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Thread: JR servo arms?

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  1. JR servo arms? 
    #1
    Join Date
    03-09-2007
    Location
    Barrie, Ontario, Canada
    Posts
    70
    I have a JR Z650M i just picked up and I also picked up a Dynamite servo arm # DYN2534 but the servo arm does not fit it?

    I have a old z270 jr servo and the arm fits it perfect so what gives?

    thanks in advance
     

  2.  
    #2
    I don't really have a solid answer for you but I can tell you my experience.
    I have never found a servo arm that fits a JR servo "well".
    The arms that came with both of my axial kits that were supposed to fit JR servos had to be forced on with a screw and pried off with a screwdriver.
    I bought aluminum arms at my LHS that were supposed to fit JR stuff. I couldn't make one fit...so I went back to the LHS to see what was up. He checked all the part numbers and stuff to make sure that was definitly the arms that were supposed to fit JR. No luck after trying 5 or 6 arms.
    Finally we just forced one of the aluminum arms on with a screw then pried it back off. The splines didn't really look messed up so I just crammed it back on and have been using it for a year now. I have two JR servos with alum arms forced onto them and I've had them both apart numerous times. The fit doesn't get any better but as long as they don't strip out on me while I'm using them I guess its no big deal to me.

    The next time I buy servos they are gonna be hi-tec's for sure.
     

  3.  
    #3
    Join Date
    02-07-2008
    Location
    the vc
    Posts
    239
    the spline size can be looked at similarly to pinion gears there are different pitches and number of splines when they dont match up perfectly it results in an unsatisfactory fit
     

  4.  
    #4
    Join Date
    03-09-2007
    Location
    Barrie, Ontario, Canada
    Posts
    70
    has anyone tried those "adjustable" arms i have seen on ebay?
     

  5.  
    #5
    Join Date
    07-04-2006
    Posts
    1,744
    23 spline arms. Airtronics/Sanwa, KO & JR should be the same. 24 splines Hitec. Futaba largest at 25 splines.
     

  6.  
    #6
    Join Date
    08-19-2002
    Location
    Wichita, ks
    Posts
    10,365
    The JR servos that have a gold anodizing were anodized after they were cut (obviously) and the tolerances were not taken into account when they were designed originally.

    Because of this, all metal JR arms will fit tight on those servos. The more expensive servos don't have the gold anodizing so they fit better, but on the cheaper servos like the 650, 126mg, z590, etc... They all have the stupid gold that makes it fit so tight you literally have to use a screw to install the horns.

    I believe the term is "interference fit."

    -Eric
     

  7.  
    #7
    Join Date
    03-09-2007
    Location
    Barrie, Ontario, Canada
    Posts
    70
    ya screwed it down and it fit great ty
     

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