Topic: Confused over PPM PCM & 2.4 (Read 6132 times)

catengineman · « **on:** November 25, 2012, 09:38:46 pm »

Hi all in the know,
I currently use 40MHz FM on the PPM side of life. so all has been sort of fine
Now I do have multi channel requirements, there is one vessel that requires the use of 14 channels to operate fully as I built it.
I have looked at converting to 2.4GHz and have found that the most I can get to is 12 channel but there is a need to purchase a new transmitter at around the £800.00 mark.
I have even thought about putting a Jeti TU2 & switch conversion into my FX18 but that is apparently no gain as I would only end up with 8 channels on the 2.4 GHz system.
I know that my Transmitter can be changed over form PPM to PCM (the latter I have read to be better at controlling the glitch from high powered EFI) but I dont seem to be able to find much in the way of info regarding receivers for the PCM is it that MY Rec I have will work or do I need to change out those for others and if so is there also PCM decoders to get the additional channels from my set-up.
.
So am I right in that a 2.4 conversion would only give me 8 channels
Do I have to replace all my receivers in the models to get to PCM
Can some pone send a truck load of asprin to cure this B***** head ache.

catengineman · « **Reply #1 on:** November 27, 2012, 08:37:15 pm »

No one to shed any light on this confusion?

Tug-Kenny RIP · « **Reply #2 on:** November 27, 2012, 08:48:09 pm »

I'm afraid this is beyond me. I was looking for the ultimate transmitter myself and wandered into this sort of problem.

If I require extra channels then I run two simple set ups from two transmitters.

Perhaps there is knowledgeable member on here ?

Cheers

ken

Stormbringer · « **Reply #3 on:** November 27, 2012, 10:31:28 pm »

well Spektrum do a DX18 that can have up to 18 channels
http://www.horizonhobby.co.uk/aeroonline/e6spektrum/e6_spm18000eu/e6_dx18.html
http://www.horizonhobby.co.uk/aeroonline/e6spektrum/e6-dx18qq/e6-dx18qq.html

JKD · « **Reply #4 on:** November 27, 2012, 10:41:39 pm »

Check out with Puffin Models the UK agent of Jeti the new Jeti Duplex DC-16 with 16 digital proportional channels.
I have been using duplex 2.4 ghz modules in my Futaba and Graupner transmitters and would not consider any other 2.4ghz system . Always works and great range of telemetry.

Stavros · « **Reply #5 on:** November 27, 2012, 10:49:52 pm »

PPM

Pulse-position modulation (PPM) is a form of signal modulation in which M message bits are encoded by transmitting a single pulse in one of $2^M$ possible time-shifts. This is repeated every T seconds, such that the transmitted bit rate is M/T bits per second. It is primarily useful for optical communications systems, where there tends to be little or no multipath interference.

PCM

Pulse-code modulation (PCM) is a method used to digitally represent sampled analog signals. It is the standard form for digital audio in computers and various Blu-ray, DVD and Compact Disc formats, as well as other uses such as digital telephone systems. A PCM stream is a digital representation of an analog signal, in which the magnitude of the analog signal is sampled regularly at uniform intervals, with each sample being quantized to the nearest value within a range of digital steps.
PCM streams have two basic properties that determine their fidelity to the original analog signal: the sampling rate, which is the number of times per second that samples are taken; and the bit depth, which determines the number of possible digital values that each sample can take.

WQell thats as clear as MUD isnt it now me is defo confused .com

Dave

deadbeat · « **Reply #6 on:** November 28, 2012, 12:46:24 pm »

I also have a query, I'm thinking of replacing an old Futaba 27MHz set with a new 2.4 outfit, if I buy Futaba can I plug the existing Futaba servo & ESC (Futaba plug) into the 2.4 receiver, I do not want to change servo and ESC?
Does the Planet5 2.4 receiver accept Futaba plugs?

essex2visuvesi · « **Reply #7 on:** November 28, 2012, 12:48:38 pm »

you might need to shave off the alignment keys on the plugs depending on the servo type... easily done with a file ot a shrp knife

Captain Flack · « **Reply #8 on:** November 28, 2012, 01:10:25 pm »

You beat me to it, I was going to say look at Spektrum if you want a multitude of channels!!!!!!

