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Continuous Rotation Servo (#900-00008) / PSC-USB — Parallax Forums

Continuous Rotation Servo (#900-00008) / PSC-USB

DutchDakDutchDak Posts: 11
edited 2006-11-04 19:12 in Robotics
Is there any one who can share experience with the use of the Continuous Rotation Servo (#900-00008) driven by the Parallax Servo Controller - USB board ?

- Does it work ?
- How do you use the position command in order to use the whole 360 degrees ?

Herman.

Comments

  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-11-02 21:13
    Hello,
    ·
    ·· When using continuous rotation servos with any controller you do not have positional control of the servo.· You can’t make it go to a specific position because it is modified to allow continuous rotation and no longer provides feedback on position.· Take care.

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    Chris Savage
    Parallax Tech Support
  • Steve JoblinSteve Joblin Posts: 784
    edited 2006-11-02 21:30
    The advantage of using the Servo Controller board is that it will act like a "set and forget" device... provide a single command and the Servo Controller will continue to run the servo until it receives a new command... this enables you to "free up" the Stamp for other processing activities... sending a command that would move a normal servo a small amount is the same as moving a modified servo slowly; sending a command that would move a nornal servo a large amount is the same as moving a modified servo quickly... this is how you can control speed of a modified servo.
  • DutchDakDutchDak Posts: 11
    edited 2006-11-03 10:53
    Steve,

    Now I understand what is happening when driving it from the PSC-USB.
    If I use the parallax continuous rotation servo it keeps turning.
    If I send a command to go to position index 762 (which is +/- halfway) it stops.
    If I give a command to position lower than 762 it will move clock wise, with 0 as fastest speed.
    If I give a command to position higher than 762 it will move anti clock wise, with 1250 as fastest speed.

    Question:
    So in order to control the position I need an additional feedback device and control loop ?
    There is no way to do this with the PSC-USB ?
    Any suggestions for a feedback device (I control the PSC directly from my PC) ?
  • Bruce BatesBruce Bates Posts: 3,045
    edited 2006-11-03 12:12
    DutchDak -

    Although the PSC will work with any R/C servo, continuous rotation or otherwise, it's usually used with ordinary R/C servos where continuous rotation is not a feature. In those applications a position command makes sense.

    Furthermore, the feedback device which you mention has essentially been REMOVED from a continuous rotation servo. Therein the "problem".

    Regards,

    Bruce Bates

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  • John R.John R. Posts: 1,376
    edited 2006-11-03 14:42
    I think DutchDak understands that the position sensor has been removed, and is asking for ways to add one back in and tie it back to the PSC:

    You won't be able to tie it back directly to the PSC, but you could do something along the lines of the following:

    * Add an encoder or other position sensor to the output of the continuous rotation servo.
    * Monitor this with your micro controller (assumedly Stamp/SX/Propeller)
    * Have the micro controller send the movement command to the PSC
    * Monitor the encoder/postion sensor
    * Send an updated movement (or stop) command to the PSC.

    Using the above, you could start the servo moving quickly, and as it approached the final position slow it down, and eventually stop it.

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    John R.

    8 + 8 = 10
  • FranklinFranklin Posts: 4,747
    edited 2006-11-03 19:55
    If what you want is to move to a position and stop get a standard servo instead. If you need to have 360 degree rotation and can't use less get a set of gears that will move one gear 360 with the servo moving 180 (or so)

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    - Stephen
  • DutchDakDutchDak Posts: 11
    edited 2006-11-03 21:18
    John, is right, I did understand that there is no position sensor.
    I am looking now for an alternative.
    Since I am driving the PSC directly from mu PC via USB, that does not seem to be that easy without adding a lot of circuits ...
    Something I wanted to stay away from ...
    Stephen's suggestion I also considered as an option. Does any one know if there are standard gear sets that can be mounted on top of a servo, or do you have to make that yourself ?
    I am also thinking of using a stepper motor by means of the BiStep Motor Controller (USB), however from the documentation I have not yet a clear picture what the level of detail is for control. For instance does one send the motor to a new position or does one have to send a command for every step ?

    - Herman.
  • Bruce BatesBruce Bates Posts: 3,045
    edited 2006-11-03 21:23
    Herman -

    Check ServoCity for gears for servo mounting.

    Regards,

    Bruce Bates

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  • FranklinFranklin Posts: 4,747
    edited 2006-11-04 19:12
    Great site Bruce!

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    - Stephen
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