PPM 18

[0j1VY96z]

what is this "PPM 18" and is the wikipedia article to PPM (Pulse-position modulation) something else?

[phildc]

PPM 18 is a PPM modulation with 9 channels (18/2).
You find it e.g. with the Graupner MX-16s and MX-22 (which has also PPM 24 with 12 channels).
Note that all channels transmitted are not necessarily working (the MX-1§ is an 8 (working) channel xmter).

Phil.



ppm18 ppm24 rc transmitter receiver radio control xmtr rcvr signal

[0j1VY96z]

I see that you have great experience with PPM.
my question remains:
is the wikipedia article about the same PPM as used in RadioControlled models? I doubt it.
For all I know there is no synchonisation needed and the absolut position of the pulses bears no information. It is the time between the pulses that carrys the servo's PWM. the frame/sequence length is not fixed but depends on the sum of the duration of the servo's impulses.
the frame length varies from 12ms to 21ms. only the frame rate is fixed to 1/(22,5ms)

[Steve Lewin]

Try looking up PWM (Pulse width modulation) on wiki. That's is a more accurate description of what an RC "PPM" signal looks like but it sounds like you already know that so what is the point of your question ?

Steve

[phildc]

Just made a quick search on wiki, and found no good definition of our RC PPM modulation.

Some short definition:
The modulation can be positive or negative.
The frame synch(ronization) signal exceeds the duration of any channel (typically 2.5 millisec (ms) or more).
The channels (their number vary from 2 to 12), are transmitted in sequence, starting with channel 1.
Each channel is represented by a channel synch (of approx 300 ms) plus a variable time. The channel position is given by the sum of synch PLUS var time. Full left position of the servo is 1000 microsec (us), full right is 2000 us. Some system can exceed, giving 800-2200. The servo travels from -45° to + 45° approx. The servo signal is always positive, and its length is the length of the ppm synch+var.time of a channel.

The full frame will be repeated approx. 50 times per second. Less (45 ? times) for 12 channels. For systems with few channels, the frame synch will be quite long, to wait for the approx. 20 ms of the 50 s-1 system.

This view gives the relation with the servo signals: ('voie' is the french for channel)

Mr. Thobois 'site is a good RC electronics site.


here a 6-channel ppm signal

from

You can find other infos on PPM and diagnostic tools on (in french)


Phil.



rc radio control modulation protocol ppm whatis signal scale model

[shamoly]

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[phildc]