Replies to This Discussion

Permalink Reply by Michael Pursifull on November 19, 2011 at 3:31pm

Experiments only, 32k - 56k, depending

If you run ArduPlane in HiL over xbee at 56k, you will be so close to the limit that you will frequently not be able to push PID or WP changes easily.

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Permalink Reply by Jesper Rooth on November 20, 2011 at 12:55am

That might explain it.

Leaves me with two options then,

1) investigate the options on lowering the amount of data APM pushes to the telemetry port per second.

2) writing a light version of the telemetry protocol - will not work with the nice Mission Planner interface :(

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Permalink Reply by Michael Pursifull on November 20, 2011 at 1:23am

what is the range you are seeking w/ the OpenLRS? What is your goal in using OpenLRS for telemetry?

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Permalink Reply by Jesper Rooth on November 20, 2011 at 2:03am

I already got OpenLRS to control the airplane. I could buy 2.4 GHz XBee for telemetry but it be really sweet if I could tunnel the telemetry via OpenLRS. It only supports 750 kilobytes/s (not bit) downstream and 100 kilobyte upstream (ground to aircraft).

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Permalink Reply by Jesper Rooth on November 22, 2011 at 3:58am

Looking at the source code there are several occasions where the MAVLink send algorithm is called. In the main loop, medium_loop and slow_loop. 

    gcs_data_stream_send(<freq min>,<freq max>);

 

Some questions I hope someone can answer,

- What is the maximum amount of data (in bytes) sent when gcs_data_stream_send is called?

- Would MAVLink protocol still work if the gcs_data_stream_send under fast_loop and medium_loop are disabled?

- Is it possible to strip down the MAVLink protocol on the APM without changing anything in Mission Planner? So for example it only sends position without info like gyro/IMU etc.

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Permalink Reply by DaveyWaveyBunsenBurner on November 22, 2011 at 4:04am

@Jesper

 

I've been pondering on using the OpenLRS as a telemetry-only TX/RX so will be interested to see how you progress with this.

 

 

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Permalink Reply by Jesper Rooth on November 22, 2011 at 1:19pm

I had another look at the specification for MAVLink.

• "The minimum packet length is 8 bytes for acknowledgement packets without payload"
• "The maximum packet length is 263 bytes for full payload"
• "heartbeat every 60, 30, 10 or 1 second (1 Hz is recommended, but not required)"

This means I could in theory send two full payload packets at 2 Hz via the OpenLRS RX/TX link. Very nice.

... back to the garage for some testing! :)

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Permalink Reply by Jesper Rooth on November 22, 2011 at 1:38pm

Success!

The OpenLRS transparent serial bridge as carrier of MAVLink protocol works. I ran QGroundControl instead of Mission Planner which had lots of more functionality and configuration possibilities regarding telemetry.

Throughput was at 700-850 bytes per second. Not sure if this was limited by OpenLRS or the protocol. But I suffered 30% receive loss and 78% send loss. Tweaking of data link did not help.

Even HUD worked pretty smoothly.

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Permalink Reply by Andrew Radford on November 22, 2011 at 2:56pm

Great work! when you get something going well please do a blog post. For some people this could be a viable XBee alternative.

 

WRT Mavlink - the APM planner does request data streams at a certain update rate per second - this is exposed on the setup tab as 'Telemetry rates'

 

Also - is OpenLRS full duplex? 

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Permalink Reply by Jesper Rooth on November 23, 2011 at 10:18am

Updated to latest version or APM planner. Setting very low values on the updates for telemetry did not make any difference. No connect. You could see that some packages were coming through but not enough to setup a stable connection.

 

Switching to QGroundControl made it work instantly.

 

I will for sure write a blog post about this will all tests are done.

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Permalink Reply by Andrew Radford on November 23, 2011 at 11:50am

Hmm I wonder if it is the initial request for all the parameters - What does the console say? Michael O will probably have to chime in. It would be great to get Open LRS working with the 'out of the box' software.

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DeveloperPermalink Reply by Michael Oborne on November 25, 2011 at 4:05pm

Jesper, what part is the connect failing at? i asume getting param 0 of  xxx is the error message you get?

to bypass try pressing control-T, after you have started the planner and picked the com port

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