Sarah Clarity Studios

Chapter 2: Rigging for Moving Parts

Created by Sarah Choi (prompt writer using ChatGPT)

Rigging for Moving Parts (Slides, Bolts, Latches): A Cross‑Discipline Guide for Weapon Concept Artists

Why Concept Artists Should Care About Rigs

Whether you work primarily in 2D or 3D, understanding how slides, bolts, and latches actually move lets you draw forms that animate cleanly and hand off clean specs to production. For concept‑side artists, it prevents “dead greebles” and sets up convincing micro‑theater for reloads and jams. For production‑side artists, it means fewer re‑builds and faster integration with combat design, animation, VFX, audio, and UI. Rig‑aware concepting produces assets that feel grounded under motion, preserve readability at gameplay camera, and communicate the TTK fantasy without guesswork.

The Metrics That Govern Motion

Before designing mechanisms, lock the numbers that protect readability and interaction: Sight height over bore determines how much the slide/bolt can rise before occluding UI reticles. Trigger reach, guard radius, and selector throw arc dictate hand clearance for animation. Magazine angle and well chamfer control entry speed; ejection port size and position determine brass arc for VFX. Barrel length, overall length, and balance point (distance from grip to mass centroid) influence recoil arcs and settle times. Set these early and reuse across variants so the roster animates with consistent ergonomics.

Motion Arcs as Design Lines

Sketch motion on top of your forms. For slides, draw the reciprocation path and max rearward travel; for rotating bolts, indicate cam track and lug engagement; for latches, mark pivot, throw angle, and detent stops. Translate these into panel breaks and chamfers that imply function. A slide with straight rails demands long planar runners; a tilting barrel needs clearance at the muzzle and underlug. When surfaces echo motion, animators get clean, motivated arcs and audio gets believable transient sites.

Slides: Reciprocation, Tolerances, and Readability

A slide is a short‑throw carriage. Design rails that visually register as bearing surfaces (flat, parallel, lightly polished) and give them just enough bevel to catch light in renders. Allow realistic rearward travel (typically 20–40% of slide length) and reserve internal volume for recoil springs or guide rods. Provide a disassembly notch and charging serrations that won’t chew hands at animation speed. Keep ejection port geometry clean and oriented to frame brass/par‑particle VFX without masking sights. Concept‑side, paint light polishing on contact edges to celebrate travel; production‑side, rig with linear constraints and a spring controller for camera‑safe return timing.

Bolts: Rotating, Tilting, Linear — Choosing a Story

Bolts communicate power and cadence. A rotating bolt suggests lock‑up authority; sketch lug count and cam path so riggers can build a driven rotation off linear travel. Tilting bolts need under‑barrel clearances and consistent feed ramps; linear blowback bolts want visible mass and buffer travel. Whichever you choose, avoid orphaned details (lugs with nowhere to lock, feed ramps that don’t meet magazines). Provide a proxy chamber and barrel extension so break‑open states look truthful and give animators an internal silhouette to time impacts.

Latches, Catches, and Selectors: The Small Parts That Carry Feel

Controls drive interaction pacing. Dimension throw angles for tactile clarity: 30–45° for selectors if you want a crisp two‑state feel; 60–90° for safety styles that dramatize commitment. Design detents (ball/spring pockets or leaf springs) and cam faces so audio has justification for clicks. Keep pad geometry consistent with gloved hands; bevels prevent finger pop through at speed. For mag catches or bolt releases, provide exaggerated chamfers and proud surfaces so animators can stage decisive presses. Rig with hinge constraints, limiters, and detent curves for snappy returns.

Constraint‑First Rigging: Simple, Predictable, Durable

Production rigs should prefer constraints over expressions when possible. A slide gets a single linear limit; the barrel receives a small tilt or none depending on system; the bolt rotates via a driven key or constraint along a cam. Latches hinge with rotational limits and spring forces modeled as simple damped constraints. Keep control count minimal and name channels human‑readably: ctl_slide.RECIP, ctl_bolt.ROT, ctl_safety.STATE. Concept artists can mirror this logic in annotated sheets: arrows for direction, degrees for limits, and timestamps for beats.

IK vs FK for Weapon Handling

Animation benefits from both. Weapon‑relative IK controls stabilize the gun in space while hands adjust; FK gives elegant arcs for reload theatrics. Design clear gripping volumes (textured flats, undercuts) so hands can anchor without clipping. In rigs, expose a local weapon space for ADS stabilization and world space for big sweeps. Concept sheets should show intended grip permutations—two‑handed brace, single‑handed, mag‑hold—so riggers plan pivots and animators stage believable transitions.

Driven Relationships: When One Part Should Move Another

Use driven keys or constraints to coordinate micro‑motions: cocking levers that reciprocate with slides, brass deflectors that spring when hit, dust covers that flip at first shot. Keep these relationships few and deliberate; each one is a promise to other teams. Document ranges: “dust cover opens at 5% slide travel and remains open until manual close.” Audio can then plan a single latch pop rather than spammy rattles.

Collision and Clearance: Preventing Animation Debt

Draw tolerances right on the concept: 2–4 mm air gaps for sliding metal, 1–2 mm for polymer‑on‑metal with lubrication. Show magnet or spring seats so latches don’t float. Provide cutaways for tight areas so riggers know where hidden mass lives. In DCC, rig simple collision proxies for hands, magazines, and sling points; animators can block quickly without penetrating geometry. VFX appreciate reliable emission holes that don’t occlude mid‑sequence.

