harley1340

Recently built Great Planes Citabria, with an OS GT33, Spektrum AR6210 reciever with optokill system. I have followed OS directions and placed the ignition at least 100mm from motor, my throttle servo is closest to ignition by about 60-70mm. When running, the throttle servo pulsates at mid to low rpm. I have moved the receiver to mid plane, same results. I have tested the throttle servo on an extension at the rear of the plane same results. I have separate batteries, one for ignition, one for receiver. I have removed the opto kill, same result. I even took the throttle lead out of the receiver and placed the rudder lead into the throttle port, no pulsation on the rudder servo. Next step, replace the receiver although I do not think it will solve the problem. This same setup was in an Ultimate biplane with no issues. The throttle servo is a Futaba 3004 non digital, I don't think replacing the servo will help either. Is it possible the receiver is picking up RF problems almost two feet away? Will test another servo, possibly the same servo as the rudder servo an XQ brand when I can get one from Redwing RC. Any ideas so far, thanks, Art.

pilotpete2

Most Likely the servo is being directly affected by RF from the ignition system. I would make sure that the ignition spark plug cap is fully seated on the plug and that you have the correct plug for the engine (I'm not familiar with your engine). I had this problem once on a 26cc powered model. The plug cap was loose and only the throttle servo was affected bt the RF interference. At mid to high throttle, the servo just went nuts, swinging from WOT to idle as fast as the servo could transit. Incidentally, the throttle servo was the only analog servo in the plane, and was the only one affected by the RF from the loose plug cap.
Good luck,
Pete

CARS II

My Feedback: (7)

Good info from pilotpete2, I had the same thing happen on my first gas airplane ( I got it that way ) but it was the Ailerons only for me, I did the same as you, separate everything and then some, I even grounded the ing box to the engine mount with 1/2 braided wire ( hard to find for me ).

I change all the servos from analogs to digital and did many other things to get it clean, I believe the analog servos were picking up the RF ( I'm still using the same extensions ) as described by pilotpete2.

On my second gasser I did everything the new way, metal roads, servos closed to the engine box even analog servos but the throttle ( JR 3241 digital mini ) the throttle servo is very important and I suggest you install there a good servo ( digital if you have one ) when it comes to throttle position it is very nice when it returns to the same position specially to idle and it is the servo that is used the most out all of them.

Check out my thread on the subject, I hope it helps.

Oh yeah! my second gasser is the Citabria, i'm sure you'v been to my thread on that airplane.

http://www.rcuniverse.com/forum/gian...hing-idle.html

dirtybird

My Feedback: (5)

I recently had the same problem.. Fortunately I have an oscilloscope and could determine the cause. The digital servos I have on the aileron and elevator put a lot of changing loads on battery leads. This creates a lot of hash on the power input to the motor control servo.The cure was to use a high capacity A123 battery and short heavy leads to the switch and receiver.Also I used a high quality double pole switch with both poles wired in parallel.
If you use a lipo with a regulator it will likely make the problem.
If you are using 2.4GHZ I am quite sure its not an RF problem

All Day Dan

My Feedback: (5)

Dirty, what kind of switch are you using? Dan.

dirtybird

My Feedback: (5)

http://www.digikey.com/product-detai...N1012-ND/13911
its rated for 40000 cycles

speedracerntrixie

My Feedback: (29)

Can you explain why a Lipo with regulator would be an issue? I have been running that combo now for years without problems.

dirtybird

My Feedback: (5)

A regulator works real well where the load is constant and the supply voltage is not constant. There is usually one in the receiver.
However, where the load changes over a wide amount as the servo load does, the regulator has a lot of work to do. When the servo is not moving, must dissipate the current the current the servo requires but is not needing. A single servo can change from 50ma to 3A depending on the load. With several servos the load can change up to 10 amps. Take a look at Smart Flys linear regulator. It has to have a fan to keep it cool. A real waste of power. Its resistance also adds to the internal resistance of the battery reducing the ultimate power of the servo and can make things unstable.
A switching regulator runs cooler but adds the possibility of interference with the servo.input pulse.
On top of all this, its a complex part that diminishes the reliability of your system. Its a single point of failure. You lose it, you lose everything.
If you want to use a Lipo for your receiver, which I think is a mistake, get HV servos.
Have you ever heard of A123's? Very low internal resistance,you don't need a regulator,they don't explode if you crash, and you don't have to remove them to charge

All Day Dan

My Feedback: (5)

