Flashlight

Flashlight is a lightweight Python library for analyzing and solving quadrotor control problems. Flashlight enables you to easily solve for minimum snap trajectories that go through a sequence of waypoints, compute the required control forces along trajectories, execute the trajectories in a physics simulator, and visualize the simulation results. Flashlight also makes it easy to simulate external disturbances, and to recover from those disturbances using time-varying LQR feedback control. Flashlight includes physical models for 2D quadrotors, 3D quadrotors, and 3D quadrotor cameras.

The following code snippet shows how easy it is to start analyzing quadrotor trajectories using Flashlight. In this code snippet, we generate the control forces required for a 2D quadrotor to follow a simple trajectory, and simulate the results:

from pylab import *; import scipy.integrate

import flashlight.interpolate_utils as interpolate_utils
import flashlight.quadrotor_2d      as quadrotor_2d

# Define a simple position trajectory in 2D.
num_samples = 200
t_begin     = 0
t_end       = pi
dt          = (t_end - t_begin) / (num_samples - 1)

t = linspace(t_begin, t_end, num_samples)
p = c_[ sin(2*t) + t, t**2 ]

# Compute the corresponding state space trajectory and control trajectories for a 2D quadrotor.
q_qdot_qdotdot = quadrotor_2d.compute_state_space_trajectory_and_derivatives(p, dt)
u              = quadrotor_2d.compute_control_trajectory(q_qdot_qdotdot)

# Define a function that interpolates the control trajectory in between time samples.
u_interp_func = interpolate_utils.interp1d_vector_wrt_scalar(t, u, kind="cubic")

# Define a simulation loop.
def compute_x_dot(x_t, t):

    # Get the current control vector.
    u_t = u_interp_func(clip(t, t_begin, t_end))
    
    # Compute the state derivative from the current state and current control vectors.
    x_dot_t = quadrotor_2d.compute_x_dot(x_t, u_t).A1

    return x_dot_t

# Simulate.
x_nominal, _, _, _ = quadrotor_2d.pack_state_space_trajectory_and_derivatives(q_qdot_qdotdot)
x_0                = x_nominal[0]
x_sim              = scipy.integrate.odeint(compute_x_dot, x_0, t)

# Plot the results.
quadrotor_2d.draw(t, x_sim, t_nominal=t, x_nominal=x_nominal, inline=True)

Installation instructions, detailed code examples, and other documentation can be found at mikeroberts3000.github.io/flashlight.

Flashlight is designed and implemented by Mike Roberts.