# Barrier Functions in Cascaded Controller: Safe Quadrotor Control

## TL;DR

This paper introduces a quadratic programming approach using control barrier functions within a cascaded control architecture to ensure safety in quadrotor navigation, considering nonlinear dynamics and multiple constraints.

## Contribution

It presents a novel method combining CBFs with cascaded control for safe quadrotor operation, explicitly handling nonlinear dynamics and multiple safety constraints.

## Key findings

- Constructed non-conservative safe regions for quadrotors using CBFs.
- Ensured safety preservation in SE(3) despite cascaded barriers.
- Validated approach through simulation with static and dynamic constraints.

## Abstract

Safe control for inherently unstable systems such as quadrotors is crucial. Imposing multiple dynamic constraints simultaneously on the states for safety regulation can be a challenging problem. In this paper, we propose a quadratic programming (QP) based approach on a cascaded control architecture for quadrotors to enforce safety. Safety regions are constructed using control barrier functions (CBF) while explicitly considering the nonlinear underactuated dynamics of the quadrotor. The safety regions constructed using CBFs establish a non-conservative forward invariant safe region for quadrotor navigation. Barriers imposed across the cascaded architecture allows independent safety regulation in quadrotor's altitude and lateral domains. Despite barriers appearing in a cascaded fashion, we show preservation of safety for quadrotor motion in SE(3). We demonstrate the feasibility of our method on a quadrotor in simulation with static and dynamic constraints enforced on position and velocity spaces simultaneously.