Subculture · « **Reply #9 on:** November 28, 2012, 02:02:08 pm »

Most of the major manufacturers produce sets which provide high levels of channels on 2.4ghz. JR/Graupner, Futaba, Multiplex are three companies that spring to mind. Spektrum are part of the JR group I believe.

Choose carefully, because once purchased subsequent radio (receivers) will have to be purchased for that brand. Unlike the old PPM standard, the sets with extended channels tend to use systems that are exclusive to each manufacturer.

If youmplan to use the transmitter with many models, the Spektrum sets have a lot to recommend them, because the inexpensive Orange receivers from hobbyking make it easy and cheap to fit out models with lower channel numbers. The Futaba systems also have compatible receivers available, although they tend to be more expensive. I also find the Spektrum transmitters very user friendly to operate.

I have never required more than 7-channels in a model to date, so 8-channels is enough for me, therefore I am quite satisfied with the limitations of PPM and older PCM sets. Unfortunately extended channel sets can be rather expensive.

tigertiger · « **Reply #10 on:** November 28, 2012, 02:43:18 pm »

I know little about RC, but would ACTion's switches be usable, if the channel is only used as a switch. Then I think you can use a switch for up to 3 functions.

Not sure what I am talking about, but I am sure someone will correct me.

Subculture · « **Reply #11 on:** November 28, 2012, 04:48:37 pm »

The problem with using some of the third party hardware is linked with the way the pulses are output from many modern receivers, and the way the pulses are read by microcontrollers on the other hardware.

On older receivers, the pulses were squirted out sequentially, one after the other. So for instance channel 1 pulse would end, then channel 2 pulse would begin after a very brief pause. As this all happened at fifty times per second, which is beyond our perception it appears to be happening in real time.

However on many modern receivers, the pulses for all channels are read in and output all at the same time.

A microcontroller will struggle to read several channels at once, unless it has parallel processing functions (many now do). The latter was less common on earlier microcontrollers, which could happily read pulses input in sequential fashion.

Hope that hasn't blinded you with science, but hopefully give you some insight into why some of the add-on hardware out there won't work with modern R/C. There are other reasons too, like lower output levels, faster frame rates etc.

deadbeat · « **Reply #12 on:** November 29, 2012, 09:08:15 am »

Thanks for that and yes it did confuse, so where do we stand with ESCs? Should manufacturers state whether they would work on 2.4GHz as well as the older frequencies. I use Action ESCs and Electronize.

essex2visuvesi · « **Reply #13 on:** November 29, 2012, 09:20:48 am »

As far as I know Action speed controllers should work on 2.4Ghz as there are many people are using them on here with Giantcod/Shark/Planet 2.4Ghz systems

malcolmfrary · « **Reply #14 on:** November 29, 2012, 01:36:55 pm »

Quote from: deadbeat on November 29, 2012, 09:08:15 am

Thanks for that and yes it did confuse, so where do we stand with ESCs? Should manufacturers state whether they would work on 2.4GHz as well as the older frequencies. I use Action ESCs and Electronize.

The radio signal that carries information from the TX to the RX should be totally independant of the signal going from the RX to wjatever is plugged into it. If a radio manufacturer chooses to make a system that will not work with anything that has gone before, it's up to him to warn the world that he has produced something that nobody can use. As it is, most manufacturers have had the sense to take the 2mS information window, repeating at 50 times per second, and based on roughly 5 volts, as a standard. Many tried to buck good sense by having different shaped plugs and pins in differing orders, but most now follow the same rules.

Subculture · « **Reply #15 on:** November 29, 2012, 02:43:33 pm »

I didn't mention 2.4ghz or ESC's. I did say some modern equipment.

Generally problems have cropped up with some types of mixers and channel extenders, so I advised caution.

