The subject line might be misleading as I have read a number of threads on this but I have a different question. I ran Sullivan Gold-n-rods to both the choke nd throttle from the servos. I am using Futaba 9202 servos so I had plenty of torque. I have the choke adjusted to an on/off switch and it works fine.........forgot to mention that I have ball-joints on both ends. I set the end points of the throttle until I reached the full travel both ways for the throttle. When the throttle is wide open I get a buzzing at the servo. When I adjust the end point to where the servo stops buzzing I then shut the throttle fully off and when I re-open the throttle I can push the carb throttle arm further to fully open the throttle.........when I adjust the servo to hold this position, it starts buzzing again. I have put on a heavier duty (Dubro) servo arm to prevent any distortion because the standard Futaba servo arms wanted to twist when operating the throttle. The rods are supported in several places so there is no flex that I can determine. The spring is on the carb throttle arm as it arrived. So why is the servo buzzing at full open throttle? Yes I tried another servo.

thanks,
Andy

Andy, where are your ignition components in relation to your radio parts? They should not be near each other. That's switches, wires, batteries, everything. Do you have another ignition module that you know is good? Dan.

Dan,

The ignition module is not in the plane yet. I am just installing stuff. I have two switches and the battery for the ignition is next to the engine and the battery for the radio is back by the servos. This is a big plane.....GP PT17 Stearman. All ignition components will be in front of the firewall except the switch and tach. I am installing a Smart Fly Optical kill switch but the transmitter for that is back by the receiver and the receiver for the kill switch is also forward of the firewall. Any wires from the ignition going to the tach and switch will be shielded by copper tape and grounded to the engine block, other than that all ignition components are together and 12" or more from the receiver and servos.

Andy, you have described a perfect installation. Since it is happening with two different servos, the common element is still in the plane. Could it be good old fashion vibration getting to that one servo mount? How about some images from several angles. Is your receiver mounted on foam? I know that Futaba discouraged a complete foam wrap at one time but on one side it will be OK. By the way, I have my Futaba receivers smothered in foam and flying well in 95 degree temps often. Dan.

Again Dan............the plane is not complete so the engine is not running. All that is installed are the servos, the engine and the two control rods going from the engine to the servos. I'm thinking there is some kind of physical strain going on but I can't figure what it would be. The servo is mounted to hardwood with the usual grommets in rubber but that's all. I've set the endpoints both equally from center so there is no adverse travel for the servo.

Odd's are your past the end point of the throttle butterfly just a little bit. Just back the endpoint up till there's no buzzing. Once you fire it up you will find the wide open, by rpm's, is far short of wide open at the butterfly.

If your throttle linkage requires a heavy duty servo arm and the servo is buzzing I would suspect that there is a significant amount of drag in your throttle linkage system.
Some servos briefly emit a nearly inaudible buzz as they stop at a null point or they may continue to buzz slightly if they feel a mild resistance from the throttle return spring. I don't know if a throttle spring can be powerful enough to bend a servo arm but you can disconnect the spring (don't remove it from the shaft) to find out if it is causing the buzz.

+1
Your described approach to setting up the throttle servo and linkage is perfect for a glow engine for which the response is linear. Not the same for gas. Install all the components get her running and make adjustments from there.

Plus two,set your throttle up well mechanically with the servo end at it's innermost point on the arm and the throttle linkage at it's outermost point on the arm.If you can't get full throttle barrel movement then adjust from there.Trims/subtrims and expo are a last resort.

This image was originally posted by JediJody

I think this is one of the best piece of informtion available to someone who is new to gas engines. I have been able to set up and operate my gas engines without the need for throttle curve by using this geometry.
DaleD
<br type="_moz" />

9202 servos are known to buzz with even the lightest load on them so I wouldnt worry to much about the buzz . I would suggest inspecting the geometry of the golden rod setup . It my be that at WOT the throttle arm or the servo arm have a side load place on them from the location of the golden rod, does the golden rod have enough side to side movement to travel with the arc of the arm travel without binding ).
If there is no apparent binding visible check the servo with an ammeter , if the current draw spikes at the end off travel at WOT or idle then reduce your ATV or end point adjustment untill the current draw drops off . If you get the ATV set to where the current draw is the same at any position between idle and WOT and the servo still buzzes then I would consider it a normal condition for the 9202
I have used the 9202 for many years and it is common for the servo to buzz while supporting the weight of a control surface or with any side load from linkages.
Invest in an inline ammeter that plugs in between the servo and the receiver . It will be a great asset in setting up your planes to use less battery per flight and may possibly save an airplane from the dreaded brown out from an overloaded servo.

Thanks to all that responded. I printed out the info above and will use it when the plane is complete and is running. Learning new things at 70 is a bit frustrating.......especially moving from a lifetime of glow engines to gas...........but I guess it keeps you young and a bit smarter before taking your dirt nap......................

Dale. I have always questioned the use of this chart. IMO when one sets up this way you will have close to full RPM by the time you hit half stick. My question for you is if you are running at full stick and back off just a tad do you see an RPM decrease? I have always set up my gassers so that the throttle servo has equal travel above and below 1/2 stick. Then I set the pushrod length so that at half stick the carb butterfly is approx 1/2 open. Any other adjustments are easily accomplished with a throttle curve on the TX. The goal is to slow the application of throttle from 1/2 to full in order to sperad out the throttle response over the whole stick movement. I think the chart defeats this. The benifit I do see with the chart is that the power comes off idle slowly and that can be of use for a newbie but it wrecks the rest of the throttle curve.

Buzzing is common in coreless servos. The noise is the result of the servo constantly trying to hold its' position. Nothing to worry about.

