Multiplex Evo PPM scope trace?

[JohnJulian]

A plea on behalf of one of the Lemon module beta testers:
Could anyone post a trace of Multiplex Evo PPM please? firmware is v2.6
Cant find anything online
TIA
Phil

[Kad370]

Multiplex uses their own protocol that comunicates only with their module. You can try to listen treiner port. Just check pio out.

[Shaun]

My first converted propo set (OS) to 2.4g used one of your encoders Phil and a Spectrum module designed for use in the 3030 and 4000 Tx's. It worked fine if that info helps.

[Phil_G]

Ok I've managed to find out a bit more.
In 12 channel mode, Multiplex PPM uses non-standard 1.4ms centres at the encoder output, and the 12ch receiver expands each channel to their own concept of 'neutral' which is 1.6ms, by simply adding 200uS.
They use quite a long sync of 6ms, so its "fixed sync, variable framerate" which is unusual these days, and with all 12 channels maxed out at 1.9ms (1.4+.5) and a 6ms sync, its frame time is 28ms - I've tested it and the latency is noticable when compared to 18ms encoders.
There is a popular add-on board made by "Shread R/C" which converts the mpx ppm stream to standard 1.5ms centres, but they dont say what it does to the framerate. It also fools the encoder into thinking there is a MPX RF module present by answering the "are you there?" query from the encoder.
From this it seems that in 12ch mode the Evo encoder has an acceptable PPM format albeit with 1.4ms centres and a lethargic framerate.
I would say that 1.4 centres are usable - its only 10 standard trim-clicks, and the new Lemon DIY module is happy with a 28ms frame.

Cheers
Phil

[MaxZ]

I am not sure about the ppm stream, but what comes out of the Rx on the servo side is definitely 1.5 ms.
The older MPX sets had their own neutral, 1.6 ms I believe, with extended puls length ( a.o. Mc3030, Mc3010, not sure about Mc4000). The Evo, and its successor/upgrade, the Pro, had the possibility to change the pulse definition between "MPX" and "UNI", the latter having the common definition with 1.5 ms neutral and 1-2 ms pulse. Up to version 2.xx you could change the pulse type per channel from the transmitter. However, on the most recent firmware versions this is no longer possible, the "UNI" pulse mode is fixed.
I believe this change happened with the 3.xx version, but I cannot be sure. Another possibility is that it is related to the HF module, which is still interchangeable between 2.4 GHz and 35 MHz, even today.

I will hook up my Royal Pro (2.4 GHz, SX firmware) trainer port to a pulse meter sometime today and let you know my findings.

Cheers,
Max.

[MaxZ]

As promised, the ppm stream from my Royal pro/SX, hooked up to a pulse meter. The only way I could get a reading is by connecting ground on the meter to the signal from the Tx, and signal in on the meter to the + 7.2V from the Tx (due to the trainer/student cable I was using, which only had those connections available).

Now I should mention that this is the outcome of the Tx in regular 2.4 GHz transmitting mode. Once you change to student mode it all becomes different, and you get to choose between MPX and UNI modes, this to allow older Tx to function as teacher.

As you can see in the top picture, the neutral is just about 1.5 ms (ch1 is the throttle on safety switch).

The middle picture is all sticks in the top-right corner (note that MPX has fixed end points, not affected by the trims, except throttle).

The bottom similar with all sticks in the bottom-left corner.

The frame rate is constant in all three pictures, the sync pulse is changing.

Hope this helps, cheers,
Max.