Chapter 2: Mobility Devices & Prosthetics — Integrated Design

Created by Sarah Choi (prompt writer using ChatGPT)

Mobility Devices & Prosthetics — Integrated Design for Character Concept Artists

Why Integration Matters

Mobility devices and prosthetics are not optional set dressing; they are core extensions of body, identity, and play. Integrated design means these tools are conceived from the same first principles as anatomy, costume, and combat loops—so they look right, move right, and feel dignified. When concept and production teams plan for diversity in silhouette, mobility, and ability, the result is a cast that reads clearly, plays fairly, and scales across content updates without special‑case debt.

North Stars: Dignity, Function, Readability, Repeatability

Anchor every choice to four north stars. Dignity avoids fetishization or pity; the device is portrayed as competent and normalized. Function explains how loads and forces travel; nothing exists only as ornament. Readability preserves class, threat, and interaction signals at gameplay camera. Repeatability encodes devices as systems—shared anchors, materials, and shaders—so variants ship without forking rigs.

Language and Framing

Use neutral, person‑first language in internal docs (e.g., “character who uses a wheelchair,” “upper‑limb prosthesis”). Avoid pejorative file names and shorthand. Treat assistive tech as gear: it has purpose, maintenance, and customization, just like weapons and tools. When the fiction calls for magical or sci‑fi augmentation, keep the ergonomics and load paths legible.

Silhouette Systems: Including Aids Without Losing Class Read

Mobility aids change outline and weight distribution. Design silhouette families that include devices from the start: seated silhouettes (manual chair, powered chair), supported silhouettes (canes, crutches, walkers), braced silhouettes (KAFOs, exos), and prosthetic silhouettes (upper/lower, one‑ or multi‑articulating). For each family, define class‑read anchors (e.g., shoulder mass, headgear bar, device profile) so faction/class silhouettes remain distinct even when a device is present. Use value blocks and negative space to keep the device legible without competing with primary role markers.

Device Taxonomy and Core Design Heuristics

Canes & Staves. Height aligns to wrist crease; handle type matches grip (derby, offset, knob). Ferrule materials match surface type; add replaceable tips. For combat roles, separate “assist” cane from “weapon staff” to keep reads honest.

Crutches (axillary, forearm). Cuff clearances respect biceps/triceps flexion; axillary pads avoid clavicle pinch. Route straps and capes to preserve arm swing.

Walkers & Rollators. Front geometry fits door metrics; storage sits behind knee swing. Avoid spokes that snare cloth.

Manual Wheelchairs. Seat/back angles tune posture; wheel camber reads sport vs daily. Hand rim material and tire tread convey terrain. Footplate geometry avoids toe clip with long boots.

Powered Chairs & Mobility Scooters. Center of mass reads stability; shroud panels provide brand/faction identity. Lighting doubles as UI hooks. Reserve mounting rails for bags/weapons without blocking joystick reach.

Braces & Orthoses (AFO/KAFO/Spine). Force routes to bone landmarks (tibia, femoral condyles, iliac crest); hinge axes align with anatomical centers. Padding thickness lives inside the material library (foam, felt, gel).

Exoskeletons/Exobraces. Distinguish assist (strength/anti‑fatigue) from boost (sprint/jump). Keep actuator count minimal; route energy storage to safe, readable volumes.

Upper‑Limb Prosthetics. Sockets mirror soft‑tissue compression zones; shoulder harness options for body‑powered devices are compatible with costume layers. Terminal devices include hook, three‑jaw chuck, precision hand; quick‑swap couplers standardize mounts.

Lower‑Limb Prosthetics. Feet (SACH, dynamic response) imply gait energy return; shank covers provide world style without hiding flex zones. Knees: single‑axis, polycentric, microprocessor. Design clothing breaks (pant hems, armor greaves) that respect swing clearance.

Function First: Load Paths, Clearances, and Grasp Logic

Draw load paths like you would for armor: arrows showing compressive/ tensile routes. Mark keep‑out zones for pits (axilla), nerves (ulnar at elbow), and soft‑tissue bulges (abdomen, thigh). For prosthetic hands, place control surfaces where the other hand or teeth could realistically interact. If the device aids grasp, design pouch pulls, zipper tabs, and magazine catches sized for the terminal device.

Materials, Shaders, and Sound

Lock assistive materials in the global library: aluminium, titanium, carbon fiber, ABS, leather, neoprene, foam, gel, silicone, textiles. Calibrate roughness and IOR ranges so gloss and edge wear match world logic. Personalization sits in overlays and covers—decals, paracord wraps, fabric sleeves—never in breaking the material family. Sound sells function: dull carbon thump vs. aluminium ‘ping,’ rubber ferrule squeak on tile, chair caster whirr. Provide audio hooks per device type for Foley/VFX to attach glints, dust puffs, and tiny vapor bursts.

Mobility and Ability as Movement Baselines

Document locomotion baselines with your animation team.

  • Cane gait: step‑to vs step‑through, cadence, pelvic drop.
  • Forearm crutch gait: reciprocal vs swing‑through modes.
  • Wheelchair propulsion: hand‑rim push phases, recovery hand shape, slope assist patterns.
  • Powered chair: joystick micro‑corrections, start/stop easing.
  • Prosthetic gait: heel strike timing, toe lever rollover, asymmetry allowances. Keep seated idle sets expressive (head tilt, torso lean, footplate jitter). Provide quick‑equip/unequip beats if fiction allows device removal.

