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How big before multiple servos on a control?

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

  1. I saved this link awhile back that is a servo torgue calculator:

    http://www.mnbigbirds.com/Servo Torque Caculator.htm

    I have not used it and have no experience or knowledge to back it up...but I'd be interested to hear if others checked it out and what they thought of its accuracy...
    stangflyer likes this.
  2. Thanks Bipeguy03, and Wacobipe
    That really helps me out. Unfortunately the servos in my 1/4 scale L-19 which has a 52cc on it only has servos rated Torque: 106.93 oz/in at 4.8V and 133.31 oz/in at 6.0V. Considering all the info and opinions I've read on this thread I may reconsider my choice I made. I haven't flown the plane yet.
  3. Are they digital servos? Digital make a big difference and also the application. Which is what makes this hole servo thing kinda murky water lol.

    With the type of flying you're going to be doing with a Bird Dog, 133 oz/in of toque will be fine, especially if they are digital.

    The rule of thumb I gave is kind of a starting point for 3D type airplanes with Over sized surfaces and are over powered to boot. Don't forget, back in the 80's you be hard pressed to find a servo that had more than 100 oz/in of torque and they had 50cc birds then!

    You'll start to get a hang of what works and what doesn't, but even still never hurts to ask!!
  4. Thanks for your comments. They're the Hitec HS-645MG, non digital, (4) for elevator/ailerons And presently my bec is set for 5v I believe. That would be the lower torque level, 106.9 oz/in. I also have the digital version of the HS-645, the HS-5645MG. It is rated 143.03 oz-in at 4.8V, 164.2 oz-in at 6V for (3) rudder/flaps. These are all installed now.

    With a total of 9 servos in the plane (throttle and kill servos added to above), should I go to 6v for the servos? Higher voltage would lower the amps, right?

    Another thing I didn't realize until I read it here is the rudder has the highest demand. At least I thought I saw that somewhere. I thought the ailerons would have the highest demand. But somehow I have the strongest servo on the rudder. It happened by chance I'm sure.
    Last edited: Mar 25, 2015
  5. For the most part the guys on here are use to flying 3D, the rudder on a 3D airplane is HUGE and takes a beating to boot.

    Again in a Bird Dog, if all the servos are about the same you'd be fine.

    While I'm not an electrical genius, I'm pretty sure that more volts in the servo will draw more amps. If you increase the colts, you increase the speed and torque of the servo which means it is working harder so it will draw more amps. Like on an electric airplane, if you add volts it will turn the prop faster, so if you don't switch to a smaller prop the motor is working harder (watts) so it is drawing more amps.

    In your airplane with nine servos, I would recommend running 6.0v. If you're running a Nimh or Nicad pack run a 5 cell (6.0v) with a high mAh rating.

    If you want to have the best batter setup for what you have, get a 2s 7.4v Lion or LiPo with a regulator, like the one from Fromeco.

    You are going in the right direction!
  6. To add, the servos you have will work just fine for your set up..

    That is unless you plan to Throw down some 3D with you're Bird Dog ;)

    (which would be totally awesome by the way!!)
  7. stangflyer

    stangflyer I like 'em "BIG"!

    This is a really good thread. Lots of useful information. Snappy mentioned quite few posts back that most guys over equip their rides with servos, batteries and such. Which is not a bad thing. I suppose I do the same to some degree. I used Hitec HS 7954's in my 30% Pilot Edge. Will it ever really need over 400 oz. per servo? Nope! But in the event I off the Edge, I have servos that were not terribly expensive for another big bird. On my 260, I also used (2) 7954's per aileron, one per elevator and two 7980's, (611 oz. each) on the rudder. I feel the 260 flies very rock solid for a 40%'er. The 35% PAU, again, HS 7954's throughout. On the Sukhoi, HS 7950's throughout.
    But back to the original question:
    Utilize at least the minimum of the recommended specs by the manufacturers if it is an ARF. If it is a stick build, the torque calculator is an awesome tool to use.
  8. The servos you have installed will work fine. Dad has a Valencourt L19 with a Saito 300 GK on it. Futaba 9152s on the tail and 3152s on wings. It fly's so smooth and easy on those servos. You don't need a 400 oz servo on this airplane.

    All you need is a good digital servo that centers well, has good speed (.18) and has good torque (150 oz or so). Make sure the linkages are nice and tight, slop free etc...
    stangflyer likes this.
  9. Rob, you've got an XG 11. You don't need the booma stuff. Trust me. If you go to power safe Rx, you wont need the smart fly either.
    stangflyer likes this.
  10. Thanks for the input. I do feel comfortable w/the servos I have. I need to get a regulator to operate them on 6v now. I've been busy a work, I plan on doing something w/the plane this weekend. Temp to be in the 70's too. Yippee!

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