I'm building my first gasser and have a question on the type of receiver I should be using. I've heard that FM has a tendency to get interference with the gas engines, and others say this is not the case. The ones that say they have interference typically use PCM receivers. So tell me guys what is the truth or doesn' it really matter as long as you have a good range check. As we all know there are a millon ways of doing things and they are all correct, but I would hate to have a $2000 lawn dart. Any help would be greatly appreciated.

Thanks

IMHO if you have a couple ginos invested in that plane, spend another $50 (over an FM) and go PCM, it's worth it.

Hi Scott,

Man, you have opened up one of the master debates. There are many threads on this topic on RCU. I would encourage you to research them for peace of mind. Also, ask those with experience using both. Let me help you in that I too just had the same question recently. Here is what I learned. Note, this was my first gas project as well, so I can only pass on to you what I have observed and learned from those with more experience than me.

Many will tell you that PCM is not a cure all for interference. Their position is that PCM can mask a potential problem that otherwise would be found with PPM. Many will suggest that you test using PPM , correct interference noise, and then use PCM for added filtering. Have also learned that many are not comfortable with the fail safe function feature with PCM. Personally I think it makes good sense. IMHO.

Couple of other things I learned in my first gas project. Some will say to definitely use PCM on gas and then others are comfortable using PPM on gas engines. Antenna outside vs inside. Keep receiver at least 16 to 18 inches away from ignition source. Keep servo extensions and any other potential interference items well away from receiver. Do extensive long range range checks with engine running and off from different angles. Of course no metal to metal contact. Many discourage using a metal throttle control rod. Use a plug with a noise resistor.

What did I do? I used a PCM receiver and programmed fail safe to idle the throttle and get the airplane down quickly. IMHO I don't think there is a perfect answer to this debate.

Now for your decision. Good luck.

I have been flying gas for some 15 years , I use both Fm & Pcm , no probs; on either , as the last guy said , keep the sero & rx away from eng; as much as possible . I don't bother with failsafe , ok for recovery with a
'cub" type , but with an "extra" , whats the point ? I have the antenna inside in a plastic tube [big stuff" , no probs; , even with WW1 & pull -pull cables .

My feeling are like this I am 35 and have been around RC for 35 years my dad was flying before I was born and flew reeds escapements and all of the pre digital proportional stuff.
I Use Hitec Supreme Recievers in all of my planes 40% aerobatic planes Including a new Fiber Classics 3 meter Extra. I Can fly Through a Glitch or hit but with PCM I can not fly through being locked out were you lose complete control. So I personally do not like PCM. As was stated above if you install everything correctly and do your range check both with the engine running and not running on the ground and compare the distance you also need to remember that Range is different with different airplanes and installations. 1 Key factor to remember is to not have any metal to metal contacts that can vibrate on your throttle setup or any where on the airplane, this will cause problems. I bought an airplane from a guy that had pcm recievers in it and when we changed out the recievers and went to fly the plane it would not range check satisfactorily so we started going through the airplane and found a metal clevis on the throttle we changed this out and the problem was cured. So this shows how PCM can hide potential problems. My advice is if you are going to fly with PCM as was stated above I would use a ppm reciever to set up and check the airplane for problems first. PPM will be fine you can and should be able to use it with no Problems. Either one will work again if setup is done properly.


Steve Hill

Shill,

Maybe you can help me with this one. I read your post and we seem to be together except for the fail safe part. I am not disagreeing with you. I am asking. If you take a hit from an outside source this will obviously activate fail safe. Wouldn't this normally be just for a few seconds in most cases? Meaning, once the radio is able to restore the signal to the receiver wouldn't the receiver then respond to the radio or are you screwed ?

My understanding is that if the radio can get through the interference, which in most cases should be for maybe a few seconds then the receiver will negate failsafe and allow the radio signal to again control the airplane.

If I am correct then wouldn't the added filtering ability of PCM be good in that it helps to filter interference that otherwise could impact control of the airplane? Likewise, wouldn't fail safe then be a good thing if it enables you to program settings such as straight and descending flight with throttle at idle vs. the airplane going out of control, even for a few seconds? This is the logic I used in making my decision. If my understanding of fail safe is wrong then I too would question it's use. Like said, I am still learning and really want to know about this just as I'm sure others do.

I really appreciate your input or input from anyone else that can help explain it.

Good question Roger, I would like to hear that response as well. I decided to go PPM instead on this plane. because it is only a 27% model.

Thanks again!!!

