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Re: [Paparazzi-devel] FRSky radio XML configuration

From: Chris Gough
Subject: Re: [Paparazzi-devel] FRSky radio XML configuration
Date: Thu, 23 Aug 2012 16:45:20 +1000

Hi Jamie

> - What's the average attribute for? Why does the sample on the wiki have
> channel E and H with average=1?

average=1 means the value used by the airframe is the averaged over a
number of samples.

average=0 means every sample is immediately assigned to the function.

Imagine your transmitter MODE switch is programmed to a value close to
the boundary between AUTO0 and AUTO1, and your PPM is a little noisy
(or, just imagine you are flying a long way away and your PPM is very
noisy). You would occasionally flick between modes, which is annoying
at best. Same deal for landing gear or any other chanels you want to
use on/off switches, settings, etc. Having "average=1" on these
channels smooths out the jitters at the expense of a very small delay.

You don't want your control surfaces sluggish/unresponsive, so set
average=0 for them.

Chris Gough

On Thu, Aug 23, 2012 at 4:06 PM, Jamie Furtner <address@hidden> wrote:
> Hello,
> I'm creating a RADIO.XML file for a FrSky CPPM signal (from a D4FR RX) and
> I've got a few questions. I've got an oscilloscope trace of the CPPM output
> and have uploaded it here:, and I'm
> using the scope for measurements - zoomed in more when needed to get more
> precision.
> The overall width of the entire CPPM frame is 18ms, with each channel being
> between 1000 and 2000 microseconds in length. This does mean that if all
> channels are maxed no synchronization is actually possible (as all pulses
> are 2000 us in length). I'm forcing channel 8 in the TX to always be the
> minimum to work around that potential problem with the CPPM frame. In the
> sample frame I captured, the first channel begins in the first division and
> is in the max position, channels 2, 3 and 4 are in the neutral position, and
> channels 5 to 8 are in the minimum position.
> If it matters: I'll be using the RXs in a Quadshot and the TX is a Turnigy
> 9X with ER9X flashed onto it.
> Here's my XML file - I took the example on the wiki and changed the values
> based on my measurements:
> <?xml version="1.0"?>
> <radio name="FrSkyCPPM" data_min="1000" data_max="2000" sync_min="2200"
> sync_max="10300" pulse_type="POSITIVE">
>     <channel ctl="A" function="THROTTLE" min="2000" neutral="1500"
> max="1000" average="0"/>
>     <!-- reversed in TX -->
>     <!-- left stick up/down -->
>     <channel ctl="B" function="ROLL" min="1000" neutral="1500" max="2000"
> average="0"/>
>     <!-- right stick left/right -->
>     <channel ctl="C" function="PITCH" min="1000" neutral="1500" max="2000"
> average="0"/>
>     <!-- right stick up/down -->
>     <channel ctl="D" function="YAW" min="1000" neutral="1500" max="2000"
> average="0"/>
>     <!-- left stick left/right-->
>     <channel ctl="E" function="MODE" min="1000" neutral="1500" max="2000"
> average="1"/>
>     <!-- left middle 3-pos switch -->
>     <channel ctl="F" function="GAIN1" min="1000" neutral="1500" max="2000"
> average="0"/>
>     <!-- left slider prop channel -->
>     <channel ctl="G" function="GAIN2" min="1000" neutral="1500" max="2000"
> average="0"/>
>     <!-- right slider prop channel -->
>     <channel ctl="H" function="SWITCH1" min="1000" neutral="1500" max="2000"
> average="1"/>
>     <!-- switch (channel 8) -->
>     <!-- DISABLED - no ch9
>     <channel ctl="I" function="UNUSED" min="1050" neutral="1500" max="2100"
> average="1"/>
> </radio>
> Here are my questions:
> - I think the pulse_type is POSITIVE - as in normally high and the high-low
> transition is what signals the next channel. Is that right based on the
> trace?
> - Is it better to be slightly low or slightly high on the min and max
> values? What happens if my min is 1000 us and the complete pulse width
> (measured based from low to low) that is captured is 990 microseconds?
> - Is the XML generally correct? Any glaring, obvious mistakes?
> - What's the average attribute for? Why does the sample on the wiki have
> channel E and H with average=1?
> If it looks good then I'll try the XML file in Paparazzi and flash the
> controller for the Quadshot tomorrow.
> Please let me know if I'm missing anything or if more information is needed.
> Thanks!
> Jamie
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