LJR

My Feedback: (8)

I've read about this sometime ago but can't remember what the solution was. Pls. anyone refresh me. Thanks.

Here is the problem . My throttle is linked at the arm with a Z bend thru the hole. The servo is an HS 55 .
With the motor running , radio on, and on my bench , I SEE MY THROTTLE JUMPING AROUND. I don't know if this would cause a problem in flight as I am afraid to try. Range check is fine . Its just the throttle when up close to the plane, with the radio antenna down or up... Does something need to be shielded, I suspect the problem is electrical in nature as the servo , motor and radio all operate fine individually.
Thanks

vpresley

My Feedback: (162)

HI

Is the carb throttle arm metal? If it is, thats your cause most likely. Should not have metal to metal contact with a Z-bend. Can cause the problem you are describing.


Vince

Lnewqban

I believe I have learned here in RCU that the HS 55 servo is too small to withstand vibrations of any IC engine.

Gray Beard

My Feedback: (-1)

I don't use the 55 often but I have used a lot of the 81s for throttle and other applications with very good luck. The problem does sound like RF from metal to metal vibration??I really haven't had any RF problems with my glow planes but when I get RF with my gassers it usually shows up on the throttle. I'm not a user of the Z bends and solid wire but I use a lot of cable with a golden clevis. Not that it still isn't metal on metal but it seems to work. It could also just be dumb luck??

red head

Metal to metal is a bad thing and I agree with these other posters, it could be your problem.

One other thing: you said it does it while on your bench ~~ do you have fluorescent lights on close. Try moving outside or something.
ENJOY !!! RED

JohnBuckner

My Feedback: (1)

Its a double whammy. First the HS 55 is totally inadaquate for the job and not up to the virbration, the first hard landing will strip the gears and finally you are using a Z bend on the carb.

HS-81, 85's and HS 225's are my preferred throttle servos.

Not sure if 2.4 is more immune to this or not but on 27, 72 PPM or PCM if that z bend goes through a metal throttle arm then if its not doing as you described now then it is certain to happen sooner or later as that hole wears and likely in flight.

Therefore when checking the fellows airplanes even with 2.4 systems I will not accept Z bends at the throttle. The only exception would be the rare case of a plastic throttle arm on the carb.

Never, never use a metal to metal z bend at the carb throttle arm.

John

LJR

My Feedback: (8)

Thank you all.

This morning I removed the Z bend and installed a Dubro ball link(plastic). Also I mistook the servo as a HS 55 when it really is a HS 82MG.

Also I wrapped each seperately my receiver , battery and on/off switch in aluminum foil. This might be overkill but what the heck.....

Once I read your replies I realized metal to metal on the throttle arm is not a good pracrtice.

Lesson learned!!!

Gray Beard

My Feedback: (-1)

FOIL????????????????????? Maybe you should give something like foam rubber a try. I use a number of types but they do sell sheets of closed cell foam at your LHS made just for wrapping your gear in. For the most part it's anti vibration. Foil is conductive.

JohnBuckner

My Feedback: (1)

LJR I know you did the foil bit as some sort shielding but that is totally uncalled for and even could lead to other problems and is a poor idea.

I think you already have found your problem.

John

TimBle

i've seen this happen to many planes, including those with plastic clevis onto the carbs throttle arm and those with metal z bend throttle control rods.In each case the fault was a sensitive servo.Many arfs are supplied with z bend throttle control rods and there are many planes flying with them successfully.However in this case the solution is correct since you are using a metal gear servo.

LJR

My Feedback: (8)

Thankyou TimBle
I think you got the real answer ; its the servo with the metal gears that's doing it. I have 13 planes in the barn, many with z bend throttle linkage(metal to metal) but only this one has the metal gears (HS 82MG ) and thus the problem.

Metal to metal is probably not a good thing; but the RF is definately [X(]coming from the metal gear sensative servo.

Thanks for the diagnosis.

