PCM, PPM, or 2.4 gig

[Jcarte]

Your friend just bought his first giant scale gasser and he asks you " Dude, is it okay to run my old PPM radio with my new plane with the electronic ignition?"

Doesn't it just break your heart when you want him to be safe but you don't want to tell him he should spend more money for new equipment, what to do?

[RTK]

Nothing wrong with ppm. If it passes range check engine off/on you will be fine.

[Izzy]

That's right, I just put up a 30% yak today on a hitec 8ch dual conversion on ppm (of course) after doing a serious range check. JR has a good article on how to range check your radio. shouldn't have any problems

[Jcarte]

You should really consider the safety factors of Fail Safe with PCM receivers and giant scale planes.

[OverTemp]

I use PPM but I have failsafe. Multiplex IPD Synth RXs are the bomb... better than PCM as far as I'm concerned... certainly rejects more noise from other TXs (on the same channel) than any PCM I'm seen. Only problem is they aren't cheap.

Let the flaming begin.

[Kiwi]

Several years ago I spent an hour on a telephone discussion with Mr Fred Marks. Likely one of the most informed people on the planet when it comes to RC radio, PPM, PCM etc etc. He is the FM in FMA and was involved in getting most or if not all the RC frequencies you use today allocated to RC and not to every tom dick and harry.

He had a very simple explanation of the difference between PPM and PCM that I will never forget.

PPM crashes are normally with the wings level.
PCM crashes are normally with the plane doing some sort of gyroscopic motion.

Results however are the same. CRASH!!!!!!!!

PCM lockout does not save your plane, it does not let you guide it away from the crowd. Until recently it allowed the engine to go to idle. BUT IT DOES NOTHING AT ALL. WHAT SO EVER to make your model safer. Its a myth and way over hyped.

PCM is slower than PPM
PCM can filter out some spurious signals but only until the strength reaches the point where it locks out.

PCM has very minimal advantages if any over a very well installed PPM setup.

But to end it all PCM. PPM and 2.4 Ghz are not capable of rejecting interference 100%. They are crashing today, they will crash tomorrow and that will keep on being the same forever unless you put an autopilot system in like the FMA autopilot so it flies your uncontrolled airplane straight and level until you get signal back.

Several years ago I demonstrated a trainer I had setup with an FMA autopilot. I lined the plane up with the wind, turned the radio off and placed it on the ground. The trainer landed itself as good as anyone could have manually.

This was a PPM 8 channel system with failsafe and auto pilot module.

PCM is old hat, its does nothing PPM cant do and in fact PPM is better, faster and just as capable as any system available today.

Kiwi

[aviti]

Kiwi - A light bulb just turned on in my head when you talked about auto pilot. I always ignored the idea because I was thinking of it only as a training device. Duh! We need auto pilot for our failsafe systems. We are foolish to think any wireless solution will be totally immune to interference but if fail safe actually could get you plane to a recovery attitude then we could save a lot of crashes.

[Kiwi]

Tony,

The facts are that unless you can default your airplane to a flying attitude then nothing else in the fail safe world is of any consequence.

I know guys who fail safe everything to full deflection, engine off or at idle. The reason is the model snaps, thats reduces the energy to a minimum and consequently and with luck that puts the plane permanently in the ground in a safe place. Safe because you should NOT be flying over the pits or people so naturally the model should crash in open ground.

The FMA autopilot weighs a few meager grams. It can be set to failsafe into a very low powered wings level climb, or a wings level turn or a climbing turn. I have had a ton of fun setting them up and turning the radio off to prove how good they work.

Actually a true story here. I was training a guy and using an autopilot and not a trainer box. He soloed in a few hours and was away free until he flew it out of eye sight range by mistake. That plane was last seen heading to Australia from Chile. Wings level, holding altitude, mid power. I guess it got a few miles out to sea and I bet it belly landed perfectly in the ocean.

The issue with the autopilots is you are not supposedly allowed them in a competition as boy oh boy can you fly straight lines with them. Its like your on a string and look no hands guys. Cheating is the word.

But you can program them so that they only work on fail safe. Trouble is convincing the judges I suppose that you dont have a secret switch.

If you have a 1/4 scale model you would like to play with go get an FMA auto pilot and see what it can do. It will blow you away, no BS.

Got a model that tip stalls and is unstable. Put one in it. You will harrier it to death. They read the airplanes attitude 60 times a second. You can set up a heli with one and hover it hands off for a full tank of fuel. If the ground slopes away it will follow the contours of the ground if it low enough.

Oh FMA don't give me anything for free at all so this is not spam, just experience.

Kiwi

[3D_Kid]

PPM and PCM are really FM, correct? so PPModulation is better than Pulse Code Modulation? Wow thats weird.

[Kiwi]

Kid,

Its not weird, its fact. PPM is faster, PPM can do all the fail safe tricks that only PCM could some years back.

PPM however does not reject as much interference as PCM does. However the new DSP and ISP PPM receivers are every bit as good if not better.

Kiwi

[3D_Kid]

But PCM costed more. and there both 72 mhz? WTH?

[Tired Old Man]

Kiwi really has this subject nailed to the wall. His comments about the auto pilots are just as accurate. I've played with them a little and was amazed at what they can do. The comments about programming the auto pilot to kick in during a fail safe are intrigueing and sound like something fun to experiment with if you have the space to practice it in.

The use of PCM was brought on initially by the radio manufacturers doing a lot of advertising about how it was better. The same happened before that with engine ignition manufacturers telling everyone about how much better electronic advance ignitions were than mechanical advance. None of those statements about one product being better than another was true, but they had products to sell, and what better way to sell them than to say they were better?

Nice job Kiwi

[DarcyWingo]

PPM is fine, but its all personal exp...I have been using the JR r2000's and love the heck out of em'...

2.4 is also an option, although it would seem it has its own set of problems..

[Tired Old Man]

As does 900 and 1.3. I still prefer to set up and check with PPM and when satisfied change to PCM or the scan select unit.

[Kiwi]

The beauty of doing your setup with a standard PPM Rx is if theres anything untoward going on in your setup then you will likely see it.

PCM and 2.4 etc will mask it so you never really know until one day it's too much.

The results are predictable , CRASH.

PPM is like soap without perfume. It ain't nice to smell. but it sure as heck gets the grime of your hands.

Kiwi