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  1. #1
    thailazer's Avatar
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    Exponential versus Linear controls

    Had a breezy day yesterday for flying so spent some time experimenting with the transmitter programming. Ended up with 30% exponential on the elevator but linear control on the ailerons. The plane felt unresponsive with the exponential cranked into the ailerons and I am wondering how others end up programming. I usually fly a fairly slow approach to flare so having the ailerons respond right away felt better.

    Had one flight where I accidentally set the elevator end point (up) to 20%. Noticed it right away but it made for a rather tense approach and landing! Have to be more careful when changing settings.
    Tiger Flyer #49

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    RE: Exponential versus Linear controls

    Years ago when I got my first Tx with expo, I was excited about exploring the possibilities. Like you, I found out it is very useful in 'smoothing out' the flying characteristics of almost any aircraft. But with a tried and trusted plane with which you are very familiar, at first it feels like the aircraft is non-responsive. That's because you are so used to the way the plane handles.

    With a new plane however, if you start inputting expo right away, you wind up with a different 'feel'. I'm sure you'll get many good replies to your question. I pretty much have expo on all functions these days but only in the 10-25% range. I know others who use 30-50% routinely. It's all in what makes you comfortable, what works best for a given airframe and how you fly. My best advice would be to dial it in slowly in small increments until you attain the characteristics you are looking for. Take your time and I think you'll find it will ultimately make you a smoother pilot. Just keep in mind every plane is different.

    Best of luck!

  3. #3
    Moderator BarracudaHockey's Avatar
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    RE: Exponential versus Linear controls

    All depends on what you're flying, and how you want to fly it.

    If for example those ailerons had more throw for flying 3D then you may very well need expo and low rates to land smoothly.

    About 20 percent expo is actually linear control response because a round servo wheel moves the surface more around center than it does at the extremes anyways.
    Andy - Helicopter Forum Moderator
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  4. #4
    Lnewqban's Avatar
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    RE: Exponential versus Linear controls


    ORIGINAL: BarracudaHockey

    About 20 percent expo is actually linear control response because a round servo wheel moves the surface more around center than it does at the extremes anyways.
    How the percent expo affects the deflection of the control surface?
    Lnewqban - "God will not look you over for medals, degrees or diplomas, but for scars. He has achieved success who has worked well, laughed often, and loved much." - Elbert Hubbard

  5. #5
    MinnFlyer's Avatar
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    RE: Exponential versus Linear controls

    removed
    Mike B. AMA# 42400 www.gettingairborne.com
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  6. #6
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    RE: Exponential versus Linear controls

    Thanks, Mike!

    I had not read that article of yours before, is very good.

    However, the percentage is what I don't understand well.

    I guess that basically the deviation from the linearity can be more or less, depending on how much percentage is input.
    Lnewqban - "God will not look you over for medals, degrees or diplomas, but for scars. He has achieved success who has worked well, laughed often, and loved much." - Elbert Hubbard

  7. #7
    MinnFlyer's Avatar
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    RE: Exponential versus Linear controls

    Correct
    Mike B. AMA# 42400 www.gettingairborne.com
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  8. #8

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    RE: Exponential versus Linear controls

    I too used to think like Barracudahockey, until a little more thought took place...granted the servo disc promotes a non linear response to the pushrod, but the horn on the control surface also move through an arc, centred on the hinge line. The total response of the system is still linear, ie the surface moves proportionally to stick movement. Expo, as advised above, provides a non linear surface response to stick movement either from the middle or the end depending on requirement.
    Evan, WB #12.

  9. #9
    MinnFlyer's Avatar
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    RE: Exponential versus Linear controls

    Pimmnz is also correct
    Mike B. AMA# 42400 www.gettingairborne.com
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  10. #10
    thailazer's Avatar
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    RE: Exponential versus Linear controls

    MinnFlyer.... That is a nice article. I did notice though that you didn't get into hyperbolic cosine functions to explain the rotational servo arm effects! Showing the A-B-C bar graphs gets the point across well.

    Augie11.... I agree with you about the "feel" issue. I made the changes after a lot of time on the Tiger 2 so it was bound to feel odd. The kinesthetic sense we get about our RC ships is pretty amazing. After flying a while, we know how much reserve lift there is, how it is flying, just as if the stick pressures are changing although they aren't! Years ago, the owner of the full scale Twin Otter my Scalemasters replica was based on saw me fly and he invited me to get some stick time in the real one. The full scale Twin Otter had the same "feel" or sensitivity as the model did.

    Tiger Flyer #49

  11. #11
    MinnFlyer's Avatar
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    RE: Exponential versus Linear controls

    I specifically kept the article from becoming too technical. Someone doesn't need to be a math genius to understand the basic concept.

    BTW, I pulled the link because the article is not finished yet
    Mike B. AMA# 42400 www.gettingairborne.com
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  12. #12
    thailazer's Avatar
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    RE: Exponential versus Linear controls

    MinnFlyer..... Let us know when you get it done. The layout is very clear and concise.
    Tiger Flyer #49

  13. #13
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    RE: Exponential versus Linear controls

    I was wondering how could I have missed one of Mike's articles!

    Returning on the exponetial........while driving home I was thinking that:

    If the expo does not change the start and end points, i.e., the range of the control surface deflection, then, the sensibility that is lost around the central point of the stick, must be amplified for the last portion of the deflection.
    For higher percentage, that difference should be more noticeable.

    Is that incorrect?

    (Sorry thailazer, no thread hijacking intended.)

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    Lnewqban - "God will not look you over for medals, degrees or diplomas, but for scars. He has achieved success who has worked well, laughed often, and loved much." - Elbert Hubbard

  14. #14
    MinnFlyer's Avatar
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    RE: Exponential versus Linear controls

    Yes, the more you add, the "softer" the center becomes.

    What's important is that at the ends, you always get 100%
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    Mike B. AMA# 42400 www.gettingairborne.com
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  15. #15
    Lnewqban's Avatar
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    RE: Exponential versus Linear controls

    Thanks again, Mike!
    Lnewqban - "God will not look you over for medals, degrees or diplomas, but for scars. He has achieved success who has worked well, laughed often, and loved much." - Elbert Hubbard


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