Voxel Types

Stable cell type constants

Constant	Value	Category	Description
EMPTY	0	—	No cell. Disables a grid position.
RIGID	1	Dynamic	Stiff structural material. Highest spring constants.
SOFT	2	Dynamic	Deformable material. Lower spring constants than rigid.
H_ACT	3	Dynamic	Horizontal actuator. Action controls horizontal edge springs.
V_ACT	4	Dynamic	Vertical actuator. Action controls vertical edge springs.
FIXED	5	Static	Anchored, immovable. Used for ground, walls, and platforms.
CONTRACTILE	6	Dynamic	Universal actuator with independent per-axis control at runtime.

Unsupported experimental values

Values 7 through 30 are reserved for legacy slope terrain fixtures:

• SLOPE_*
• SLOPE2_*
• SLOPE3_*

These values remain in jax_evogym.constants so older fixtures and internal tests can still be inspected. They are not exported from the package top level, are not shown in the public designer palette, and are rejected by compile_world_template(...) unless allow_experimental_slopes=True is passed.

When explicitly enabled, slopes are geometry-only. Sloped edges receive normal collision response, but slope friction, slope grip, near-contact support, stiction, and persistent slope manifold behavior are disabled. They are omitted from the designer and stable examples because that friction/support model is still unresolved.

Type sets

ACTUATOR_TYPES = {H_ACT, V_ACT, CONTRACTILE}

STABLE_STATIC_TERRAIN_TYPES = {FIXED}

DYNAMIC_VOXEL_TYPES = {RIGID, SOFT, H_ACT, V_ACT, CONTRACTILE}

STABLE_WORLD_CELL_TYPES = {EMPTY, FIXED, RIGID, SOFT, H_ACT, V_ACT, CONTRACTILE}

Where each stable type is allowed

Type	In robots	In terrain	Dynamic	Static
EMPTY	Yes (disables cell)	Yes	—	—
RIGID	Yes	Yes	Yes	No
SOFT	Yes	Yes	Yes	No
H_ACT	Yes	No	Yes	No
V_ACT	Yes	No	Yes	No
CONTRACTILE	Yes	No	Yes	No
FIXED	No	Yes	In mixed objects	In pure fixed objects

A terrain object containing only FIXED cells is compiled as static — it contributes collider/render geometry but no dynamic points, masses, or springs to SimState. A terrain object containing SOFT, RIGID, or actuator cells is compiled as dynamic.

Spring constants

Spring constants are material properties sourced from C++ ObjectCreator.h. They are not scaled by cell size.

Material	Main K	Diagonal K
Rigid / Fixed	~85,714,286	~42,857,143
Actuator (H_ACT, V_ACT, CONTRACTILE)	60,000,000	30,000,000
Soft	50,000,000	12,500,000

Main springs connect adjacent grid points (horizontal and vertical edges). Diagonal springs connect corner-to-corner within each cell.

Physics constants

Most square-cell constants are EvoGym-derived. A few values are documented JAX-side corrections or extensions, including ground normal velocity damping and disabled-by-default flat-contact stiction hooks.

Constant	Value	Notes
DT	0.0001	Physics step size.
GRAVITY	110.0	Gravity acceleration.
VISCOUS_DRAG	0.1	Linear velocity drag.
PHYSICS_UPDATES_PER_STEP	30	Substeps per environment step.
CELL_SIZE	0.1	Cell width/height.
POINT_MASS	1.0	Point mass.
ACTUATOR_CONVERGENCE	0.006	Rest-length convergence factor.
COLLISION_CONST_GROUND	14,000,000	Ground normal stiffness.
COLLISION_CONST_OBJ	2,100,000	Object-object normal stiffness.
COLLISION_VEL_DAMPING	2,030	Object-object damping extension.
GROUND_VEL_DAMPING	5,238	Ground normal damping extension.
COLLISION_BASE_DIST	0.005	Collision base distance.
STATIC_FRICTION_CONST	0.5	Static-friction coefficient used by opt-in non-slope terrain stiction paths.
DYNAMIC_FRICTION_CONST	0.2	Dynamic friction coefficient.
FRICTION_CONST	1,200	Object/static-object friction scale.
GROUND_FRICTION_CONST	10	Ground-plane friction scale.

SLOPE_CONTACT_* and SLOPE_GRIP_* constants are compatibility values only in the current stable boundary. They are retained for old configs but do not enable slope friction/support.