Dirty, thanks for the switch information. That switch is designed for a panel mount application and I see no reference to performance in a vibration environment. The number of operations over its lifetime is no concern for RC applications since we do not turn the switches on and off so much. Obviously, you have had success with them over the years. What makes you think that they are any better than the ones supplied by the RC manufacturers? They understand the operating conditions of the switches and put their name on them. They also know that one bad switch would put a blemish on their whole RC system. I started to use Futaba radios in 1984 and have been using their switches ever since. They have been mounted on that Dubro switch mount. The worst that has ever happened was an increase in the voltage drop through them. Whenever I take one apart, it looks brand new. By the way, thanks for that missive on regulators. The guys that use them usually do not understand their limitation. Dan.

dirtybird

My Feedback: (5)

I think its a better switch because its rated for 40000 operations. In order to meet that spec the have to show it has less than a measure of resistance after that many operations. I dont know offr hand what that resistance is but I think it is Milli ohms. This is where you found the problem with Futaba's switch.This could be the root of the OP's problem.
Vibration can be a problem with any switch.Too bad we cant get the 4pole slide sw that came with the Radios in the 60's.
For that and other reasons I soft mount my gas engines.

mustangman177

Are Futaba's Heavy Duty switch harnesses any better ? I'm using 2 of these on my DLE 35 RA Gasser. ? Was using smaller Hitec switch on the ignition side, unitl I too was experiencing sone surging on the throttle servo. Futaba switch and carb.adjustments cleared it up.

http://www3.towerhobbies.com/cgi-bin...?&I=LXXA49&P=3

757jonp

My Feedback: (48)

Had the same problem a couple times (throttle servo going nuts). Careful exam of the spark plug lead revealed the braided shielding was broken right where where it exits the ignition module. Might be worth a look.

speedracerntrixie

My Feedback: (29)

Looks like we are going to have another thread where we disagree. Just keep in mind that this is intended to be a friendly exchange of opinion. That said everything you claim is correct inworse case scenario theory. I have my doubts that your answer is coming from actual experience using the items in question. Please let me know if I am incorrect. My last 3 40% contest airplanes have all been Lipo and Smart Fly Turbo regulator equipped. I chose that regulator due to it is the highest rated regulator available, has a solid state switch and Smarf Fly has great customer service. Lipo batteries were chosen because of price, high discharge rate and you can get them in a hard plastic case. In flight a servo is NEVER going to draw 3 amps and ganged servos are NEVER going to draw 10 amps, that is as long as the set up is correct. Bottom line is that the regulators are the best way to keep a constant voltage to your servos. That's important to guys who require the same servo speed and power from the first flight of the day to the last. As far as reliability goes, those 3 airplanes accumulated well over 1,000 flights between them with zero power delivery issues. Without the regulator you are limited to using mechanical switches unless you go to expensive Powerbox or Emcotech solid state switches.

as722

My Feedback: (1)

Why not try a new servo?

Limitless Aero

My Feedback: (17)

It's the servo. That sentence makes it pretty clear. I would never use a 3004 for a throttle servo in a gas plane. Get a decent metal gear servo on it.

littlera

I had a similar problem with a throttle servo in a gas plane. The servo was mounted vertically originally, and would pulse at mid throttle. There was lots of vibration in the direction of the output shaft of the servo. I believed the position potentiometer was resonating, causing the wiper to vibrate against the resistor, making it "float." I tried another servo, got same result. I reoriented the servo to a horizontal position, and the problem completely went away, confirming that the resonance was the problem.

Larry882

Had the same problem with an old Bud Nosen aeronca champ. I was using a 1" diameter aluminum wing tube from Ace Hardware and I replaced it with a wood dowel rod. Eliminated the problem. I fly Airtronics 2.4.
Larry

pilotpete2

One thing I'll never do with a throttle servo is mount it on the engine box or firewall. The further from the engine, the better. Now, MG servos on throttle???? Why not just setup the throttle linkage corrctly in the first place! The hallmark of a good throttle is minimum slop in the gear train and good centering. The last thing you need is a high torque servo. I realize that most of those who fly the larger gassers will disagree, so be it.
Pete

pilotpete2

I'll put 2 2500mAh A123 packs with dual switches against any regular and lipo setup for voltage stability from the first to last flight of a charge. As for relability, there's no contest. Regulators are an added point of failure....
Pete

speedracerntrixie

My Feedback: (29)

