Throttle Linkage Geometry

[Phil.Griffin]

bob_nj;19618 wrote: How exactly do you mean "skipping" a tooth on the servo Phil?

Bob,

I'll try to explain it. There's a fair chance this'll come out wrong or stupid sounding though...

Stephen Washington (P-Huck) showed me how to do this, and has to explain it to me again every time I set up a new plane.

As I understand it, what's happening is by skipping one tooth forward on the throttle servo, and lowering the low end number, it gives me a little more stick movement than throttle at the lower half of the throttle. And I adjust the top end number to end up with a little more throttle at the top end.

Its sort of like adding mechanical expo I think?

I love to hover, and do other low/slow stuff. In my mind, this set up seems to give me finer control of the 0-50% throttle. I had the pleasure of getting to hang out with Steve for over a year, and I really got used to his set up and liked it. I will say this though. Throttle set ups are very subjective things. (Like most everything else in RC I guess)

There will be folks who think this is crazy, and will swear by a linear setup. And that's fine. You'll just need to experiment around and figure out what's best for you. Good luck with it...

 

[reyn3545]

I usually set mine up where half stick on the transmitter is about half throttle on the carburetor, then I'll adjust the throttle curve by setting points so that each 1/4 increment on the sticks gives me 1/4 of the RPM increase between idle and full speed.



You could do this by simply adding expo to flatten out the bottom a little.



The reason I do the initial setup with the stick and throttle arm at about half is so that I can adjust the low and high ends of servo movement without worrying about hitting the limit on either end.

 

[stangflyer]

reyn3545;19633 wrote: I usually set mine up where half stick on the transmitter is about half throttle on the carburetor, then I'll adjust the throttle curve by setting points so that each 1/4 increment on the sticks gives me 1/4 of the RPM increase between idle and full speed.



You could do this by simply adding expo to flatten out the bottom a little.



The reason I do the initial setup with the stick and throttle arm at about half is so that I can adjust the low and high ends of servo movement without worrying about hitting the limit on either end.

But you can achieve the same thing with end point adjustments. Right? I do with my A9X.

 

[reyn3545]

You can. I don't know if the A9X will do multipoint throttle curves, most radios do. There are at least a dozen ways to skin this cat, none of them are wrong.



People will also point out differences in actual throttle arm movement in relation to the servo arm movement. For example, if your servo arm is at 6:00, and you move it to 7:00, you'll get less throttle arm movement than when the servo arm is at 8:00 and you move it to 9:00... although the servo arm is moving the same relative distance, the forward movement is less in the first movement, so a lot of people want the servo arm near 6:00 at idle. That will give you a "throttle curve" where there's less throttle arm movement near idle.

 

[bob_nj]

Which of the seven servo pictures in my attached .pdf in the first post best represents 6:00?

I have throttle servos mounted several different ways and am curious.





Thanks

Bob

 

[stangflyer]

reyn3545;19695 wrote: You can. I don't know if the A9X will do multipoint throttle curves, most radios do. There are at least a dozen ways to skin this cat, none of them are wrong.



People will also point out differences in actual throttle arm movement in relation to the servo arm movement. For example, if your servo arm is at 6:00, and you move it to 7:00, you'll get less throttle arm movement than when the servo arm is at 8:00 and you move it to 9:00... although the servo arm is moving the same relative distance, the forward movement is less in the first movement, so a lot of people want the servo arm near 6:00 at idle. That will give you a "throttle curve" where there's less throttle arm movement near idle.

Good point. My objective is always the same. Set my EPA's, get my motor running.... find out where the throttle response is in relation to the movement of the throttle plate. Adjust my travel volume, epa and throttle curve to achieve the best possible linear rpm increase over the entire throttle plate movement.

 

[reyn3545]

bob_nj;19724 wrote: Which of the seven servo pictures in my attached .pdf in the first post best represents 6:00?

I have throttle servos mounted several different ways and am curious.





