servo question

I'm trying to control some servos (model: Turnigy TG9e) using Arduino. I power them from an external power supply (5V, 3Amp) and not forgetting to make a common grounding. This works fine.

The problem is whenever I press the 'reset' button (on the Arduino), the servos are twitching fast all the way to one end which is a total disaster in my project :-/

I tried the following: (1) adding a resistor between the output pin and the servo command input. same problem. (2) adding a resistor between the servo command input and the ground. same problem.

what am I missing ?

ps: I also noticed that without ANY input signal to the servo (just power and ground), when I touch its signal wire - the servo still twitches...

I am having this exact same problem. I think the problem is in the code.

The variable I am using to write the angle is initialized as equal to 1. Therefore the arduino writes this value to the motor before entering the loop. This creates a total disaster as my project uses fragile parts not meant to accelerate so quickly. Here is the code I am using.

#include 

Servo myservo;  

const int pin0 = 0;
const int pin1 = 1;
int angle = 0;

void setup()
{
  Serial.begin(9600);
  myservo.attach(9);
}

void loop()
{

  Serial.print(analogRead(pin0));
  Serial.print(",");
  Serial.print(analogRead(pin1));
  Serial.print(",");
  Serial.println(angle);

  if (((analogRead(pin0)) > (analogRead(pin1))) && (analogRead(pin0) - (analogRead(pin1)) > 50))
  {

angle = (angle + 1);
myservo.write(angle);
delay(10);
}

  if (((analogRead(pin0)) < (analogRead(pin1))) && (analogRead(pin1) - (analogRead(pin0)) > 50))
{
angle = (angle - 1);
myservo.write(angle);
delay(10);
}

}

Thanks Justin, but I don’t believe that it’s a code problem. As I mentioned, it does the sudden jump even without any control signal (signal wire - unplugged !), just by the mere touch over the servo wires. I think it has something to do with static charges, or capacitance… (?!)

how does one properly deals with these erratic out-of-range jumps ? do I need an external servo controller?

You probably could lightly ground the signal lines with a high resistance resistor to keep the lines from having a floating charge. I think I've read that the arduino cycles thru the pins when it resets, which also could cause a problem.