Robot simulation (Webots, Gazebo)

What you’ll learn

Why engineers simulate robots
The main free 3D robot simulators
The sim-to-real gap

Why simulate?

Test ideas before buying parts.
Crash without breaking anything.
Run thousands of tests overnight (and train AI).
Everyone can work on the robot at once.

RoboLearn’s robot simulator is a simple 2D version of the same idea.

3D simulators

Simulator	Notes
Webots	Free and open source; easy to start; many ready robot models; Python, C, C++ controllers; works with ROS 2
Gazebo	Free and open source; the classic partner for ROS 2
NVIDIA Isaac Sim	Photorealistic; needs a powerful NVIDIA GPU; used for AI training
CoppeliaSim	Flexible; free educational licence

They simulate physics (mass, friction, collisions), sensors (cameras, lidar, distance) and actuators (motors, joints).

The sim-to-real gap

Simulations are simplified. Real wheels slip, real sensors are noisy, batteries sag and floors aren’t flat. Code that works perfectly in simulation can fail on the real robot.

Reduce the gap by:

Adding noise to simulated sensors
Using realistic masses, motor limits and friction
Testing on the real robot early and often
Writing robust code (thresholds with margins, timeouts, fail-safes)

Example: a Webots controller (Python)

from controller import Robot

robot = Robot()
step = int(robot.getBasicTimeStep())
left = robot.getDevice("left wheel motor")
right = robot.getDevice("right wheel motor")
for m in (left, right):
    m.setPosition(float("inf"))   # velocity control mode
ds = robot.getDevice("ds_front")
ds.enable(step)

while robot.step(step) != -1:
    if ds.getValue() > 800:       # sensor-specific units: close
        left.setVelocity(-2); right.setVelocity(2)
    else:
        left.setVelocity(4); right.setVelocity(4)

(Device names depend on the robot model you load.)

Example: the gap in action

In the RoboLearn simulator the line follower never misreads the line. On a real track, a shiny patch of floor read as “black” made it turn suddenly. The fix, requiring two readings in a row before turning, also works in simulation, so test it there first.