I have been flying planes for about 20 years now and just got my new Raptor 30. (Friends say I've gone to the dark side) I would like to use my futaba T6XAs and my FM Hitec Supreme reciever to learn some basic hover before I invest in that new Futaba 9CHP.
The T6XAs will switch to heli mode and being able to use my current reciever will save me some $$
what do you think PCM or FM? will the FM be glitch city?

PCM period. Never use a FM receiver in a helicopter. I know that FM has " higher resolution" but it does not reject noise like Pulse Code Modulation. Will FM work yes , would I trust my $1,500.00 helicopter with it ? NO WAY.

Another vote for pcm here, as long as you set fail-safe to reduce throttle (as a minimum).

Consider. You're in a hover and a bearing goes bad creating all kinds of RF noise.

ppm = heli chases you
pcm = heli settles to the ground

It's not so much the noise rejection, it's what happens when you lose control (for whatever reason).

Thanks a lot for the info guys, looks like its time to go shopping.

I have to disagree, somewhat. I have been using FM since I started flying, and have had no problems, ever!. That's both airplanes and helis. I have been flying helis for the last 2 years, and just moved into a 60 size ship. I would rather be able to put it into the ground than have it go into PCM hold, and fly into a crowd. Even if the the throttle is set to idle by default, you will still have the possibilty of hitting someone, including yourself.

However, I just bought a gas ship, and I am debating the issue due to the increased RF noise from the ignition. My dad flies giant scale(35%+), and had decided to switch to PCM. I will probably set it up with FM, and do a range check, and if not sufficient then I will go PCM. Just wish Futaba made it cheaper to do so. The module and receiver alone are pretty close to a PCM JR8103.

Either way, PCM is not necessary, and most will tell you it comes down to personal preference. If I was in need of a new radio I would probably go PCM, just because the price if pretty close.

In your case, you're just starting out, and don't even know if you will like it. They are very challenging, and require an immense amount of concentration. Try to minimize your investment first time out, and spend the money on fuel!

Of course this is just my opinion, and I could be wrong

Well said. Of course, I'm just a newb and dont even own a heli yet, so I cant weigh in an opinion, but once I get one, and a sufficient radio, I will let you all know.

Oh yeah, um, quickie: how do you guys get the custom phrases where for me it says "member"? Thanks,

This is an often, and hotly debated topic and associated with many myths.

Some simple facts

- HOLD is not fail-safe
- all PPM units will be twitching uncontrollably long before the interference level will cause a pcm unit to stop listening

I won't debate that you can fly aircraft without problems on ppm... the difference is what happens when a problem occurs.

When I lose that tenuous radio link, I want the power delivered to my blades to drop to minmum and the flightpath to be as predictable as possible, not surging around erratically . It's about safety , not saving a replaceable (although relatively expensive) piece of equipment.

PCM delivers on this requirement, PPM does not. It's a pretty simple choice to me.

Correction to my previous post:

It is not actually all that expensive to convert Futaba to PCM, just need a new receiver. Granted they are still $129.99 on Tower. However, If I do go PCM, it will only be on the gasser.

As for Myths: A radio link just doesn't go dead, unless the battery dies or the antenna is cut(Frequency change).

The problem is that if their is sufficent noise the receiver can not make out the input signals. Any noise problems are generally sorted during your range check, but this is generally only an issue with gassers (Plane or Heli, due to the ignition).

Now I have never had a bearing fail on anything yet, but I would theorize it would probably be something that is progressive, and could be noticed in the early stages of failure. To continue on topic, I would rather notice that early shake, than have it go unnoticed and become a real problem.

Basically:
FM allows you to see the glitch, and troubleshoot
PCM masks the issue until it is too late. (This is by design, as the input signals are incoded and filtered, similar to TCP/IP for any networking folks)

Now it may be possible to notice the slower response of the heli due to the PCM receiver chucking the garbled signal pulses, but that depends on how good a pilot you are. For a newbie, I doubt they would be that in tune with their heli. People new the the Heli Hobby need obvious indicators of a problem not subtle ones, I know I did. Come on, how many of use have put the gyro in reverse on a new heli, now that is obvious.

With FM I might start to see the glitch, and be able to land safely before it becomes a problem.

Either way, make your choice, but don't say one way is better than the other. They are two different technologies, and both have their good points and bad.

Thanks for you time.

Well Jim, I know we have crossed paths on this one, but now you do have a choice with PPM FM its called the IPD receivers from Multiplex. Fully failsafe programmable and faster response then PCM.

Don't forget, Multiplex invented PCM and they have since evolved with the IPD and have stopped making the PCM receivers completely.
Here is some explanation for the interested.
http://www.multiplexrc.com/ipd_info.htm

Sound like good points from both sides on this issue. Looks like that shopping spree is gonna have to wait, I've got some homework to do.
All input greatly appreciated.

