Why does turning on my water pump turn my servos?

[purpleudon]

I am trying to build a car that shoots water using the esp32 with Bluetooth compatibility. Everything has been working well so far except when I turn on the water pump which forces all the servos to get set to 0 degrees no matter what their previous setting was. It seems that when these servos go to 0 degrees, they keep trying to push beyond their mechanical range of motion because they loudly buzz instead of snapping to a position. I have tried a flyback diode ( 1N5819 Schottky) across the relay switching the pump on and off but that doesn't seem to work. Also the relay I used is rated for 3V, not 5V like the one in the schematic drawing. The motor driver I am using is the L298N All 6V sources are from 4 AA batteries in series. Thanks. I will attach my schematic, code, and image of circuit:

// this header is needed for Bluetooth Serial -> works ONLY on ESP32
#include "BluetoothSerial.h" 
#include <ESP32Servo.h>

Servo vertical;
Servo horizontal;
BluetoothSerial ESP_BT; 

int enA = 13;
int in1 = 12;
int in2 = 14;  

int enB = 4;
int in3 = 2;
int in4 = 15;

int pump = 18;
int servoPinv = 21;
int servoPinh = 23;
// Parameters for Bluetooth interface
int incoming;

void setup() {
  Serial.begin(19200);
  ESP_BT.begin("ESP32_Control"); //Name of your Bluetooth interface -> will show up on your phone
  ESP32PWM::allocateTimer(0);
	ESP32PWM::allocateTimer(1);
	ESP32PWM::allocateTimer(2);
	ESP32PWM::allocateTimer(3);
  vertical.setPeriodHertz(50);
  horizontal.setPeriodHertz(50);
  vertical.attach(servoPinv, 500, 2400);
  horizontal.attach(servoPinh, 500, 2400);
  pinMode (enA, OUTPUT);
  pinMode (in1, OUTPUT);
  pinMode (in2, OUTPUT);
  pinMode (enB, OUTPUT);
  pinMode (in3, OUTPUT);
  pinMode (in4, OUTPUT);
  pinMode (pump, OUTPUT);
}

void loop() {
  
  // -------------------- Receive Bluetooth signal ----------------------
  if (ESP_BT.available()) 
  {
    incoming = ESP_BT.read(); //Read what we receive 

    // separate button ID from button value -> button ID is 10, 20, 30, etc, value is 1 or 0
    int button = floor(incoming / 10);
    int value = incoming % 10;
    
    switch (button) {
      case 1:  
        Serial.print("Backward:"); Serial.println(value);
        digitalWrite(in1, 1);
        digitalWrite(in2, 0);
        digitalWrite(in3, 1);
        digitalWrite(in4, 0);
        vertical.write(0); 
        horizontal.write(0);
        Serial.print("Servo:0");
        break;
      case 2:  
        Serial.print("Forward:"); Serial.println(value);
        digitalWrite(in1, 0);
        digitalWrite(in2, 1);
        digitalWrite(in3, 0);
        digitalWrite(in4, 1);
        vertical.write(20); 
        Serial.print("Servo:20");
        horizontal.write(20);
        break;
      case 3:  
        Serial.print("Still:"); Serial.println(value);
        digitalWrite(in1, 1);
        digitalWrite(in2, 1);
        digitalWrite(in3, 1);
        digitalWrite(in4, 1);
        vertical.write(40);
        horizontal.write(40);
        Serial.print("Servo:40");
        break;
      case 4:  
        Serial.print("Left:"); Serial.println(value);
        digitalWrite(in1, 1);
        digitalWrite(in2, 1);
        digitalWrite(in3, 0);
        digitalWrite(in4, 1);
        vertical.write(80);
        horizontal.write(80);
        Serial.print("Servo:80");
        break;
      case 5:  
        Serial.print("Right:"); Serial.println(value);
        digitalWrite(in1, 0);
        digitalWrite(in2, 1);
        digitalWrite(in3, 1);
        digitalWrite(in4, 1);
        vertical.write(100);
        horizontal.write(100);
        Serial.print("Servo:100");
        break;
      case 6:  
        Serial.print("Pump:"); Serial.println(value);
        if(value == 1){
        digitalWrite(pump, HIGH);
        digitalWrite(in1, 1);
        digitalWrite(in2, 1);
        digitalWrite(in3, 1);
        digitalWrite(in4, 1);
        }
        if(value == 0){
        digitalWrite(pump, LOW);
        digitalWrite(in1, 1);
        digitalWrite(in2, 1);
        digitalWrite(in3, 1);
        digitalWrite(in4, 1);
        }
        Serial.print("Pump: done"); Serial.println(value);
        break;
      default:
        Serial.print(":(");
        digitalWrite(in1, 1);
        digitalWrite(in2, 1);
        digitalWrite(in3, 1);
        digitalWrite(in4, 1);
        break;
    }
  analogWrite(enA, 255); // Send PWM signal to motor A 
  analogWrite(enB, 255); // Send PWM signal to motor B
  }
}

[groundFungus]

Monitor the servo supply voltage, during operation, with your DMM. Is the voltage steady or does it fluctuate? Servos can misbehave if their supply voltage is unsteady.

[sterretje]

I don't know the answer. But if the pump has its own battery, you should not have the line that I crossed.

[LarryD]

We always strive to keep electrical noise to a minimum in our circuits.

Place a kickback diode across the pump’s coil ( 1N400X ).

[groundFungus]

You can also reduce the noise that the motor puts onto the power supply wiring by putting caps across the motor and to ground to bypass noise.

[kairuiwater]

Thanks for sharing, I learned a lot