LJR

My Feedback: (8)

thanks John Buckner & GreyBeard

You guys are probably right, alum foil is not a good idea after all. I'll remove and wrap with foam.[>:]

ARUP

Either put a plastic clevis onto the end of a metal threaded rod to connect throttle arm or make sure there is no intermittent connection between 'Z'- bend causing the interference, i.e. a ground strap needed from throttle arm to 'Z'-bend.

JohnBuckner

My Feedback: (1)

LJR in the past when all our radios were AM they were/are very supceptable to extrainious RF generated by any metal to metal contact anywhere on the airplane but the very worst spot is metal to metal at the throttle arm and of course due to the high vibration at that point.

Along came FM systems and these were indeed far better in this noise rejection and there were far less Mystery crashes however given a sufficiently sloppy hole it can and does still appear.

Because the FM system were better folks tended to forget and revert back to old ways and begin using S's at the throttles agine.

What will happen in many cases is when new the problem frequently does not occur however as that hole wears with use The frequency of the noise can indeed trip that type of servo glitching at full throttle not only the throttle servo but also other servos. Metal to metal at the throttle is a ticking time bomb.

I have caught many cases of just this type of glitching. As noted earlier I do not know how well 2.4 systems do in rejecting this type of noise however I will not experiment with my aircraft or those I may be mentoring.

Indeed some ARF's do come with hardware for 'S' bends at the throttle arm however that I consider irresponsible.

Only Just My Opinion

John

Gray Beard

My Feedback: (-1)

And RF can get you from plane to plane with the same set up. I'm a big rule breaker, or I was , I have changed my ways!! I had one gas plane set up with the throttle servo and choke servo mounted right on the engine box next to the ignition, a very bad thing!! Never had a problem with RF. Down the road a bit, same engine and ignition in a new plane, same throttle set up, no choke servo, almost lost the plane on maiden, I started getting hammered with RF soon after take off, for the most part the throttle servo but I was getting bumps from all my controls. I knew what it was right away and killed the engine and came in dead stick but it did open my eyes to doing things by the book.
To date I have never had an RF problem with a glow plane but I still watch my set up. It can be something really simple that you over look even when your staring right at it. That happens to me a lot, I blame it on age but a brain fart is a brain fart.

TimBle

its also worth remembering that RF is not generated by a glow motor that is electrically insolated. There is some RF generated by combustion but thats very weak and to my knowledge too weak to affect a servo and if this was the sourse it should clear up with increasing rpm....
So typically, RF issues due to electrical interference in glow motor applications are unlikely and extremely rare. In every case I've seen this it has always been a servo at fault and replacement of the servo was the solution. It is possible that intermittent electrical contact WITHIN the servo was the root cause but that is yet to be established since the owners usually conduct the fix at home and bin the servo. I'll hang on the next one and test this theory.

on Gasoline motors the engine has an ignition device that is electrically active and through which the engine is electrically connected (usually its the ground or earth contact) to that circuit. Intermitant contact between throttle control rod and carb actuator arm here will generate RF noise that can affect a servo.

At the moment, I use plastic gear servo's on the throttle and will continue to do so. Any engines throttle is a relatively low force application. If I would opt for a metal gear servo I'd opt for Dubro Lazer rods or Sullivan's Golden rods for the actuator arms since the plastic rods are great dampers.

Rodney

Metal to metal vibration has caused many a problem with both AM and FM radios. This can happen easily on metal to metal connections between pushrods and control horns. It is even more common on bipes where flying and landing wires cross and/or connect using metal fasteners. It makes no difference whether glo or gasoline although the spark on any gasoline engine can be a major source of RF interference if not properly installed. 2.4GHz is more immune to RF interference but not completely. So far we have had one plane on 2.4 that suffered major problems with one electronic ignition system (ignition system design problem).

TimBle

ok so two metal parts intermittantly touching is touted as a source of RC EMI fact.

Please explain how two non electrically charged components are able to create this EMI that caused glitching in an electrically isolated application like a glow engine.

on Electric planes we have a huge source of EMI yet that does not affect normal functioning servo's.

yet it is claimed on glow engines with no electrical circuit between the engine crank case and the servo that the intermittent touching between throttle control rod and carb actuator arm is a source of EMI... I'm really struggling to see how rubbing two non charged pieces of metal together creates enough static electricity to glitch a servo that has an electric motor inside with much higher EMI.

