Turnigy 9x + HK T6A - PPM channel limit? - RC Groups
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Nov 21, 2011, 04:40 AM
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Turnigy 9x + HK T6A - PPM channel limit?


Hi there,
I have a Turnigy 9x with ER9x firmware, I'm using all 8 channels on the rx and was thinking about using PPM sum instead of individual PWM signals (it is connected to a flyduino board so less wires = less problems).

It looks like 9x original receiver has no PPM sum pin (correct me if I'm wrong), but the transmitter binds and works with HK T6A receiver (which has PPM sum).

Is it possible to get 8 (or more) channels from this receiver from the PPM sum pin? It's my understanding that the RX just passes PPM from the stream to the PIN, so it should work no matter what is encoded inside (4ch or 32ch), only the spacing will be different - and this can be set on the transmitter.

Can somebody please advise?

Thanks
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Nov 21, 2011, 01:01 PM
Suspended Account
HK T6A receiver has only 6 channel output pins.

Why do you need more than 6 channels at TX?

6ch receiver works with 8ch transmitter. Why is modification necessary?
Nov 21, 2011, 01:36 PM
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Yes, it only has 6 separate (PWM) outputs, but I was hoping all 8 channels will get to the PPM pin unchanged by the receiver (i was hoping it is "dumb" enough to just passthrough whatever goes from the transmitter, but it looks like it strips everything but 6 channels)).

I'm using arducopter (actually megapirateng), and channels 7 and 8 are used for led sequencer and special functions (autolevel trim, alt hold adjustment etc..)
They are not essential for flight, but I spent considerable time getting them to work.

So unless somebody knows how to convince the receiver to pass on those channels, I guess I have my answer :-)
Nov 21, 2011, 02:10 PM
Suspended Account
Get 8ch receiver. What is the problem?
Nov 21, 2011, 04:40 PM
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no problem, but TR6A is very small and I have 2 spare...
Nov 21, 2011, 04:53 PM
RC beginner
maybe hes using it with a microcontroller and is running out of pins. in any case i thought the hkt6a and original like all flysky lack ppm. i know mine dont have it and thats one reason i use frsky too.

ps whats with "ppm sum" or "cppm" ? as far as i know theres only one kind of ppm: ie ppm. never heard of "uncombined" or "un-composite" variety.
Nov 21, 2011, 05:24 PM
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one channel PPM is in fact a PWM (with a delimiter, right?)

First I heard it was called "PPM SUM", then "SERIAL SUM"... I guess it should be called PPM but PPM SUM is more accurate in this case :-)

And yes, you are right, I'm looking at a way to save pins and at the same time have a more reliable connection (apparently, I'm not that good at making plugs as I had them vibrate loose yesterday - that's why I'd prefer to just use one cable - less entropy in the system :-))
Nov 22, 2011, 05:48 PM
RC beginner
Quote:
Originally Posted by zviratko
one channel PPM is in fact a PWM (with a delimiter, right?)
no. they are completely different and do not look even similar on a scope.

pwm uses pulse width (high time vs low time) aka "duty cycle". it is what a rx sends to the servos. each channel comes out on a separate pin. all the pulses are equally spaced and contain data for just one stick position. several pins are required.

with ppm all chanels come out on a single pin. is uses the time from the beginning of one pulse to the beginning of the next. aka period or cycle time. it is what a radio sends to its rf circuit for transmission over the air. spacing between these pulses changes radically depending on position of all the sticks ending as you say with a delimiter.

in other words with pwm the high time contains info and varies. high time is always the same for ppm pulses and it is the spacing between them that contains the info.

as you implied some rx are able to provide ppm in addition to the pwm channels. usually this is so a copter or uav controller only needs 1 input instead of the normal 4-8 inputs. frsky rx can do that but flysky cannot.
Nov 22, 2011, 05:58 PM
RC beginner
Quote:
Originally Posted by zviratko
And yes, you are right, I'm looking at a way to save pins and at the same time have a more reliable connection (apparently, I'm not that good at making plugs as I had them vibrate loose yesterday - that's why I'd prefer to just use one cable - less entropy in the system :-))
ppm is more reliable for exactly that reason.
Nov 22, 2011, 06:05 PM
Registered User
monkeyhanger's Avatar
I recently bought a 6 ch hobbyking receiver (v2) to use as a wireless sim interface, but unfortunately I didn't see any ppm sum output on the BAT port with my scope. I'm wondering if it is simply no longer available.
Nov 22, 2011, 06:17 PM
RC beginner
was it ever available? none of my flysky/hk rx have ppm out.
Nov 22, 2011, 07:21 PM
RC beginner
hmmm... thanks. i missed that. none of mine put out. i just checked.

maybe you need to short some pins. my frsky need 2 other pins shorted to activate that feature.
Nov 22, 2011, 08:15 PM
Registered User
monkeyhanger's Avatar
Quote:
Originally Posted by dave1993
hmmm... thanks. i missed that. none of mine put out. i just checked.

maybe you need to short some pins. my frsky need 2 other pins shorted to activate that feature.

Well there's no mention of anyone having to do that though. Maybe our V2's are 'V3's' and no longer have it.
Nov 23, 2011, 02:22 AM
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I have V2 and it does have PPM... at least I think it's V2? I'll take a look when I go home...

dave1993: thank you very much for the explanation, do you know how the whole "sequence" is delimited? I'm wondering what happens when software (in this case arduino) decodes PPM but assumes wrong number of channels - I expected it to go crazy when I set it to expect 8 channels in some order but it only receives 6 - but what I see is 6 perfectly working channels with two set to default (1500). When I mess with my TX settings (spacing, pulse width) I can make them garbled a little (overlap, one channel affecting more than one channel etc, but still just 6 channels - even when I change to wrong modulation (like TRAC), only 6 channels are affected. I don't have an oscilloscope so I don't have a way to check what exactly goes out of the PPM pin...

Thanks!


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