jc4me2

I'm thinkin about a gasser for my next bibe and have been told that it's best to use a PCM radio for your gasser. All I have is a JR 662. Is this addequate or do I really NEED a PCM? Thanks Jordan

wgeffon

My Feedback: (4)

No.

I fly my gassers with PPM. As long as your set up is correct both PPM and PCM can be used very reliably.

Both can be interfered with. The difference is in how each react to it.

PPM will glitch and be visable
PCM will go into Fail Safe. May or may not be noticeable depending on what you have set for fail safe. If you havnt set anything most systems will go to neutral controls and idle power.


You just have to decide whats better for you.......

jc4me2

Thanks for the quick reply. I really don't want to spend the money right now on a PCM but I thought I would have to if I bought a gasser. Thanks. Now I look at the gasser without feeling guilty. Thanks Jordan

wgeffon

My Feedback: (4)

Keep in mind that the set up is very important.

All ignition components seperated from the reciever.
Heavy duty wire on any long extensions
Loctite all nuts and bolts and check FREQUENTLY...


What are you gonna build? What motor?

fritzthecat

My Feedback: (4)

The JR 662 transmitter is switchable between FM/PPM, Z-PCM and S-PCM. So all you need is a PCM receiver.

Fritz

thunderbolt-RCU

My Feedback: (14)

A PCM Receiver will mask a noise problem. Make sure you range check frequently with either receiver. Keep all receivers, flight packs and servos at least 12 inches from the engine and it's electrical components. Do not put the throttle servo or flight pack anywhere near the engine. Run only plastic OR nylon (no Metal) pushrods to the engine.

Most interference problems can be eliminated with the proper set up.

Most competition flyers use PCM, but it is not mandatory.
Brian

jc4me2

I'm scratch buildind/kit bashing a 66" ws Ultimate. I'm lookin for a good gasser like a G-45. How much would a Cheeta 42 run? Jordan

RCRC

My Feedback: (56)

PCM provides additional reliablity to an RC link when pulse type interference is present - period!

People will argue about this endlessly but that is the bottom line. PCM will not go into failsafe unless the signal is lost for a significant amount of time. Instead, it will hold the servo position mandated by the last intelligable information.

Range testing is the solution to detecting electrical noise that can be masked by PCM. But there is no question that the PCM systems will continue to work under conditions so adverse that PPM is rendered useless.

I want to use all the protection from interference I can get and I range test fairly often to find problems. Be sure to range test with engine off and engine running. If you loose more than about 10% of range you need to fix the problem.

I would hesitate to fly a spark ignition engine with a PPM radio system.

krayzc-RCU

My Feedback: (31)

i have seen flyer stack 2 batteries on top of each other(those 2 batteries being int. and reciever). I am told with today electonics you can get away with more than you could years ago. Has anyone else seen this type of practice?

wgeffon

My Feedback: (4)

Gerald,

Not only that, but Powerflite makes a system that will allow you to run the IGN and RX from ONE battery.

RCRC

My Feedback: (56)

Yes, wgeffon and krayzc are correct. However, those sophistcated power management set-ups cost hundreds of dollars and are designed with RFI (radio frequency interference) filters built into them.

Those power systems go a little beyond the simple question asked by Jordan. Flyers who employ them will need to insure that the wiring is designed to prevent RF noise coupling to the receiver. I would advise against using such a system as it introduces an additional chance for interference.

rfw1953

My Feedback: (2)

I am new at gas and the Pitts is my first gas project. I have purchased a Futaba PCM receiver with a 1700 mah battery. Using two Futaba S9405's in the ailerons and two S9303's in the elevators and one one 9405 in the rudder. The PCM receiver with be at least 16 " from the engine. As in the Feb. MAN articles, I was going to mount the throttle servo with a metal rod on the engine firewall box. Not planning on using any noise filters and using the standard wiring through out with Parsons clips for extensions. Planning to mount the receiver with foam under the cockpit area well away from the engine.

Here is my question. Since I am new with gas engines and learning about the concerns over noise from the ignition am I ok with this set up? If not, please let me know what changes you would recommend and why they are needed. I have read both cons and pros on this and would really like good information from you that have good experience with gas, PCM, single battery set up.

Thanks for your help

JohnW

My Feedback: (6)

RFW1953: As mentioned earlier in this thread, you need to keep ALL radio related items as far away from the ignition system as possible. This includes wires, servos, batteries, etc. The only change I can see to your described setup is to not use a metal push rod on the throttle servo. The metal rod can conduct ignition noise right up to your throttle servo. The noise can then travel down the servo leads right to your RX (even if it is 16 inches away.) In addition to using a nonconducting throttle push rod, you might also consider moving the throttle servo farther away from the engine.

By single battery setup, do you mean one batt for the RX? If so, that is fine. However, do not use the same battery for the ignition module if your engine has one.

In short, be sure to keep all ignition related items (wiring, switches, battery, ignition module, etc.) away from all radio related items (batteries, rx, servos, switches, wiring, push rods, etc.) Be sure to range check to loss of signal with both the engine off and engine on. If there is a large diff in range (say over 10%-20%), you need to recheck your layout.

Forgues Research

My Feedback: (7)

For those of you that would like to have your throttle and choke servos closer to the engine, I have made a package Firewall Forward availlable to help in eleminating some of these problems.