I would like a better answer than metal to metal causes glitching. Thats non sense because if true it would happen on every single rc airplane and it simply does not.

LJR

My Feedback: (8)

For what it's worth the flutter/jitter occured at idle or attempted idle. It seemed to to clear up at increased RPM to non existent.
I haven't had a chance to run the new set up yet and I will report back on using the Dubro ball link set .
The plane is an old timer, Brooklyn Dodger , with the affected servo up front just behind the the fire wall in a sort of pylon with the receiver and battery seperated by another bulkhead and rudder& elevator servos way back towards the tail. The motor is a Magnum 32 ,2stroke. .

Reading repelies, I see mention of many bad conditions.
Thanks guys

TimBle

If it clears up as the revs rise then it is more likely a bad potentiometer in the servo. If it was RF induced then moment the revs change the glithc should disappear since the frequency will have changed.

I beleive a lot of "intereference" related to servo's on throttle arms of glow engines is vibration affecting the potentiometer not RF. If you fit a plastic clevis you damp the vibration and reduce the "glitch".

In my previous career I spent a ot of time with EMI specialised engineers testing various devices  designed. A vibration test was one of those tests to check for electronics component failure. We never picked up significant EMI generated by any metal parts touching intermittently. We did see a lot of failures of components especially potentiometers if they were not munted correctly of their subassembly was not vibration isolated.

Rodney

TimBle, I also spent well over 30 years in instrumentation in the aircraft and spacecraft field with some medical instrumentation and I can guarantee you that metal to metal vibration can and does create a great deal of RF that can (and often does) interfere with electrical measurements. Any time that any action occurs that can excite the electrons in an atom or molecule, you can create electron flow which can create an electrical field that can cause interference. I've personally witnessed this hundreds of times.

JohnBuckner

My Feedback: (1)

Thats a mighty fine looking Dodger ya got yourself there LJ, I dare say you are gonna love it. The .32 you find will take your airplane vertical at full power so 95% of your time will be at idle which is a fun way to fly and essentially the throttle becomes the climb control and the elevator just a trim device.

My eighty inch Playboy with an OS .25AX hand launchs to a vertical climb to altitude and then just pulls back to idle for the remaining 30 minutes on the three ounce tank with no lift.

Here are three of my old timers just for fun and includes the Playboy, An Aero Nine vintage RC rudder only with an OS Pet .09 and a radio assist Kerswap with a Mvvs 2.5cc (.15) diesel.

John

LJR

My Feedback: (8)

Wow John,
Truly vintage .
As much as I enjoy sport flying, there is no denying the majesty of old timers.
I just had to build one.

Hopefully I'll get it in the air soon.

JohnBuckner

My Feedback: (1)

You will and we all will enjoy hearing about the adventure.

John

LJR

My Feedback: (8)

Finally got to fly this plane last evening (we only fly 2days/wk).. Ran 2 tanks thru the motor on the ground w/radio on- NO throttle flutter. Thanks to you guys.
Then the big flight test, what a ride.... As predicted she climbs like a rocket, quickly had to go to idle the motor and even apply down elevator. CG at glide is fine , but way to much rudder on the climb out. Wings were wobbling like crazy,plane snaking all over the sky!!! I really wanted to be sure she turned both ways ; but it was overkill . I'll use duel rates for climb and glide.
Landed at a snails pace, just beautiful.
Made adjustments and back up we go, this time nice wings level ,slow climbing circle. Went to idle and nice flat guide. Pinned her against a white cloud so I had good visibility.. Spent a good 10 minutes looking up, till my neck started to ache.
In a nut shell - I'm very happy with her.
Old timer/ 3channel models are far from boring. Long glides, motor control and slow spirals to decend are necessary. Rudder on the right stick instead of airlerons.. Gosh Its been a long time since I flew that way!!

LJR