Timing and Cadence: Matching the Combat Envelope

Tie motion timing to the designated combat role. Precision roles want short, tight reciprocation with fast settle; suppression roles tolerate longer rebounds and visible buffer travel. Publish a mini timing chart with beats (fire → max recoil → return → ready) in frames at target FPS. Keep reload windows distinct: snappy latch pops for twitch guns, heavier throw‑and‑seat for big hitters. UI uses these beats to rhythmically pulse ammo counters or overheat bars, and audio aligns transients and tails.

VFX Handshake: Spawn, Path, and Exposure

Reserve clean spawn points: a chamfered muzzle crown, vent slits with clear outward normals, and ejection ports with unobstructed arcs. Avoid designing busy geometry exactly at effect origins; leave a “quiet pixel” pad for bloom and smoke to read. Provide directional hints (flute direction, shroud perforation bias) that VFX can echo in particle travel. In rig, tag locators as fx_muzzle, fx_eject, fx_vent_L/R so integration is trivial.

Audio Handshake: Transients, Resonance, and Foley Sites

Rigs suggest sound. Expose hard stops (slide hits, bolt lock) and soft returns (spring homes) so audio has transient vs body contrasts. Provide resonance cavities—buffer tubes, shroud hollows—that justify tails. Annotate materials near moving parts (rubber overmold vs bare steel) to guide filtering. Audio can layer a satisfying “success” snap on latches if the rig gives a crisp limit with bounce.

UI Handshake: Sight Picture and State Displays

Moving parts must never eclipse reticle information at expected cadences. Keep slide and bolt silhouette below the sight line during cycling or design optic mounts with enough standoff that motion sits outside the UI cone. If diegetic UI is planned (charge bars, ammo windows), reserve planar, player‑facing surfaces that won’t be covered by reciprocating pieces. Provide ADS orthos at gameplay FOV with overlaid safe zones.

Documentation for Handoff

Package a rig‑aware concept sheet: orthos with movement arrows, throw angles, travel distances, and clearances; an exploded view of moving subassemblies; a timing strip for key beats; and a glossary of control names. In production, deliver a layered PSD or PDF with callouts, and a short note file listing constraints and limits. Semantic naming prevents integration friction across tools and teams.

Testing Protocols: From Blockout to Final

1. Blockout test: neutral rig with slide/bolt/latch motion at exaggerated ranges; verify no occlusion of sights and no hand collisions. 2) Raking‑light render: hunt smoothing errors along rails and cam faces. 3) ADS crop test: rapid cycling viewed at gameplay size to ensure reticle remains interpretable. 4) VFX dry run: plug in placeholder muzzle flash and brass; confirm spawn points and arcs. 5) Audio dry run: drop clicks and slaps at rig limits; adjust detent curves as needed. 6) Final polish: reduce exaggerated ranges to final metrics; lock naming and limits.

Photobash Ethics for Mechanisms

Use photo reference for micro‑textures, not for tracing proprietary mechanism geometries. If you lift a latch silhouette or patent‑distinct slide serration, redesign to generic principles (ergonomics, tooling reality) and document sources in a reference layer. Align photobash lighting to the 3D render so animation/VFX/UI plates stay consistent. Your authored rig logic—not the photo—must determine motion.

Common Failure Modes and Fixes

Over‑busy slides that strobe under motion; latches with throw arcs that intersect hands; bolts with invented lug math; ejection that sends brass through optics; selectors that flip opposite to on‑screen iconography. Solve by pruning surfaces at motion origins, sizing throws for gloved hands, drawing proper lug engagement, testing brass arc locators, and aligning physical selector states with UI conventions. When in doubt, prototype with a simplified rig before committing ornament.

Example Workflow: Slide‑Lock Pistol

Start with metrics: sight height, barrel length, grip angle, magazine dimensions. Sketch slide travel and lock‑back notch; place ejection port and serrations; define latch throw and detent. Block out in 3D with truthful rails and a proxy barrel; rig slide linear limit and spring; drive a tilt on barrel if design calls for it. Add locators for fx_muzzle and fx_eject; verify ADS crop during rapid cycling. Render neutral plates and raking light. Paint polish on rail edges and micro wear at latch. Package orthos, motion arrows, timings, and naming sheet. Hand off.

Example Workflow: Rotating‑Bolt Carbine

Define bolt rotation (e.g., 15–22.5°), cam path, and buffer travel. Model barrel extension and bolt lugs; leave clearance for feed ramps. Design charging handle throw and release latch with detent pockets. Rig: linear bolt travel drives rotation via a cam constraint; buffer tube spring adds damped return. Tag spawn points and brass arc. Test with placeholder burst cadence; verify that optic mount height keeps UI clear. Render, paint, package as above.

Closing: Design Motion Into the Form

Rigs are where your form proves itself. Draw motion first, then let design celebrate it: rails that gleam where slides run, cam faces that catch the eye, latches that invite the thumb. When metrics, motion, and interaction align, combat design gets the envelope it needs, animation gets clean arcs, VFX gets stable origins, audio gets honest transients, and UI keeps the player informed. That’s how a weapon moves from beautiful drawing to believable instrument in the player’s hands.