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Old 09-12-2019, 10:08 AM
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Question
Throttle servo set up

When using a spectrum servo, would you program neutral on the servo to be at half throttle on the carb then set forward throw for full open and back throw to throttle off. Then bind receiver at low stick so it returns to off position in the event of fail safe. Watched some online vids of throttle set ups to maintain linier response but no one talks about servo position to start from.
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Old 09-12-2019, 10:58 AM
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binding is a separate function from set up. once you get the throttle set up properly and the idle established, then rebind so the failsafe is set.

the way to achieve so called linear throw is for the servo arm to move in the same plane as the carb arm, and that's rarely the case. works just fine if it isn't.

there's multiple ways to do throttle set up, mine is to center the throttle trim, make sure the travel adj is at 100 in both directions, and close the carb. then try to get the throws as close as possible without needing to add or remove too much from the starting point. for example I may need to go to 115 to fully open the carb and drop down to 93 to get a good idle. I use the travel adjustment to set the idle, not the trim. the tricky part is finding the right hole on the arm - the Goldilocks quest so to speak.
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Old 09-12-2019, 12:59 PM
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I attach throttle arm to servo, mount servo on servo box and attach linkage. all before servo box is permanently attached to fuse then cycle through set points and travel with servo box loose. gives me the ability to get the optimum 1:1 stick/carb control and box located then glue in place
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Old 09-12-2019, 04:11 PM
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If I'm understanding the first post correctly, I think I'm doing it very similar to that.

With throw values at 100%, I set throttle stick, and servo arm(center the servo also), to as close to the half-way/center of throw as I can.

I also find the mechanical center of throttle arm on the carb... as close as I can tell... and that's where I get the basic length of pushrod I'm using.. to match the mechanical centers.

Then yeah, I start studying what the end-points should be, and dialing in the end-point throw... of each, high and low throttle. I try to get to the pushrod position on the gives me near 100% throw in the end-point range I'm looking for.

This gets me in the ball-park to electronically adjust it, and still seems to give the servo a good range of movement. It's been a way to start the engine and go from there... and if a curve is needed for a more linear throttle feel, I can address that also electronically once I've ran the engine and see where it's at. If that all makes sense. It seems to work decently.
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Old 09-13-2019, 07:31 AM
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Thanks All, I think I'm Close. I programed center on the servo, mounted in the servo box, set the arm on the carb to center, held the servo box in place and adjusted arm to fit on at that point wile holding the servo box were I was planning on mounting it. Then mounted the box. was close at that point but had a little buzz out of servo at low throttle, adjusted low travel just enough to stop the buzz. now my high is 100% and low is at 89%, May mess with it some more with servo programmer to reduce the throw as opposed to using travel ajust in radio.
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Old 09-13-2019, 12:07 PM
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That sounds about right... probably about where I end up as well.

From what I'm thinking, if the throttle servo is right around 100% travel.... give or take 10% or so... there's more/better resolution to be had... incremently better in some form anyway.
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Old 09-13-2019, 12:50 PM
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Old 09-13-2019, 01:24 PM
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Originally Posted by jersey flyer View Post
Thanks All, I think I'm Close. I programed center on the servo, mounted in the servo box, set the arm on the carb to center, held the servo box in place and adjusted arm to fit on at that point wile holding the servo box were I was planning on mounting it. Then mounted the box. was close at that point but had a little buzz out of servo at low throttle, adjusted low travel just enough to stop the buzz. now my high is 100% and low is at 89%, May mess with it some more with servo programmer to reduce the throw as opposed to using travel ajust in radio.

Set the way you are, don't be real surprised if you have a hair trigger throttle (some have described it as an on/off switch) below 1/2 stick and not much going on above 1/2 stick.

You need to realize that the butterfly carb on a gasser is making just about all the power it's going to at about 60% open. The trick is to spread that 60% throttle arm travel out across 90%+ of your stick travel. Check out the above illustration to see how that's done mechanically, or plan on setting up a throttle curve to do what needs to be done electronically.

