# Skate 3 physics engine for Zero `skate_physics` integrates a reconstructed Skate 3 physics engine into Zero. Use this package for Skate 3-style skateboard and rider physics, or use its custom rigid-body solver components independently. It exposes a reconstructed Skate 3-derived Rust solver through editable entities, components and assets: physical bodies, collision volumes, joints, constraints, motors, forces and simulation state. It is a reusable simulation system, not just a skateboarding controller or a park scene. ## Why use it? Build and tune connected physical assemblies without first writing the integration between a custom solver and Zero. Inspect velocities and forces, change mass and inertia, configure joint limits, and drive mechanisms with spring/damper or hard motors. Motors apply impulses through the solver rather than teleporting bodies. The general body/joint/drive layer does not require a rider or animation clips. The package connects physics authoring, fixed-step simulation and entity presentation. Use it to experiment with constrained bodies, motor-driven mechanisms and vehicle assemblies; the skateboard and rider are included applications of the system, not its definition. ## What it provides - `World`: authority-gated fixed-step simulation and publication of solved entity state. - `Body` and `CollisionVolume`: editable mass, inertia, forces, velocities, primitive/compound collision geometry and bounded static-mesh collision. - `Joint` and `Drive`: body references, local frames, linear/angular limits and independently configurable motors. - `API`: in-engine authoring helpers and an explicit-state solver interface. - Input and actuator components for device-driven or scripted physical assemblies. - An integrated skateboard/rider system with control maps, rig mapping, visual bindings and animation-slot overrides. - Example scenes, a modular park, an authored skateboard, and the `GettingStarted` guide. ## Where to start Read **GettingStarted** for the distinction between the general physics components and the specialized rider integration. The low-level **Demo** workbench illustrates bodies, joints and a vehicle assembly. **SampleScenes** exposes rider, vehicle-only, self-propelled, scripted-control and physics-tuning examples. The world's default **RiderFidelity** scene demonstrates the coupled rider/board system with Zero's avatar and the authored park. ## Integration boundaries Static mesh collision has documented size limits; see `Body`. The specialized native rider/board integration requires a fixed body layout; that restriction is distinct from authoring assemblies with the general body/joint/drive API. The rider demo retains converted reference animations for testing, replaceable through normal Zero assets and animation bindings. These are not required by the general motor component. The default showcase uses the authored skateboard and Zero avatar; unused reference character and board models are excluded from publication. See the component documentation for supported shapes, units and solver-specific conventions.

# Actuator Connect world and body, then set force/torque at full command. command is a synchronized scalar from -1 to1; input, AI or other Zero components can write it. For a vehicle, one actuator can apply forward thrust and another yaw torque. Choose body space to follow the chassis orientation, or world space for fixed directions. Set command0 to release or active=false to disable. Multiple actuators sum in deterministic entity-id order without overwriting Body.force/torque. Commands are sampled at each World request boundary (up to four fixed steps). They feed the existing Skate solver and do not move transforms directly or add a rider. Input-device bindings stay in normal Zero input components; this asset does not assume keyboard keys, a game genre or a multiplayer transport.