Analog vs Digital Servos

Discussion in 'Scratchbuilding!' started by trying2fly, Nov 27, 2015.

  1. trying2fly

    trying2fly Top Gun

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    I need replacement servos for my Hawk Sky Dynam Transmitter-Receiver. I see very inexpensive servos(analog) on sale this week. I don't know the difference in digital and analog servos and don't know what will work with what I have. I do know I have read about how 9gm servos are best but that is about it. Could someone advise me. Thanking you in advance!!
     
  2. Thelic

    Thelic Ace Pilot

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    Digital servos come to full torque/rotation faster than analog servos. They know exactly what position they want to be in immediately. Analog servos work by homing in on a position, they play the temperature game (hotter...hotter...red hot).

    For general use parkjets you will likely not notice the difference. However things like helicopters need them because it helps to have full torque immediately to change the pitch on the tail rotor. This helps the gyro in the sense that it responds sooner and will not have overshoot.

    Digital servos also draw slightly more current than an equivalent size analog.

    For parkjets, analog won't be a problem.
     
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  3. trying2fly

    trying2fly Top Gun

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    Thank you so much...do you think a "Hawk Sky-like" foamie would notice the difference in 9 gn servo and a 34gm servo(x4)? thanx again for the comeback
     
  4. Thelic

    Thelic Ace Pilot

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    That's about a 100g difference, I'm sure you would notice that. A hawksky is only 600g flying weight stock, so an extra 100 is considerable.
     
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  5. trying2fly

    trying2fly Top Gun

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    Yeah...I guess I should go for the 9 grammers.
     
  6. JettaManDan

    JettaManDan Administrator

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    My suggestion is buy metal gear servos...analog is fine...but plastic gear servos can strip and break..metal gear servos are on sale all over..at 11grams they are perfect replacements...
     
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  7. whatmovesyou

    whatmovesyou Top Gun

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    Some other points about analog servos.

    Did you know that the movement speed of a digital servo is up to 4 times as fast as analog. Now say your plane is moving along at 60MPH. That is 88 ft/sec. Take a couple of tenth of seconds longer(analog) and that could mean the difference between a crash and saving the plane.

    Gyros:
    Can't use them.

    Radios:
    Looking at the new radios(2.4) and many of the frame rate speeds are either 22 ms or 11ms. The manuals states"analog and digital servos must be used for 22ms, but only digital can be used for 11ms. Reason being, they tend to burn out even at 22ms, so why buy them. That's 1970 technology.

    In my opinion, teaching quite a number of new pilots, when your learning to fly, have sloppy controls(analog) , the person plays the game of "ketchup". Adding extra slop to the controls, it will take the person a longer time to learn how to fly.
     
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  8. Baufritz96

    Baufritz96 Ace Pilot

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    To be honest I think my reaction time is the bigger issue here.
    On a 1.000.000$ turbine jet yes, go with digital, on a parkjet, analog does fine.
     
  9. Thelic

    Thelic Ace Pilot

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    I've never had an issue using analog servos with my fixed wing gyro. It still works very much, makes a ton of difference in the wind, flipping that gyro on/off switch midflight is like night and day.

    I've run both the digital and analog versions of the same servo.
    http://www.hobbyking.com/hobbyking/...g_Analog_Micro_Servo_2_8kg_0_10sec_12_4g.html
    http://www.hobbyking.com/hobbyking/..._Digital_Micro_Servo_2_8kg_0_10sec_12_4g.html

    Which are really just rebranded Emax. Great servos (both digital and analog).

    As for slop, its minuscule compared to slop from flex, hinges, and linkages. I seriously doubt any parkjet would have been saved from a crash had it been using digital over analog servos. To be clear, analog servos start moving immediately (22ms), they just don't know where they are going, just that its in that direction.
     
