Chapter 2: Variant Families

Created by Sarah Choi (prompt writer using ChatGPT)

Variant Families (Civil / Police / Military / Racing)

Optimization, Modularity & Families

Designing a vehicle family means you can ship four believable trims—civil, police, military, racing—without rebuilding the same machine four times. The trick is to compose around a stable platform (spine + bays + hardpoints), then express role through a small set of interchangeable modules, materials, and tuning profiles. This article shows concept‑side and production‑side vehicle artists how to architect variant families for maximum reuse, clean handoffs, and consistent LOD behavior.

1) Start with a platform, not a hero

A platform is a set of invariants: wheelbase/span, track/gear width, bay geometry (power, cooling, payload, crew), and a grid of hardpoints (mechanical, electrical, thermal, data). Sketch these as ghost frames during proportion passes. Write a one‑paragraph platform sentence (metrics + role ceiling) and keep it pinned to every sheet. When the platform is explicit, variants become swaps on a backbone; when it isn’t, every variant becomes a one‑off.

2) Trim philosophy: 70/20/10

Target 70% shared parts across the family (by count), 20% role‑specific modules, 10% unique flair. Shared parts include spine, suspension/gear, cabin tub, core cooling, and most skins. Role parts might be bumpers, racks, fairings, turrets, light bars, aero packs. Flair covers livery, beacons, and interior props. This ratio keeps art budgets predictable and QA manageable while preserving identity.

3) Civil baseline: the quiet truth source

Civil trims establish believable packaging and service logic. Keep panelization simple, cooling conservative, and interiors readable. Reserve flat livery pads where other trims will place insignia or numbers. Export clean orthos, a neutral light rig render set, and the exact hardpoint coordinates. Civil defines the standard of truth for geometry, collisions, sockets, and rig naming that other trims must inherit.

4) Police / security: authority through kits, not new geometry

Police variants add visibility, pursuit capability, and detainee/crew accommodations without breaking the civil shell. Modules: push bar kit on the front BCD, light bar + A‑pillar flashers on a lights.std rail, siren and PA on an audio hardpoint, cabin divider, weapon/utility rack, reinforced wheels/tires with the same hubs. Livery: high‑contrast XOR numerals, precinct shields on reserved pads, checker or chevron hazard bands at door apertures. VFX/audio sockets: siren, beacon rhythm (steady/double‑pulse), tire‑squeal thresholds tuned for higher brake bias. Keep collision hulls identical to civil to preserve pursuit gameplay fairness.

5) Military / paramilitary: protection and systems, anchored to standards

Military variants express protection, mission systems, and serviceability. Modules: bolt‑on armor skirts using skirt.hp BCD, RWS turret or ISR mast on deck.hp.600, blackout lighting with formation strips, NATO‑style tie‑downs, convoy light logic, and sealed intakes. Thermal plumbing and keep‑outs must remain valid; armor cannot starve radiators. Damage states reuse the same pivots and sockets. Livery is low‑chroma, high‑value‑contrast with stencils; numbers occupy the same zones as civil pads. Physics hulls add skirt breadth but must honor approach/departure angles set by the platform; do not silently erode metrics.

6) Racing / performance: aero and weight, without breaking lineage

Racing trims trade durability for speed and cooling headroom. Modules: front splitter and rear diffuser on aero.hp rails, brake‑cooling ducts on duct.hp with guaranteed cross‑section, lightweight door skins, roll cage insert sharing cabin mounts, pit‑latch hardware on standard fastener families, and telemetry pod on data.hp. VFX hooks: tire smoke tuned to soft compounds; audio hooks: higher RPM bands, pit limiter beep. Livery moves to high‑contrast bands aligned with flow; numerals shift to roof/dorsal pads for overhead cameras. Maintain the same collision base to keep multiplayer contact physics consistent.

7) Throughlines that make the four cousins read as a family

Hold these across trims: signature shoulder crown, greenhouse ratio, wheel opening geometry, DRL/taillight outline, and two persistent livery anchors (roof/dorsal pad + shoulder pad). Change stance and aero sparingly—lower 15–30 mm for racing, raise 15–30 mm for military with skirts—while keeping wheelbase/track and overhangs fixed. Persist the center console or core cockpit layout to ease UI, animation, and photo mode reuse.

