Sarah Clarity Studios

Chapter 2: Gears, Belts, Chains, Harmonic Drives

Created by Sarah Choi (prompt writer using ChatGPT)

Gears, Belts, Chains, Harmonic Drives — Visual Cues for Power Transmission

Power transmission is the “proof of effort” in a mecha design. Actuators create force, but transmissions decide what that force becomes: slow torque, fast rotation, precise positioning, compliant motion, or brute pulling. For a viewer, transmission cues answer the silent question: “How does the mech actually move that mass?” For a production team, transmission cues reduce ambiguity: where the pivot truly is, what clearance must be protected, what can be armored, and what needs flex routing.

This article is a depiction guide—how to show gears, belts, chains, and harmonic drives so they read as intentional, mechanically plausible, and consistent with your chosen actuator family (hydraulics, pneumatics, electric, or muscle-mimic). You do not need to engineer the internal tooth counts. You do need a reliable visual vocabulary and a few “don’t break believability” rules.

Transmission cues are silhouette cues

Transmission components are not tiny garnish details. They change the silhouette because they need volume, alignment, and protection. A geartrain implies a housing bulge at an axis. A belt drive implies pulleys and a planar route that must stay clear. A chain drive implies sprockets and a guarded loop with tension control. A harmonic drive implies a compact ring-like package around a joint with precision cues.

If you place these cues where the audience can see them, the mech reads more functional even with fewer details elsewhere. Conversely, if you hide every transmission hint behind smooth armor, you must reserve believable internal volume and provide at least one clue (panel seams, access covers, venting, cable routing) or the limb becomes a “magic hinge.”

Start with the motion intent: speed, torque, precision, compliance

Transmission depiction begins with intent. Ask what the joint needs most.

If the joint needs high torque (hips, shoulders, heavy wrists), your cues should feel thick and protected: gear housings, reduction bulges, reinforced collars, and short power paths. If the joint needs high speed (light arms, tools, agile ankles), your cues can be slimmer and more open, but still aligned and guarded. If the joint needs precision (aiming, stabilization, fine manipulation), harmonic-drive cues and sealed housings read better than exposed chains. If the joint needs compliance (shock absorption, muscle-like give), belts, tendon routing, and pneumatic “soft” cues feel right.

For concepting-side artists, this keeps your design consistent with role and tone. For production-side artists, this tells riggers what to prioritize (smooth rotation vs springy behavior) and tells modelers which volumes must not be compromised.

A quick taxonomy of the four transmission looks

Gears read as “torque and ruggedness.” They want enclosed housings, coaxial stacks, and structural collars.

Belts read as “quiet, smooth, lightweight, serviceable.” They want pulleys, planar routing, and cover guards.

Chains read as “industrial, dirty, field-fixable.” They want sprockets, tensioners, and rugged guards.

Harmonic drives read as “precision, compact reduction, robotics.” They want ring-shaped housings and clean, sealed joints.

You can mix these, but mixing should look like a deliberate architecture. A common believable mix is “harmonic/gear reduction at the joint, belt/chain routing to an offset accessory.”

Visual cue fundamentals: alignment, guard logic, and service access

Most transmission cues succeed or fail on three depiction fundamentals.

First is alignment. Gears must share axes or mesh with visible spacing. Belts and chains must wrap around pulleys/sprockets that live on parallel planes. If your pulleys are skewed or your chain loop kinks, the viewer senses “fake.” You can stylize the shapes, but the geometry should still imply a path.

Second is guard logic. Exposed teeth and moving loops are dangerous and vulnerable. A believable design either encloses them (sealed housing) or guards them (cages, partial covers, finger-safe shrouds). Even a thin guard plate tells the audience the designer thought about hazards.

Third is service access. Transmissions imply maintenance. A few access panels, bolt rings, inspection windows, or removable covers make the system feel real. For production, those panels become natural places for decals, wear, and damage states.

Gears: how to show reduction without drawing every tooth

Gears are the easiest way to communicate strength. In depiction, you rarely need to draw teeth. You can suggest gear function through housing shapes and layering.

A gear-reduced joint often reads as a bulged hub or collar around the pivot. If you want “heavy industry,” the housing is chunky, with stepped rings and visible fasteners. If you want “sleek robotics,” it’s a clean ring with a subtle seam and a bolt circle.