Steve J · « **Reply #16 on:** November 29, 2012, 05:55:16 pm »

Quote from: catengineman on November 25, 2012, 09:38:46 pm

Now I do have multi channel requirements, there is one vessel that requires the use of 14 channels to operate fully as I built it.
I have looked at converting to 2.4GHz and have found that the most I can get to is 12 channel but there is a need to purchase a new transmitter at around the £800.00 mark.

The cheapest transmitter that I am aware of that will give you 14 channels is the Futaba 8FG (2.4, 12 proportional and 2 switched). Next up are the Spektrum DX10t and DX18 (effectively the same transmitter), as I understand it, these will give you either 10 high resolution proportional channels and 8 low resolution ones or 12 high resolution channels. Then there is the Jeti DC-16 (and DS-16) and the top end units from the other major players.

The only device that I have that is sensitive to the receiver type (I have Schulze PPM, JR PCM and Spektrum receivers, all my boats are Spektrum) is an aircraft wing gyro that works with my PPM and Spektrum receivers, but not with the JR PCM ones.

HTH

Steve

Steve J · « **Reply #17 on:** November 29, 2012, 06:00:23 pm »

Quote from: Subculture on November 28, 2012, 02:02:08 pm

Spektrum are part of the JR group I believe.

Spektrum are part of Horizon Hobby. Horizon Hobby are the JR agent in the US. Some JR transmitters and receivers have Spektrum RF sections, others have JR's own 2.4 system.

Steve

essex2visuvesi · « **Reply #18 on:** November 30, 2012, 05:57:09 am »

JR have seperated themselves from Spektrum almost completely. Most if not all of the current range of JR Transmitters and receivers are no longer compatible with the Spektrum system. However I beleive that both Spektrum and JR are still both subcompanies of Horizon Hobby

Subculture · « **Reply #19 on:** November 30, 2012, 11:24:46 am »

I think the lack of compatibility between manufacturers is the most objectionable thing about the 2.4ghz system. I do wonder in the fullnes of time if some enterprising company will come out with a TX which can 'emulate' other systems, so you can switch between different modes.

essex2visuvesi · « **Reply #20 on:** November 30, 2012, 11:31:43 am »

There is a "Hack" for the current range of Walkerea Devention Range of Transmitters
http://www.deviationtx.com/
Still in its infancy but looks interesting as the Transmitters are not that expensive in a price/feature comparisson

The main problem is that Walkera have had a reputation for "Cheap Tat" in helicopter circles, and quite rightly so. However in that last 1-2 years they have stepped up their game, releasing better quality gear.

Subculture · « **Reply #21 on:** November 30, 2012, 11:51:32 am »

Ah good it's already starting to happen.

The other thing I think we should see in due course is the increasing integration of smart phones, and tablet computers into R/C

At present high end R/C sets with lots of memory, touch screens and flexible mixing cost a bomb. But we have smart phones that are perhaps a couple of generations out of date, which are far more powerful and flexible, yet can be picked up very cheaply secondhand. Imagine a transmitter which provides hardware and a module connection for a tuner of your choice, which you then hook-up to say an Android based or Apple device.

essex2visuvesi · « **Reply #22 on:** November 30, 2012, 11:57:55 am »

Been done as well
http://wirc.dension.com/wirc

4 channel RC receiver controlled by IOs or Android

Subculture · « **Reply #23 on:** November 30, 2012, 12:52:28 pm »

No, I'm aware of thsoe gadgets, and the iphly gadget too.

What I'm talking about is a conventional stick type transmitter with a space or cradle for the phone to sit in, and it adds functionality to the set, or becomes the brain of the set. Hitec have done some integration with smart phones for telemtry etc. but I haven't seen anyone do the above....yet.

upscope · « **Reply #24 on:** February 22, 2013, 08:26:53 pm »

The cheapest transmitter that I am aware of that will give you 14 channels is the Futaba 8FG (2.4, 12 proportional and 2 switched.
The above was true until last week, the futaba 14sg , with telemetry that works on 2.4ghz FHSS, FAAST and FAASTEST is only £439.99 at hobbystores.
www.hobbystores.co.uk

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Author Topic: Confused over PPM PCM & 2.4 (Read 6132 times)

catengineman

catengineman

Stavros