Rigging and Skinning: Sockets, Constraints, and Retargeting

Standardize anchor sockets on the skeleton: cane hand IK, crutch cuff, axillary pad, wheelchair push‑rim IK, caster ground constraints, prosthetic mounts at wrist/elbow/shoulder, ankle/knee/pelvis. Name anchors to match rig conventions. Use constraint stacks: parent + aim for canes, hinge + spring for braces, wheel rotation driven by ground speed. Provide retargeting tables so animations scale across height/mass ranges. Skinning profiles must anticipate padding compressions and strap indentation without normal map swimming.

Collision, Capsules, and Keep‑Out Maps

Publish keep‑out maps per device: cane swing arc, crutch crutch‑tip cone, wheelchair wheel envelope, footplate zone, exo actuator sweep. Expand collision capsules where needed (seated width, turning radius). Level metrics must include door width, ramp pitch, curb cuts, and cover heights usable from seated and supported stances. Vehicles and mounts require transfer animations and secure lock points for chairs if diegetically plausible.

Costume and Loadout Integration

Design fit families for costume layering around devices: jacket vents that clear prosthetic elbows, pants gussets that avoid knee hinge snags, skirt weights that don’t foul casters. Belts, holsters, and tool rolls must mount on accessible sides—consider dominant hand and terminal device. For chairs, create bag and sheath systems on frame rails that respect wheel clearance. For exos, route armor plates to avoid actuator pinch and provide quick‑release pins as diegetic storytelling.

UI, Camera, and Accessibility Hooks

Preserve fair targeting and composition: seated characters shouldn’t crop in dialog framing; reticles account for device offsets (e.g., muzzle attached to chair). Provide UI toggles for device audio cues and subtle VFX assists (wheel skid marks, cane tip dust) that help tracking under motion blur. Avoid color‑only reads; reinforce device state (stowed/deployed, assist/boost) with shape change or emitters.

Inclusivity and Tropes to Avoid

Do not cast devices as tragedy or cheap villain markers. Avoid “miracle cure” skins that erase disability without narrative consent. Don’t sexualize devices to justify attention. Ensure parity of competence and fashion—glamour, grit, and prestige tiers should exist for mobility gear just like weapons. Normalize wear patterns: taped grips, anodized scratches, mud on casters—signs of use, not neglect.

Culture, Research, and Co‑Design

Research with primary sources—users, clinicians, makers. Observe maintenance rituals: tightening bolts, changing tips, swapping sleeves, charging batteries. Catalogue regional materials and motifs (woven cane sleeves, beadwork cuff covers, anodized camo). Create a vetted motif library and annotate meanings in callouts so localization and legal can review early.

Production Deliverables That Downstream Teams Love

For each device, supply:

  • Orthos with anchor IDs and clearance bands.
  • Exploded views of moving parts and quick‑release routes.
  • Gait thumbnails for interaction windows (e.g., safe dangle lengths, wheel free‑spin).
  • Material map tied to studio shaders.
  • Variant matrix (Base/Plus/Deluxe) with personalization via covers/decals instead of geometry.
  • Naming schema that matches rig bones and physics assets.

Performance, LOD, and Physics Budgets

Set dangle budgets: cane tassels limited; crutch straps rigid below LOD1; wheelchair spoke counts collapse to discs at distance; exo cables swap to baked normals beyond mid‑range. Avoid cloth that occludes device read. Keep physics to one or two controlled elements per device; suggest motion elsewhere with animated normals or VFX.

Live‑Ops and Skins Without Erasure

The device persists across skins; do not “remove the wheelchair for a sprint skin” unless the narrative explicitly supports a different, equally valid mobility baseline (e.g., exo‑chair vs. manual chair). Seasonal looks apply via sleeves, decals, spoke guards, grip tapes, and shrouds that fit the same anchor system. Market shots should feature the devices proudly, not cropped out.

Case Study Heuristics (Apply, Don’t Copy)

  • Urban tracker with forearm crutches. Carbon cuffs with replaceable neoprene liners; triangular ferrules for grip on wet stone; jacket vent panels to preserve arm swing; camera emphasizes crutch placement beats on parkour drops.
  • Desert courier using a manual chair. 10° camber wheels with sand tires; paracord spoke guards for brush; quick‑release axle pins shown in reload animation; water skins mounted to back uprights.
  • Arc‑mage with myoelectric hand. Socket panel inlay matches faction filigree; terminal device swaps between precision and power grippers; HUD flashes when EM interference disrupts myo sensors; staff grip geometry sized for the prosthetic palm.
  • Frontline medic in soft‑assist exo. Actuators at hip/knee with visible springs; load routes painted on callouts; backpack battery with safe jettison; crouch animations maintain thigh‑cable slack.

Testing and Review Gates

Gate 1 (Concept): silhouette legibility with device present; function sketches of load paths. Gate 2 (Fit & Costume): garment clearances, holster reach, cape/strap reroutes. Gate 3 (Rig/Anim): anchor IDs verified; constraint stacks; gait baselines signed off. Gate 4 (Accessibility): camera framing, UI prompt placement, audio/VFX assist toggles. Gate 5 (Perf): LOD/dangle budgets; spoke collapse, cable swaps, physics limits.

Your Checklist in Paragraph Form

Before locking a mobility device or prosthetic, ask: does it preserve dignity and role readability? Are load paths and clearances anatomically sound? Do anchors, constraints, and collision maps match rig conventions? Can costume and gear integrate without bespoke geometry for every variant? Are UI and camera fair for seated/supported postures? Do performance budgets hold across LODs? Has cultural/sensitivity review cleared motifs and narrative framing? If yes, you have an integrated design ready for production.

Closing: Tools That Expand Worlds

Assistive devices and prosthetics are tools that widen who gets to belong in your world. When you systematize anchors, materials, and gaits—and let style and story flow through those systems—you avoid tokenism and pipeline pain. Integration is not extra work; it is the work that makes your cast richer, your play fairer, and your art more human.