A useful cue is the stack. Reduction implies multiple stages, so a joint can look like two or three concentric rings—outer structure, inner drive ring, central axle cap. Even if the internals are imaginary, the layered silhouette sells “there’s a mechanism in here.”

If you do show exposed gears, keep them in safe contexts: inside an open maintenance bay, behind a protective grill, or as a small accessory train that is clearly guarded. Exposed large gears on an external limb read as extremely hazardous unless the world tone is explicitly “industrial hazard aesthetics.”

Belts: pulleys, plane discipline, and the quiet-tech look

Belt cues give a design a smooth, modern feel. Belts are also a great depiction tool because the loop path is readable at a distance.

To draw belts believably, commit to a plane. The belt must live in a consistent plane, wrapping around pulleys that are aligned. A belt that twists implies a twist belt system, which is rare and should be a deliberate design call.

Belts also imply tension control. A small idler pulley, a sliding bracket, or a tensioner arm instantly makes the system feel “real.” You don’t need to label it; the silhouette does the work.

Belts like guards. A partial cover over the top run suggests safety and debris protection, while leaving the lower run visible for readability. This is especially helpful for concepting-side sheets: you can show the mechanism while still implying engineering care.

Belts pair nicely with electric motors. A visible belt stage between a motor can and a joint hub reads like “motor → reduction → joint” without requiring you to explain it.

Chains: sprockets, grime stories, and field-repair language

Chains read as rugged and maintenance-heavy. They bring an immediate industrial vibe, and they tell a story: lubrication, dirt, wear, and noise.

A chain system must show sprockets. Even if the chain links are simplified, the sprocket tooth silhouette (or at least a scalloped rim) signals “chain interface.” Chains also want a tensioner. A small spring-loaded arm or an adjustable idler is a high-value cue.

Because chains are exposed, they strongly benefit from guard design. A chain guard can be skeletal (cage bars) for a gritty, utilitarian faction, or more enclosed for a military design. Either way, if the chain is completely unguarded near limbs or crew areas, it reads unsafe unless that is part of the worldbuilding.

Chains can be a smart choice for external power routing to tools—like a forearm saw, winch, or shoulder-mounted accessory—because the route is visible and the narrative reads “mechanical power delivered here.”

Harmonic drives: compact precision cues for mecha joints

Harmonic drives are a favorite in robotics aesthetics because they imply high reduction and precision in a compact package. Depiction-wise, they are less about visible moving parts and more about a clean, ring-like housing that feels engineered.

A harmonic-drive joint often reads as a thick ring around the pivot with a bolt circle and a clean seam line. The ring can be nested—an outer ring for structure and an inner ring for the drive. You can add subtle cues like evenly spaced fasteners, a dust seal lip, or a cable exit grommet.

The key is restraint. Harmonic drives look “credible” when they are tidy and sealed. Too many exposed teeth or chaotic piping breaks the precision vibe.

Harmonic drives pair naturally with electric actuation. If your mech is high-tech, a harmonic-drive look at the major joints is one of the fastest ways to communicate “servo precision” without text.

How transmission cues shift across actuator families

Transmission cues should harmonize with your actuation choice. The same gear housing can feel hydraulic or electric depending on the surrounding ecosystem.

Hydraulics + transmissions

Hydraulic systems often imply that pressure is created centrally and delivered via hoses to actuators. Transmission cues can still exist—especially for rotary joints where a cylinder drives a crank, which then turns a gear-reduced joint.

Hydraulics read best when your gear housings feel heavy and your hose routing feels protected. Think of a joint as a “power node”: thick collar, guarded moving parts, and hose ports that feel like they belong. If you depict belts or chains in a hydraulic system, they often read as secondary drives—external routing to a tool or accessory—because primary heavy joints typically prefer enclosed mechanisms.

Pneumatics + transmissions

Pneumatics tend to read as lighter and snappier. A pneumatic design can still use gears, belts, and chains, but the silhouette usually becomes more modular and standardized.

Belt cues pair especially well with pneumatics if you want a factory-automation feel: quick-service covers, standardized brackets, and clean loops. Chain cues can work too, but they push the vibe toward “industrial machine” rather than “precision robot.” If you use harmonic-drive cues with pneumatics, it suggests a hybrid system—compressed air for certain motions, high-precision servo joints where needed.

Electric + transmissions

Electric systems are where transmission depiction shines. Motors want reduction; reduction wants gears or harmonic drives; and external routing can be belts or chains.

