Hey Guys

I was at my LHS the other day and a freind of myne told me he crashed his plane with a DA 50 in it. He said it was because of the hitec revievers he had. He said that you cant use hitec recievers with electronic ignition because there is too much interference. He said that you have to use PCM..

BUt this is odd because i was told not to use PCM because if there were interference the PCM would go to the preset position and you wouldnt know about it.

Soo im a little bit confused. Thanks again

You do not have to use PCM receivers just because you have EI. Fact is, Rf interferrence can be generated by gas ignition engines regardless of what is providing the spark. Just make sure you eliminate the avenues of RF interference, and you'll be fine. The dual conversion receivers that Hitec offer are as good as any other brand on the market, IMO.

One thing that some people fail to do is isolate their ignition parts. Put everything that deals with the engine in front of the firewall. This includes the ignition battery on EI units. Put everything that deals with the rx behind the firewall, and preferrably 12 inches behind the engine and it's electrical components. Then, run a nyrod pushrod from the throttle servo to the throttle, and use plastic or nylon clevices. Do all of that, and you should be fine. Of course, always do a thorough range check first!

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No offense to your friend, but he doesn't know what he is talking about.

I use FM (PPM) receivers to help me get the bugs out of the model's electronics before switching to PCM. When the model has been made safe to fly with FM, then and only then will I use PCM.

What most folks do not understand is that the RF sections, the part of the receiver that does the listening, is essentially the same in both PCM and PPM (FM) systems. The PCM part of it all comes in when we get to the decoder. The decoder is the second part of the receiver. Its job is to tell which servo how far and when to move. FM utilizes an analog decoder (well - sort of), while PCM utilizes a digital decoder. The latter has the ability to ignore codes that it does not consider to be legitimate. The PPM decoder reacts to each and every pulse of significant amplitude and duration, thus driving the servos erroneously. The PCM system does not drive the servos at all during ignored pulses.

Most PCM systems have provisions for default servo positions if the codes are ignored for longer than a preset period. Some FM/PPM systems have similar provisions, depending upon the manufacturer of the system.

During the checkout period, it is better to "see" if your model is glitching itself with unintended emissions from the ignition system, or other noise creating systems onboard the model. One can't fix it if one can't see it.

Wow... Your LHS doesn’t know Jack. PPM & PCM both work great on Gas planes. Many thousand planes have flown well on both. Most of the TOC/ Expert IMAC/Pattern type guys fly PCM not PPM, so don't worry about lock-out cr@p. Hitec receivers also have a great reputation in gas planes, often out performing the Futaba/JR counterparts.

The set-up and the precautions you take before you fly is what are important. It sounds like this guy didn't get that right either!

Go take a look at your friends plane.

Did he seperate the ignition unit from the RX by at least 12" ?
Did he keep the switch for the ignition unit at least 12" away from the RX?
Did he keep the ignition switch at least 12" from the RX switch?
Did he keep the ignition battery at least 12" from the RX?
Did he keep the ignition battery at least 12" from the RX switch?

Both systems--the RX and the ignition--have to be kept at LEAST--BARE MINIMUM 12" away from each other.

That doesn't mean that you put the ignition box on the firewall and then slap the ignition battery next to the RX for balance.

That doesn't mean that you put your throttle servo on the firewall because you need nose weight or your too lazy/incompetent to make up a good throttle linkage that will put the servo 12" away.

That doesn't mean that you stack all your switches up on top of each other on the left side of the plane.

Every component from the ignition system must be at least 12" away from the RX. You strap your ignition module to one side of the morotbox and you put the battery on the other side. You put the ignition switch in the fuse--as FAR FORWARD as you can get it. I find out where my cowl bolts on and I put the ignition switch within an inch of that. You have to keep all your ignition stuff up front. NOT just the ignition module. The battery and switch too.

You can't put your RX battery up front for nose weight. You just can't. PERIOD.

All the RX stuff has to be 12" away from that ignition switch. The ignition switch is the 1 item thats going to be the closest to all your RX stuff. The ignition switch is mounted in the fuse and the rest of the ignition is out on the motorbox.

So, you get out a tape measure and you make a mark about 12"--14" away from the ignition switch.

NOTHING from the RX can be in front of that mark. No matter what. You put your RX battery switches on the side of the fuse. Put them in the back. They don't weigh squat.

You mount your RX, and the RX batteries on a lite ply tray and you find a spot to glue it in the fuse. You keep it 12" away from that ignition switch. Hopefully, you can put it somewhere that allows you to balance the plane with the weight of the RX and batteries--but if it doesn't balance--you don't do something stupid and shove the RX and batteries right up front behind the firewall to add nose weight. Thats a splatter waiting to happen.

