Mavlink Bad Packets when connected over XBee

Hi there,


I am hoping someone can help me with this...


I have my APM board hooked up to the GPS, magnetometer, XBee and groundstation software. I have connected using my XBee com port at 57600 and everything seems to be working ok, I get what seems to be very good IMU feedback on the HUD and GPS position updates... and I always say "don't fix what ain't broke"


However.... when I look at the console part of the Mission Planner application, there are a bunch of messages about Mavlink Bad Packets being displayed as follows :


Mavlink Bad Packet (crc fail) len 45 crc 61283 pkno 32

Olost 16 pkts 81

20/01/2012 00:04:33 action received:

Request stream MAV_DATA_STREAM_POSITION at 3 hz : currently 0

Ylost 60 pkts 83

Mavlink Bad Packet (crc fail) len 109 crc 25766 pkno 27

qMavlink Bad Packet (crc fail) len 45 crc 10082 pkno 32

ZZlost 65 pkts 88

Mavlink Bad Packet (crc fail) len 45 crc 37560 pkno 32

]lost 107 pkts 91

Mavlink Bad Packet (crc fail) len 45 crc 21200 pkno 32

Elost 149 pkts 94

'`lost 191 pkts 96

Mavlink Bad Packet (crc fail) len 109 crc 36964 pkno 27

BNMavlink Bad Packet (not addressed to this MAV) got 227 45 vs 1 1

BCI?Wlost 196 pkts 101

Mavlink Bad Packet (crc fail) len 45 crc 42789 pkno 32

lost 238 pkts 104

Mavlink Bad Packet (crc fail) len 45 crc 59556 pkno 32


I am now wondering whether this is normal behavior of if I am missing messages and it is affecting the efficiency of my telemetry feedback... perhaps this can be sorted out by a firware update or something else I am missing.


The XBee modules themselves work 100% when wired in loopback and also fine when running the com port test scetch, I have also used then to transmit large amounts of data without using the APM and had no problems so I doubt it is that.


Has anyone else noticed these messages.


I can post the actual HEX data of the messages or even the logic timings from my osciloscope/logic analyser if that would help...


Thanks in Advance for any help...





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  • I hope this thread can help :

    For series 2 xbees Sparkfun Regulated board is needed.

  • 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.

  • This may help

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


  • 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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