OK this is a weird one...

I have a EF yak 74" with a Brillelli 36GT. Have about 1.5 gallons through it...so about 15-20 flights. Yesterday I noticed something really weird as I was coming out of a blender. It sounded like my engine was reving up and down. I was able to land no prob and killed the engine at the end of rollout. I checked over the plane and saw nothing loose. I am running the Spektrum AR7000 and a Hitec MG225 servo on throttle. There seemed to be nothing wrong as I moved all my control surfaces and the throttle. So I started the engine and it was running rough. But actually I found the throttle servo "glitching" through its idle to half throttle range. I had some control over the throttle but it continued to twitch. There were no loose wires. I re-binded the Spektrum and did a range check..still had the problem. I have never had a problem before. I don't think it is RF interference since it just started and I have so much flight time on it with no problems at all. Any suggestions as to the most effecient and cost effective way to diagnose and treat this problem?

Thanks mark

Yeah, swap out the servo. If that solves the problem, then you had a bad servo. If it doesn't, start checking for mechanical noise from the engine or throttle linkage. Good luck with it.

Dr.1

in my deal i usually find my 225 on the choke go out every so often so i am just left that servo along this last time it went out on me last month....

I had this problem and it turned out to be a bad electronic ignition module. For some reason it only affected the throttle servo (a relatively low cost analog servo) while the digital servos in the plane were unaffected.

How close is your throttle servo your ignition wiring?

My throttle servo is about 6 inches from the ignition module. The throttle-serov connection is via the carbon flex rod sold from TBM. I am going to try a few trouble shoots today.

Hope I can figure this out.

Mark

Forgett all the diagnosise of the position of the wires to the throttle servo, you are using a system that does not accept RF interference, it can only be direct electrical spikes through the wiring or a bad servo. My guess is a servo gone down, the amount of vibration comming throgh the operating rod too the servo and the heat etc, is going to cause a throttle and or choke servo to go occasionally. I tend to use an Analoge coreless for both and change them at the end of each season.

Mike

A coreless servo is a bad choice for a throttle servo. The delicate armeture is very sensitive to vibration.
Chose a servo with dual ball bearings and a three pole motor. Nylon gears are probably best as they would tolerate vibration better than metal.
Take a look at the digital sport servo. It would probably give you the best operation and reliability.
As for the interference go to 2.4 ghz and forget it.

This is where you and I will dissagree and you also disagree with Quique who I think knows a thing or two, QS recommends not to use a digital servo as its constant reference to its certre or operational point will drain the battery as most petrol engines have sprung throttle levers, oh yes I used coreless servo's in my competition helicoptors for years prior to digital servo's appearing, so I think the vibration issue is a non starter.

But I agree about 2.4Ghz

Mike

Is it better to place the throttle and choke servos in the fuse, rather than in the engine box where it is subject to higher vibration and temp, plus RF interference from the ignition module? Thoughts?

He is on 2.4Ghz so is not getting RF interference. Oh yes just remembered Hitec 5955TG's are coreless.

Mike

Yes I do dissagree. A coreless motor cannot be made as rugged as a cored motor. They are not made in larger sizes for that and other reasons. Take a look at a drawing of the coreless motor. Note that the armeture is cup shaped and only supported on one end. It also has no metal core to serve as a heat sink. Its much more likely to burn out if stalled.
The extra current drawn by a digital on the motor control will be negligible compared to those 5955 servos on the controls. If it bothers you get a programmable from Hitec and open the deadband.
As for Quique, I realize he is a great flier but I think he is wrong about this. Its just too little current to worry about unless you stall the servo. Then you would be in trouble with any servo.
When you say you have been doing something for years and have had no trouble I have to think of the guy who said he has been playing russian roulette for years and has never had any problems.

I had same problem with a hitec 5245 on my throttle, changed it out to non-metal digi, no problem. I assume noisy ignition is the cause. dead sticks about drove me nuts till I figured it out. T.

