ROBO | Servo Motor

Servo Motor

converts electrical energy to mechanical energy
used for precision control in engineering, robotics, and automation
position can be controlled with a controller, as the device is sent signals telling the motor exactly how far to rotate

Closed Loop

can only rotate for 180º as there is a pin to stop the motor from rotating further

Open Loop

can rotate the full 360º degrees

Weight

represents the torque of the motor
- how much force it can apply to a lever, which rotates the arm around the pivot
- in kg-cm or oz-in
can be found on the side of the motor
- the farther a point on the arm is from a pivot, the lower the maximum weight it can support
higher weight or torque rating leads to higher size as it requires larger gears and electrical motor

Rotation

The higher the voltage, the higher the torque, the stronger the motor, and the faster the motor will rotate
The motor uses more power when moving
measured in seconds per 60º of rotation

Parts

Outside

Main Housing

holds the internal components

Electrical Connections

red → positive/voltage wire
brown → ground wire
orange → pulse width modulation signal wire

Splined gear

where rotation occurs
the various attachments are placed here

Inside

Compound Gear Train

has gears and corresponding beairings
alternates between small number toothed and large numbered toothed gears to ensure a compact design
one side has the output and the other the input
- the input is connected to a DC motor that drives the gear
the motor has a high rotational speed but low torque
the gears convert this to an output with low speed but high torque

DC Motor

connected to a circuit board in the unit that controls the motor’s rotation and direction

Potentiometer

connects to the output gear and is a variable resistor
as it rotates, the resistance changes and the circuit board reads this to know the position of the output

Process

The controller sends a signal to the servo motor which determines the position it should rotate to. Pules of voltage are sent down the wire, every 20 miliseconds which vary in length.
- Wide pules entail that the servo moves to the left.
- Small pulses entail that it moves to the right.
- The position is between these two points, and is dependent on the width of the pulse.
The signal enters the circuit board and is converted to a voltage.
It passes through a comparator then to a motor driver, which controls the rotation of the DC motor.
- An internal H bridge circuit is used to control the direction of the rotation, which causes the gears to rotate.
The potentiometer rotates which divides and adjusts the resistance based on the position.

Potentiometer

If the potentiometer is pointed to the left, the voltage is 5V while to the right, it is 0V
It is connected to the comparator, which monitors the voltage to provide feedback.
As the pontentiometer changes the resistance from a minimum to maximum value, the voltage of the potentiometer and controller signal are compared.
The motor will turn until the difference between the two is zero.

Wiring

Breadboard

Connect 5V of Arduino to positive of breadboard.
Connect GND of Arduino to negative of breadboard.

Potentiometer

Connect 5V of breadboard/Arduino to left pin.
Connect GND of breadboard/Arduino to the right pin.
Connect A0 of Arduino to the center pin.

Servomotor

Connect 5V of breadboard/Arduino to red wire.
Connect GND of breadboard/Arduino to the brown wire.
Connect 9 of Arduino to the orange wire.

Code (does not include potentiometer)

#include <Servo.h>
//commands from a premade library will be used.
int pos = 0; //declares starting position
Servo servo_9; //declares name of servo
void setup()
{
  servo_9.attach(9, 500, 2500); //links servo to the needed pins
}

void loop()
{
  // sweep the servo from 0 to 180 degrees in steps
  // of 1 degrees
  for (pos = 0; pos <= 180; pos += 1) {
    // tell servo to go to position in variable 'pos'
    servo_9.write(pos);
    // wait 15 ms for servo to reach the position
    delay(15); // Wait for 15 millisecond(s)
  }
  for (pos = 180; pos >= 0; pos -= 1) {
    // tell servo to go to position in variable 'pos'
    servo_9.write(pos);
    // wait 15 ms for servo to reach the position
    delay(15); // Wait for 15 millisecond(s)
  }
}

#include <Servo.h> 
//commands from a premade library will be used.
int pos = 0; //declares starting position
Servo servo_9; //declares name of servo
int servoPin = 9; //declares connected pin
void setup()
{
  servo_9.attach(servoPin); //links servo to the needed pins
}

void loop()
{
  // sweep the servo from 0 to 180 degrees in steps
  // of 1 degrees
  for (pos = 0; pos <= 180; pos += 1) {
    // tell servo to go to position in variable 'pos'
    servo_9.write(pos);
    // wait 15 ms for servo to reach the position
    delay(15); // Wait for 15 millisecond(s)
  }
  for (pos = 180; pos >= 0; pos -= 1) {
    // tell servo to go to position in variable 'pos'
    servo_9.write(pos);
    // wait 15 ms for servo to reach the position
    delay(15); // Wait for 15 millisecond(s)
  }
}