Fighterpilot

My Feedback: (2)

I just went through this problem with a friend of mine and a new 3W70. With the throttle servo and choke servo mounted in front of the firewall, the servos would jump all over the place with the engine running. Without the engine running, everything was solid and range checked well. Using HI Tec 8 channel Prism FM receiver.(That receiver has been very reliable)
We moved the throttle servo and choke servo into the airplane,14" behind the firewall. All linkage form in front to behind the firewall was non conductive. We still had the same problem. With the engine running, the servos would surge in each direction and would, in general, glitch all over the place.
The only thing we did at this point was change the receiver to a Futaba 148DP PCM receiver. All of the servo settled down and no longer jumped around and we had no more violent glitches on any servos with the engine running. It range checked well over 90 feet with the antenae down on the transmitter, moving the servos up an down, left and right, the whole time we walked away from the aircraft.
Flew it the next day and it was solid as a rock. I guess RCRC, in his above post, knows what he is talking about. In all my gassers, especially those with ignition system modules and batteries, I'll use PCM. Our little experiece was proof enough for me and my buddy.

wgeffon

My Feedback: (4)

My throttle servo is mounted to the motor box. No problems at all.
PPM RX in mine also.

ml3456

Aerographics,

Saw your fiber optic link, but does this only isloates the signal wire. You still have 2 power wires going up to the servos that can pick up RF. Is this true?

ML

Forgues Research

My Feedback: (7)

Here is how the system works, First, the signal wire is the culprit.

With the throttle and choke servo, by using the ignition battery everything is kept in front of the firewal so that nothing electrical is remotely close to the receiver.

When using the Fiber Optic extensions on all channels, then it goes further where the receiver has its own battery, and no servos are connected to the receiver. Only the encoder part of the Fiber Optic extensions are connected and the rest is done with light beams within the Fiber Optic cable. The servos have there own battery/s
This way no PCM is needed ever which only masks the problem until it gets bigger and then it locks up.

Also with no load ever on the receiver, it actually has better range, better noise rejection, and it has a very linear voltage applied to it,. Also if the receiver battery should loose a cell is a 4 cell pack, it would still work perfectly since you are not driving any servos with this battery,

On my own application as an exemple, on a 33% aircraft, I use a 500ma battery for the receiver and that should last about 20 hours since there is no load.

I have tested the fiber Optic extensions up to 300 ft, which we don't need this long, but you can see that it has all kind of reserves.

Fighterpilot

My Feedback: (2)

Wayne, what type of ignition system are you running? I've installed throttle servos forward of the firewall just as you have, but that was with a magneto CDI type ignition. I can only relate to you the facts as they occurred during our problem and the solution that worked for us. Moving the servos back into the airplane and away from the ignition source was not a fix. It was only until after we installed the PCM receiver that the problem was cured. This also happened on a new Corsair with a 3W80 and a 128DF Futaba FM receiver. Took that receiver out and installed a new 148DP and all the jittering a servo movement stopped. Range checked very good.

The attached picture is of my Byron P-47 with the throttle servo mounted right on the firewall. I have never had a problem and this airplane has been flying for over 3 years.

sfaust

My Feedback: (11)

The problem was not cured, only hidden from you. I can assure you that if you put any PPM receiver back in the plane, the problem will still be there. If you put a scope on the PCM receiver, you will still see the interference.

The masking ability is both a benefit and drawback to PCM. The problem will be hidden, so many believe the problem has been solved. However, the problem is still alive and well, and waiting to someday pop back up if the problem gets any worse over time. If the ground becomes faulty on the engine/ignition, or the interference increases for any number of reasons, you could loose the entire link.

Because of this, it is highly recommended that either a glitch detector is used to 'unmask' the problems, or a PPM receiver installed and tested prior to use a PCM receiver. This way, if the PPM receiver works fine, you can go ahead and install the PCM receiver with confidence. If the PPM receiver shows interference issues, you can resolve them prior to putting in the receiver.

It souds like your setup has some interference leak somewhere, and it should be dealt with. While not recommended, with a magneto system you should be able to mount those servos right up near the engine without interference. Its not recommend because if any interference problems crop up, the servo is in a prime location to catch it. Moving it back eliminates the problem all together, and is preferred.

If it was my airplane, I would park it until I could find out the source of the problem, and eliminate it all together. Then I would fly PPM or PCM with a glitch detector with complete confidence.

Fighterpilot

My Feedback: (2)

Let me see if I understand this correctly. With my PCM radio I won't know if I have a problem, I'll just fly my airplane around with this problem and not know it existed. Now if I had a PPM receiver, I'd know I had a problem before I flew and therefore would not fly or if the problem developed while I was flying I would crash. Now that makes sense to me. With one receiver I sit on the ground trying to find out how to fix a problem that I've been fooling with for 3 days, including changing all of the wiring with new plug wires and caps, and following along with the advise of a representative from 3W. With the other receiver, PCM, that range checks perfectly, I go fly my airplane and never experience any problems at all and spend a day at the field enjoying my new airplane. Let's see is that sort of like the tree that falls in the forest. If there is no one there to hear it, does it make a sound?
I'd like to refer to the post above by RCRC, I think it explains it pretty well. The man seems to know what he is talking about. I like keeping things simple and the more electronic crap we install in our aircraft, the more there is that can go wrong.

roywiglesworth

put a ferrrite bead on each one of those servo wires and you should eliminate those problems.
roy

krayzc-RCU

My Feedback: (31)

what is a:

ferrrite bead?

does that bead allow those flier to mount stuff closer? i hear 12 inch is the rule of thumb but 6-8 is what is really needed, has anyone heard this?

again i am seeing flyers get away with 1-5 inches like it's cool!

roywiglesworth

put a ferrrite bead on each one of those servo wires and you should eliminate those problems.
roy

Forgues Research

My Feedback: (7)

I know with your answer you don't want to hear this, but Steve is right, if you have a problem with a PPM receiver, you should find the source and fix it. Your fooling yourself in thinking that the PCM receiver has fixed your problem. It masks it and when it gets bigger, it locks up and your in the ground.

Why do you think Multiplex stopped making PCM and they are the ones that inroduced it.