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Thread: Servo Quesion

  1. Servo Quesion

    Hi.

    What's the different between servo and serial servo?

  2. #2
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    Re: Servo Quesion

    Hello there!
    A servo is addressable via Pulse Width Modulation. Which basically pulses high, then pulses low at certain times for certain lengths. A 90* Pulse is typically, depending on your servo 1500ms. However this can vary. Servo's are often driven from a separate servo controller, or from a radio controller, rather than the microcontroller itself, however it is still possible to directly control a servo from a microcontroller.

    Serial servos are different, infact a whole different game. Instead of pulsing each servo individually, servo's are given an ID. You then tell the servo where to go via a serial connection. This is theoretically a better approach as it removes the need for a servo controller and for examples the AX-12's boast a 300* range and pretty good torque. However this does come at a price.

    Standard servos also come in digital and analog form but both are more common than serial servos.

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    Re: Servo Quesion

    >> However this does come at a price

    I think if we crunched the numbers, we'd find that oz-in for oz-in, the AX-12's are the less expensive choice actually...
    I Void Warranties´┐Ż

  4. Re: Servo Quesion

    Hi noogle .

    Now I understand. So if come across a serial servo how can we know the ID. Is it provide by the manufacturer or theres a way to find out.

    If possible how?

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    Re: Servo Quesion

    Quote Originally Posted by Adrenalynn View Post
    >> However this does come at a price

    I think if we crunched the numbers, we'd find that oz-in for oz-in, the AX-12's are the less expensive choice actually...
    Not to even mention the features like thermal shutdown, overload protection, and already having a built-in pivot point on the opposite side of the case (something you'll only find on the really high-end PWM robot servos)

    However, on the subject of "removes the need for a servo controller", I might have to disagree a bit. While you don't need a crazy number of I/O that can generate very precise PWM, you will be forced to implement certain features that controllers like the SSC-32 have: for instance, interpolation will be entirely left to you the programmer, it's not incredibly tough, but it's something to take into account.

    -Fergs

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    Re: Servo Quesion

    Quote Originally Posted by brickbob View Post
    Hi noogle .

    Now I understand. So if come across a serial servo how can we know the ID. Is it provide by the manufacturer or theres a way to find out.

    If possible how?
    If we are talking AX-12+, they default to 0 (or is it 1) from the factory... after that you set it to whatever you want. Most interfaces to the AX-12 bus have a feature for "scanning" the bus to see what's out there...

    -Fergs

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    Re: Servo Quesion

    Quote Originally Posted by Adrenalynn View Post
    >> However this does come at a price

    I think if we crunched the numbers, we'd find that oz-in for oz-in, the AX-12's are the less expensive choice actually...
    This wouldn't surprise me in the slightest. You pay for what you get and you should only pay for what you need. Therefore only get what you need. You wouldn't use an ax-12 to pan an ultrasonic sensor or to mod to become a continuous rotation servo, not at that price. I've you're building a mech, it's a different question.

  8. #8

    Re: Servo Quesion

    The use of an AX-12 is determined by your project requirements. If your project takes advantage of the a dynamixel bus (AX-12) then adding a pan to the network is simple work.

    AX-12s come out-of-the-box with continuous rotation mode - see the manual.

    Quote Originally Posted by noodle
    A servo is addressable via Pulse Width Modulation.
    PWM is used to set the angular position of a standard RC servo. RC servos are not addressable unless connected to device like a controller or RC receiver.
    Last edited by MikeG; 07-08-2009 at 08:43 AM.

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    Re: Servo Quesion

    And given their other features and terribly inexpensive cost - yeah, I would. As Mike pointed-out - they don't need to be modded, and "modding" is software, not hardware as it is with traditional servos. They actually make really effective little drive motors for a small bot.

    Buying one or two starts looking pretty inexpensive when you start figuring on needing a PWM controller for some servos but not others on a bot.
    I Void Warranties´┐Ż

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    Re: Servo Quesion

    Quote Originally Posted by Adrenalynn View Post
    And given their other features and terribly inexpensive cost - yeah, I would. As Mike pointed-out - they don't need to be modded, and "modding" is software, not hardware as it is with traditional servos. They actually make really effective little drive motors for a small bot.

    Buying one or two starts looking pretty inexpensive when you start figuring on needing a PWM controller for some servos but not others on a bot.
    Don't forget the nicer voltage range (7-12V)... cheap hobby servos on 5V can be tough, since either you have to have a separate battery, or add an extra regulator (as you typically can't run 5V electronics off 4-1.5V cells)

    -Fergs

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