Jittering motors ( and bad logic?..)

Projects Programming
1

Hello, I have made the following code, trying to move 2 servo motors at different speeds so they sweep at the same time. However I have noticed that they can get a bit jittery, so I was wondering if anyone knew how I could fix this, by increasing the speed or the wait time ( I actually have no clue since I've never worked with motors before, if its useful to know, they are sg90 motors ). Any help is appreciated :slight_smile:

#include <Servo.h>
Servo servoMotor; 
Servo servoMotor2;
unsigned long previousMillis = 0;  
const long interval = 40000;
int initialPosMotor = 90; 
int initialPosMotor2 = 90;
int maxPosMotor = 100;
int maxPosMotor2 = 150;
int minPosMotor = 90;
int minPosMotor2 = 90;

bool goingBack = false;

void setup() {
  Serial.begin(9600);
  servoMotor.attach(7); 
  servoMotor2.attach(8);
}

void loop() {
   unsigned long currentMillis = micros();
   // Check if enough time has passed
  if (currentMillis - previousMillis >= interval) {
    previousMillis = currentMillis;
 	int speed = 1;
	int x = maxPosMotor - minPosMotor;
    int y = maxPosMotor2 - minPosMotor2;
    int ratio = abs(y) / abs(x); // ratio for second motor
       //initialPosMotor += speed;
    
    if (!goingBack) {
      servoMotor.write(initialPosMotor);
      servoMotor2.write(initialPosMotor2);

      initialPosMotor += speed;
      initialPosMotor2 += ratio;
      Serial.println("This is the ratio");
      Serial.println(ratio);

      if (initialPosMotor >= maxPosMotor) {
        goingBack = true;
      }
    }

    else {
      servoMotor.write(initialPosMotor);
      servoMotor2.write(initialPosMotor2);

      initialPosMotor -= speed;
      initialPosMotor2 -= ratio;

      if (initialPosMotor <= minPosMotor) {
        goingBack = false;
      }
    }
	Serial.println("This is the first motor");
    Serial.println(initialPosMotor);
    Serial.println("This is the second motor");
    Serial.println(initialPosMotor2);
  }
}
3

The main problem in your sketch are that many Serial.prints() in your loop - especially at 9600 Baud only. These prints slow down your loop significantly, what makes the jitter.
At least use higher baud - e.g. 115200. Or delete the prints at all.

4

you could consider a time based interpolation

#include <Servo.h>

const byte motorPin1 = 7;
const byte motorPin2 = 8;

Servo servoMotor;
Servo servoMotor2;

const float minPosMotor = 90.0;
const float maxPosMotor = 100.0;
const float minPosMotor2 = 90.0;
const float maxPosMotor2 = 150.0;

const unsigned long forwardTime = 400000; // 400 ms in microseconds
const unsigned long cycleTime = forwardTime * 2; // forward + backward

float mapf(float x, float in_min, float in_max, float out_min, float out_max) {
  return (x - in_min) * (out_max - out_min) / (in_max - in_min) + out_min;
}

void setup() {
  servoMotor.attach(motorPin1);
  servoMotor2.attach(motorPin2);
}

void loop() {
  unsigned long t = micros() % cycleTime;
  float fraction = t < forwardTime
                   ? mapf(t, 0, forwardTime, 0.0, 1.0)
                   : mapf(t, forwardTime, cycleTime, 1.0, 0.0);

  float posMotor = mapf(fraction, 0.0, 1.0, minPosMotor, maxPosMotor);
  float posMotor2 = mapf(fraction, 0.0, 1.0, minPosMotor2, maxPosMotor2);

  servoMotor.write(posMotor);
  servoMotor2.write(posMotor2);
}
5

Hi, @Duinojr

What are you using for a power supply for the servos?

Can you please post a copy of your circuit, a picture of a hand drawn circuit in jpg, png?
Hand drawn and photographed is perfectly acceptable.
Please include ALL hardware, power supplies, component names and pin labels.

Tom.... :smiley: :+1: :coffee: :australia:

6

That won't really help, because servo.h can't handle float. If you need a better resolution, you need to use µs instead of angle for the pulslength.

7

Sure but the value will be truncated and it will (or should) work OK anyway

➜ test it here

8

humm sooo for this project in particular I am also using a light sensor and 4 RGB LED so the only circuit I have is with all of those, so here is the circuit, ( It's a bit messy and the RGBs dont do the right color, but everything else is working, sorry )

Capture d’écran 2026-02-08 100119
Capture d’écran 2026-02-08 1001191461×561 157 KB

( I dont know if this is readable :melting_face: )

Capture d’écran 2026-02-08 100532
Capture d’écran 2026-02-08 100532782×567 28.3 KB

( No idea if this picture helps but I can’t take a better one :confused: )

Capture d’écran 2026-02-08 100813
Capture d’écran 2026-02-08 100813980×804 129 KB

9

So where ary getting the power from for the servos?
The UNO USB?

Tom.... :smiley: :+1: :coffee: :australia:

10

uh well right now I am indeed, I connected them to the 5v :sweat_smile: , but when I just used a simple code to sweep them, it worked well, so I did not move them

11

Hi, @Duinojr

Driving two let alone one servo from the UNO is not recommended from the PC supply, you need a separate supply, possibly 3 x AA batteries to test.

Tom.... :smiley: :+1: :coffee: :australia:

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