Troubleshooting Arduino RC Car ESC Programming: Solving Forward and Backward Control Issues

Are you new to Arduino programming and diving into the exciting world of RC cars? Controlling your RC car with an Arduino board opens up a realm of possibilities, but it can also come with a few initial hurdles. One common challenge beginners face is getting their Electronic Speed Controller (ESC) to behave correctly, especially when it comes to forward and backward motion. Let’s break down a typical problem and explore how to get your Arduino RC car project running smoothly.

Many hobbyists encounter an issue where their RC car correctly turns left, moves forward, and stops, but then falters when attempting to move backward. Instead of reversing, the car might just stop completely, or only sporadically go in reverse. This can be frustrating, especially when forward motion works perfectly fine.

Let’s examine a sample code snippet and understand why this might be happening and how to fix it.

//Test Routine Program - By Stezipoo
#include <Servo.h>

//create servo objects
Servo steering;
Servo throttle;

int ledPin = 13;
int center = 95;
int right = 55;
int left = 130;

void setup() {
  pinMode(9, OUTPUT);    //sets pin 9 to output
  pinMode(10, OUTPUT);
  steering.attach(9);   // attach steering servo to pin 9
  throttle.attach(10);   // attach ESC to pin 10
  steering.write(95);    // centers steering
  throttle.write(90);    // sets mid throttle
}

void loop() {
  goLeft();
  goRight();
}

void goLeft()    // turn left, then go foward and stop
{
  steering.write(left);    // turn left
  delay(10);
  digitalWrite(ledPin, HIGH);
  delay(500);
  throttle.write(120);   // go forward
  delay(500);
  throttle.write(90);
  digitalWrite(ledPin, LOW);
  delay(2000);
}

void goRight()    // turn right, then go backward and stop
{
  steering.write(right);    // turn right
  delay(10);
  digitalWrite(ledPin, HIGH);
  delay(500);
  throttle.write(60);   // go backward
  delay(500);
  throttle.write(90);
  digitalWrite(ledPin, LOW);
  delay(2000);
}

This code is designed to make an RC car perform a sequence of actions: turn left, go forward, stop, turn right, go backward, and stop, repeating this loop. However, as the user described, the backward motion in the goRight() function is unreliable.

Understanding the Problem: ESC Calibration and Signal Range

The most likely culprit is how the ESC interprets the signal from the Arduino. ESCs for RC cars are essentially servo motors that control the speed of the motor. They require proper calibration to understand the range of signals that correspond to neutral, forward, and backward.

Here’s a breakdown of potential issues:

1. ESC Neutral Position: The throttle.write(90) in the setup() and stop sections of the code is intended to be the neutral or stop position. However, different ESCs might have slightly different neutral points. If 90 is not precisely the neutral signal for your ESC, it could be misinterpreting the forward and backward commands.

2. Throttle Range: The values throttle.write(120) for forward and throttle.write(60) for backward are based on a servo range of roughly 0-180. However, ESCs often have a narrower effective range for throttle control. It’s possible that 60 is not far enough below the neutral point to reliably trigger backward motion on your specific ESC.

3. ESC Programming Mode: Some ESCs need to be programmed to enable reverse. Consult your ESC’s manual to ensure that reverse is activated and to understand the specific signal ranges it expects.

Troubleshooting and Solutions:

1. ESC Calibration: The first and most crucial step is to calibrate your ESC with your Arduino. Most ESCs have a calibration procedure that you initiate upon powering up. This usually involves sending minimum and maximum throttle signals to the ESC so it can learn the endpoints. Refer to your ESC’s manual for the exact calibration steps. Typically, this involves something like:

   • Start with the throttle signal pin disconnected from the ESC.
   • Power on the ESC.
   • Connect the throttle signal pin to the Arduino pin sending a ‘full throttle’ signal (e.g., throttle.write(180)).
   • Wait for beeps from the ESC.
   • Send a ‘minimum throttle’ signal (e.g., throttle.write(0)).
   • Wait for more beeps.
   • Send the ‘neutral’ signal (e.g., throttle.write(90)).
   • The ESC should now be calibrated.

2. Adjust Throttle Values: After calibration, experiment with the throttle.write() values in your goLeft() and goRight() functions.

   • Forward: Increment the forward value (currently 120) in small steps (e.g., 125, 130, 135) to see if a higher value improves forward response.
   • Backward: Decrement the backward value (currently 60) in smaller steps (e.g., 55, 50, 45) to see if a lower value reliably triggers reverse. You might need to go significantly lower than 60.

3. Servo Library Range: The Arduino Servo library typically uses a range of 0-180 degrees (or microseconds equivalent). However, some ESCs might respond better to a slightly different range. While less common, you could explore if your ESC documentation suggests a different PWM range.

4. Code Logic: While the basic logic of the provided code seems correct for simple forward/backward control, double-check for any unintended delays or logical errors that might be interfering with the backward command. In this specific code, the delays seem reasonable for testing purposes.

Refined Code Example (with potential adjustments):

//Test Routine Program - By Stezipoo - Adjusted for potential ESC range
#include <Servo.h>

Servo steering;
Servo throttle;

int ledPin = 13;
int centerThrottle = 90; // Experiment with this neutral value
int forwardThrottle = 130; // Adjusted forward value
int backwardThrottle = 45; // Lower backward value
int rightSteer = 55;
int leftSteer = 130;


void setup() {
  pinMode(9, OUTPUT);
  pinMode(10, OUTPUT);
  steering.attach(9);
  throttle.attach(10);
  steering.write(95); // Center steering
  throttle.write(centerThrottle); // Set initial neutral throttle
  delay(3000); // Give ESC time to initialize
}

void loop() {
  goLeft();
  goRight();
}

void goLeft() {
  steering.write(leftSteer);
  delay(10);
  digitalWrite(ledPin, HIGH);
  delay(500);
  throttle.write(forwardThrottle); // Go forward - adjusted value
  delay(500);
  throttle.write(centerThrottle); // Stop
  digitalWrite(ledPin, LOW);
  delay(2000);
}

void goRight() {
  steering.write(rightSteer);
  delay(10);
  digitalWrite(ledPin, HIGH);
  delay(500);
  throttle.write(backwardThrottle); // Go backward - adjusted value
  delay(500);
  throttle.write(centerThrottle); // Stop
  digitalWrite(ledPin, LOW);
  delay(2000);
}

Key Improvements in the Refined Code and Troubleshooting:

• Descriptive Variable Names: Using names like centerThrottle, forwardThrottle, and backwardThrottle makes the code easier to understand and adjust.
• Initial Delay: Adding a delay(3000) in setup() after setting the initial throttle value can give the ESC more time to initialize properly before receiving commands.
• Emphasis on Calibration: The troubleshooting guide highlights ESC calibration as the primary step.
• Iterative Value Adjustment: The guide encourages systematic adjustment of throttle values to find the optimal range for the specific ESC.

By focusing on ESC calibration and carefully tuning the throttle signal range, you should be able to resolve the issue of unreliable backward motion in your Arduino RC car project and enjoy full control over your vehicle. Remember to always consult your ESC’s manual for specific instructions and recommended settings.