Robot with Wheel Steering

How to Control a Robot with Wheel Steering (Car-Like Design)

Robots with wheel steering, similar to a car, are less common in robotics due to limitations in agility. However, it’s entirely possible to implement this design using Synthiam’s ARC software and the Custom Movement Panel v2. This tutorial will guide you through the process, highlight key considerations, and explain the limitations of this approach.

Why Caster Wheels Are Preferred

Wheel-steered robots lack the ability to pivot in place, which impacts their agility. This makes them less suitable for navigating tight spaces or complex environments. Instead, designs with caster wheels or pivoting mechanisms allow for smooth directional changes and reduce strain on motors or servos. Nonetheless, if you opt for a car-like wheel steering design, here’s how you can make it work effectively.

What You Need

  • A robot chassis with wheel steering.
  • Synthiam ARC software.
  • Custom Movement Panel v2 (available here).
  • Motor controller and servos connected to the robot’s hardware.

Steps to Implement Wheel Steering

1. Set Up the Custom Movement Panel

Add the Custom Movement Panel v2 to your ARC project and configure the ports for:

  • Forward motor control.
  • Reverse motor control.
  • PWM (speed control).
  • Servo (steering).

2. Understand the Movement Manager

In ARC, the Movement Manager controls all movement panels. When a robot skill requests to "move forward," it specifies left and right wheel speeds. For wheel steering:

  • Forward and reverse motions can include slight turns (differential speeds).
  • Steering adjustments are based on these speed differences.

3. Write Control Scripts

Forward Script


// Set the motor direction to forward
Digital.set(d0, true); // Enable forward direction on motor
Digital.set(d1, false); // Disable reverse direction on motor

// Calculate the speed for the PWM
var topSpeed = Math.max(Movement.getSpeedLeft(), Movement.getSpeedRight());
var speed = Utility.map(topSpeed, 0, 255, 0, 100);
Pwm.set(d2, speed);

// Calculate the speed difference
var diffSpeed = Movement.getSpeedLeft() - Movement.getSpeedRight();
var steeringAngle = Utility.map(diffSpeed, -255, 255, 1, 180);
Servo.setPosition(d3, steeringAngle);

Reverse Script


// Set the motor direction to reverse
Digital.set(d0, false); // Disable forward direction on motor
Digital.set(d1, true); // Enable reverse direction on motor

// Calculate the speed for the PWM
var topSpeed = Math.max(Movement.getSpeedLeft(), Movement.getSpeedRight());
var speed = Utility.map(topSpeed, 0, 255, 0, 100);
Pwm.set(d2, speed);

// Calculate the speed difference
var diffSpeed = Movement.getSpeedLeft() - Movement.getSpeedRight();
var steeringAngle = Utility.map(diffSpeed, -255, 255, 1, 180);
Servo.setPosition(d3, steeringAngle);

Stop Script


// Disable motor movement
Digital.set(d0, false); // Disable forward direction on motor
Digital.set(d1, false); // Disable reverse direction on motor

4. Test and Calibrate

  • Assign ports (d0, d1, d2, d3) to match your robot’s wiring.
  • Test each script to ensure proper behavior.
  • Adjust servo angle ranges in Utility.map based on your servo’s specifications.

5. Limitations of Wheel Steering

  • Reduced Maneuverability: Without a pivoting mechanism, tight turns are challenging.
  • Increased Servo Strain: Continuous adjustments during steering can wear out servos faster.
  • Navigation Restrictions: Difficult to handle complex environments or obstacles.

For better performance, consider using caster wheels or designs inspired by robot vacuums.

Additional Notes

  • Forward and reverse movements can include slight directional adjustments using speed differentials.
  • The Movement Manager cannot handle pure left or right turns in this setup.
  • Ensure proper power supply to avoid hardware failures.

By following these steps, you can control a robot with wheel steering effectively in ARC. While this design has its drawbacks, it’s a functional and interesting way to experiment with robotics.