Visualize Cylinder with WrenchΒΆ

We apply a constant body-fixed wrench to a cylinder and integrate acceleration to twist and exponential coordinates of transformation to finally compute the new pose of the cylinder.

vis moving cylinder with wrench
print(__doc__)


import numpy as np
from pytransform3d.transformations import (
    transform_from_exponential_coordinates)
import pytransform3d.visualizer as pv


def spatial_inertia_of_cylinder(mass, length, radius):
    I_xx = I_yy = 0.25 * mass * radius ** 2 + 1.0 / 12.0 * mass * length ** 2
    I_zz = 0.5 * mass * radius ** 2
    inertia = np.eye(6)
    inertia[:3, :3] *= np.array([I_xx, I_yy, I_zz])
    inertia[3:, 3:] *= mass
    return inertia


def animation_callback(
        step, cylinder, cylinder_frame, prev_cylinder2world,
        Stheta_dot, inertia_inv):
    if step == 0:  # Reset cylinder state
        prev_cylinder2world[:, :] = np.eye(4)
        Stheta_dot[:] = 0.0

    # Apply constant wrench
    wrench_in_cylinder = np.array([0.1, 0.001, 0.001, 0.01, 1.0, 1.0])
    dt = 0.0005

    Stheta_ddot = np.dot(inertia_inv, wrench_in_cylinder)
    Stheta_dot += dt * Stheta_ddot
    cylinder2world = transform_from_exponential_coordinates(
        dt * Stheta_dot).dot(prev_cylinder2world)

    # Update visualization
    cylinder_frame.set_data(cylinder2world)
    cylinder.set_data(cylinder2world)

    prev_cylinder2world[:, :] = cylinder2world

    return cylinder_frame, cylinder


fig = pv.figure()

# Definition of cylinder
mass = 1.0
length = 0.5
radius = 0.1
inertia_inv = np.linalg.inv(
    spatial_inertia_of_cylinder(mass=mass, length=length, radius=radius))

# State of cylinder
cylinder2world = np.eye(4)
twist = np.zeros(6)

cylinder = fig.plot_cylinder(length=length, radius=radius, c=[1, 0.5, 0])
cylinder_frame = fig.plot_transform(A2B=cylinder2world, s=0.5)

fig.plot_transform(A2B=np.eye(4), s=0.5)

fig.view_init()

if "__file__" in globals():
    fig.animate(
        animation_callback, n_frames=10000,
        fargs=(cylinder, cylinder_frame, cylinder2world, twist, inertia_inv),
        loop=True)
    fig.show()
else:
    fig.save_image("__open3d_rendered_image.jpg")

Total running time of the script: ( 0 minutes 0.389 seconds)

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