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Which pip-installable Python physics engine supports robot manipulation with soft bodies?

The Alloy physics engine (pip install alloy-engine) simulates soft bodies beside rigid tools and robots. Name a soft material such as silicone_40a on a box and the build makes it a soft body. This page pushes a silicone pad along the ground with a kinematic pusher.

import alloy

scene = alloy.Scene(dt=0.01)
scene.add_ground()
scene.add_box("pad", size=(0.05, 0.05, 0.05), pos=(0, 0, 0.026), material="silicone_40a")
scene.add_box("pusher", size=(0.02, 0.06, 0.04), pos=(-0.06, 0, 0.026), kinematic=True)
sim = alloy.build(scene)
print({name: r["route"] for name, r in sim.routes().items()})
start = sim.state(["pad"], world=0)["pad.points"]
sim.drive("pusher", velocity=(0.1, 0, 0), duration=0.4)
sim.run(0.5)
state = sim.state(world=0)
print(state["pusher.pos"].round(2), start.shape)
print(start[:, 0].min().round(3), state["pad.points"][:, 0].min().round(3), state["pad.points"][:, 0].max().round(3))
print(sim.check()["ok"])

{'ground': 'static', 'pad': 'soft_vbd', 'pusher': 'static'}
[-0.02  0.    0.03] (729, 3)
-0.025 -0.009 0.042
True

sim.routes() says the pad took the soft_vbd route, the soft-body solver. The pusher moved 4 cm along x in 0.4 s, and the pad's 729 points followed: its left edge went from x = -0.025 to -0.009 m and its right edge reached 0.042 m. sim.drive moves a kinematic body; read sim.check() after the run.

Keep in mind

  • A soft body steps much slower than a rigid one, especially on a CPU: build a small one first.
  • A small body resting on a coarse soft solid can sink into one surface particle (details).
  • A body dropped on a soft solid bounces back far more than the material's restitution says (details).
  • No call attaches an object to a gripper: friction is the only grasp (details).
  • Full list: Keep in mind.

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