Six rounds of reward shaping (~700M steps) failed to produce upright ground
driving. A critical review of the simulation rather than the reward found
why:
1. The hull was a 1x1x4 box with inertia (1,1,1) and no restoring torque
anywhere, so belly-down and rolled-90 were geometrically identical
resting states. "Upright" was not a physically distinguished state at
all - the reward was paying for a property the simulation did not have.
2. ~65% of episodes spawned ships via _random_position, which samples Y
uniformly over the full 18m volume (mean ~8.7m). The measured
airborne_fraction ~0.44 was largely that spawn distribution, and every
ground-handling term fades out above 3m, so the shaping being tuned
barely ever applied.
3. air_drill_chance 0.20 spawned deliberately unreachable-without-climbing
states in the stage meant to teach ground driving, and its own
air_touch_fraction (0.0002) shows the drills were never solved.
Fixes land in the physics and the task distribution, not the reward:
- ship.tscn: hull 1x1x4 -> 1.6x0.6x4 so it has one stable resting face;
inertia (1,1,1) -> (7,1,7), physically correct for the hull, making
tumbling reluctant while keeping yaw snappy.
- ship.gd: new altitude-faded righting torque (spring-damper toward
belly-down, faded out by 3m so aerials keep full attitude freedom).
This is the grav-plating analogue of Rocket League's auto-righting and
helps human pilots land cleanly too.
- training_mode.gd: new ground_start_chance branch spawning ships level and
resting on the floor with a floor-level ball - the state the handling
stage's rewards are actually written for.
- generation5.py: ground-start-chance 0.50, air-drill-chance 0.20 -> 0.0.
Reward terms are left exactly as they were; they should finally pull in a
direction the ship can go.
Adds a [layer_names] section to project.godot (Ships/Ball/Arena/
GoalSensor) and sets collision_layer/collision_mask on the 4 physics
body roots (Ship, Ball, Goal Area3D, ArenaBoundary StaticBody3D),
which previously all sat on the default layer 1 / mask 1 so every
body broadphase-tested against every other.
Ships collide with ships/ball/arena but no longer test against the
goal sensor; the goal's mask (Ball only) is the physics-level fix for
what goal.gd's is_in_group("ball") check was doing defensively in
code (left in place, now a no-op guard). ArenaBoundary's runtime-
generated CollisionShape3D children inherit layer/mask from the
StaticBody3D root automatically.
Verified live via godot-mcp under Jolt Physics: ship-vs-ship and
ship-vs-ball collisions still transfer momentum, the ball still
bounces off arena walls, a ball entering a goal still fires
goal_scored (score updates / HUD reset), and a ship teleported into a
goal recess produces zero overlapping bodies on the goal Area3D (was
reachable before, physics-level fix confirmed, not just the code
guard). Headless smoke test (free_play.tscn) is clean.
Hull/Canopy/EngineGlowL/EngineGlowR are runtime-baked into one ArrayMesh
in _ready via SurfaceTool.append_from, dropping 4 MeshInstance3D children
to 1 (Nose/TailFin stay separate, they're retinted per-team). Skipped in
headless mode like the goal/arena_boundary visual builds, since physics
only cares about CollisionShape3D.
All 6 source surfaces (hull, canopy, engine_l x2, engine_r x2) carry
distinct materials, so this doesn't literally cut draw calls 6 to 3 as
TODO.md assumed — Godot still issues one draw call per surface regardless
of node count. The real win is scene-tree/transform overhead, not batching.
Ship gets a greebled hull, tapered nose, swept canopy, twin engine nacelles,
and tail fin (built via the vendored Blender MCP, generator committed at
tools/blender/gen_ship.py) in place of the 5 flat primitives. The ball is
fully remodeled as a smooth round sphere with a crossed emissive accent
pattern (gen_ball.py), replacing the old flat-shaded gold_ball rather than
just tweaking its material.
Node names (Nose/TailFin) are preserved for Ship._apply_team_color(), and
the RigidBody3D/CollisionShape3D physics on both ship.tscn and ball.tscn are
untouched so RL-trained bots and flight feel stay valid. Each part's mesh is
extracted to a standalone .res (tools/blender/extract_meshes.gd) rather than
referenced via glb::ArrayMesh_xxx sub-paths, which don't reliably resolve
across scene files and were silently rendering both models invisible.
Josh Creek