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How big before multiple servos on a control?

Discussion in 'Beginners' Lounge' started by Bartman, Aug 7, 2014.

   
  1. 7oneWo1f

    7oneWo1f 30cc

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    I've only built one gas plane so far, but another factor may be servo arm length. I built my 91" Extra per the manual, but experienced some aileron flutter using ridiculously strong MP82T (current model is JR MP82T MKII) JR servos powered by 2S, sealed aileron hinges, and no side force generators. These servos are 563.8 oz/in @ 7.4V according to manufacturing specs.



    The lingages are all very tight tight. Horizon is currently looking at the servos, and initial indications are they are good--but one other issue might be the servo arm length I used. I used 2" per the manual, but the new recommendation is 1.75" now from what Chris told me.



    This 91" Extra has large control surfaces for a 50-70cc sized plane from what I understand.





    Anyway, my next plane is a 105" Pau Extra with a DA120, and I'm still trying to figure out how I am going to do the two servos per wing. I think I am going to run both servos per wing to the ailerons, and use a current meter and servo/radio programming to minimize how much they fight each other.



    I'm guessing that this will be a several hour process, especially if I get programmable servos, because there are so many trade offs and I recalculate things a million times it seems, and mechanical engineering and thinking in 3D is not my cup of tea.
     


  2. You'll be surprised...not really than hard to do and you may never get them perfect...I've used programmable Hitechs in the past and JR 8711s on my 37.5 now...get a quad meter to see the amp draw during the entire throw...BoomaRC has a device that auto adjusts to synchronize servos....http://www.boomarc.com/en/im22-intellimatch-dual-intelligent-servo-matching-system
     
  3. Erikv79

    Erikv79 30cc

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    /// Very cool device!///
     


  4. I have one waiting at home. I'll let y'all know how it works next week..
     
  5. Please do jaybird...I was wanting to get some feedback from people that has used it to see if they think it's worth the money.
     
  6. stangflyer

    stangflyer I like 'em "BIG"!

    Mikeq... So is the intellimatch to remain connected to your servos after matching is complete? Or do you remove it? I have never used anything like this before. Just wondering if it would be a good idea to get them. With all my multi servo control surfaces, I set range of throw with each servo then set rest point. After that is done, slight subtrim adjustment in my radio takes care of the last little bit of matching. Have not had any issues at all as it stand. However, am curious if this is the better way to go.
     
     
  7. ericb

    ericb Team WTFO GSN Contributor

    What radio do you have?  The easiest process is to have a decent radio and do it all from there.  
     
  8. Patroller

    Patroller 70cc twin V2

    Mikeq... So is the intellimatch to remain connected to your servos after matching is complete? Or do you remove it? I have never used anything like this before. Just wondering if it would be a good idea to get them. With all my multi servo control surfaces, I set range of throw with each servo then set rest point. After that is done, slight subtrim adjustment in my radio takes care of the last little bit of matching. Have not had any issues at all as it stand. However, am curious if this is the better way to go.
     
    When I setup my EF 104 I purchased the Fromeco quad meter. It shows current draw from up to four servos while you setup the surfaces. If you want to give it a try sometime you can borrow mine. I currently only have one plane that is big enough for multiple servos, but my plans include more. 
     
  9. Since no one has mentioned it, I assume there isn't a calculator available for sizing servos. I've used motor and prop calculators online. I understand the variables mentioned in this thread, but w/o knowing the force needed to handle the forces imposed on the servos, should a new guy (like myself), just guess or do some overkill? Sorry if my question sounds dumb.
     
  10. I don't think there is a calculator for them but there is kind of a rule of thumb that we use (well I do at least).

    20cc-30cc------- 80 oz/in +
    30cc-70cc------- 140 oz/in +
    85cc-120cc------ 200 oz/in + for each elevator and 2x 200 oz/in + for each aileron, 350 oz/in + total for rudder
    150cc-up -------- 3x 200 oz/in + for ailerons, 2x 200 oz/in + for elevators, 600 oz/in + total for rudder

    Larger airplanes (100cc and up) should have ganged servos on ailerons to help fight flex in the surface. most 150cc sized planes should also have ganged servos on the elevator halves to help fight flex.
     
    thurmma likes this.
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