Validity check on trainer input

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If no new valid PPM frame received for 100ms or so, all PPMx inputs would be 
set to 0, mixers using them would be disabled, as would trainer custom 
functions. Maybe also check each non-zero channel is between 800 and 2200.

Original issue reported on code.google.com by bernet.a...@gmail.com on 19 May 2013 at 5:21

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The proposed enhancement has some very dangerous drawback when applied to 
engine.
0 ppm value on engine channel may be dangerous, as well as the command 
returning to the master without leaving the master know it some way.
About validity check of the input I agree..

Original comment by romolo.m...@gmail.com on 19 May 2013 at 5:43

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It would be safer than now - currently it just stays where it is, or jumps 
anywhere depending on what broken pulse arrived before disconnection! 
You just really wouldn't want to put just a PPMx mix on the throttle channel in 
the first place.
And if you did you'd use it as Replace, with my proposition as PPMx mixes would 
get disabled when signal is invalid it would fall back to the default control. 
That's not possible now.
About the command returning to the master all radios I know do that, it's 
rather common to pull the cable during training by mistake. The cool thing 
compared to those other radios is that we could add an audio warning/beep :)

Original comment by bernet.a...@gmail.com on 19 May 2013 at 6:31

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yes the audio could let the instructor know that trainer link was lost and he 
had control..
This enhancement is very important because at the moment if we forget to 
disable trainer mode for a model and flick the switch by mistake, we will most 
likely lose the model. when we'd realize what happened, would be to late.
Just my 2c

Original comment by joaoalve...@googlemail.com on 4 Oct 2013 at 6:23