Servo stops working after first rotation

i've got 5v arduino nano (it still works despite it's age) hooked dgservo s05nf std , i'm trying rotate 180 , 0 after receiving serialevent. rotation sort of works, starts twitch , forth few seconds , doesn't receive more serialevent calls. if comment out servo calls, builtin led works fine indicator, , serialevent works on several messages. using usb supplied 5v , tested sweep successfully.

any thoughts appreciated:

code: [select]

#include <servo.h>

const int servo_pin = 9;

servo servo;
int pos = 0;
string input = "";
bool inputcomplete = false;
bool servorunning = false;
unsigned long pmillis = 0;
const long delay = 3000;

void setup() {
  serial.begin(9600);
  input.reserve(200);
  servo.attach(servo_pin);
}

void loop() {
  if (inputcomplete) {
    if (input.equals("d")) {
      initservo();
    }
    input = "";
    inputcomplete = false;
  }

  if (servorunning && millis() - pmillis > delay) {
    returnservo();
  }
}

void serialevent() {
  while (serial.available()) {
    char inchar = (char)serial.read();
    if (inchar == '\n') {
      inputcomplete = true;
    } else {
      input += inchar;
    }
  }
}

void initservo() {
  pmillis = millis();  
  servorunning = true;
  digitalwrite(led_builtin, high);
  servo.write(180);
}

void returnservo() {
  servorunning = false;
  digitalwrite(led_builtin, low);
  servo.write(0);
}


a servo can suck more power standard usb port can provide. usb supposed give 500ma negotiation , 100ma without. nano doesn't attempt negotiation.

power separate supply - phone charger source of 5v. have higher current limit.

Arduino Forum > Using Arduino > Motors, Mechanics, and Power (Moderator: fabioc84) > Servo stops working after first rotation

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