Last Updated: 08/01/2024
#57 GS-1502 Linear Servo
Components >> #57 GS-1502 Linear Servo
GS-1502 Linear Servo
I'm always on the look out for components that would make model railway control easier. At the moment I am using MG90S servos for point control and one of the issues is rtansalating the rotary motino of the servo to a linear movement of the point. Wouldn't it be nice if there was a linear servo.
So while searching for something else I came across some linear servos on Ali express, as the servo was so cheap i ordered one to give it a try.
IMPORTANT
These servos come in a right of left handed versions and are often sold in pairs.
Mine came with a very small connector so I had to solder on the usual 2.54mm pitch connector. You can buy them with the standard servo connectors but watch what you are buying.
Below are the specifications.
| Item | Specifications |
|---|---|
| Weight | 1.8g(include connector wire) |
| Speed | 0.11 sec @3.7v |
| Torque | 29.5g of force |
| Rotation | maximum 180° |
| Voltage | 3.7V-5V |
| Gear | Nylon |
| Dimensions | 21 x 15 x 12mm (LWH) |
| Type | digital. |
| Life Cycle | 15000 unloaded |
| Movement | approx 7mm |
WARNING: Although it states the life expectancy is 15000 moves, that is unloaded. If the servo is pushing/pulling any type of load that is going to be drastically reduced as the servo movement is a plastic gear moving up a metal thread.
although the servo may have some uses for light weight animations I certainly won't be using them for point control.
I tested mine with a PCA9685 PWM Servo driver board with some very basic code listed below.
It worked without any problems so the control side is no complicated.
Pros:
Very small
Easy to control
Can be mixed with other types of servo on the same PCA9685 board
True linear movement
Quiet
Cons:
Life Expectancy
Lower torque than SG90/MG90 so can only move very light loads.
Cicuit Diagram
If you have never used the PCA9685 PWM Servo driver board please check out this tutorial: PCA9685 PWM Servo Board
Wiring:for a few common boards
SDA/SCL connections
Arduino UNO:
A4 (SDA), A5 (SCL)
:
Arduino Mega 2560:
20 (SDA), 21 (SCL)
:
ESP32: 21(SDA), 22 (SCL)
For other Arduino boards see:https://www.arduino.cc/en/reference/wire
Example 1: PCA9685GA1502v1.ino
Click to Download code: PCA9685GA1502v1.ino
A very simple sketch that moves the servo backwards and forwards at maximum speed followed by a slower movement.
This code is just for testing the board works.
/* PCA9685GA1502v1
08/01/2024
Test of a GS-1502 Linear Servo with PCA9685
some quick and dirty code just to see how the board performs.
Visit http://www.digitaltown.co.uk/projectPCA9685PointControl.php for some better control code
that does NOT use delay()
*/
#include "Wire.h"
#include "Adafruit_PWMServoDriver.h"
//PCA 9685 settings
Adafruit_PWMServoDriver servoBoard = Adafruit_PWMServoDriver(0x40);//Address found from I2C scanner
#define USMIN 832 // This is the rounded 'minimum' microsecond length based on the minimum pulse of 150
//#define USMIN 600 // This is the rounded 'minimum' microsecond length based on the minimum pulse of 150
#define USMAX 2400 // This is the rounded 'maximum' microsecond length based on the maximum pulse of 600
#define SERVO_FREQ 50 // Analog servos run at ~50 Hz updates
//end pca9685 settings
//sets the position of the servo in degrees.
void setServoPos(int servo, int pos) {
//This first bit of code makes sure we are not trying to set the servo outside of limits
int sendPos;
if (pos > 179) {
pos = 179;
}
if (pos < 0) {
pos = 0;
}
sendPos = USMIN + ((USMAX - USMIN) / 180 * pos);
if (servo > -1 && servo < 16) { //only try to move valid servo addresses
servoBoard.writeMicroseconds(servo, sendPos);
}
}
void setup() {
Serial.begin(9600);
Serial.println("PCA9685GA1502v1");
servoBoard.begin();
servoBoard.setOscillatorFrequency(27000000);
servoBoard.setPWMFreq(SERVO_FREQ); // Analog servos run at ~50 Hz updates
delay(10);//let the above values take effect
}
void loop() {
int q;
setServoPos(15, 179);
Serial.println("179");
delay(2000);
setServoPos(15, 0);
Serial.println("0");
delay(2000);
for(q=0;q<180;q++){
setServoPos(15, q);
delay(50);
}
delay(1000);
for(q=179;q>-1;q--){
setServoPos(15, q);
delay(50);
}
delay(1000);
}
Additional Resource Links
PCA9685 PWM Servo Board 27/12/2023
PCA9685 Servo Control with buttons, point/turnout control for model railways 01/01/2024
Contact
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and use #57 GS-1502 Linear Servo as a reference.