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My servo controler drains batteries too fast — Parallax Forums

My servo controler drains batteries too fast

Capt. QuirkCapt. Quirk Posts: 872
edited 2006-10-02 20:00 in BASIC Stamp
"Parallax uses the Futaba S-148 servo which draws around 125mA to 1amp depending on the torque that is applied."

Dave

I have a board (using a B2SX module)·that receives PULSIN commands from 1 servo to constantly control another servo with PULSOUT. No matter what batteries I use (6v 0r 7.2v w/400 to 500watts), they drain very fast. In fact they drain so fast, it makes my servo controller unusable for my application.
·
I am only using PAUSE 25 between program loops that continually update the servo. Is this a programming·or possibly a "Duty Cycle" issue that is causing my batteries to drain so fast??

TY

Comments

  • Capt. QuirkCapt. Quirk Posts: 872
    edited 2006-09-28 07:12
    Here is the code
    bsx
    bsx
    select_case_v1.1.bsx
    3K
  • Chris SavageChris Savage Parallax Engineering Posts: 14,406
    edited 2006-09-28 14:21
    Bill,
    ·
    ·· Where did you get those battery ratings from?· Also, are you powering the BS2sx from the same supply as you’re powering the servos from?

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    Chris Savage
    Parallax Tech Support
  • Mike GreenMike Green Posts: 23,101
    edited 2006-09-28 14:34
    Most radio control/hobby vehicle battery packs have capacities ranging from 2AH to 3.3AH (ampere hours) at 7.2V this would be roughly 14 to 24WH (watt hours). With a drain of 125 to 1A, a 3.3AH battery pack should last 3 to (stretching it) 24 hours depending on how often the servo has to change and what the physical drag on the servo is. How often you pulse the servo shouldn't matter that much as far as current draw is concerned. The Stamp itself doesn't take much and we don't know what the sensors take. If you get 6-12 hours per charge, you're probably doing well.
  • Capt. QuirkCapt. Quirk Posts: 872
    edited 2006-09-28 15:38
    Yes the battery pack powers the stamp and the servos. I'm no electrition, but I am pretty sure there is a· mosfet or some other 3 wire electronic switch that isolates the stamp from the power supplied to the servo.

    It is also sensitive to the size of battery packs it uses, 6v and 7.2v packs I know are proper for a B2SX. But it will only operate with small·"park flyer" battery packs around 400 to 600 mAH (not watts, SRY). I have a new 6v·1800 mAH "JR" battery pack and for some reason, it will not work with it.

    The board itself was designed by an engineer in the UAV field, it also has 2 servo outputs, 2 thermocouples and 2 hall sensors for multiple engines and many expensive chips.·I have been finishing up the programming and converting it for use in our nitro methane powered Giant scale pylon racers, but right now it will go thru a batterey pack before the end of a 6 min race.
  • metron9metron9 Posts: 1,100
    edited 2006-09-28 16:08
    What is the ohm reading you get when you measure without the battery across the + and - terminals

    Can you put an amp meter on the battery input line to see at idle what the amp draw is, with and without the servos connected,

    it's probbly not the servos, I suspect a voltage regulator and something should be getting hot is you are draining that much amperage that fast.

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    Think outside the BOX!
  • Beau SchwabeBeau Schwabe Posts: 6,559
    edited 2006-09-28 16:10
    "Yes the battery pack powers the stamp and the servos."

    For this particular application, you really need/"must have" two seperate battery packs that share a common ground.

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    Beau Schwabe

    IC Layout Engineer
    Parallax, Inc.
  • Capt. QuirkCapt. Quirk Posts: 872
    edited 2006-10-02 06:23
    First my next board will have 2 power sources,
    ·
    But what I don't understand is, why it drains so fast within my board? That same battery pack would have powered a gear reduced 280-size park-flyer motor, a·speed control, 2 servos and the receiver for about 6 minutes and not loose servo control. My setup is the BS2sx, 2 egt's, 1 hall effect sensor, a pulsin from a servo connected to the transmitter, 1 180' servo and it won't operate a servo for·more than a couple minutes straight.
    ·
    If my program sends a single pulsout, will the servo hold that position indefinitely until a +/- pulsout value is sent? And will it draw less current while it's stationary? (My program loops over and over sending out the same pulsout value, about 40 times a second).
    ·
    Or does the current draw effect the certain parts of the stamp, more than others when the power supply reaches a certain point?


    TY
  • Mike GreenMike Green Posts: 23,101
    edited 2006-10-02 08:01
    There is nothing obvious from your description that would explain what's happening so the answer might depend on the details of how things are actually connected. It would help if you could post a schematic diagram of the board. You will find part of your answer if you can measure the actual current drawn by the individual servos and sensors.

    A servo requires a periodic pulse (about once every 20ms) for proper functioning although its current consumption should not increase if the pulse occurs less often than that. It will draw more current when the position changes (because the motor moves), but the current should decrease again once the motor reaches the new position.

    The Stamp will not work as well when the power supply voltage (Vin) drops below 6V, but its current draw should not increase significantly and it should operate certainly down to maybe 5V and, at some point, will go into reset state.
  • allanlane5allanlane5 Posts: 3,815
    edited 2006-10-02 13:32
    Most current draw associated with Servo's depends on the mechanical load the Servo is seeing.
  • Beau SchwabeBeau Schwabe Posts: 6,559
    edited 2006-10-02 16:38
    Bill Mazzacane,

    "...But what I don't understand is, why it drains so fast within my board? That same battery pack would have powered a gear reduced 280-size park-flyer motor..."

    It might be possible that the Stamp is being held in "reset" mode, or starts to go into reset mode because the "gear reduced 280-size park-flyer motor" could be pulling
    the voltage down enough that the brown-out circuitry of the Stamp·engages.

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    Beau Schwabe

    IC Layout Engineer
    Parallax, Inc.
  • metron9metron9 Posts: 1,100
    edited 2006-10-02 20:00
    Heck put a current sense resistor on the battery, connect a scope to measure the voltage across the sense resistor turn it on and log the data. Ohms law will tell you how much current it is drawing.

    Before applying power to any circuit I make, I check to see how much resistance the circuit has, if it's too low then there may be a short, solder bridge or something amis. You should be able to calculate the current draw and should for battery operated devices.

    You need to breakdown the circuit, disconnect components and test it, if you have a schematic you can figure out what the current should be and then test it. Shooting in the dark 2 min vs 6 min, like I said, just hold your hand on some components something has to be getting hot.

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    Think outside the BOX!
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