Servo Motor Random movement after powering it

[siren215]

Hello all,

I am using TowerPro MG996R motor for my testing purposes. Once i make sure that the code is ok, i will buy a better motor. My aim is to move it from 0° to 50° according to analog input 0 to 5 VDC. It moves when i keep it powered on, no problem with that. Now when i power it off and the power it on again, it moves right by say 45 to 50° and then gets its position(in between 0 to 50). This changes the fixed range of the motor to move and a new range of 0 to 50 ° is obtained i.e its initial position when I start it is changed. I want it to start at exact 0 when i power on. I am using a simple knob program to start off with, but this initial position keeps worrying me.

Code: [Select]

#include <Servo.h>

Servo myservo;  // create servo object to control a servo

int potpin = 0;  // analog pin used to connect the potentiometer
int val;    // variable to read the value from the analog pin

void setup()
{
  myservo.attach(9);  // attaches the servo on pin 9 to the servo object
}

void loop()
{
  val = analogRead(potpin);            // reads the value of the potentiometer (value between 0 and 1023)
  val = map(val, 0, 1023, 0, 50);     // scale it to use it with the servo (value between 0 and 180)
  myservo.write(val);                  // sets the servo position according to the scaled value
  delay(15);                           // waits for the servo to get there
}


Motor Specifications

Also now i am powering it from UNO itself, how much power supply is needed to power it externally? i tried 5v/1Amp supply, but it loads.


Thank You

[MarkT]

Always allow an amp per servo minimum, never power a servo from the Arduino's 5V.  Common the grounds.

[siren215]

Can you suggest a suitable supply for it? Why my power supply didnt work?

[Chagrin]

In your setup() you need to write() the initial position before you attach() it. If you skip that step then the servo is written the DEFAULT_PULSE_WIDTH (1500us, defined in Servo.h) for a fraction of a moment before you perform your own write() in main().

[MarkT]

Can you suggest a suitable supply for it? Why my power supply didnt work?

Ah, read the specs, the stall current is 2.5A.  You'll need a PSU rated for that current or it'll
just reset every time you try to move (servos pull stall current everytime they do a move
or any size - you might get away with slow ramping at 1A, but not a step change)

[siren215]

In your setup() you need to write() the initial position before you attach() it. If you skip that step then the servo is written the DEFAULT_PULSE_WIDTH (1500us, defined in Servo.h) for a fraction of a moment before you perform your own write() in main().

Thx, did that. Hope that issue is resolved.

Ah, read the specs, the stall current is 2.5A.  You'll need a PSU rated for that current or it'll
just reset every time you try to move (servos pull stall current everytime they do a move
or any size - you might get away with slow ramping at 1A, but not a step change)

Exactly the same thing happened. I will try to get a 2.5 Amps supply or 3 Amps supply for it, and lets see how it goes. Thanks again for suggestion guys.

[TomGeorge]

Hi,

When you use a separate supply for the servo, do you connect the gnd of the arduino and the gnd of the separate supply together?

Tom.....