newton.solvers.FeatherstoneSolver#

class newton.solvers.FeatherstoneSolver(model, angular_damping=0.05, update_mass_matrix_interval=1, friction_smoothing=1.0, use_tile_gemm=False, fuse_cholesky=True)[source]#

Bases: SolverBase

A semi-implicit integrator using symplectic Euler that operates on reduced (also called generalized) coordinates to simulate articulated rigid body dynamics based on Featherstone’s composite rigid body algorithm (CRBA).

See: Featherstone, Roy. Rigid Body Dynamics Algorithms. Springer US, 2014.

Instead of maximal coordinates body_q (rigid body positions) and body_qd (rigid body velocities) as is the case in SemiImplicitSolver and XPBDSolver, FeatherstoneSolver uses joint_q and joint_qd to represent the positions and velocities of joints without allowing any redundant degrees of freedom.

After constructing Model and State objects this time-integrator may be used to advance the simulation state forward in time.

Note

Unlike SemiImplicitSolver and XPBDSolver, FeatherstoneSolver does not simulate rigid bodies with nonzero mass as floating bodies if they are not connected through any joints. Floating-base systems require an explicit free joint with which the body is connected to the world, see newton.ModelBuilder.add_joint_free().

Semi-implicit time integration is a variational integrator that preserves energy, however it not unconditionally stable, and requires a time-step small enough to support the required stiffness and damping forces.

See: https://en.wikipedia.org/wiki/Semi-implicit_Euler_method

Example

solver = newton.solvers.FeatherstoneSolver(model)

# simulation loop
for i in range(100):
    solver.step(state_in, state_out, control, contacts, dt)
    state_in, state_out = state_out, state_in
__init__(model, angular_damping=0.05, update_mass_matrix_interval=1, friction_smoothing=1.0, use_tile_gemm=False, fuse_cholesky=True)#
Parameters:

  • model (Model) – the model to be simulated.

  • angular_damping (float, optional) – Angular damping factor. Defaults to 0.05.

  • update_mass_matrix_interval (int, optional) – How often to update the mass matrix (every n-th time the step() function gets called). Defaults to 1.

  • friction_smoothing (float, optional) – The delta value for the Huber norm (see warp.math.norm_huber()) used for the friction velocity normalization. Defaults to 1.0.

  • use_tile_gemm (bool, optional) – Whether to use operators from Warp’s Tile API to solve for joint accelerations. Defaults to False.

  • fuse_cholesky (bool, optional) – Whether to fuse the Cholesky decomposition into the inertia matrix evaluation kernel when using the Tile API. Only used if use_tile_gemm is true. Defaults to True.

step(state_in, state_out, control, contacts, dt)#