Servo choices

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  • ConcreteTurtle
    Lieutenant, Junior Grade
    • Jan 2009
    • 40

    Servo choices

    Hello again everyone,

    The prodigal sub newbie returns. With questions.

    I'm getting my subdriver 3.5 decked out finally and I wondered if there were any servos that the more experienced folks here use.
    Currently I'm playing around with some HXT900 servos from hobby king, but these seem to draw a lot of current when stalled, and I don't know if I trust my first submarine to $3 servos... I did a forum search, but couldn't find anything directly related.

    I'm really looking at the smallest I can get away with, saying that space is a premium in my cut down alfa subdriver is an understatement.

    Anyway, good to be back and look forward to getting the good oil as this forum always does.

    CT.
  • He Who Shall Not Be Named
    Moderator
    • Aug 2008
    • 12186

    #2
    Put the cheapie servoes in there -- don't agonize over the stall current.

    Don't stall 'em!

    Duh.

    David,
    Who is John Galt?

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    • tsenecal
      Lieutenant
      • Dec 2009
      • 63

      #3
      i disagree with the almighty merriman here.

      it isn't about stall current.

      i buy the largest hi torque micro servos with metal gears that i can fit in the WTC (usually hitec hs-255mg or hitec hs-65mg).

      be warned. they are not $3 servos. try $25.

      I have stripped the cheap plastic gears in the cheapo chinese POS servos just by banging a dive plane or a rudder against the workbench.

      these servos also have the benefit of being high torque, which means they usually also have the torque rating similar to older generation full size servos. the hs-255mg has over 50oz inches of torque, which is enough to move the big 5" prop and shroud on my Alvin.
      Last edited by tsenecal; 11-22-2011, 08:29 PM.

      Comment

      • Slats
        Vice Admiral
        • Aug 2008
        • 1776

        #4
        CT...
        thought you were missing in action....good to see you back. How is that Alfa coming along?
        All my subs with that diameter cylinder utilise the normal S3003 Futaba servos. - Never missed a beat.

        As David points out make sure your installation does not stall the servos. Easy way to tell if you have a potential stall problem is observe any flex in a push rod and you will be heading to problems. Make sure you do not have excess throw on the servos. Adjust the servo horn points. Whilst I prefer to mechanically get the setup as near perfect as it can be, if your radio allows for end point adjustments for the servos throw, utilise these too.

        Best

        John
        John Slater

        Sydney Australia

        You would not steal a wallet so don't steal people's livelihood.
        Think of that before your buy "cheap" pirated goods or download others work protected by copyright. Theft is theft.



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        • Slats
          Vice Admiral
          • Aug 2008
          • 1776

          #5
          Originally posted by tsenecal
          i disagree with the almighty merriman here.

          it isn't about stall current.

          i buy the largest hi torque micro servos with metal gears that i can fit in the WTC (usually hitec hs-255mg or hitec hs-65mg).

          be warned. they are not $3 servos. try $25.

          I have stripped the cheap plastic gears in the cheapo chinese POS servos just by banging a dive plane or a rudder against the workbench.

          these servos also have the benefit of being high torque, which means they usually also have the torque rating similar to older generation full size servos. the hs-255mg has over 50oz inches of torque, which is enough to move the big 5" prop and shroud on my Alvin.
          There are cheap servos and there are cheap servos.

          Nothing wrong with standard Futuba, I'd put them in the cheap category compared to what you are describing but they would be probably a few dollars more than the mini chinese blue ones Mike sells (which I also have had no problems with in smaller diameter subdrivers).

          Tower has the Futaba S3003 for around $11 a piece - hardly what I'd call expensive.


          Originally posted by tsenecal
          i disagree with the almighty merriman here.

          it isn't about stall current.
          Actually it is.
          All servos including my favoured S3003 can chuck out high current at stall.
          Key is avoiding that.

          There has been long established discussions on this before. A primary reason why the onboard BEC or VR included within an ESC will occassionally trip out and halt proceedings is due to servo loads exceeding the linear BECs. A separate more beefed up VR can be of assistance but boat setup is paramount in insuring that servos aren't set up to stall.

          J
          John Slater

          Sydney Australia

          You would not steal a wallet so don't steal people's livelihood.
          Think of that before your buy "cheap" pirated goods or download others work protected by copyright. Theft is theft.



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          • ConcreteTurtle
            Lieutenant, Junior Grade
            • Jan 2009
            • 40

            #6
            Thanks for the good advice guys.

            The Alfa is good, thanks Slats. I'm forging ahead with the Akula for now, as I have big plans for the Alfa involving my upcoming 3d printer.

            Not stalling the servos is good advice indeed, I'll be sure to avoid that with the kinematics of the linkages.
            I use HS-65mg on my t-rex heli, so I should have a few spares kicking around. I'll give them a whirl too and let you guys know how I get on.

            Thanks again,

            CT.

            All my radio gear is JR, not sure if the futaba is compatible.

            Comment

            • He Who Shall Not Be Named
              Moderator
              • Aug 2008
              • 12186

              #7
              Unless you got some old Airtronics stuff laying around, it's all good.

              R/c submarines are dumb, slow machines, with minimal demand of servo torque or speed. Here, you can play it cheap without much consequence.




              David
              Who is John Galt?

              Comment

              • greenman407
                Admiral
                • Feb 2009
                • 7530

                #8
                If I remember correctly, you cant plug a Futaba servo into a JR reciever without modifying the plug. Even then the wires are backwards and itll fry the servo.
                Last edited by greenman407; 12-02-2011, 11:03 AM.
                IT TAKES GREAT INTELLIGENCE TO FAKE SUCH STUPIDITY!

                Comment

                • Slats
                  Vice Admiral
                  • Aug 2008
                  • 1776

                  #9
                  Originally posted by greenman407
                  If I remember correctly, you cant plug a Futaba servo into a JR reciever without modifying the plug. Even then the wires a backwards and itll fry the servo.
                  The biggest compatibility problems were Futaba with Sanwa (err %$&@), but that was a simple signal / positive wire swap around. Its no big deal these days. Futaba puts little plastic tabs on their servos plugs that won't fit a lot of smaller after-market RX slots but 3 seconds with a hobby knife, tab gone and your ready to go.
                  John Slater

                  Sydney Australia

                  You would not steal a wallet so don't steal people's livelihood.
                  Think of that before your buy "cheap" pirated goods or download others work protected by copyright. Theft is theft.



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                  • KevinMc
                    Commander
                    • Feb 2009
                    • 305

                    #10
                    Originally posted by greenman407
                    If I remember correctly, you cant plug a Futaba servo into a JR reciever without modifying the plug. Even then the wires a backwards and itll fry the servo.
                    Correct on the required connector mod, but not on the wires being backwards between these two. Futaba's White/Red/Black maps 1:1 with JR's Orange/Red/Brown. As usual David's correct in that the odd-man-out are the old Airtronics servos (with the black connector) but even they switched over to a "JR" style (blue) connector years ago. Come to think of it, on one of my boats I'm running Airtronics servos plugged into a Hitec receiver, all being driven from a Futaba transmitter. How's that for a mix!
                    Kevin McLeod - Oscar II driver
                    KMc Designs

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