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Setting up throttle servo

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Old 08-23-2003, 02:11 AM
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Dylwad
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Default Setting up throttle servo

Okay, this may be a dumb question, but im going to ask anyway. im setting the throttle up on my UCD3D, Jr 549RX futaba s3101 servo, os70 surpass, my question is which part of the throttle is more sensitive to stick movement? Do you have finer control of RPM on the idle-half stick range or from half stick-full throttle range? if i set up the closed side of the servo travel first i have coarse control over the throttle from idle-half and finer control from half-full because i have to turn the high ATV down, but if i set it up from full throttle i have to turn down the idle ATV respectively, and have finer throttle control on the bottom half than the top. Hope this makes sense... its a JR-X347 radio, so the throttle trim only works on the bottom half of the throttle stick.

Im guessing i want the finer control below center, so i should set the top end first.

I was also thinking of going in a hole on the servo arm and turning the ATV up-this would cure the half***** expo im seeing



What do you guys think?

Dylan
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Old 08-24-2003, 08:15 PM
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strato911
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Default Setting up throttle servo

Since I started out with radios which didn't have end-point adjustments, I am in the habit of setting up the throttle manually for the proper throw. It can be difficult sometimes, but I've always managed. I recommend settings your end-points to 100%, then get as close as you can by adjusting which hole you use on the servo, on the throttle linkage, and even what part of the servo's arc you use.
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Old 08-25-2003, 01:29 PM
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Darryl Usher
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Default Setting up throttle servo

Use 100% servo travel, set low almost over center on the arm as the engine is most sensitive at closed throttle.
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Old 08-25-2003, 07:55 PM
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hilleyja
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Default Setting up throttle servo

The simplest solution I have found with a computer-controlled radio:

1.) Manually set up the throttle the same way you set your other servos, i.e., center the throttle servo to the center position of your thottle arm (I eyeball the hole in the carburetor to about middle).

2.) In most of my configurations after I complete #1 I need to adjust my high and low endpoints to some point below 100% -- with my trim in the middle I look for just slightly open.

3.) I refine the above by adjusting the control rod manually until my endpoints are equi-distant, e.g., high endpoint is 70% and low endpoint is 70%.

4.) Now you can use the radios's sensitivitie's adjustment (expo) to modify your throttle curve to the way you like it. I strive for linear control -- I keep adjusting the expo until it sounds like my throttle goes from idle to full in a linear fashion.

It's worth the time and effort you put into this setup.
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Old 08-25-2003, 08:21 PM
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Dylwad
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Default Setting up throttle servo

Thanks for the replies, im used to setting up the throttle servo without endpoint adjustment, so thats not a problem. i dont have throttle expo on my radio, but it does have a feature where the throttle trim doesnt affect the throttle position when its above half stick, which can give it a sort of expo because when you adjust the endpoints it gives non-linear servo travel. I think what its going to come down to is how the plane flies, ill try a few different methods untill i feel that the throttle responds like it should, like if i get into a point that it wont quite hold a hover at half stick, but one click more throttle its climbing, ill make it less sensitive at half stick.. make sense?


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Old 08-26-2003, 11:44 AM
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Default Setting up throttle servo

Your original question suggests that you understand that the throttle should be less sensitive near it's low range.
That's true, and is important because very small throttle adjustments are preferable during the landing phase in order to barely change the engine speed to adjust for proper glide path.
If the throttle is too sensitive at the low end, you'll end up porpoiseing in because of the aggressive throttle changes.

If you don't have exponential available to you from the radio, set it up mechanically as per the following "sort of" diagram.

Like this:

|
|
|
|
+
+
+
+
0

Assume the engine is directly above the straight lines, the straight lines represent the linkage, the +'s are the servo arm with the 0 being the pivot point of the arm on the servo, and that the position everything is at is at engine idle position.
You can see that as the servo turns (advances) to the left, it is going to move the linkage back very little; it's more pushing it to the side. That's what you want. After about 1/4 throttle or so, the throttle movement becomes more pronounced.
This is how you get mechanical "exponential" on the throttle at the low end without a computer radio.

EDIT: The message software strips away intentional spaces that I placed in the above diagram so it doesn't look like I intended.
What it's supposed to have shown is the straight lines as they are, but with the +'s and 0 angling very slightly off to the right (I put one space additional in each line).
Just imagine beginning with the first +, that the +'s and 0 form a straight line but angle slightly down and to the right (just slightly).

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Old 11-17-2003, 12:48 PM
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sizam
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Default RE: Setting up throttle servo

Wow, I had no idea I should invest any time in setting up the throttle servo besides making sure it opens/closes all they way and a kill setting, I guess I'll have to futz with my expo now around low. However, if I'm planning on experimenting with Hovering/Torque rolling for the first time should I set some expo in the upper end to make it less sensitive as well so I can get the right amount of thrust?
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Old 11-17-2003, 03:03 PM
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Default RE: Setting up throttle servo

ORIGINAL: sizam

Wow, I had no idea I should invest any time in setting up the throttle servo besides making sure it opens/closes all they way and a kill setting, I guess I'll have to futz with my expo now around low. However, if I'm planning on experimenting with Hovering/Torque rolling for the first time should I set some expo in the upper end to make it less sensitive as well so I can get the right amount of thrust?
It depends on too many variables, the best method would be to fly the plane, and see what it needs. also make your throttle linkage as slop free and smooth as possible, and ive been told by hitec not to use a servo smaller than hs-81 size on a throttle, the smaller park flyer servos werent designed for the vibration~some people have had good luck, some have not. i used a futaba mini, more precise than a hitec servo. Also the bigger the engine doesnt really mean it needs a bigger throttle servo, i dont see why a servo with 30+ oz in of torque wouldnt handle the throttle on any engine. Another trick i do is to use a dubro heavy duty servo arm on my throttle servo, and use a dubro ez connector. the thickness and width of the heavy duty arm prevents the ez connector from swaying side to side, adding slop.

Sorry i just kind of answered your other thread....

Dylan
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