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standard servos

Nick DNick D Posts: 7
edited 2010-04-30 02:44 in Robotics
Would anyone know the repeatability of the Parallax standard servo? In other words, If I give the servo a certain pulse, will it always return to the same spot or will it be off by some degree? Are they repeatable from servo to servo?
Thanks for the help.
Nick

Comments

  • allanlane5allanlane5 Posts: 3,815
    edited 2010-04-29 17:38
    My understanding is that the "standard servo" was originally created for use in gas-powered model airplanes. The positioning was done in response to signals from a radio-control unit on the ground.

    As such, exact repeatability wasn't really a goal -- close enough was close enough, if it was a little off the person holding the radio-control unit would tweak the joystick or adjust a trim control.

    Having said that, I understand that repeatability is "pretty good" -- but I don't know +- how many arc-seconds that is. Also, different servo's position slightly differently given the same input -- probably depends on manufacturing tolerances, and the repeatability of the variable resistor inside each one.
  • W9GFOW9GFO Posts: 4,010
    edited 2010-04-29 23:19
    Nick D said...
    If I give the servo a certain pulse, will it always return to the same spot or will it be off by some degree? Are they repeatable from servo to servo?
    Thanks for the help.
    Nick

    The Parallax standard servo that I have has a dead band of 5 microseconds. Each microsecond of pulsewidth is approximately equal to .1 degrees. It's been a while since I tested it but I think it's repeatability is a little more than +/- .5 degrees.

    So yes, they will be off by some small degree and no, I would not expect each servo to respond identically. Close maybe, but not identical.

    If you need better accuracy look for a digital servo with low dead band.

    You can also increase accuracy through gearing, though you would lose travel.

    Rich H

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    The Simple Servo Tester, a kit from Gadget Gangster.
  • Spiral_72Spiral_72 Posts: 791
    edited 2010-04-30 02:44
    Digital servos have a LOT better repeatability and resolution..... They cost a bit more.

    As far as an exact error...... the manufacturer might be able to help with that or buy one and see? The standard analog servos are pretty rough for any precise and repeatable motion though.

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    "puff"...... Smile, there went another one.

    Post Edited (Spiral_72) : 4/30/2010 2:49:54 AM GMT
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