8) LOD & materials: per‑module budgets, shared atlases

Author per‑module LODs with identical pivots and sockets so effect and rig layers never pop. Share trim sheets for fasteners/vents, and decal atlases for numerals/insignia across the family. Reserve unique textures for only the racing aero and military armor where bakes differ meaningfully. Lock texel density tiers (e.g., 512 px/m interior mech, 1024 px/m exterior skins, 2048 px/m hero panels) and keep them consistent per module so visual quality scales evenly.

9) VFX, audio, gameplay: sockets that always exist

Define a minimal socket set that ships on every trim: vfx.tire.(FL/FR/RL/RR), vfx.exhaust.(L/R), vfx.brakeSpark, vfx.intake, vfx.wake/contrail as applicable; and audio twins for engine, intake, exhaust, brakes, hinges, siren/beacons (police), convoy/formation (military), pit beeps (racing). The existence, naming, and axes of these sockets do not change across trims, only the parameter curves and mix.

10) Metrics discipline: never lie with variants

Publish a metric lock table on the platform sheet: overall L/W/H bands, wheelbase, track/span, approach/departure/breakover minima, ramp slope, curb hop, and turn circle. Variants may opt in to stricter numbers (racing lowers CG and raises curb limits; military may reduce breakover with skirts but stays within documented bounds). If a variant must change a locked metric, elevate it to a platform revision, not a quiet exception.

11) Assembly & validation workflow

Concept: block civil with primitive‑grade kit; prove stance and light; annotate hardpoints. Spin out police/military/racing by swapping modules and livery masks, not redrawing. Production: assemble each trim from approved modules, validate collisions/angles/rig limits, then polish surfacing. Run a family review with side/plan/front orthos aligned and a neutral light rig so throughlines and deltas are obvious. Export a per‑trim manifest and a family‑wide module inventory with versions.

12) Case study: compact fastback platform

Platform: 2.7 m wheelbase fastback with front‑mid power bay, roof rail 60 mm pitch, deck hardpoint 600 mm square. Civil: base bumper, neutral cooling, luggage bay; livery pads on shoulder and roof; DRL signature persists. Police: push bar kit on front BCD, light bar on roof rail, cage insert, XOR numerals; identical collision hull; siren/beacon sockets. Military: armor skirts on skirt.hp, ISR mast on deck, blackout lights + formation strips, sealed intake module; metrics preserved. Racing: splitter/diffuser on aero.hp, brake duct modules, roll cage, telemetry pod; lower ride height 20 mm, tuned VFX/audio; dorsal number pad. Reuse: 76% shared parts by count, 83% shared texture memory, identical rig names and sockets; per‑module LODs across the board.

13) Ethics, branding, and fiction

Police and military aesthetics carry cultural weight. Use generic, respectful branding unless you have clear approvals. Avoid distinctive real‑world insignia; use faction fiction and hazard standards documented in your style guide. Ensure readability for allies and clarity for civilians: hazard chevrons and beacons must signal intent, not intimidation, where your fiction calls for it.

14) Common failure modes & fixes

  • Unbounded variants: geometry drifts until trims no longer swap parts. Fix with a hardpoint plate and assembly linter.
  • Metric rot: pursuit bumpers or armor skirts destroy approach angles. Fix by validating angles on the assembled trim before polish.
  • Socket entropy: light bars or exhausts renamed per trim. Fix by freezing socket sets and validating on export.
  • Texture sprawl: every trim gets unique 4K maps. Fix by family atlases and trim sheets; reserve uniques for true hero differences.
  • Camo vs readability: military livery hides class. Fix by preserving value contrast in anchors and using XOR glyphs.

15) Handoff: family pack contents

  • Platform sheet (spine/bays, hardpoints, metric lock)
  • Module library (primitive + production grades, LODs, rig specs, sockets)
  • Per‑trim manifests (module list + versions, livery masks, emissive signatures)
  • Aligned orthos & neutral clay renders (family comparison)
  • Collision pack (physics/damage/raycast hulls)
  • VFX/Audio socket table (names, parents, axes, parameters)
  • Risks/open items (e.g., thermal margins with armor, aero legality for racing)

16) Closing thoughts

Variant families succeed when identity rides on a disciplined platform. Hold throughlines that make cousins recognizable, swap a few honest modules to speak role, and lock sockets, metrics, and LOD behavior so every discipline can reuse their work. Do that, and you’ll ship civil, police, military, and racing trims that look intentional, play fair, and scale like a product line—not a pile of bespoke one‑offs.