I would agree that metal gears are not needed but they won't hurt either. Minimum slop and good centering usually come with high end digitals so that's what gets used by some. If one uses the throttle as more of an on and off switch the just about any standard servo would work. Then again some guys are still shutting down the engine via throttle. When you use the servo to completely close the throttle butterfly the servo gets a good dose of vibration for that second or two, metal gears would last longer.

speedracerntrixie

My Feedback: (29)

Depends on the airplane, 2500 mah batteries would not cut it in my airplane LOL. I guess we will disagree, I cant see how a linear regulator with redundancy is less reliable then mechanical switches. I have seen and experienced far more switch failures then regulators. As far as voltage consistency I just can't see where you are coming from. A LiFe battery right off the charger is around 7.2V it does not drop off that peak voltage as quickly as nicads would so flight 1 may be at 7V and each flight after will be about a 1/4 volt drop. With a regulator the voltage my servos see is a constant 6V and is verified by telemetry. My TX is set up to give me an audible if the voltage drips .2 volts. Hasn't ever happened with my regulated setups. It did once on a pylon airplane equipped with a LiFe battery while dropping the gear ( Electric retracts ). Almost all pattern and IMAC pilots are running regulated systems, there is an obvious reason. This all really has nothing to do with this thread however except Dirtybird claimed that a regulated Lipo setup can be the cause to a twitchy throttle servo but has yet to answer the question to as how. My question to you Pete, have you used both power setups in a competition environment to come to your conclusions?

dirtybird

My Feedback: (5)

OK speede,I have to admit you are right about one thing. I don't buy a Chinese toy and go up and do the same thing all day. If I did I sure wouldn't have a lipo in it. They are temperature sensitive as well as fragile. If one decides to blow that plastic case would not contain it.
In talking to the world class flyers in my club, they say they can tell the difference in the servo res ponce in the 1/2 volt difference in their servos when the A123's degrade in a flight. So they use a lipo and a regulator. If you are in that case OK. 99 percent of the rest of us are not.
If I were, I could design a better regulator and still use A123's.
BTW I have never seen 7.2 volts on my A123's after they were removed from the charger.They quickly degrade to 6.6V.They would do so while you taxied out.
You say LIFE, are we talking about the same battery? A123's are an LIFE but they are different from the ones called LIFE in ads.
Another thing, Pete is using two batteries in parallel. Thats 5AH. not 2.5.
And I differ about switches. A regulator can never be as reliable as a simple switch. If you are worried about the switch just don't use one. Get a deans plug and just plug it in.

speedracerntrixie

My Feedback: (29)

Dirty, I have no doubt that you are a highly educated man and in most cases your theories are correct however what good are theories without application? There are thousands of high powered electric airplanes out there pushing Lipo batteries far harder then using them as an RX battery. Pulling 70 amps from a 30C 5,000 mah pack is certainly going to get the battery hotter then the packs ( dual 5,000 mah packs = 10 amps total ) that sit 10" above the headers in my Fiberclassics ( Not Chinese made ) Extra. I think your perception on Lipos may have been correct 10 years ago but advances in the technology and more importantly the chargers have made them much safer. Is my setup right for everyone? Certainly not. Would I tell anyone that anything other then my setup is a mistake? No. Fact is that different people with different airplane have different needs and that will drive what they use. So please back to the question I had asked in the first place, How does a lipo/regulator power system create and issue with a jittery throttle servo? That is what this thread is about is it not?

Limitless Aero

My Feedback: (17)

The vibrations will strip a nylon gear servo over time on a big gas plane. Its not really about the torque for me more about speed and accuracy and durability. Why risk several thousands on a big gas plane to save 40$ on a servo.

dirtybird

My Feedback: (5)

The internal resistance adds to the internal resistance of the battery. As other servos move the current required running thru the resistance causes the voltage to drop. Other servos might respond to change in voltage and dither slightly. The whole system becomes unstable and you notice it on the throttle servo. There have been other cases where an aileron servos dither and you notice it there. A lot of people think its rf interference.
Remember there are a lot of regulators of questionable quality being used. I expect it would not happen with your Smart Fly.

On an other matter:
I just use a standard servo on the throttle. I dont remove the spring on the carb. and just use a cable to pull it open. With a standard servo the spring does not have enough pull to overcome the friction of the gears so the current required is negligible.It saves wear and tear on the gears and there is no slack in the system. Works for me. You are free to do whatever you like.