How to create a stable pile of cylindrical objects in a tray?

[onishu]

First of all, I want to express my admiration for your fantastic work. I'm eager to use your simulator to develop robotic algorithms.
I'm trying to create a simulation of bin picking using a Franka Panda robot.
Specifically, I want to create a scene with cylindrical parts randomly piled in a tray.
However, I'm encountering an issue: when I execute scene.step(), the pile of parts in the tray explodes or scatters.
Could you please provide guidance on how to create a stable pile of parts in the tray?
What settings or techniques should I use to prevent the parts from scattering when the simulation starts?
Thank you in advance for your help. I'm looking forward to using your simulator for developing robotic algorithms.

import genesis as gs
import numpy as np

gs.init(backend=gs.gpu)


scene = gs.Scene(
    viewer_options=gs.options.ViewerOptions(
        camera_pos=(3, -1, 1.5),
        camera_lookat=(0.0, 0.0, 0.5),
        camera_fov=30,
        res=(960, 640),
        max_FPS=60,
    ),
    sim_options=gs.options.SimOptions(
        dt=0.01,
    ),
    show_viewer=True,
    rigid_options=gs.options.RigidOptions(
        enable_joint_limit=True,
        enable_collision=True,
        gravity=(0, 0, -9.8),
    ),
)

plane = scene.add_entity(
    gs.morphs.Plane(),
)


tray_material = gs.materials.Rigid(rho=1000)
tray_surface = gs.surfaces.Default(color=(0.8, 0.8, 0.8))


entities = {}

entities["tray_bottom"] = scene.add_entity(
    material=tray_material,
    morph=gs.morphs.Box(
        pos=(0, 0.50, 0.005),
        size=(0.3, 0.3, 0.01),
        fixed=True,
    ),
    surface=tray_surface,
)

# トレイの側面
side_positions = [
    (0, 0.00 - 0.15, 0.025),
    (0, 0.00 + 0.15, 0.025),
    (-0.15, 0.00, 0.025),
    (0.15, 0.00, 0.025),
]
side_sizes = [
    (0.28, 0.02, 0.04),
    (0.28, 0.02, 0.04),
    (0.02, 0.28, 0.04),
    (0.02, 0.28, 0.04),
]
for i, (pos, size) in enumerate(zip(side_positions, side_sizes)):
    side_name = f"tray_side{i + 1}"
    entities[side_name] = scene.add_entity(
        material=tray_material,
        morph=gs.morphs.Box(
            pos=pos,
            size=size,
            fixed=True,
        ),
        surface=tray_surface,
    )
    scene.link_entities(entities["tray_bottom"], entities[side_name], "box_baselink", "box_baselink")

num_cylinders = 40
cylinders = []
for i in range(num_cylinders):
    cylinder = scene.add_entity(gs.morphs.Cylinder(radius=0.02, height=0.05, pos=(np.random.uniform(-0.13, 0.13), 0.50 + np.random.uniform(-0.13, 0.13), 0.03 + np.random.uniform(0, 0.04))))
    cylinders.append(cylinder)

cam = scene.add_camera(pos=(3, -1, 1.5), lookat=(0.0, 0.0, 0.5), fov=30, res=(960, 640), GUI=False)


########################## build ##########################
scene.build()

cam.start_recording()
for i in range(100):
    print("hold", i)
    scene.step()

    cam.render()
cam.stop_recording(save_to_filename="video.mp4", fps=60)

video.mp4

[wangyian-me]

They are expected to be scattered if they are in collision from the beginning. You can tune the damping of the dofs to let it solve the collision and in the meantime won't explode.

[onishu]

Thank you for your comment.
I understand the first setting to avoid bumping into each other, but I don't know how to set the damping of the dofs setting.
What should I do?

[onishu]

Dear @wangyian-me

As per your advice, I first arranged the cylinders so they wouldn't collide with each other. Then, I simulated them falling freely due to gravity and hitting the tray below. However, when I defined the material using Rigid(), the bounce was too high, and they disappeared from the top of the tray. I tried using MPM.ElastoPlastic(), but they remained suspended without hitting the tray. Is this MPM method correct for implementing the damping you advised? Below is the code I created. I would appreciate your advice.

import genesis as gs
import numpy as np

gs.init(backend=gs.gpu)

scene = gs.Scene(
    viewer_options=gs.options.ViewerOptions(
        camera_pos=(3, -1, 1.5),
        camera_lookat=(0.0, 0.0, 0.5),
        camera_fov=30,
        res=(960, 640),
        max_FPS=60,
    ),
    sim_options=gs.options.SimOptions(
        dt=0.00001,
        gravity=(0, 0, -9.8),
    ),
    mpm_options=gs.options.MPMOptions(
        dt=0.00001,
        lower_bound=(-0.3, -0.3, -0.1),
        upper_bound=(0.3, 0.8, 0.3),
        particle_size=0.002,
        gravity=(0, 0, -9.8),
    ),
    # fem_options=gs.options.FEMOptions(
    #     dt=0.00001,
    #     damping=1.0,
    # ),
    show_viewer=True,
)

# plane tray
tray = scene.add_entity(
    gs.morphs.Box(
        pos=(0, 0, 0.02),
        size=(0.5, 0.5, 0.04),
        fixed=True,
    ),
    material=gs.materials.Rigid(),
)

num_cylinders = 10
for i in range(num_cylinders):
    cylinder = scene.add_entity(
        gs.morphs.Cylinder(
            radius=0.01,
            height=0.03,
            pos=(np.random.uniform(-0.2, 0.2), np.random.uniform(-0.2, 0.2), np.random.uniform(0.05, 0.1)),
            euler=(np.random.uniform(0, 2 * np.pi), np.random.uniform(0, 2 * np.pi), np.random.uniform(0, 2 * np.pi)),
        ),
        material=gs.materials.MPM.ElastoPlastic(),
    )

scene.build()

for i in range(20000):
    scene.step()

[wangyian-me]

when I defined the material using Rigid(), the bounce was too high, and they disappeared from the top of the tray

Can I see the video?

but I don't know how to set the damping of the dofs setting

set the mass of the cylinders so they are not too light

for link in cylinder.links:
        link._inertial_mass = 1.0

...
scene.build()

...

for dof in range(cylinder.dof_start, cylinder.dof_end, 1):
        cylinder.solver.dofs_info[dof].damping = 0.5