Thanks

Bob

The example on the far right... with the throttle at 53 degrees (closed) and the servo at zero (pointing straight at the throttle arm). would have the least throttle movement at the beginning of the servo movement.

 

[orthobird]

great thread, since it covers a real good topic for discussion.

setting it up is not easy, and takes several adjustments as you go, til it gets right.

i have tried the 1:1 linkage set up, seems to not make a difference.



now, what i do is this:



consider that on my radio, for throttle servo

i can adjust:

center = i leave at 0

max positive end point = i start at 100

max negative end point = i start at 100



before i begin, on the tx, i will set the idle trim all the way down, to in effect, create the full down throttle.



ok, next step, i see which direction is full throttle up on the carb and on the servo direction, and make sure it does not require me to reverse the servo



once that step is done,



then i put throttle stick at middle, and then i place the carb butterfly at like 50% open, based on looking at the position of the throttle arm on the carb. this is an estimate of where i think middle is by gently moving it back and forth and looking at the angles made.



once i do that, i then will move throttle stick up and down and see if there is binding with end points set at 100



if there is none, i prefer to not increase end points, what i will do is change the hole position on the servo arm to the next hole out. or get a servo arm that is longer if it were already maxed out.



ok, if i move out to where it now open up almost all the way, and just needs a little bit, then i will adjust the end points.



ok, lets say, with my servo arm hole, i have to decrease end points due to binding down to 60 or so, then i will use the hole on the servo arm that is one hole closer in, to decrease the throw, and etc.., you see what i mean, i am trying to get end points of 100



ok, lets say, when i am done with my excursion and there is no binding, and lets say my end points are 100 on top and 60 on bottom (roughly speaking), then i will move the servo arm on the spline one tooth over, to try and get closer to same on both sides, so that is it like 80 and 80 or close to that, you can see what i am trying to do here.



it also helps to get the servo arm on the servo at mid stick, to be perpendicular to the long axis of the servo. if most of the throw is more one way than the other, this creates a throttle curve of its own. ( I believe).



ok, this i learned recently, and i have known this fact all along, once the throttle valve plate is about 70% open, seems to me, that movement from 70% to 100% does not increase output of motor (increase in RPM stays same).



but, what i failed to recognize was, that i was setting up my servos so that when it was wide open, and it was barely binding at full throttle, i would back it off one click at a time to stop the buzzing of the servo, meaning, no binding. (throttle valve plate was open 100%) i never took into consideration that once the motor is running and at top rpm, the vibrations were probably causing a binding issue. so now, once it is full wide open throttle, i will now decrease the end point by another 10%, so the throttle does not open up to 100%, but instead, about 90% or so.



likewise, this has not been a problem with the low end, since after set up, the low position is set to open the carb by a bit, to trim the idle. so in theory, i can kill the motor with the trim, if i had to do that. but i also have a kill switch anyways.



well those are my 2 cents

 

[orthobird]

stangflyer;19732 wrote: Good point. My objective is always the same. Set my EPA's, get my motor running.... find out where the throttle response is in relation to the movement of the throttle plate. Adjust my travel volume, epa and throttle curve to achieve the best possible linear rpm increase over the entire throttle plate movement.

this is a great idea to do also, especially with a tach. if at mid stick your rpm is 5600 and at full throttle it is 6000, you will have to make adjustments with a throttle curve.

 

[stangflyer]

orthobird;19878 wrote: this is a great idea to do also, especially with a tach. if at mid stick your rpm is 5600 and at full throttle it is 6000, you will have to make adjustments with a throttle curve.

Basically we do the same procedure. In essence the same result achieved. I think your method may be a little more "pre-set" than mine. I do use a tach which helps immensely. While I see mine just a tad quicker in set up, I think yours may be a little more precise. (I like it) I may have to give your method a try to see what differences there are. Thumbs up dude.....:winking-thumbs-up-s