Bandwidth utilization of MAVLink over a 3DR radio

[Michael Day]

Howdy,

Has anybody already measured (or have some ideas for tools to measure) the amount of bandwidth being utilized by MAVLink for communication between an aircraft and the GCS?  I know the 3DR radios operate at 57600 baud (so probably around that number of bps) -- how can I measure how many bits the GCS or aircraft is sending and receiving?  

The reason I ask is we're ramping up to getting multiple planes flying at once and we are curious how many can controlled by a single GCS.  Tridge has already pointed me to:

https://github.com/RFDesign/SiK_Multipoint

to get firmware that should allow the 3DR radios to handle sharing the spectrum with more than 2 radios (I think that method uses TDM).  However, my team and I are curious how chatty MAVLink is and what the implications would be to use a naive solution and just use MAVLink as-is.

Thanks ahead of time,

Michael Day

[Bill Bonney]

MAVLINK is pretty efficient for packet sizes. The main challenge is going to be how frequently you want attitude and HUD updates for these vehicles. It might be advisable to configure the GCS to request data rates for attitude etc, when its the 'active' one being monitored, and de-request those updates when you are only monitoring in the background. APM Planner has the concept of activeUAS, but doesn't yet send requests to switch data rates off.

If you want to monitor traffic amount, you could use WireShark to capture network data. Not sure it has a MAVLINK plugin yet, but it would be useful to create one.

Bill

[Monroe King]

You could also take a look at the FFT using a SDR TV dongle at the true RF bandwidth available. You might be able to push through a little more using SDR.