Hello rfw1953

As to the fail safe yes it is only susposed to be for the amount of time for it to restore the signal. Here is my thoughts and I have heard from several fliers around here that when thier airplane went into fail safe, they never recovered control so the signal was never restored. My guess is it never got a good enough signal to regain control. and total losses for several 40% airplanes around here. My thoughts are if I can get any type of signal to the reciever to get some control inputs to the airplane fighting a hit I am better off than not having control at all.
Now if you are flying competition pattern or IMAC you would be better of with PCM because you are less likely to see any small glitches with it as you might see with PPM. My preference is PPM as again I have seen people around here lose airplanes with PCM and some have seen us fly and ask what recievers we are using and tell them HITEC supremes and they seem suprised but now several have changed to using them. This is all preference both will work just fine but I do recommend to use a ppm reciever to set up and test the airplane on the ground before installing the PCM reciever. I also feel that the required having the fail safe setup to give low throttle and down elevator and left aileron as some suggets people say different things is unsafe setting a fail safe to do certain things is asking for troubl depending where you are and how high you are set the fail safe and watch it headed toward the pit are depending on your position on the field so I do not see a safe fail safe setting other than hold from the last inputs but that can still be unsafe, but I think all of it is unsafe not saying any of it is safe because it is all man made stuff and all is prone to failure no matter what.
This has been a highly debated subject and all of this is my opinion and I am sure that by tomorrow evening other people will be flamming what I have said but all of it is just opinions you have to look at all facts or semi facts or statemenst made and judge for your self what you think is for you. I fly mostly 3D or am Learning ????? and all planes I fly 30% and up use 2 recievers and seperate batteries and switches for safety of the airplane more than to distribute the servo load as I have personally landed an airplane on 1 reciever working only and it saved a 2.6 meter FC from destruction but that is another flame war to start.So it is entirely what you can make of other peoples opinions and not just people telling you to use one or the other get reason for it and not just use this and that. If I have not elaborated enough you can email me or post again with any questions I will be Glade to add my opinion and opinion only no hard facts I ant no Inginere.


Steve Hill

I agree with using Hitec Supreme receivers. I have them in all my gas planes now. These are regular FM(PPM?) ones. I never get glitches anymore like I used to occasionally with my Futaba receivers.

shill,
If your plane got hit and was headed toward the pits wouldn't you rather have it at an idle instead of full bore? I agree that one should check for any and all sources of possible interference within the plane itself but if you're gonna get hit or lose complete control of a giant scale aircraft I personally wouldn't want my plane flying off to who knows where at full throttle. I also believe there's less chance of a beginner accidentally shooting down a plane that's on PCM because most small aircraft stick to FM and an FM transmitter won't affect a PCM receiver.

I would rather have some type of control if it were headed to the pits yes I would want it to be at idle but I do not use PCM and will not unless I need more than 8 channels and I will not be using it by choice. So my choice not to use PCM gives me more of a chance to save the airplane and keep it out of the pits as I have a chance of getting some type of signal to the airplane to fly it you might be getting hit but it usually is still getting some type of inputs from the TX also. with PCM you are locked out till it gets a good signal again which also does not sound like a good thing to me either. So many arguments can be had about this and as I say this is just my opinion I do not like PCM I just can not justify the lockout from control of the airplane. I will also add how many people actually do program the failsafe on the radio. I do not know very many who do. so it is still of no benefit because they program it to hold the last imputs. I am not saying the low throttle for fail safe is a bad Idea but you have to look at how people are setting up or not setting up the failsafe mode. As to flying off airplanes you could get the same with a PCM set up to hold last imputs. Also I have yet to see very many planes make it very far when a loss of control happens.


Steve Hill

Stick Jammer

"I also believe there's less chance of a beginner accidentally shooting down a plane that's on PCM because most small aircraft stick to FM and an FM transmitter won't affect a PCM receiver"

This is one of RC's best urban legends.

We use to fly at a field that was notorious for interference. The final solution was almost everybody tossed the JR and Futaba PCM's and went to Hitec supreme. End of problems. Yes, I know in theory the PCM has better noise rejection. It may be that Jr and Futaba PCMs are better than their PPM receivers. In the field, the Hitec has shown to be better.

Steve ( shill ) is my brother. He mentioned an airplane we bought that had metal to metal on the throttle. What he didn't say was that we got it cheap because it was a problem plane. The guy couldn't get it to stop going into failsafe. It did it only in the air and not on the ground. We put an FM receiver in it and found the problem quickly.