Excellent posts thanks

Another vote for PPM!!

Nice to see noise problems in the early stages... There are two ways to tell if your $1500 machine has noise problems...

1. The PPM way: flying along when your heli gitches, you see the glicth and think nothing of it. A few seconds later you get another glicht. You put down as fast as possable for diagnostics and save yourself $1500.

2. The PCM way: flying along for 2 hours when your helicopter goes to idle and stops responding; 20 feet inverted at 40 MPH. Oops, that cost $1550.

Just two days ago my rappy glitched on me and smacked the ground from 4 feet up (NO DAMAGE!). I did a range check and I have 16 feet before it goes crazy. If this was PCM it may have froze on me while doing FFF. I used to have PCM but seeing how much better PPM is for this reason I changed. Glad I did! I may have saved myself $400.

Now if I had a gasser I would go with PCM!!!

Heck, I used to fly helis on AM without any trouble - of course I never did much more than hover and shot hops, but still

HAHAH!! I wouldn't trust AM more than I can range check it.

You obvioulsy haven't flown helis long, it's fairly common for the starter shaft bearing to go on some models, likely because of the direction force is applied with the starter. I can't say it's very progressive, one minute it's ok, the next you spin the bearing.

And... w/o mincing words, the most common source of interference I've seen is metal noise (broken header, loose muffler bolt etc.), often more progressive but, still very detectable. The next most common source is another Tx on the same frequency. Neither is very progressive in nature and PCM has better noise rejection so, you can maintain control under conditions where the ppm unit would be nothing more than a random movement generator .

I agree that a newbie might be confused by the slow reaction intermittent problem but, you soon learn to listen to that feeling that "somethings wrong". If you're in doubt about your ability to detect the 'progressive' type problems, invest in a glitch counter. More accurate than the "I don't think I commanded that hiccup".

AND... it's not about saving the aircraft, it's about saving lives.

Oh, and Roger, I don't hink we "crossed paths", I'm just not convinced one way or the other on IPD. I just need something more quantifiable than a marketing claim that it works better.

All are good valid points. I too have been flying planes for the past 20 yrs, and never needed PCM. FM was fine, and never had a problem related from it.
I do know this..... one of my Gyro's did not work safely until I switched from FM to PCM. (I don't feel like starting a debate on brands) but it is a G550T. Just another thing to consider when trying to decide on what gyro etc....
This might sound dumb, but.... I feel better with the PCM receivers in my Heli's.

Kevin

With an airplane that has a natural stability designed in, I can see the advantage of a fail safe. Fail safe mode in a heli would only seem to help in a 6 foot or under hover. In any other attitude, I don't care where you set the FS controls at, it's coming in hard. With my heli, where I'm thinking "I'd rather have SOME control than none", I'd take PPM.
All things being equal, AM would be the winner in distance and interference, but it's too susceptible to mechanical noise.

Until we get real error correction and prediction algorithms in RC pcm, not just *stop until something good comes in*, I don't see any real advantage. I might be wrong, but I don't think you can change the packet id's on a pcm radio. If someone else turns on a pcm on your freq, (same brand) you're still dead. And the bearing/metal noise still gets in there, it's just masked by a hold until good instruction.

" Neither is very progressive in nature and PCM has better noise rejection so, you can maintain control under conditions where the ppm unit would be nothing more than a random movement generator .
"

I think it would be pseudo random returning back to the commanded input every few miliseconds, as opposed to " I give up and am turning off for now"



But hey, wadda I know. I thought Pons and Fleischmann were on to something.

I have a simple recommendation. If you choose PCM, use a glitch detector. That increases your advance warning of interference issues just as on PPM, but you also get the advantages of failsafe and error correction.

I don't fly PCM without a glitch detector if I can help it. And I fly my expensive sutff on either PPM or PCM without worrying about either. They both work well in our application, and in the end its the failsafe capabilities that lean me towards using PCM over PPM. That way I can decide what I want to happen if it looses the signal completely, rather than having no control at all.

Other than that, I have never had problems with PPM over PCM regarding interference. Even when going for eye challenging distance limits.

PPM is just fine as some have indicated. I have experienced glitching from various sources and have always been able to resolve it. The cause of a few of my glitching experiences are:

1.)small crack in aluminum boom support (vibrating metal)
2.)anodizing worn off on pinion radiating RF on tail drive wire
3.)defective gyro (interference in rx from gyro control wire)
4.)loose screw on aluminum boom support (vibrating metal)

Most of the glitches I have ever had were a quick momentary glitch that did not prohibit landing the helicopter.

Some glitching has lead me to suspect damage (notched bearings) in the main shaft bearings, starter shaft bearings and engine bearings but have never been proven since I would just replace notchy bearings as they were discovered.

Hope this helps,
GOODDAY!

