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Pan & Tilt servo controlls? — Parallax Forums

Pan & Tilt servo controlls?

jfizerjfizer Posts: 15
edited 2007-06-18 05:34 in Robotics
I've picked up a pan and tilt addon for the Boe-Bot, however the servos it uses are not 360 degree but limited in the amount they can rotate. Does anyone know off hand the pulse commands they are expecting? Odds are I can trial and error it, but if someone has the information I'd rather not repete the work.

Comments

  • Tom CTom C Posts: 461
    edited 2007-06-15 13:13
    jfizer,

    Most standard servos work over a PWM range of 1.0ms to 2.0ms with 1.5ms being the center of travel, however your results may vary depending on the servo.

    Most servos travel from 140 to 180 degrees over their PWM range.

    With a pan and tilt servo system, it is best to actually find the PWM values for the end stops and the center. It only takes a few minutes.

    Hope this helps.

    Regards,
    TCIII

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    If you are going to send·a Robot·to save the world, you·better make sure it likes it the way it is!
  • allanlane5allanlane5 Posts: 3,815
    edited 2007-06-15 13:33
    Typically you control servo's from the BS2 using the "PULSOUT" command. A 1.5 mSec pulse 'centers' the servo, 1.0 mSec is full left, 2.0 mSec is full right. Then you MUST repeat the PULSOUT every 20 mSec to 50 mSec.

    This is actually a good thing -- that 20 to 50 mSec gives your program time to do something else -- like drive a second servo. That way, it has a larger purpose in life than simply running a PWM signal to a single servo.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2007-06-15 14:29
    Are you sure the servos are 360? That would imply continuous rotation and those don’t have limits on them since there’s no way for the servo to know its actual position. If you send a pulse value to a CR servo and don’t actively monitor its position with a limit switch and stop it when it reaches the stop then you could easily damage the servo.

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    Chris Savage
    Parallax Tech Support
  • jfizerjfizer Posts: 15
    edited 2007-06-15 16:07
    Chris Savage (Parallax) said...
    Are you sure the servos are 360?

    You missunderstand. I'm sure the servos are NOT 360. Unlike the wheel servos that come with the Boe-Bot kit.
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2007-06-15 16:25
    Okay, I saw the 360 and missed the "not"...Standard servos are covered in our "What's A Microcontroller?" manual which is freely downloadable from our website in PDF format. Take care.

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    Chris Savage
    Parallax Tech Support
  • jfizerjfizer Posts: 15
    edited 2007-06-15 16:32
    Chris Savage (Parallax) said...
    Okay, I saw the 360 and missed the "not"...Standard servos are covered in our "What's A Microcontroller?" manual which is freely downloadable from our website in PDF format. Take care.

    Very good, I'll take a look as soon as I'm no longer supposed to be working.
  • HandtoolHandtool Posts: 17
    edited 2007-06-18 05:34
    http://forums.parallax.com/showthread.php?p=624789
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