Tracy Hill

Maybe I didn't phrase that correctly but it's not an urban legend. I use Futaba and have tested this myself. With a second Tx on FM it won't affect the PCM Rx on the same channel as long as the PCM Tx has a strong signal and a good charge in the battery, otherwise it will cause a failsafe mode. I suppose just like most everything in this hobby, it's what makes you comfortable that matters. I have seen a couple of planes get hit that were on FM and the pilots didn't have enough control to save their aircraft. I have also seen planes fly off into the sunset at full throttle and personally, that is what worries me about flying large scale on FM. IMO, anyone using PCM should program the throttle failsafe to idle. It doesn't guarantee that you won't lose an airplane but at least it has much less chance of flying to a populated area and possibly killing someone.

I would like to mention another feature of Futaba PCM receivers. The throttle will go to idle when voltage gets dangerously low. This is very desireable since it forces you to land before the battery goes dead. It works just like the ESC used on electric planes.

Tom

Reading some descriptions of PCM, one might get the impression the receiver "locks out" at the slightest interference and you don't get to fly anymore. This is not correct.

There are two distinct phases of interference which are processed by PCM receivers. First, invalid signals which occur for brief intervals are ignored, meaning they are not sent to the servo. This is why you don't notice minor interference with PCM. During this intermittant interference, any valid signal continues to be passed on to the servo. In effect, you can "fly through" minor interference without even knowing you are doing it.

The second phase of interference only occurs when there is absolutely no valid signal for an extended time (about 2 seconds). This is when the receiver goes into failsafe mode. In failsafe mode, the servos are moved to a predetermined position and the receiver waits for the signal to reappear. You can easily demonstrate this by turning the transmitter off and watching the servos move to their failsafe position. As soon as the signal comes back on, you resume normal operation.

Personally, I believe PCM is superior without question. I also think the radio companies are grossly overcharging for them and because of that, I only own two which I have in my "best" planes.

Tom

Hey Fellas,

I don't want to add fuel to a smolder here, but let me relay my experience. I fly what is the mother of all glitch producing models........helicopters (please reserve hard objects to be thrown until after the post <G>)! And before I get cerimoniously pounded here, I need to let everyone know I have a Comp-Arf 2.6 Extra on the way with all the trimmings (VBG).

Ok....heli's have all kinds of moving parts that can create the infamous metal to metal interference. And while in newer heli's it is really a very low occurance, the issue does occasionally rear it's head as it did with certain models regularly in the past. Basically PCM is the way to go with a heli.

Now on to my "story". A good buddy of mine and I ran a heli fly-in here about 3 years ago. On day one there were two guys flying right next to each other and experiencing some "weirdness" with their helis. As it turns out, one eventually did failsafe and crash. Well.............the reason is that one of the guys grabbed the WRONG MODULE (read....did not check the frequency he was flying on and thought he was on a differerent one) and they were both standing next to each other flying on the SAME FREQUENCY! Yes one did eventually crash...but it took nearly 10 minutes of flying! That to me is an incredible testimony to the ability of a good PCM reciever to withstand outside signals. If one of those guys were using an FM rx the crash would have happened instantaneously. If both those fellas were using
FM rx I believe that BOTH machines would have been lost...not to mention what else could have happened.

Now I should also add that I believe one was flying a Futaba and one was flying JR (for those who must know.......the JR crashed <g>). I honestly don't know if the brand difference made a difference or not (I suspect it did to some degree) in regard to why they were able to fly for "any" amount of time without crashing.

I won't go into all my experiences with FM vs PCM but suffice it to say that I have decided on a dual rx setup for the extra for numerous reasons.........and yes they will be PCM. They will both be set to fail safe to neutral positions so I hopefully will maintain partial control of the plane in the event one does go silly. This way I believe I will get the best of both worlds...the PCM signal isolation and the abilty to maintain control even if one does lock out for a few seconds.

Good luck with however you decide to go.

Leardriver

One interesting observation. There sure is a good deal of concern over getting hammered. One can only wonder why when people are asking logical question, to learn and better understand from a others, with different skill levels, using all different products with different views. In the end we all have to make our own decision.
I for one honestly appreciate the different views on this subject.

I now have a question. I have been a die hard Futaba user right up until I just experienced my first apparent receiver problem. I use a Futaba PCM in my 1/3 scale gasser. I was flying my Giles and the PPM receiver went nuts resulting in a crash. No one was hurt, but the airplane was a total loss. I am sending the receiver off to be tested to hopefully find out if it was actually the receiver. Not certain at this time, but it is highly suspect. I think vibration got to it. Had it well padded. I have read on this thread and heard from others that the Hitec Supreme is a more durable receiver. Anyone else have this opinion? If so why? Is there a design or mfg. explanation to support this logic? Or, is it just 6 of one and a half dozen of the other???