If you WANT to use PCM--then here's what you do:
You install a PPM RX in the plane and do your range checks FIRST with the PPM RX. It won't hide interference. If something is going to glitch or quiver--you'll know it.

If everything checks out--and you get a good range check with the engine OFF, then you start the engine and do the range check again with the engine idleing.

If everything checks out and you get a good range check with the engine idleing--then you run it up a bit and see if you still get a good range check. Run it up to full throttle and range check it.

Now--assuming everything is good and your got bulletproof range checks with the PPM RX--you can take the PPM RX out and install the PCM RX and do all your range checks again. If it checks out--go fly it.

If it doesn't check out and you want to see something spectacular--put it up in the air anyway and watch how much worse the interference gets once the plane is airborn.

RF interference is basic preventative stuff.

RF 101 is to keep all your stuff seperated by 12" or more. Thats Basic RF 101. Anyone who doesn't know or heed that rule--is an idiot and shouldn't be flying.

Go look at your friends plane. See if he had all his ignition stuff 12" away from the RX.

I'll bet he didn't.

I've been flying for 5 years now and im starting to get into gassers.. So when this guy told me i got a lil worried.. BUt then again i doubt he had set it up properly and there are a number of factors that can contribute to a plane crashing.. I fly hitec in all my 27 -28 % birds and there good and i even run them in my trucks.. Honestally i think this joker must have had sumthing set up wrong or it was pilot error.. Thanks agian guys

Go with Rcpilet. I think most of us that have been doing the gas thing for awhile are in agreement with about 95% of what he's told you. The 5% balance is only a matter of style.

The reason your friend lost his plane was more likely due to pilot error with his flying skills, or a poorly set up radio/ignition/engine/fasteners installation. Next time you see him, casually ask how much money he saved in the build by using old and discounted components. I'll wager he has a rough number to provide. All of the manufacturers make excellent receivers in either flavor, ppm or pcm. They only require that attention be paid to a few simple guidelines.

Pat

Well Pat said it all.
I agree.
It's real easy to blame something else other than the dumb thumb or the numb brain.
I know a guy that crashed three (3) planes and blamed it on RF, come to find out he had placed the SAME Rx in all three planes. Never sent it off to have it checked out. Said it worked well on the work bench.

I have 3 gas engines all flying on Hitec FM receivers. Actually I had a JR 700 rec. in a gas plane once and I experienced small "bobbles" from time to time, took it out and installed a Hitec - no more "bobbles".

I was flying HITEC Supreme 8 ch RXs in planes up through 35%. Last year I switched them all to Mutiplex IPD RXs because of the failsafe feature, but they are STILL PPM!!!

Another thing to consider is the vibration issue with gassers. They will vibrate more than the typical single cylinder glow engine will. THerefore, it is imparitive that you wrap the receiver in PLENTY of foam. I use 1 1/4 inch foam all the way around my receiver, and then set that into some more foam if possible. Too much vibration is hard on the receiver board, and crystal. THat can lead to rx failure as well. Make sure that thing is isolated from the vibration!

Well, you just got a lesson on gasser set-up that most people would be willing to pay for. These are the guys that I have learned from here on RCU. Iwish I could be of some help, but they pretty much covered what I was going to say. Thanks guys.

2slow2matter,

I'd like to see a pic of all your foam.

Cheers,
j

thanks guys all the help is much appriechiated.. me and my dad were worried that we were gonne have to change a bunch of recievers. BUt yeah i bet that that guy had a bad set up.. Thanks Again

Sillyness
Consider it done. As soon as I get a chance, I'll take one or two. It's not that hard to put a bunch of foam around a receiver--especially in a plane large enough for a gas engine. Foam is lightweight, and cheap insurance.

Adding a piece of Scothch tape over the rx crystal goes a long ways to solving some problems as well. Can't vibrate out that way.

I always tape my crystal in place. It's not the vibrating out that I'm worried about. It's the vibrating apart on the inside. Good advice, though, I had fogotten to mention that point!

I use black electrical tape to secure my crystals. I go around the RX a couple times and stretch it snug. Never had one come out.

Damn, now I'm starting to type with a lisp

As a heads up, if you take your plane to some fields they will require an idle failsafe on the throttle... some even require 2 ways to kill the engine from the TX.

You can do the failsafe several ways:
1) Multiplex IPD RX (What I have)
2) PCM RX
3) Hitec programmable digital servo
4) Aftermarket throttle failsafe device (I prefer not to add additional devices that I don't use on a normal basis... something else to fail)

You can do the engine kill several ways (low throttle counts as the first one):
1) Choke servo (my prefered method)
2) Optical kill switch
3) Mechanical kill switch

I don't think these are AMA required (don't quote me) but I think it may be going that way, especially the first one. I know Joe Nall requires the failsafe.