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Re: [Paparazzi-devel] First power-up of Autopilot OK, some questions

From: Martin P
Subject: Re: [Paparazzi-devel] First power-up of Autopilot OK, some questions
Date: Fri, 15 May 2009 09:13:04 +0200

Yes, this does help! Thanks for this very informative answer. 
First, I will switch to the highest possible baudrate. 

I do not have an FTDI cable, but can I just pull the modems out of their 
sockets and connect receive and transmit of the Tiny and of the ground station 
adapter directly? 

Another thing that I found somewhere is that they do not work well on very 
close range, i.e. within the same room. Is it a good idea to set the power down 
to 1mW for trying at home? 

And finally, I would appreciate if the Paparazzi SW would give any information 
that points to the problem rather than just doing nothing. Well, I know, open 
source, I could program this. Not yet. 

Greetz, Martin 

-------- Original-Nachricht --------
> Datum: Thu, 14 May 2009 23:10:12 +0100
> Von: Gareth Roberts <address@hidden>
> An: address@hidden
> Betreff: Re: [Paparazzi-devel] First power-up of Autopilot OK, some   
> questions

> Martin, I also use 9600 with my XBEE 2.4GHz pros.
> The problem you are having I suspect (and the problem I had with my 
> 868's) is that the DUTY CYCLE of the XBee Pro 868 is only 10%.
> This means it can only transmit for 10% of the time, and needs to rest 
> for the remaining 90%.
> If you run it at 9600, that means you'd only get 960 baud realistically, 
> and at their maximum rate you'd get 2.4kb/s, which is not enough for 
> proper telemetry.
> Also, Paparazzi is designed to stream data continously, and there is no 
> easy way of "saving" all the data and then burst sending it, because the 
> rate is too slow.
> If your modem is not working when you launch GCS, the screen will go 
> blank as you describe - after about 4-5 minutes of streaming, the XBee 
> (usually on the aircraft side as it sends more) senses it's duty cycle 
> is too high and just stops working, after which it'll need a reset or 
> power cycle.
> That would explain why on first launch it works. Once GCS is populated, 
> leave it about 10 minutes and come back. If the link indicator is red 
> and displays a number (seconds since link lost) it's your xbees.
> This has bitten a lot of people, as Maxcomm are advertising them as 
> drop-in replacements for XBee 2.4GHz (which can support a 100% duty 
> cycle) when in fact they are for different uses. 
> One chap managed by having paparazzi reset the airbourne xbee every few 
> minutes, but this seems a bit extreme. There is also work ongoing if you 
> look at DiyDrones to try and cool the chips to stop them cutting out, 
> but nothing successful so far.
> To be honest, I'd recommend getting some 2.4ghz's to start with, they 
> are fairly cheap and are good to over a mile. You can also test by 
> connecting the serial port of your tiny directly to an FTDI convertor - 
> if it works, it's your XBee's that are the problem.
> Hope this helps!
> --G
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> Paparazzi-devel mailing list
> address@hidden

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