Wow...thanks for all the input. As for servo choice the HS-225MG is an analog servo. I have to agree with QS that a digital servo is not the best choice for a throttle servo on a vibrating gas engine. I was able to run a few tests today and figured it out. I switched the servos connection to make sure that it was not the receiver so I put the throttle in the rudder slot and used that to control the throttle. Still got the glitching. So I tried a different location for the ignition battery...still glitching. I unplugged the servo and and manually adjusted the throttle by turning the servos head. I then plugged a brand new servo into the throttle spot and held it next to my installed throttle servo...IT STARTED TO TWITCH!!!. SPEKTRUM is not imunue to RF noise!!!! I found that the Roy Scholl Ignition module that comes with the Brillelli engine has had some problems with their circuitry. Not a big problem. I called Scott at Brillelli (a wonderful person to deal with) and he is sending me a new CH ignition module FREE of CHARGE. That is excellent customer service. He also took some time to mentally trouble -shoot the issue. I hope this fixes the problem.

Will post the results once everything is installed.

All the reports I have read say that Spektrum is imune to RF noise, I suggest that as only the throttle servo was affected what you where getting was an electrical spike down the servo lead from the ignition. IMO

MIke

[/quote]

Yes I do dissagree. A coreless motor cannot be made as rugged as a cored motor. They are not made in larger sizes for that and other reasons. Take a look at a drawing of the coreless motor. Note that the armeture is cup shaped and only supported on one end. It also has no metal core to serve as a heat sink. Its much more likely to burn out if stalled.
[/quote]

dirtybird,

not made in larger sizes? the Hitec 5955 is a coreless motor servo, its the most powerfull servo for an aeroplane that Hitec manufacture in a standard size heat sink case.

And lay off the platitudes please.

Mike

The 5955 motor is the same size as the motor used in a standard servo. It just has heavier wire.
The advantage of the coreless motor is its greater efficiency. If it could be used in larger sizes than our motors it surely would be.
BTW the JR 8611A I am told uses the same motor that the 5955. You must be very careful not to get that servo stalled or the motor will burn out. The amplifier limits the current in the 5955 to prevent burn out. This limits the torque produced by the 5955 to about 60% of what Hitec claims.
In the late 50's the coreless motor appeared in the RC field. It was called the Micro max in Europe and the Micro Mo in the US. There were a lot of attempts to use it for electric flight. It was just too small to be a great success.

Understand, also the 5955 is not recommended for 7.4 volts unlike the 5995 robot servo which is, or have we said all that before, they say its short term memory that goes first, where did I put my keybo........

Mike

The 5995 is the same servo as the 5955 with different gears. Its a 180 degree servo. It's rated for 7.4 volts for robotic use - not for aircraft use.

The 5955 is also available for 180 deg. rotation.
Ref. information from ServoCity:

"We offer the HS-5955TG servo in several configurations, 90° stock rotation, 180° modified rotation, continuous rotation (potentiometer is left outside the servo case) and reverse rotation. "

I don't know if this is just a programming thing, or if the gears are different from the standard 90 deg. rotation units.

Regards,
Magne

Hey Magne I just returned from a visit to Norway. Beautiful place! I used to live there in the late 50's installing RADARS for NATO. It sure has changed in fifty years. Expensive! It cost me 50kr for a glass of beer. That's nearly $10 US. $300/night for a hotel room. How do you manage to live over there?
As for the 5955 I think they just change the pot to make it a 180 degree servo.

So the problem was fixed. Scott at Brillelli sent me a new CH ignition unit. Removed the Roy Scholl ignition (apparently there has been increased reports of RF noise from these units) and took her to the field. First of all the engine started much easier with the new ignition. There was not a single glitch from the start of the day until a 1/2 of gallon of gas later. Thanks for all the input...But a hugh thanks to Scott at Brillelli engines for great customer service. Problem fixed an ignition unit that was emitting RF noise or eletrical spikes.

Mark

GO EXTREME FLIGHT!!!!

Its so nice to be right. [sm=shades_smile.gif][sm=thumbs_up.gif]

Mike