Quadrotor Lab: Exploring Cascade Control and Real-World Dynamics

What Quadrotor Dynamics Are

Quadrotors are unmanned aerial vehicles (UAVs) that use four rotors to achieve lift and control. They operate in six degrees of freedom: three translational movements (pitch, roll, yaw) and three rotational movements (forward/backward, side-to-side, up/down). The dynamics of a quadrotor involve complex interactions between these movements.

The simulation allows you to explore how these dynamics are managed through cascade control systems. This involves multiple layers of controllers working together: position, velocity, attitude, and rate. Each layer addresses specific aspects of the vehicle's behavior, ensuring stability and precise control.

Cascade Control Systems

A cascade control system is a hierarchical structure where each controller manages one aspect of the system while being influenced by the output of the next higher-level controller. In the context of quadrotors, this means that the position controller adjusts the desired altitude and horizontal position based on feedback from the velocity controller. The attitude controller then stabilizes the orientation to maintain the desired position and velocity.

The rate controller ensures that the angular velocities are controlled accurately, which is crucial for maintaining stability during maneuvers or gusts of wind. This multi-layered approach allows for precise control over each aspect of the quadrotor's movement.

Rotor Thrust and Battery Sag

The thrust generated by a quadrotor’s rotors is governed by momentum theory, which describes how the rotor blades transfer energy to the air. The simulation models this with an accurate representation of the rotor dynamics, showing how changes in power input affect the lift produced by each rotor.

Battery sag refers to the decrease in voltage as the battery discharges under load. This can significantly impact the performance and stability of a quadrotor. The simulation includes a step-response test that verifies how the battery voltage affects the system's response, ensuring realistic behavior.

Gust Rejection

Gust rejection is critical for maintaining control in the face of external disturbances such as wind. The cascade controller must be robust enough to counteract these disturbances without losing stability. The simulation demonstrates how each layer of the controller works together to reject gusts and maintain a stable flight path.

By simulating various gust conditions, you can observe how the system adapts and whether it remains within safe operating limits. This is essential for designing real-world quadrotors that can operate reliably in unpredictable environments.

Frequently asked questions

Try it live

Everything above runs in your browser — open Quadrotor Lab: Cascade Attitude Control, Rotor Thrust, Battery Sag and Gust Rejection and change the parameters while it is running. Nothing is installed, nothing is uploaded, the whole model lives in one tab.