1. Dependency Upgrades (Cargo.toml)

• bevy: 0.16.0 → 0.17.3
  • Added new features: bevy_ui_render, zstd_rust, trace, reflect_auto_register
• avian3d: 0.3.0 → 0.4.1
  • Added feature: xpbd_joints
• Removed: iyes_perf_ui
• Added: bevy_anti_alias (0.17.3), bevy_utils (0.17.3)

2. New Motor Model (src/motor_model.rs)

New module centralizing physics constants:

• MOTOR_MAX_ACCEL_G = 10.0 (max acceleration in multiples of g)
• Shared geometry constants (CART_, ROD_, densities)
• total_mass_kg() - computes cart + rod mass from colliders
• force_from_power(power, mass) - converts motor power to force

Before: Force was motor_actuation.power * 2.0
After: Force is power * MOTOR_MAX_ACCEL * mass (physics-based)

3. API Migration (world/mod.rs, sim.rs)

4. Physics Improvements

Drag handling refactored:

• Replaced parent hierarchy traversal (get_rigid_body_entity) with direct drag.target()
• Added DragState resource to track override_motor flag
• Cart dragging now properly overrides motor control

New AppliedForce component: Tracks the force being applied for visualization (separate from physics forces)

New lock_cart_rotation system: Clamps cart rotation to initial orientation in FixedPostUpdate, preventing unwanted rotation even with joint constraints

Reset logic improved:

• Now resets Position, Rotation, PreSolveDeltaPosition, PreSolveDeltaRotation
• Uses ParamSet to avoid borrow conflicts
• Resets accumulated accelerations via Forces query

5. Type Registry for Scenes

Added explicit type registrations for scene serialization:
app.register_type::();
app.register_type::();
// ... etc
Plus assert_reflected_types startup system for validation.

6. UI Updates

• Removed iyes_perf_ui integration
• Added IsDefaultUiCamera marker to camera
• Minor formatting/style changes in UI setup

Thank @joshuaPurushothaman for the initial migration attempt and suggestions!