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  10. JettaManDan

    JettaManDan Administrator

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    Never had an issue with analog servos and reaction times...maybe digital servos are necessary for larger planes with higher torque and control surface transition times...but definitely not for a foamie parkjet. Can they give you every advantage? Sure...but disagree it is necessary. $5 analog metal gear servos work terrific for me for over 70 buids to date.
     
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  11. Fz1Fazer

    Fz1Fazer Ace Pilot

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    For all our Foamies analoag servos will do their job well and 20ms response is ok, also a heli swashplate can work with them as long as the heli has a flybar, but the moment you use a digital flightcontroler, flybarless system for heli or gyros digital servos are recommended cause digital controling -> analog servo will result normaly in swinging servos cause the servos are to slow for the controler, analog servos for a heli tail or FBL system can result in critical situations and will wear out very fast.

    All in all digital servos are much faster, can hold the position much better, have more torque and a better torque curve (torque from the beginning) but where is light there is shaddow so you have to pay for all that fine behavior with a higher price and a higher powerconsumption and as long as your gears wear out first analog is fine and I'm sure that most of us will not realize if there analog or digital servos inside.
     
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  12. trying2fly

    trying2fly Top Gun

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    Where do you get your digital metal gear 11gm servos Jetta?
     
  13. trying2fly

    trying2fly Top Gun

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    Thank you very much!!
     
  14. trying2fly

    trying2fly Top Gun

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    For neophyte clumsies like me analog probably would be ok...I guess I'll search for the cheapest and lightest servos. ha
     
  15. JettaManDan

    JettaManDan Administrator

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    I usually buy the cheapest hobbyking metal gear servos...the 929 or 939's...they are like $6 usually...hobbyking just ran a special on the turnigy metal gear servos for $2 a pop...I bought 8 lol...but the 929/939's have been perfect for me for years...I highly recommend them.
     
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  16. JettaManDan

    JettaManDan Administrator

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    Don't get too hung up on weight....anything under 15 grams is just fine...if you can't find a deal on metal gear ones at least look for the carbon gear ones also...the standard plastic gear ones can break if a control surface like a elevon gets pulled/pushed on a hard landing or something...
     
  17. trying2fly

    trying2fly Top Gun

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    Thank you for the lead...I really appreciate it!!
     
  18. whatmovesyou

    whatmovesyou Top Gun

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    I am speaking from an club instructors viewpoint, you are bringing up all the points ( slop in controls, excessive flexing, linkage, excessive weight, slow moving servos) all work against the newbee flyer. You need to help the new flyer learn to fly by reducing the odds that are against him.

    The point trying to be made, is reduce the number off factors going against him since you must remember, there are all types learning how to fly. Some have faster reaction times than others. Try training someone and you will have a different view. Enough said.
     
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  19. trying2fly

    trying2fly Top Gun

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    For Heaven's Sake , I need all the help I can get and your point is well taken....Fazer is right also in my case.....I wouldn't know one from the other because of my inexperience and reaction times are about as fast as an aging toad!!
     
  20. TomMonton

    TomMonton Administrator

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    I wouldn't sweat the detail. The primary advantage of digital is the reaction time "latency" between actual input (be it a stick input control or a stabilizer circuit) and the reaction again the servo arm.

    Unless you are flying competition air shows or are talking something other than a foam park jet. .. go with the typical 9g analog servo.

    The choice going metal gear is recommended if all you ever fly is with elevon. They take a little more abuse.

    Most of the actual slop will be caught up in the linkage someplace. Holes wobbled out, hinge line flexing. ..those sort of things.

    Look at it this way. The human eye can react at around 100ms .1/10 a second. You need a moment to connect visual to motor, you make a movement on the stick.... a whole bunch more delay.

    Control input to servo is measured at .10 again. .100ms.

    Even if you can react to some event in less than a half a second. ... servo speed is not going be much of an equation in your net result.

    Measurable. .. and a delay yes. But not in the areas you may need to concentrate on.
     
    Last edited: Nov 29, 2015
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