This example is also available as a Jupyter notebook that can be run locally The notebook can be found in the
examples directory of the package. If the notebooks are missing, you may need to run
using Pkg; Pkg.build().
Please note that RigidBodySim.jl now provides a more capable simulation environment.
We'll just use the double pendulum model, loaded from a URDF:
srcdir = dirname(pathof(RigidBodyDynamics)) urdf = joinpath(srcdir, "..", "test", "urdf", "Acrobot.urdf") mechanism = parse_urdf(urdf)
Spanning tree: Vertex: world (root) Vertex: upper_link, Edge: shoulder Vertex: lower_link, Edge: elbow No non-tree joints.
Let's write a simple controller that just applies $10 \sin(t)$ at the elbow joint and adds some damping at the shoulder joint:
shoulder, elbow = joints(mechanism) function simple_control!(torques::AbstractVector, t, state::MechanismState) torques[velocity_range(state, shoulder)] .= -1 .* velocity(state, shoulder) torques[velocity_range(state, elbow)] .= 10 * sin(t) end;
Basic simulation can be done using the
simulate function. We'll first create a
MechanismState object, and set the initial joint configurations and velocities:
state = MechanismState(mechanism) zero_velocity!(state) set_configuration!(state, shoulder, 0.7) set_configuration!(state, elbow, -0.8);
Now we can simply call
simulate, which will return a tuple consisting of:
- simulation times (a
- joint configuration vectors (a
- joint velocity vectors (a
final_time = 10. ts, qs, vs = simulate(state, final_time, simple_control!; Δt = 1e-3);
For access to lower-level functionality, such as different ways of storing or visualizing the data generated during the simulation, it is advised to simply pattern match the basic
For visualization, we'll use
MeshCatMechanisms, an external package based on RigidBodyDynamics.jl.
MechanismVisualizer and open it in a new browser tab (see
MeshCat.jl for other options):
mvis = MechanismVisualizer(mechanism, URDFVisuals(urdf));
┌ Info: MeshCat server started. You can open the visualizer by visiting the following URL in your browser: └ http://localhost:8700
MeshCatMechanisms.animate(mvis, ts, qs; realtimerate = 1.);
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