Roger, I know how painful such a a nasty crash can be. But are you ready to close the door on Futaba based on this one incident? I'm not trying to stick up for the company, but think about it. There are TONS of futaba receivers out there that work fine. There are bound to be some failures, but why give up on a brand that you like?

If you end up having a crash with your Hitec, I suppose you will become a JR man. Then Airtronics, then what??

Tom

Reply to Greenboot,

Good question, but may have misinterpreted my inquiry regarding the Hitec product.

I haven't made any decision to change anything at this time. In researching this a little, I was told by a person in the hobby business that Futaba has a ceramic filter that 'can' crack causing reactions similar to what I experienced with mine. Until I get the Futaba receiver tested and checked out, I'm not sure that the receiver was the cause of the crash. I would feel much better about losing the airplane if I could tell you it was a simple matter of dumb thumb and be done with it. I sent the receiver off this morning to be checked out. If this ceramic filter is the culprit, then my inquiry about the Hitec Supreme is to determine if they use anything better than a ceramic filter that may more effectively stand up to potential vibration problems. Still in the investigation stage, but I sure would like to know if there are advantages in the design and manufacturing of one product over another.

Other than losing an airplane, the most frustrating thing about any crash is not being able to determine the actual root cause. In this case, I am still trying to determine what caused my receiver to go nuts. I'll let you know what I learn about the receiver after it's tested. Until then, I am still flying Futaba and believe in their products.

For the crash details you can go to this RCU thread and to post #17 if you are intrested.
http://rcuniverse.com/showthread.php...535&forumid=38

I have been using the Hites supreme and superslim recievers in all of my large gas airplanes. If you have read my other post I do not like PCM But that is my preference. I have not had any crashes due to reciever problems with the Hitec reciever due to radio interference. If I am reading your post correctly you say you use a PCM reciever in your Gasser so I an assumming your giles was A glow Powerd ship. I have had 2 hitec recievers quit on the ground. Had gotten to the field and put the airplanthing was together and 1 reciever did not work replaced reciever and every thing wqas fine. sent it to Hitec and it was replaced no questions asked Hitec has a great service department and really stands behind its products. As someone said earlier everything or brand has failures and I do mean all. I guess it is a matter of preference I have really had good luck with the Hitec. I had a futaba PPM reciever in a plane and it would get hit or sometype of interference at a certain field in the area and changed to a hitec on the same frequency and no problems do not know if it was a problem at the field or airplane or combo of things but the plane flew fine at other fields with the futaba reciever. Since then I have been very sold on the Hitec recievers. I do not know if this answers any of your questions as I do not have any definate facts just experiences and I ant no engineree but it might help.
as you said 6 1 half dozen or another. most products out there are good useable stuff. But I do fly with a Futaba TX.

Steve Hill

Futaba will replace the filter regardless if they can determine it has or has not contributed to a problem. They do so, every time an RX is serviced... Furthermore if the filter is cracked, how does one discern if it's not a casualty of the crash? What other items were eliminated as problematic?

I have been told by a well known and respected published RC Tech guru that Hitec's Supreme 8 PPM/FM RX's score much better than other OEM units in his rigorous test and evaluation scheme... BUT the "other's" that score lower seem to work fine in field use. What does this mean??? It means some reject noise better than others, some develop noise internally more than others, all the while they all seem to get the job done most of the time and there's more.

These test scores are evaluated in like groups of RX's as well. This means that OEM #1 one may have a higher scoring unit with his 4-channel RX than OEM #2 with his 4-channel RX and or vise versa as we progress through the various OEM's product lines.

My personal preference is for PCM in my GS models. What many do not associate with regard to a comparison is that PCM equipment is able to score nearly 20 point higher SNR (signal to noise ratio) compared directly to PPM before it is affected by the same level of noise that starts to render PPM unstable.

FM/PPM is analog, the pulse positions can be shifted by RF noise after the signal has been transmitted to the RX (RF noise typically causes the wave to change in amplitude and width, herein lies the problem). This is known or realized as interference, servo dither, glitching and or NO control of the model.

FM/PCM is digital, PCM pulses don't have to in perfect wave form, they can change in amplitude, width or both. The decoder is only looking for the presence of pulses, either they exist or they do not. If you miss a pulse train the RX doesn't get excited, either!

