Polariman

I am looking at getting a gasser. I heard PPMs are compromised by the ignition of the gasser. Is this true?

Rodney

PCM and PPM are equally effected by interferance. PCM will mask some types of interferance so you may not realize that there is a problem until it is to late. However, if you set up fail safe properly, there will be some occasions when PCM might help. The real solution is to make sure you do not have any RF interferance to start with which is not difficult if you take the proper precautions which are well documented in many places in this and other forums. I fly big gassers with magneto igniton for the last 12 years and have never had any interferance problems.

Geistware

My Feedback: (16)

I fly PCM due to the danger large gassers can be if the transmitter has an issue. I had a tranmitter die while in the pits and the plane begin to take off. It hit a table but just as easily could have hit a bystander.

sfaust

My Feedback: (11)

I assume you are talking about the failsafe feature on the PCM receiver that would shut down the engine if the transmitter is turned off, or if a good signal is lost? If so, that is in fact a very nice feature on PCM receivers. PPM and PCM will both work equally as well on gas engines with regard to interference issues if installed properly, they just behave differently to it. One doesn't have much of an advantage over the other, with the exception of the failsafe feature. The failsafe feature is also offered on the Multiplex receivers, and as an add on device. The add on device can be added to any channel on a PPM receiver between the receiver and the servo, and is advised on the throttle servo of any PPM receiver setup IMHO.

amcross

My Feedback: (2)

Stephen,
Actually PCM *DOES* offer additional protection against the interference in that an FM (PPM) receiver will simply obey the random signals coming from the ignition or elsewhere. PCM is looking for its specific language and will disregard data coming in that is bad even though it is on its frequency, etc.

Basil Yousif

My Feedback: (3)

I've heard this at my field that the PCM recievers have a greater tendancy prevent being shot down by someone turnig on a transmitter with the same frequency. Don't know if this is true but as a engineer I know this can be done because the software in the RX can filter out another transmition on the same frequency simply by using time. You were the first one to transmit to it so it takes your signal and filters out the other incomming signal. The filtering can be software controlled which adds more automatic failsafe functions. I am only using a PCM reciever on my 1/4 scale gas plane all others have the PPM. Stick with newer PPM good quality recievers if your going to use them I have been shot down twice with a 10 year old FM Airtronics reciever setup the interfearance protection isn't great on some of the older recievers. I have had good luck with older Futaba recievers though.

branded

My Feedback: (9)

Yes, and so the act of "disregard" is indeed a loss of control, since the communications link is broken....

Personally, I'd rather see, and react to the "random signals" than to be fooled by my reciever that's 'holding', while engaged in the act of "disregarding" signals it no longer recognizes.

Many an airplane is lost to this 'hold' feature before it's recognized for what it is, a masking of the effect of an errant, or lost input signal.

Whenever are we going to understand that ignoring the incoming signal does not relate to control of the airplane?

Mr_Scale

My Feedback: (7)

One could argue this point till the cows come home. Personally, it is PCM for me regardless of gas or glow. I have had no problems whatsoever using PCM. (Knock on wood) I cannot say that about FM. Facts are the facts, PCM is clearly the preferred choice IMHO!

sfaust

My Feedback: (11)

I do understand the above very well. But, its a matter of personal choice as to whether its a benefit or detrement. As you can already tell, some believe its a bad thing, while others think its the next best thing since toast. Either way, there is a loss of control during the 'interference event', they are just different. So its hard to say one has an advantage over the other since in either case, the pilot doesn't have it.

But I think the point being argued, is whether the PCM receivers are in fact better at receiving a cleaner signal leaving the pilot will full control past the point the PPM receivers would havae stopped responding to the pilots inputs. I have seen technical arguments that suggest such, but as pointed out, it may not have been backed up with real data.

branded

My Feedback: (9)

Hahahaha...."the facts are the facts"! And whose flavor of "facts" would you be referring to?

Who/whom is preferring PCM over PPM? Is this based on one of your "facts", hehehehe.

Mr_Scale

My Feedback: (7)

The FACT is I prefer PCM. You can fly what ever it is you prefer.

FLYBOY

My Feedback: (11)

I fly PCM simply because I like PCM. I us FM or PPM in 2 of my planes, but PCM in all the big ones. I have been in the air when a guy on the boat (same freq) turned his radio on. His went nuts, luckily it wasn't running. Mine never missed a beat. If it were the other way around, He would have crashed, and I would have not known the diff (if I had been on the boat starting mine and he in the air).

Have seen this happen many times. Some guys don't check freq and just take the radio out and turn on. PCM has saved more than one of my planes.

Herb Brown

My Feedback: (1)

I agree that the early Airtronics FM receivers were susceptible to interference. Airtronics corrected this problem when they produced their Dual Conversion receivers, and the DC receivers have been super reliable ever since.
IMO, they are the best receivers out there.

Geistware

My Feedback: (16)

Yes, I do use PCM just to protect from Transmitter failure while the plane is on the ground. WHile I can say that PCM vs PPM can be argued, I have been convinced that PCM is the way to go for high dollar investments.

Forgues Research

My Feedback: (7)

Steve,
One bit of correction if I may, with the Multiplex IPD receivers, there is no add on devices. The receiver is fully programmable for failsafe and it is a PPM receiver which means that you can use them with any TX with the same Phase shift. Such as JR, Airtronics.

sfaust

My Feedback: (11)

Does the PPM failsafe work with JR and Airtronics? If so, how do you set it up? My JR 10X does not show the failsafe settings unless the transmitter is in PCM mode.

Forgues Research

My Feedback: (7)

Steve,
You program the failsafe at the receiver level with a small included plug.

You set the controls the way you want them and then insert the plug in the battery port for 1.5 seconds and that's it. So it works with any compatible TX.,

sfaust

My Feedback: (11)

Cool...thanks.

amcross

My Feedback: (2)

To clarify, a PCM receiver can disregard bad information and obey good information in a split second....with no change being noted by the user...whereasthe PPM system has jumped all over while receiving that faulty information.

If it receives 2 separate commands -- one good one bad -- PCM obeys good ignores bad; PPM obeys both.

Wont argue further, just trying to clarify this one point.

AirBearMA

My Feedback: (1)

For me having that extra bit of intelligence in a PCM receiver that will determine whether to accept a valid command, ignore a bad command, or enable failsafe is worth the extra cost in the receiver. In my bigger planes, I'm most concerned about safety which is why my failsafe always kills the engine.

Forgues Research

My Feedback: (7)

I understand what you are saying , but now with Multiplex's IPD receiver and FMA's S.M.A.R.T Receiver, you have all you want and more. PCM is slowly going away.

Forgues Research

My Feedback: (7)

Read up on this about the
FMA receivers.