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Servo Spins Continously — Parallax Forums

Servo Spins Continously

GrizzletorGrizzletor Posts: 1
edited 2011-09-21 12:35 in Propeller 1
Hello, I am trying to get a servo working on my Parallax REV G Propeller board and all it does is spin. I am using the serial REV B servo driver and the demo spin files from: http://obex.parallax.com/objects/51/ The servo spins continuously no matter if the input port is connected or not. Any suggestions or directions?

Comments

  • Beau SchwabeBeau Schwabe Posts: 6,568
    edited 2011-09-19 15:04
    Grizzletor,

    Welcome to the Forums!!

    Does the power supply to the Servo share the same ground as the power supply to your Propeller?

    Also, I know you made reference to the code that you are using, but if you can provide the exact code that you are trying to run that would be of better help.
  • TtailspinTtailspin Posts: 1,326
    edited 2011-09-19 21:23
    If it is a Parallax continous rotation servo, then you might need to calibrate it for center position.

    there is a small hole for a small screwdriver just above where the cable goes into the servo.
    turn it SLOWLY and see if that helps...

    -Tommy
  • prof_brainoprof_braino Posts: 4,313
    edited 2011-09-20 05:43
    I had a small inexpensive servo (I think it was Hi-Tech HC-55) that I was calibrating. I was trying to find the ablsolute maximum range I could get from it. I would increase the range until it would "chatter" at the stops. This process work fine 3.3 volts (connected to Vdd), when I tried is using 5 voolts (connected to Vin) instead of "chatter" at the end points it blasted right through the stops. Now this servo spins continuously unless I keep the pulses well within the requireed range of 1.0 and 2.5 ms. (I.E. at power up initialize to 1.5 ms) Check if your pulse is too short (set to zero?) This could be a cause.
  • Andrew E MileskiAndrew E Mileski Posts: 77
    edited 2011-09-21 12:35
    Grizzletor wrote: »
    Hello, I am trying to get a servo working on my Parallax REV G Propeller board and all it does is spin. I am using the serial REV B servo driver and the demo spin files from: http://obex.parallax.com/objects/51/ The servo spins continuously no matter if the input port is connected or not. Any suggestions or directions?
    I don't know if this will help, but it might be useful:

    A typical continuous-spin servo hack is simply to:
    1. Remove the end-stops inside the servo that prevent the servo output shaft from rotating continuously.
    2. Remove the position feedback potentiometer and replace it with a resistor network for an equivalent center value.

    The servo will then only react to pulses:
    * 1ms to <1.5ms: continuous rotation in one direction
    * 1.5ms: stopped
    * >1.5ms to 2ms: continuous rotation in the other direction

    This hack has the disadvantage of removing position feedback, so the servo can't hold a position except by geartrain resistance.
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