Andy, I know you said it twice already but I'll say it again for you. He has not yet run the engine on this plane.
I think you answered your own question by stating that the servo arm bends. It should not bend even with a standard servo arm. I think you have a bind somewhere. I would disconnect at the servo end and operate by hand and see how it moves. It should move easily and not require much torque. I use old S148s on throttles.
I don't know how stiff the return spring is on your engine. You can disconnect it, but not remove it or stretch it out some so it is not as tight.
You don't need much servo travel to operate a throttle on gas engines. Mine are almost always on the first or second inside hole.
There is not much rpm change anyway from half butterfly to full open on gas engines anyway so use care when setting your end points on throttle as you really don't need to "slam" it full open.

Duplicat post. Crap.
</p>

yes disconnect the spring,just take it off the arm dont take it off the carb,the servo is overworked with spring hooked up.

First, it needs to be noted this chart is promoted by somebody that has likely forgotten more than I'll ever know, as well as many other well seasoned expert flyers. Second, the fact our gassers are pretty much "all in"/developing 100% available power by time the butterfly is half open also need to be acknowledged. That diagram even helps illustrate that by the fact the carb arm is not moving through a full 90 degree arc? It's only moving through 65 degrees. The fact this works fine is not hard to back up. Some time spent on a test stand with a tach should verify it pretty easily. There's nothing going on through that last 1/3 or so of the throttle arms travel.

So, if the carb's arm is set up to move through a 45 degree arc on the bottom half of the sticks movement (like a nitro engine might be set up, 1/2 travel below, 1/2 travel above) you end up with better that 2/3 of the gas carbs usefull travel below half stick (45 degrees vs. the diagram's 21 degrees), thus making the throttle very (too) sensitive below half stick. Granted, that can be straightened out using your radio in many cases, but I think the point here, is that set up as that set up per the diagram, there's either no or little need to do that. It is obviously a matter of personal taste, but that chart's setup is a pretty good plan....

I have always set up my gasser throttles with differential though not quite to the extreme shown in the diagram. I prefer to have a fair amount of adjustment towards idle so I can adjust the end point there and allow for a throttle cut at that end of the travel. As a result, my servo arm is not parallel to the servo body at idle but at maybe 20 degrees or so. I've always found that differential prevents the "toggle switch, on or off " effect that gasser throttles can have if everything is set at 90 degrees as you would with a glo engine. In many cases, with mechanical differential, no radio throttle curve is necessary. I did this long before our radios had a throttle curve available in aero mode.

As for the throttle springs overloading the servo ...... that has long since been debunked. Use an amp meter and measure how much your throttle servo draws to overcome that minor spring tension from the carb. It is minimal at best and far less that what any servo draws on a flight surface. I see no reason to ever disconnect a throttle spring and in fact can think of quite a few reasons to leave it in place. This is just another one of those subjects that has been discussed until the horse was beat to death. Quite a bit of real info out there if one is willing to do the searches so I will leave it at that.

The main thing about any gasser throttle is you NEVER have to adjust either servo endpoint to a stop resulting in a servo stall / overload. At a stop servos can and do fail from electrical overload, motor failure and even gear failure. This is the main reason so many people insist on metal gears for a throttle servo .... poor installation!

Well here we are again. I am not trying to knock Jodi however the statement that the engine is developing full RPM when the butterfly is just half open in just plain wrong! As far as backing it up, I suppose you refuse to acknowledge my multiple wins in IMAC as proof that my setup does work. I realize that you are not up to that level and my never be but perhaps one day you will stop being a follower who just spits out what your preceived expert has published and open your mind to other ideas that also have a proven track record. As far as I know Jodi or TOM were not competive pilots. Once you get to a certain level and expect more from your setup it highlights areas that need work. Throttle curve is one of them. It's a case of you don't know what you don't know.

Pretty proud of yourself aren't you? So proud you bring absolutely no logic with you to your discussions... while telling us Jodi (and the rest of us that do see the logic behind using this chart) don't know what we're talking about?

I'm just a retired old man. Will never be able to compete on your level (can't afford to for starters!), but generally I have an open mind and I do fly several gassers. So without telling me how good/smart you are again, convince me I should go with your 50/50 setup. If you tell me it's because I can do everything that needs to be done in the radio, you've managed to completely miss the point, again.

All of the above is why I run mine first. Let's me see where no throttle to full throttle is actually at. Then after marking this point I set my linkage up for that amount on movement.

Truckracer,
I agree on the extreme level and do the same as you do with the servo arm (never measured how much) for the same reason. I think it's the point that matters here though. Understand that and you're good to go? -Al

AH, I see the logic. My guess is that the graph was published because Judi got too many calls from guys who were complaining that the throttle was coming on too fast at the bottlon of stick travel. This was causing all kinds of problems because when the power came on quickly the airplane would become difficult to handle. This is actually an issue with airplane setup more then anything. If the airplane is set up so it reacts alot to airspeed changes then yes having the power come on quickly is an issue. If the owner of the airplane has taken the time to properly trim his aircraft then it is less of an issue. So Jodi was smart and realized that most of his customers are sport pilots who would prefer the power coming on slowly and because most sport pilots do not use the throttle to the same degree as a competitive pilot then this would be the lesser of the two evils. Take your airplane and perform a rolling circle with a roll every 120 degrees and reverse rolling direction after each roll is complete while trying to maintain ground speed and a round circle in front of judges and you will see how important it is to have throttle spread out over the intire stick travel. If throttle curve was not widely used then the radio manufactures would not have included it in the firmware. If you are happy with what you have them by no means am I trying to get you to change. What I am trying to do is when the question arises I am trying to share information that I have learned over the past 15 years as a competitive pilot that will make anyones airplane operate just a little better. If he choses not to do so then fine but why do you insist on browbeating anyone who illistrates a different approach? Sounds like you are the one with an issue not me.