How do I lock an axis on RigidBody3D?

Enable the corresponding axis_lock_linear_x/y/z or axis_lock_angular_x/y/z properties in the Inspector under Axis Lock. The physics solver zeroes velocity along those axes each step, preventing motion or rotation.

Why does my body still move along the locked axis?

The lock applies to physics-driven motion. If you directly assign position or linear_velocity from script, the assignment isn’t filtered. Either honor the lock yourself or use apply_central_force / apply_impulse which respect the lock.

Can I change locks at runtime?

Yes. Set axis_lock_linear_x = true via script anytime after add_child. The next physics step honors the new constraint. For dynamic gameplay (e.g., lock when holding a button), toggle freely.

Fix: Godot PhysicsBody3D Axis Lock Not Respected

Quick answer: Axis locks zero physics-driven velocity along the locked axis each step. Direct position or linear_velocity assignment from script bypasses the lock — use apply_central_force or honor the lock manually.

A 3D side-scroller pins the player’s movement to the XY plane by locking the Z axis on the RigidBody3D. The character starts on Z=0, but over time drifts to Z=-3.2. The lock is on; the body still moves.

What Axis Lock Actually Does

For RigidBody3D, axis lock zeroes linear_velocity.z (or other axes) after each physics step. Forces applied along the locked axis still produce zero net motion because the solver clamps velocity each tick.

What it doesn’t do:

Doesn’t intercept direct position assignment from script.
Doesn’t prevent linear_velocity = Vector3(...) overrides.
Doesn’t lock kinematic motion via move_and_collide on CharacterBody3D.

Fix 1: Use Forces, Not Direct Velocity

# RIGHT: respects axis lock
body.apply_central_force(Vector3(input_x * 100, 0, 0))

# WRONG: bypasses lock
body.linear_velocity = Vector3(10, 0, 5)   # Z component sneaks through

Forces are integrated through the solver each tick, and the lock clamps the resulting velocity. Direct velocity writes are taken at face value.

Fix 2: Honor Lock Manually

If you must write velocity directly:

var v = Vector3(10, 0, 5)
if body.axis_lock_linear_z: v.z = 0
body.linear_velocity = v

Explicit. Clear. Future you sees the constraint in the code path.

Fix 3: Use _integrate_forces

For complex motion that should respect locks fully:

func _integrate_forces(state: PhysicsDirectBodyState3D):
    var v = state.linear_velocity
    if axis_lock_linear_z: v.z = 0
    state.linear_velocity = v

_integrate_forces runs inside the physics step. The solver applies its own lock after this; combining the explicit zero with the lock guarantees no drift.

Char Controller Special Case

CharacterBody3D doesn’t have axis_lock_* in the same way. Implement manually:

func _physics_process(_delta):
    var v = velocity
    v.z = 0   # 2.5D constraint
    velocity = v
    move_and_slide()

Zero the velocity component each frame. The character can’t accumulate Z motion regardless of input or collisions.

Verifying

Print body.global_position.z over time while applying forces. With proper lock + forces, the value should stay constant (within ~0.0001 floating-point noise). If it drifts, you have a write-site bypassing the lock.

“Axis locks constrain physics integration. Direct velocity/position assignments aren’t physics integration — they bypass.”

For 2.5D games, prefer CharacterBody3D + manual axis zeroing — cleaner than fighting RigidBody’s direct-write loopholes.