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How many mA required to power Parallax servos? — Parallax Forums

How many mA required to power Parallax servos?

RaymanRayman Posts: 14,833
edited 2009-06-09 22:01 in Propeller 1
This seems to be hard information to find!
I don't know why there isn't some clue in any of the documentation...

I'm guessing (after a forum search) that it's around 200 mA at full load (which I suppose means at full torque).

Anybody know for sure, or seen data?

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My Prop Info&Apps: ·http://www.rayslogic.com/propeller/propeller.htm

Comments

  • BeanBean Posts: 8,129
    edited 2009-06-02 14:07
    Rayman,
    I bet it's higher than that if the servo is stalled. But I'd have to check to be sure.
    Which servo do you have ? Parallax Part # if you have it.

    Bean.

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    There is a fine line between arrogance and confidence. Make sure you don't cross it...

    ·
  • RaymanRayman Posts: 14,833
    edited 2009-06-02 14:22
    I have a few of the standard futuba servos:
    http://www.parallax.com/StoreSearchResults/tabid/768/txtSearch/servo/List/0/SortField/4/ProductID/101/Default.aspx



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    My Prop Info&Apps: ·http://www.rayslogic.com/propeller/propeller.htm
  • Jessica UelmenJessica Uelmen Posts: 490
    edited 2009-06-02 15:53
    Hi Rayman,

    We'll be releasing updated servo documentation within the coming weeks, but both the Standard and Continuous rotation servos draw 140 +/- 50 mA of current when operating at 6.0 V, and 15 mA when in static state.

    Hope this helps!

    Jessica

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    Jessica Uelmen
    Education Department
    Parallax, Inc.
  • RaymanRayman Posts: 14,833
    edited 2009-06-02 16:03
    Thanks, that's what I was looking for.

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    My Prop Info&Apps: ·http://www.rayslogic.com/propeller/propeller.htm
  • rokickirokicki Posts: 1,000
    edited 2009-06-02 17:10
    But don't forget, a stalled servo can draw a lot of current. This is a common cause of
    frequently-resetting robots---if you don't carefully design the way you're powering your
    servos, a stalled or quickly-moving servo can draw enough current to drop the logic
    power main and reset the propeller.
  • Robot FreakRobot Freak Posts: 168
    edited 2009-06-02 18:04
    So, you shouldn't regulate the servo(s) power supply if the battery is within the servo specifications.
    Or, you should use a dedicated regulator for the servo(s) with a big capacitor near it.
  • SRLMSRLM Posts: 5,045
    edited 2009-06-02 18:21
    Robot Freak said...
    So, you shouldn't regulate the servo(s) power supply if the battery is within the servo specifications.

    I'd disagree. I think you should always regulate the servo voltage so that you get consistent movements, not ones that get slower and weaker as the voltage drops.
  • rokickirokicki Posts: 1,000
    edited 2009-06-02 22:50
    There are two schools of thought on regulating servo voltage.

    If you have movement feedback (through optical encoders on your shafts, for instance) or if you are strictly doing
    positional movements (not continuous rotation), then there's an argument to be made that you should not
    regulate your power to the servos; it's just throwing away battery power.

    If you are trying to get repeatable behavior out of continuous rotation servos without an active feedback control
    loop, then you could regulate your servo power to enhance the repeatability. You better make sure your
    regulator is up to the task, though; servos can really generate current spikes.
  • Ole Man EarlOle Man Earl Posts: 262
    edited 2009-06-02 22:57
    Always use a separate PS for servos and microprocessor. But don't forget to tie the grounds together !
    A cap on servo regulated PS is good also...
  • W9GFOW9GFO Posts: 4,010
    edited 2009-06-08 20:30
    I measure 640 ma @ 6.38 v on the Parallax Standard Servo when stalled.

    Rich H
  • RaymanRayman Posts: 14,833
    edited 2009-06-08 22:25
    Maybe it's better to ask for a graph of current versus torque...

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    My Prop Info&Apps: ·http://www.rayslogic.com/propeller/propeller.htm
  • Chad GeorgeChad George Posts: 138
    edited 2009-06-09 01:48
    From my experience using hobby servos in various FIRST robotics competitions...
    15mA - idle current (absolutely no load)
    100-200mA - changing position
    600-750mA - stalled or moving under heavy load

    but the good news is you don't have to be able to supply 500+mA for very long ... because they quickly release their magic smoke inside if they're drawing this much power.
  • JonnyMacJonnyMac Posts: 9,195
    edited 2009-06-09 15:22
    This is very servo-dependent. At EFX-TEK we work with a lot of animatronics folks. We recently designed a plug-in board for our controllers that would supply 5A at 5v and two customers burned it up, too! -- we're now modifying the design to use a switching supply. The lesson: don't take servos or their supplies for granted; we learned the hard way.
  • Mike HuseltonMike Huselton Posts: 746
    edited 2009-06-09 22:01
    I always use two linear regulators, 1 for main and 1 for servo. But replacing the linear servo regulator with a switching regulator makes all the sense in the world to me. Hang the noisy and spikey stuff off of a switcher. Thanks for the design tip!

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    JMH
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