless transmission. When I connect to the Pixhawk 2.1 in Mission Planner, then it downloads all the settings from the flight controller. With a wireless link, this takes aroun 3-5 times longer than with a USB cable. The variables in the “status” tab update maybe with 1-2 Hz wirelessly, while they update with 10-50 Hz when using a USB cable. I tried increasing the “airspeed” of the telemetry modules, and also increased the baud rate to 115200. This didn’t change anything. I tried MAVlink 1 and MAVlink 2 protocols. Also, changing the telemetry rates in Mission Planner doesn’t really change anything. The link quality of the wireless link shows >95%.

Is is maybe just normal that the telemetry is at such a low rate? Or are there differences between radio modules…?

2

the usb baudrate is alot higher than the telem radio. typically 57600 for telem, and the baudrate on usb is actually ignored.
usb can hold around 200kb/s where as the telem radio is more like 5kb/s
ie 57600 / (8+2) = 5.76kb/s (baudrate / (bits + start and stop bit)), and its half dupex, meaning that 5.76 is shared for both the upload and download, unless the air rate is set to accommodate

3

Dear Michael, thanks for your reply. So that means that the speed that I am getting is totally normal I guess?

4

at a guess, yes. click the link status link near the connect button, and it will display stats about the receive rate you are getting.