Hitec's Digital servos offer a true programmable failsafe feature without the need for a special RX (PCM / IPD) and work with any system to the best of my knoweldge.

That's my nickle's worth....

I have been flying futaba for 27 years actively. I would fly 4 days a week on average spring through fall. In all that time I have had only two radio failures. These were both Futaba silver series from the early 80's (can't remember the exact name).

Since flying gassers 13yrs I have only used PCM, without problems. I have heard all the debates and never heard any agreements from the die-hards except fly what you want. Even the fail safe debate has been bounced since the beginning and I have yet to experience a single lockout.

I believe alot of what we suspect as radio problems are occurring from other sources - Servos going bad, switches, batteries and the pilot. It would be nice to actually be able to graph the problem areas in a honest fashion, but can't be done.

As for the Hi-Tec debate, I have seen interference in these receivers when used with on-board ignition. This went away with a futaba receiver (all sorts or moving things around did not help). So as usual it is circumstantial and people will fly what they feel comfortable with through experience.

For the receiver that failed in flight due to vibration, one of the first checks I do after a crash (lot of dumb thumbs) is strap the receiver to a jig saw (remove blade first) with the servos attached and turn both on. The vibration is horrendous and any vibration problems show up. I have never had a receiver fail in flight following this check. I have had them fail during the check.

Good Luck.

And in answering this thread I am currently knocking on wood.

V-SNAP

V-snap and Mglavin,

Well thought out and and very helpful responses. Thanks for your input.

Products keep getting better and we all keep pushing the envelope. A good friend of mine told me that sometimes you just can't figure out what went wrong. In my case I would actually feel better and wouldn't have invested time researching this if I truly believed this was a simple matter of pilot error. I'm not too proud to admit an error. If it was something I did wrong possibly in the construction or in flying then I would want to know to keep the same from happening again. This was the first time losing a plane due to some kind of electronics glitch. Maybe I should feel lucky.

I take my time when assembling an ARF and look for potential problems. The battery and the receiver were less than one year old. Same with all the electronics. All new with roughly 15 flights or so. Battery was well padded, charged and checked as a part of the preflight check. No metal to metal. The receiver was well padded and behind the battery with no wiring or metal connections within inches. I had the receiver tucked and supported under the cockpit. The antenna was mounted inside the fuse with an antenna tube. No kinks, or bends. Used parson clips for all connections and a JR switch with a charge jack. Did a range check. Radio was on the proper model, set to PPM and controls were checked in preflight. Airplane flew fine two weeks prior with no maintenance between flights. No one was on the same frequency at the time of the crash.

Until I get the receiver back I won't know if it was the cause. As for one product over another, well, they all can fail. Nothing is perfect. The argument goes on and on regarding PCM vs PPM. In the end, we all have to make our own decisions with imperfect answers to these issues. Time, experience and product performance will reveal the best overall answers. Purchasing power will push manufactures to keep getting better. I was going to suggest that maybe a receiver with built in redundancy would make a difference, but then this could be applied to everything on the airplane and the idea becomes unrealistic. Conversely, If the receiver is the weakest link in the electronics path, well, maybe this isn't such a bad idea. I know you can add a second receiver and battery which does in it'self provide some redundancy, but from a practical perspective, aren't dual receivers and batteries mainly used for driving multiple servos to control surfaces in 33%-40% airplanes? Just a thought........

Time to move on. Scott started this thread. I hope he got what he was looking for. Not sure he did, but it sure helped me remember the obvious. This hobby is alot of fun, even when things don't go just perfect.

Roger,
I hope you didn't feel I thought you made the mistake. I was just referring to the debate over receivers and glitching.
The test was a good method of checking a radio prior to sending it off for service.
The Radios I had fail were both top of the line Futabas and they were sent back multiple times in a 2 yr period. One was finally diagnosed by a good friend who had his own T.V. shop following years in the air force repairing their equipment. Finally lost a plane and actually threw the radios and receivers in the trash. I know what not knowing is like.
Good Luck
V-Snap

reply to V-snap,

No, not all all. I really appreciate this kind of forum for a good debate on topics like PCM vs PPM. I just purchased a W.M. 300 Extra and I'm going to use a Futaba PCM in this new airplane. I know this too could fail. Like I said, there isn't a perfect answer to all this and in the end we all have to make our own decisions. I am flying a PCM in a G.P. 1/3 scale Pitts and I for one like the idea of fail safe, though the term is not totally accurate. Thanks again for the input. I will let you and others know what the test results are from the receiver I sent in. I am now hoping it was the culprit. If not, well, all I can say is that something got to it.