Electric designs also want cable logic. A harmonic-drive ring with clean cable exits reads “servo joint.” A motor can feeding a belt stage reads “quiet, serviceable reduction.” Gear housings with cooling fins and access panels read “high torque, heat management.”

If your mech is sleek, you can show transmissions as subtle volumes rather than exposed mechanisms. In production, that means you still reserve space and provide panel seams and access covers to justify the internal complexity.

Muscle-mimic + transmissions

Muscle-mimic systems change the transmission story. Instead of classic geartrains, you often depict tendon routing, pulleys, cams, and compliant elements.

Belts become “tendons” visually if you flatten and bundle them, while chains generally feel too rigid and noisy unless the world tone wants that contrast. Gears and harmonic-drive rings can still exist, but they read as “skeletal joints” inside a soft exterior.

The most important cue for muscle-mimic is direction change. Tendons need guides and pulleys. Even one visible pulley cluster at a joint makes the routing feel believable and gives animators a clear mental model.

Depicting direction change: the power-routing moment

A transmission is most readable when it changes direction. A belt that turns a corner via a pulley cluster, a chain that routes around a sprocket near a pivot, or a gear housing that transfers rotation to a perpendicular axis—these moments are where you can “show the mechanism” without clutter.

Use direction change moments as focal points on your sheet. For concepting-side work, they sell the idea quickly. For production-side work, they establish how the joint is intended to behave and where collision clearance matters.

Protective covers as design language

Covers are not afterthoughts. They are a major part of power transmission design language.

A skeletal guard (bars, partial cage) reads rugged, field-repair, and aggressive. A sealed cover reads military, premium, or safety-conscious. A modular cover with quick latches reads industrial service culture. A soft boot or sleeve reads contamination control and pairs well with muscle-mimic.

The cover also helps you control visual noise. You can hint at complexity without drawing every link by giving the cover a believable volume and a few access cues.

Production-side notes: make it buildable and riggable

For production, transmission depiction should answer “what is fixed, what rotates, what slides?” Provide at least one view where the power path is visible or implied clearly. If you show a belt or chain, ensure the path won’t intersect armor during range of motion. If you show a gear housing, indicate the axis and the likely rotation group.

A simple, high-value callout is a “keep-clear” volume around loops and pulley clusters. Another is a note that certain covers are removable modules. These cues help modelers separate parts logically and help riggers avoid impossible interpenetration.

If your design repeats transmission modules (same harmonic ring in multiple joints, same belt stage on both arms), call that out. Repetition is a gift to production: it reduces unique asset count while increasing cohesion.

Concepting-side workflow: fast, readable cues

In early ideation, choose one primary transmission cue per joint category. For example, “harmonic rings on major joints, belts for accessory routing, chains only for tools.” Then place those cues consistently.

Do a silhouette pass that only shows transmission volumes: hub bulges, belt planes, chain loops, and cover shapes. If it reads from afar, it will read in gameplay. Then add a second pass for mounting and service seams.

A helpful habit is to sketch one “maintenance-open” vignette—a small cutaway showing gears or belt stages inside a cover. You don’t need to do this everywhere. One vignette convinces the viewer that the rest is equally engineered.

Common depiction mistakes and fixes

A frequent mistake is misaligned belt/chain planes. Fix it by drawing the pulley/sprocket discs first, then wrapping the loop.

Another mistake is overexposure. Exposed chains and gears look cool, but they become implausible without guards. Fix it by adding partial covers, cages, or placing exposure only in protected recesses.

A third mistake is “gear texture spam.” Teeth everywhere turn into noise. Fix it by using gear housings and bolt circles as your primary read, and only show teeth in small, intentional windows.

A fourth mistake is forgetting tensioners. Loops without tension control feel fake. Fix it with one idler pulley or tension arm per loop.

Closing: transmission cues as a storytelling layer

Gears, belts, chains, and harmonic drives are not just mechanical decoration. They are a style dialect that communicates torque, precision, maintenance culture, and technological era. For concepting-side artists, these cues let you sell motion and function fast, with minimal rendering. For production-side artists, these cues create clear part grouping, predictable rig behavior, and believable clearance planning.

When you pick a transmission language, commit to a few repeating motifs—housing shapes, cover styles, loop routing rules—and apply them everywhere. Consistency is what makes a mech feel like a designed system rather than a collection of cool parts.