Rigid Body
Make particles solid bodies that tumble, hit each other, stack and come to rest: bricks, crates, rocks, debris, dice; each the shape it shows.
Particles are solid: they tumble, hit each other (and those of other events with this operator), stack and come to rest, on this event's Collide objects and ground. Each one is the shape it shows: its object from the Shapes collection, its piece of a mesh, or its sphere.
- Add it
- EventAdd OperatorPhysicsRigid Body
- Sends on
- Nothing: it has no wire.
- Influence
- No: a value can’t weigh it.
When to use it
Hard things: bricks and crates, rocks and rubble, dice, cans, pieces of something broken. Each particle becomes a body of the shape it shows, that tumbles, stacks, slides and comes to rest.
Set it up
Make the shapes, and put them in a collection. In the simulation's Display panel, set Shapes to it. Add a Shape operator to pick among them; without one, every body is the first shape.
In an event, add Birth, Position, Gravity, Rigid Body and a Collide with Ground or the objects they land on.
Pick the Shape the bodies hit with, and their Density.
Settings
As the flow editor’s sidebar shows them. Changing any of them marks the bake old; none of them can change through a bake.
The shape each body collides as.
- Box: The box around each one's shape from the Shapes collection, or a cube as wide as its sphere. Fastest, and best for bricks and crates.
- Ball: A ball holding the longest side of each one's shape, or its sphere. Rolls.
- Hull: Each one's shape from the Shapes collection, wrapped tight with no hollows (its convex hull). For rocks and debris.
- Concave: Each one's shape from the Shapes collection, hollows and all, split into convex pieces. For cups, bowls, frames and other hollow things; slower.
A Hull keeps at most this many of its mesh's points, the outermost first. A hull is tested point by point against every face it nears, so a mesh of thousands of points stalls a bake when it touches something: 128 is plenty for most shapes. 0 keeps every point.
How heavy for its size, in kg/m³: water 1,000, wood about 600, sand about 1,600, stone about 2,500, steel 7,850. A heavy body pushes light ones aside, and particles push rigid bodies by it.
Times overlaps and contacts are pushed apart, and binds pulled back, each substep. More holds piles and stacks up and binds tighter; slower.
Moved only as this event's other operators say (Speed, Spin, or Pin with an object, turning with it), through colliders and the ground, pushing other bodies without being pushed. Sent to an event where it isn't, it carries on as it went.
Shape
Each body is the shape its particle shows:
- with a Shapes collection, its object's mesh, at the particle's scale;
- born On Pieces, its own piece of the mesh;
- otherwise, its sphere (the Display panel's Sphere Radius).
Shape says how closely the body follows it. Box (the box round it) is fastest and right for bricks and crates. Ball rolls. Hull wraps it tight with no hollows: rocks and debris. Concave keeps its hollows, for cups, bowls and frames, and is slowest. Hull and Concave need a Shapes collection or pieces to take the shape from.
Hull Points caps how many of the mesh's points a Hull keeps, the outermost first. A hull is tested point by point against every face it nears, so a sculpted mesh of thousands of points stalls the bake the moment it touches something; 128 is plenty for most shapes and the hull lies within a hair of the full one. 0 keeps every point, as older files do.
Density and friction
Density is in kg/m³: water 1,000, wood about 600, stone about 2,500, steel 7,850. A heavy body pushes light ones aside, and particles and liquids push bodies by it. Friction and Bounce are as the names say; bricks want Bounce near 0.
Rounds is how many times each step the contacts are worked out. Stacks and walls stand steadier with more; loose debris needs fewer, and bakes faster.
Kinematic
Kinematic bodies don't fall or get pushed: they move only as the event's other operators say (a Speed, a Spin, or a Pin with an object, turning with it), through colliders, pushing the others aside. A wrecking ball, a paddle, a conveyor's blocks. A Struck Test can free them when hit: sent to an event whose Rigid Body isn't Kinematic, they carry on as they went.
Works with
- Bodies hit the rigid bodies of every event, and their own event's Collide objects and ground.
- Bind: joints (chains, hinges, sliders) and glue (things to smash).
- Liquid in another event: bodies float, and are pushed by it.
- Particle Physics in another event: balls push bodies, and are pushed.
- An event takes one Rigid Body, and can't also hold Particle Physics, a Liquid, a Follow Curve or Goal, or a Pin (unless its bodies are Kinematic).
Name the shapes alike
Bodies get their shapes by their objects' order in the collection. Blender can sort some mixes of names either way round (case, dots and numbers), so the editor asks for them to be named alike: Rock.001, Rock.002…
Problems you may see
event: a Rigid Body moves on its own, so it can't take operator as well
A Rigid Body moves its particles itself; an operator that moves them too can't share its event.
event: a Struck Test is for rigid bodies: add a Rigid Body
event: operator takes its shapes from the Shapes collection's objects; 'object' has no mesh to make one from
event: operator: an event takes only one
event: operator: Blender can put shapes named 'name' and 'name' in either order, so bodies might not get the shapes they show. Name the Shapes collection's objects alike, such as Rock.001, Rock.002
Rigid bodies take their shape by its place in the Shapes collection. Name the objects in a numbered series so the order holds.
event: operator: shape takes each particle's shape, and there is no Shapes collection or Birth On Pieces
Errors stop a bake; warnings don’t. Every message is on the Messages page.
Related
Bind
Hold particles together: cloth, ropes, soft bodies, sticky goo and things that tear; and hold rigid bodies on joints, or glue them into something to smash.
Liquid
Make particles a liquid that keeps its volume: it pours, splashes and fills, floats rigid bodies and pushes cloth, with a surface mesh made by the bake.