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problem with servo — Parallax Forums

problem with servo

eagle4ceseagle4ces Posts: 14
edited 2010-01-22 12:36 in BASIC Stamp
am using 4.90volts for a parallax standard servo, amfter sending a pulse the servo vibrates continously instead of turning. i must complete a project by next week

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2010-01-20 23:28
    You really need to attach your code to a message for specific help.

    4.90V is well within 10% of 5V which should be fine. What you're not saying is whether the supply voltage stays at 4.90V. Remember that a servo can draw up to about 1 Amp for a short time and the power supply needs to be able to provide this.

    Servos also need the control pulse repeated about every 20ms (50 times a second) or the servo will turn itself off somewhere after 20ms.

    You can get the kind of vibration you describe if the delay between servo pulses is much more than 20ms or if the power supply voltage drops under load below the point where the servo functions properly. It needs to be at least 4.8V typically. If the Stamp is running off the same supply, a voltage drop below about 4.3V will cause the Stamp to reset. The restarting of the program every time it does a PULSOUT to the servo can cause the vibration you describe.
  • eagle4ceseagle4ces Posts: 14
    edited 2010-01-21 18:22
    am using 8volts for the stamp.when the servo starts vibrating the voltaage drops to 4.4.usin this code below
    do
    pulsout 7,750
    pause 20
    loop
  • Mike GreenMike Green Posts: 23,101
    edited 2010-01-21 18:34
    Your Stamp is repeatedly restarting as the voltage drops too low for it to operate when the servo starts to move.
    Are you trying to run the servo off the regulated 5V output of the Stamp? That won't work. There's not enough current available.
    Servos are designed to operate off a power source from about 4.8V to about 7.2V with current drain peaking around 1A.
    You can damage a servo if you try to operate it on higher voltages.
  • eagle4ceseagle4ces Posts: 14
    edited 2010-01-22 10:58
    let me come clear.the i use 8volts to power the stamp,and 4.9 for the servo which drops to 4.4 when servo starts running.please i dont understand what u meant by trying to run the servo off the regulated 5v output of the stamp.does that mean the signal should not be connected directly to the i/o pin.
  • allanlane5allanlane5 Posts: 3,815
    edited 2010-01-22 12:36
    The problem it looks like you're having is that your 4.9 volt power supply does not have enough CURRENT for the servo.

    Power supplies are specified in both VOLTAGE (4.9 volts) and CURRENT (in amps, or milli-amps). You need both. If your power supply cannot supply enough CURRENT (1 amp, in this case) then its output voltage drops. When its output voltage drops, this resets the BS2.

    Ah -- if that is NOT your problem, then you could still have the problem of not having connected the BS2 ground and the Servo ground together. The BS2 control signal needs to be 'referenced' to the Servo power ground. You achieve this "reference" by connecting the two grounds together.

    If you want to know if your BS2 IS resetting, put a DEBUG "Reset" statement at the beginning of your program. If, when you try to move the servo, you see "Reset" on your debug output screen, it's a power supply problem.
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