Ever head of pet rocks? There was a major market for them at one time. Sure they worked but, were they superior to other pets?

I like the superior noise immunity : I 've proven this many times. 2 Radios, one ppm, the other pcm, both on the same channel, both turned on and at identical distance from their receivers. The pcm unit responds (although a bit hesitant), the ppm glitches all over the place uncontrollably (fly through interference my a**) and if left to it's own can destroy it's servos.....

I like the failsafe feature : I switched to pcm because I had a glitching plane end up over a large crowd. Scared the hell out of me. If I'm not in control, I want the aircraft on the ground now. It's not about saving the plane, it's about saving bystanders.

I like the battery low feature: I've experienced it twice and saved the aircraft (one fixed wing, one heli). My last ppm radio toasted a perfectly good aircraft when the rx battery failed (bad cell). I'm convinced I would have been given enough warning if I had installed one of my pcm radios. Thankfully it didn't get behind the flightline as it went in at 3/4 throttle (battery low on pcm would have had it at idle before voltage dropped too low).

How's that for actual experience/reasons?

FWIW: Been here on the who, when and why of PCM's creation. A little research divulged the following information.

It is true that Multiplex was the first RC Company to put PCM technology to work. However, Futaba brought it the masses...

PCM Pulse Code Modulation
There seems to be some confusion as to the actual date PCM was invented, I have found numerous refernces all fall into 1936,1937 or 1939. Suffice it say the late 30's would be a safe bet... PCM as we know it today is the same technology as when invented in the late 30's by Alec Reeve's.

The difference between then and now [modern day] are the methods used to encode and decode the digital data. The application first envisoned for PCM was telephony. [telephone data comunications] Vacuum tubes, relays and amplifiers were used to convert analog data signals to digital data prior to transmission.

An "A/D" [Analog to Digital Converter] is used to convert the analog data to digital data, in the first PCM system's these devices were seperate devices. As we know PCM today of our models, the A/D or encoder is a microprocessor imbedded into the TX and an D/A [Digital to Analog Converter] or decoder is a microprocessor imbedded into the RX.

In the early days of Radio Control the encoding was done with discreet transistors, later these were replaced with Integrated Circuits and later again these were replaced wih computers on a chip [IC] known as micro-processors.

I beleive in almost all stages of the evolution of Radio Control systems, superior encoding schemes were understood long before the electronics required to implement them were either available or practical.

Historical time line of PCM:

1939
Pulse Code Modulation

Invented by Alec Reeves. Pulse Code Modulation is used to turn an analog signal into a digital signal. Digital signals tolerate large amounts of noise, interference, and distortion. Repeaters were used to regenerate the original signal instead of amplifiers. Amplifiers strengthen a signal, but they also strengthen the noise. Repeaters will detect the original digital signal and retransmit it removing the noise. This increases the quality of the received signal when traveling very long distances

1939
First Digital Computer

George Stibitz built the first digital electrical relay computer. It is the first such machine to use binary logic, it was reffered to as a "Binary Adder". This machine was the first step towards what is today called the "Computer Revolution."

1940
The first relay computer was put into operation by Bell Labs, known as the Complex Number Calculator.

1947
Transistor

The first solid state amplifier known as a transistor was developed at Bell Labs by Bardeen, Brattain and Shockley. Effectively replacing vacuum tubes

1948
Digital High-Speed Digital Transmission System [PCM]

The first Digital High-Speed Digital Transmission System was developed by Shannon, Pierce and Oliver based on coded electronic pulses. Using PCM, they find they can transmit multiple phone conversations over the same set of wires

Early 1980's
The technological revoulution made it practical [affordable] for wide spread use of PCM technolgy.

"Get a clue"? Boy are you being harsh. Surely you jest.

In the real world, some idiots have turned on two radios on the same channel. Like the guy that turned on his radio at Joe Nall which happened to be on the same channel as Frank Noll. He wrote a very expensive check to Frank that day in the parking lot. Idiot? Probably not. Just an unfortunate incident due to his spotter grabbing the wrong pin, and the pilot forget to check. There are dozens, maybe hundreds of other examples if one takes the time to investigate.

I like flying in the Garden of Eden you fly at. Never a frequency conflict, no idiots. Never a chance for someone to make a mistake. Perfect. I love it.

Bottle it and sell it to all the other clubs. You'll make a fortune, as the rest of us are saddled with the unfortunate real world experiences that prove frequency conflicts happen from time to time. Should it happen to me, I hope I am flying one of my planes that have the PCM receiver, rather then the ones I have with PPM in them just to increase the odds in my favor.

Before you jump over the fence at me, I am not saying PPM doesn't work, or is inferior. I use them both almost interchangeably, with my deciding factor whether I want failsafe in that specific plane or not, and whether the cost increase to get it is justified. The decision is the same whether its a plant or heli.

That's good info.