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Every procedural object you place — a wall, a rack, a crate — is either fixed base (welded to the world) or free base (a physical body that falls under gravity and can be pushed).

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Where to set it

Select the object in the environment editor. The right-hand panel has a Physics section with a Fixed base switch:
  • On — the object stays exactly where you placed it, no matter what hits it.
  • Off — the object is simulated: it drops onto whatever is beneath it, and robots or other objects can move it.
Reset puts it back to the default for that kind of object. Fixtures (walls, racks, floors, tables) default to fixed; loose objects (boxes, spheres, cylinders, pallet stacks, carts) default to free.

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What changes in simulation

  • A free object gets a free joint in MuJoCo, so it obeys gravity and contacts. Its live pose is streamed back, and the 3D scene follows it.
  • A fixed object is welded to the world. Its pose is a constant, so nothing is streamed for it.
  • The editor’s own physics preview follows the same setting once you enable the physics toggle in the viewport.

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Things worth knowing

  • A freed fixture is still heavy. Freeing a concrete wall or a loaded pallet rack is allowed, and it will topple or slide once the simulation starts.
  • Very thin objects cannot be freed usefully. A marker with essentially no volume has no mass to simulate, so it stays welded — the editor warns you when this happens.
  • The setting sticks. Switching an object to a different template keeps your choice; use Reset if you want the new template’s default instead.

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Setting it from an agent

cw_create_procedural_primitive takes a fixed_base argument, and cw_edit_environment can change it on an existing object. Leave it out to inherit the default for that kind of object.