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Permalink Reply by Chris Mulder on January 21, 2012 at 3:38am

As a further update to this, I have found that I AM losing some information in the lost packets... I will often not get a GPS fix although the LEDs on the APM and GPS show that I do have one... then when diconnecting over the telemetry port and reconnecting over USB I have a 3D GPS fix right away, I guess the info about the GPS fix was one of the lost packets.

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Permalink Reply by Peter Seddon on January 21, 2012 at 4:33am

This may help http://www.diydrones.com/forum/topics/mavlink-data?xg_source=activity

Are the Xbee's very close together and there is a swamping issue? Try moving them apart. 

Peter

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Permalink Reply by Chris Mulder on January 21, 2012 at 6:04am

Thanks for the sugestion Peter... tried your suggestion but no luck... I even put them at opposite ends of the property and although the data was transmitting without any problems (good hud feedback) - the packet/CRC erors are still coming through

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Permalink Reply by Chris Mulder on January 21, 2012 at 6:16am

OK I take my words back... it is definitely realted to my XBee modules...

 

I disconnected them completely and put a USB to TTL cable/module on the telemetry port and connected to the MP software... no errors at all!

 

I am using the XBee Pro Series 2 modules (yes I know they are not officially supported) and I suspect that what is hapening is that the Mavlink packets are not arriving in one burst i.e. the RF modules are doing some sort of buffering into their own packets. I think that when the serial data arrives on the serial port (PC side) it may not yet contain all of the bytes required to complete the Mavlink packet as these bytes are in the next RF packet being sent by the XBee, which has not yet arrived. I have tried to disable buffering on the XBees with various parameter changes but no luck, the Packet/CRC errors persist. I may knock together a quick .NET application to try and test this though I suspect it will be difficult to reproduce the same timings in debug mode....

 

Perhaps it is time to go shopping for some standard, supported 900Mhz XBee modules...

 

It would be interesting to know if anyone has the Mission Planner Software working with the Pro version of the XBee modules.... and if so what settings are being used on the modules.

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Permalink Reply by Emiliano Fortunati on February 8, 2012 at 2:41pm

Hi Chris,

 

same for me, I'm trying two XRF modules, and with them I'v a lot of crc errors. If I use Xbee pro 900 the errors goes away...

 

After severals hours of test I suppose that the problem is in the packet size or in the radio conversion "inside the module".

 

With these cheap XRF modules I've a 10% of loss packet, that is 10% at 1 meter and remain 10% at 100 meter.

 

the packet loss are in communication from APM to PC in MAVLINK, others stream work fine with no loss, for explample if I read or Write 100 waypoints I've no CRC errors, when I finish to read/write waypoints crc errors start again.

 

I hope my experience may help.

 

BYE!!

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Permalink Reply by Fatih Gokce on February 10, 2012 at 2:21pm

I hope this thread can help : http://diydrones.com/forum/topics/2-4ghz-xbee-suggestions?id=705844...

For series 2 xbees Sparkfun Regulated board is needed.

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Permalink Reply by Graham Boucher on February 10, 2012 at 4:41pm

I've been through exactly the same with my Xbee journey.  I kept reading comments like the following in the Digi International Support forums:

"

...If you are using this as a simple point to point application, is there a reason why you chose the XBee Series 2 radios to do this? Point to point applications may be performed much easier using the XBee Series 1 radios instead, as they use only the 802.15.4 standard and do not rely on the ZigBee protocol with it's accompanying overhead. Unless mesh networking is required, I would suggest working with the Series 1 over the Series 2 for point to point applications.

"

The extract was taken from this forum post.

So it seems the extra data overhead required for Mesh radio networks has a big impact on a simple point to point connection.

I finally gave in and bought a pair of 2.4Ghz Series 1 Xbees from Martin at Build Your Own Drone.  Perfect 100% link every time :o)

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