And last, when setting your wide open travel limit, there so little going on in the last few degrees, there's no point in fully maxing your travel right to the stop. Leaving a little slop there will be MUCH easier on your servo.
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Old 09-13-2019, 01:28 PM
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Interesting.
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Old 09-14-2019, 07:56 AM
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Originally Posted by AHicks View Post
Set the way you are, don't be real surprised if you have a hair trigger throttle (some have described it as an on/off switch) below 1/2 stick and not much going on above 1/2 stick.

You need to realize that the butterfly carb on a gasser is making just about all the power it's going to at about 60% open. The trick is to spread that 60% throttle arm travel out across 90%+ of your stick travel. Check out the above illustration to see how that's done mechanically, or plan on setting up a throttle curve to do what needs to be done electronically.

And last, when setting your wide open travel limit, there so little going on in the last few degrees, there's no point in fully maxing your travel right to the stop. Leaving a little slop there will be MUCH easier on your servo.
Yes, I have seen much about how the throttle does not do much for rpm change at a certain point. when I get the plane all rigged up I'll fire it up and see how it acts at the upper end and ajust from there, really don't want to put a throttle curve in if I don't have too. I have a 35cc edge I bought used last month that has a hair trigger throttle now that I need to change. All the power is between off and half, real touchy off the bottom.
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Old 09-14-2019, 08:26 AM
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Most of the time, the servo arm hole distance from center of servo output shaft, needs to be a small distance.

If you use a long arm, then you end up with a very poor resolution
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Old 09-14-2019, 08:43 AM
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Originally Posted by jersey flyer View Post
Yes, I have seen much about how the throttle does not do much for rpm change at a certain point. when I get the plane all rigged up I'll fire it up and see how it acts at the upper end and ajust from there, really don't want to put a throttle curve in if I don't have too. I have a 35cc edge I bought used last month that has a hair trigger throttle now that I need to change. All the power is between off and half, real touchy off the bottom.

Yes, so you already know what's going to happen on the second plane. The same thing. The setup is "flyable", but nice landings are nearly impossible due to the plane's tendency to balloon when adding throttle, and as regarding an Edge, all of that plane's outstanding low speed handling is left on the table due to the fact good throttle control is so important to get the low speed handling/control that plane is famous for (when set up correctly!).

Good throttle control is so important a lot of us will start with a mechanical setup similar to the illustration above, then add a throttle curve to trim as necessary.

If you do decide to try that mechanical setup, the top section is for illustrating purposes only. If you set up that way, your idle and low speed cut off will be difficult to set. Start with the second section. That will give plenty of the differential you're after to do what needs doing.
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Old 09-14-2019, 08:57 AM
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A very basic approach to a transmitter throttle curve is that 1/3 carb opening is about 1/2 power. When setting up the linkage with the carb and servo arms always parallel, a decent starting point on a transmitter is around 35% carb at the 50% point on the throttle stick and the 1/4 and 3/4 points about half between each of those points. Sound confusing? Look at your throttle curve in the radio and read this again. Start there and fine tune as desired. Fighting a gas engine set with a 1:1 ratio (no curve) isn't fun after a while. All of your power hits around half stick making the upper half useless and reduces smooth and easy flying. At first it's "cool" as the plane feels overpowered but the "new" wears off when you figure out there's nothing left on the high side.
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Old 09-14-2019, 09:02 AM
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Pretty much everyone I know sets up their throttles to be sensitive on the low end. It affords much greater control at low speed especially on landings where sometimes all that is needed is a blip. And this is true regardless of the aircraft type - including the Edge to which I am quite familiar. In many years of competition and thereafter I have never needed to setup a throttle curve.
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Old 09-14-2019, 09:15 AM
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Pretty much everyone I know sets up their throttles to be sensitive on the low end. It affords much greater control at low speed especially on landings where sometimes all that is needed is a blip. And this is true regardless of the aircraft type - including the Edge to which I am quite familiar. In many years of competition and thereafter I have never needed to setup a throttle curve.

Some like flying a sensitive setup, but thinking many more don't. That's why they use tools like expo - for those that don't want to fly with the precision finger control a brain surgeon requires.
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