35 mhz and ppm output

[CARPERFECT]

Hi all any radio/electronic experts out there ?

I have been playing with wireless trainer systems for the last few weeks. Why?

Well we have a club tx and trainer plane on mode 1, and was looking for an easy and cheap way to train on mode 2 as well. Now the way to get wireless training is 1.Bind the club TX to the Club Plane 2. bind the students rx to the students tx in CPPM/PPM MODE the plug the students rx into the club (master tx ) trainer port and that`s it. Well we have plenty of mode 1 and 2 Tx and Rx`s around on 35mhz. So the big question is how do you get all the channels to come out of one slot on the rx of a 35mhz ?

[Alan Gorham_]

Err, you can't unless you hack around inside the receiver!

It is possible to have the master and student Tx's on different modes using a conventional buddy lead. I know because I do it. With Futaba anyway.

[Denis Watkins]

For 1st flights CP

2 competent flyers have to trim each set as master then slave,

It does not take long

[Alan Gorham_]

What's that got to do with the original question?

[Denis Watkins]

Posted by Alan Gorham_ on 16/10/2018 18:40:34:

What's that got to do with the original question?

E by gum Alan, I dont have a clue why i wrote that

[Alan Gorham_]

Me neither!

[Chris Bott - Moderator]

One of these might be your best bet.

Click on photo to see it at hobbyking.

This uses two receivers in the model, one working from each transmitter (Instructor and pupil). An extra channel on the instructors receiver controls which Rx flies the model. The two receivers can be completely different systems and different modes.

Edited By Chris Bott - Moderator on 16/10/2018 19:44:33

[CARPERFECT]

Or me lol. I have been flying for over 30 years, so not a novice, But when it come to magic smoke dept ( electric bits) i no nothing. As Rene Artois from Allo Allo says

[CARPERFECT]

Trying to avoid using the 35mhz as a direct transmitter, Electric planes get a few glitches on 35 mhz at our field. i know i have tried

 

Edited By CARPERFECT on 16/10/2018 19:51:29

[Chris Bott - Moderator]

OK.

I don't know of a PPM 35Mhz Rx.
What make are the two sets of kit?

I do have an idea about making PPM from the servo channels of the pupils Rx.
Back in a min.

[Simon Chaddock]

I thought "I know nothing" was a line by Manuel in Fawlty Towers!

[Chris Bott - Moderator]

This looks like it should do the job PWM - PPM encoder

[Martin Harris - Moderator]

Posted by Simon Chaddock on 16/10/2018 19:59:00:

I thought "I know nothing" was a line by Manuel in Fawlty Towers!

Surely it was Sergeant Shultz's catch phrase (in Hogan's Heroes) long before Andrew Sachs uttered it?

[CARPERFECT]

Chris Bott. 35mhz receivers output ppm not pwm i think

[Peter Beeney]

With regard to the PPM/PWM conundrum I’ve always understood, rightly or wrongly, it’s really just a combination of both.

Does the basic 27/35 MHz kit operate like this?

The transmitter controls create a sequential Pulse Width signal which is sent to the Encoder which turns it into a series of very short pluses, each one being the start and end of each long pulse; so this now becomes a Pulse Position signal. This carries on to the transmission compartment where it Modulates, or is superimposed, on the carrier wave. Now it takes to the airways and has the title Pulse Position Modulation; it then reaches the receiver and after being Demodulated by the Radio Frequency section is send on to the Decoder. This sorts out the string of short pulses and turns them back into a sequential Pulse Width signal which in turn is divided up and sent to the appropriate servo.

So I would say that strictly speaking the expression Pulse Position Modulation, PPM, is the more accurate description for this operation as it is this signal that is actually modulating the carrier wave. I think the word ‘modulation’ is often used just as as a general descriptive term, ‘Waveform’ might sometimes be more appropriate…

This is a very very minimalistic account of affairs but it’s how I’ve always thought that this system works.

PB

Edited By Peter Beeney on 17/10/2018 11:03:42

[Peter Christy]

PB: Yes, that is a pretty accurate description of the process!

--

Pete

[Chris Bott - Moderator]

Generally PWM tends to be used to describe the individual signal for each servo. The width of the pulse (in mS) signalling the required servo position.

While PPM is a shortening of CPPM and seems to be used to describe a signal that contains all the PWM pulses in sequence along with a frame period.

OK it can be argued about whether the definitions fit but that's not what the OP was about.

The item I linked to will take a number of servo channels from a receiver as it's input and I believe that it's output will be a single signal that will work exactly as a buddy signal does.

Whether it will work with the OPs chosen Tx types is unknown. But I think it would work fine as the input to JR or Spektrum transmitters.

I have another type that I could try. I'm not sure when I'll have time though.

[nigel newby]

I thought "I know nothing" was a line from Shultz, in Hogen's hero's.

[CARPERFECT]

Here is an explanation of pwm/ ppm/cppm

https://www.youtube.com/watch?v=GbUMC8h2uhU

[Peter Christy]

A brief history lesson: The very first digital proportional system was designed by Don Mathes and Doug Spreng around 1961. Doug Spreng designed the "pulse width tracking" servo system at the heart of that, and all subsequent systems right up to today.

Initially, the Mathes-Spreng Digicon system transmitted a pulse width signal, but in the days of AM radios, this suffered from AGC problems due to the long periods of "no signal" between pulses.

It was Frank Hoover of F&M (one of the "big names" in RC back in the 60s) that suggested converting the signal to PPM for transmission, in order to overcome this problem. All the Digicons were recalled for modification, but the reputational damage was done. Mathes and Spreng sold out to C&S, who put the modified system into production with considerable success.

The whole saga can be found here: **LINK**

Checkout the "history" link underneath the pictures.

Of course, none of this helps the OP, but the widget suggested by Chris ought to do the job!

--

Pete

 

Edited By Peter Christy on 18/10/2018 08:16:16

[Chris Bott - Moderator]

This setup works. That is it does accept 6 servo (PWM) signals from a receiver and it makes a single PPM signal that my Horus X12 accepts as a trainer signal.

I'll post a link to this widget a little later.

[Chris Bott - Moderator]

Here is it is working with 8 channels buddied up from the left hand Tx to the right hand one.

The screens are showing servo positions of 8 channels. I've set the right hand Tx as an instructor Tx but as if the trainer switch is permanently held on. The left hand Tx is bound to the Rx you see.

[Chris Bott - Moderator]

This is the widget I'm using. Whether it will work with other makes of radio - I'm not sure. (Click picture to go to Banggood. I believe Hobbyking carry them too)

Edited By Chris Bott - Moderator on 18/10/2018 12:49:37

[CARPERFECT]

Thanks Chris. You have basically the same system as i have, but you have used an extra gizmo. If you use a Fr sky D4R-11 or the Delta 8 receiver instead of the d8r you would not need the converter as the D4R -11 will output a cppm signal if a jumper is placed across pins 2 and 3. Have you still got and 35mhz gear you could try the converter on ?

[Chris Bott - Moderator]

CP I would never use this setup with FrSky gear, there are far better options as you suggest. I buy these units to decode S.Bus and only put this together for your benefit.

To answer your question - no, I don't have any 35Mhz gear. But there's no difference in the servo signals.

What I can't test is that the PPM output will suit the instructor Tx that you intend to use. My Horus was set to expect a JR or Spektrum type buddy signal.