Chapter 4: Climb, Brachiate, Burrow & Leap

Created by Sarah Choi (prompt writer using ChatGPT)

Climb, Brachiate, Burrow & Leap — Center‑of‑Mass Thinking

Why Center of Mass Matters for Creature Locomotion

No matter how many limbs a creature has, how fantastical its anatomy is, or how dramatic the pose looks, one thing always applies: its center of mass (COM) has to make physical sense. The center of mass is the imaginary point where the creature’s mass is balanced. When you understand where that point is and how it moves, you can draw climbing, brachiating, burrowing, and leaping poses that feel grounded and powerful.

For creature concept artists—both on the concepting side (fast ideation, cinematic framing) and the production side (clear, rig‑friendly poses and motion sheets)—center‑of‑mass thinking is a universal tool. It ties together:

  • Footfalls on land.
  • Climbing on walls and ceilings.
  • Brachation (arm‑swinging) through trees or ruins.
  • Burrowing through earth or sand.
  • Leaping between surfaces or into flight.

In this article, we’ll explore how to track the COM across these different locomotion modes so that your creature designs look like they can truly inhabit and move through their environments.

1. Center of Mass 101

1.1 What Is the Center of Mass?

The center of mass is the average location of an object’s weight. For a creature, it typically sits somewhere near the middle of the torso, influenced by:

  • Size and density of the head, chest, belly, hips, and tail.
  • Distribution of heavy armor, shells, or packs.

You don’t need to calculate it exactly. Instead, imagine a weighted dot inside the creature’s body where it would balance if you could place it on a thin pole.

1.2 Support Base and Balance

On land or on a climbing surface, a creature’s COM must fall within a region where its supports (feet, hands, claws, tail tips) can realistically hold it. This region is called the base of support.

  • On flat ground, the base of support is the polygon between contact points (feet, hands, tail).
  • On a wall or ceiling, the support polygon is defined relative to that surface, but gravity still points down.

If the COM falls inside the support base, the pose looks stable. If it falls outside, the creature looks like it’s slipping, falling, or lunging—which can be good if that’s your intention.

1.3 COM Path and Locomotion

In movement, the COM follows a trajectory. For example:

  • In walking, it oscillates up and down over a zig‑zagging line between footfalls.
  • In leaping, it follows a ballistic arc (parabola) from takeoff to landing.
  • In brachiation, it swings like a pendulum beneath the arms.

As a concept artist, you can think of the COM as a simple path to design your poses around. Limbs and details then “hang” from that path.

2. Climbing: Vertical and Overhead Support

Climbing is essentially walking with the ground tilted up. The rules of COM and support still apply, but your support base is now on a vertical (or angled) surface.

2.1 Climbing on Walls

When a creature climbs a wall:

  • Hands and feet (or claws, pads) act as anchors.
  • The COM must remain close to the wall to avoid peeling off.

Visually, this means:

  • The torso often hugs the surface; the spine angle leans into the wall.
  • Limbs are spread to enlarge the support base—like a climber using multiple holds.

When drawing:

  • Start by placing the COM (a dot) slightly off the wall surface.
  • Arrange limb contacts so that if you project lines from the COM to the wall, they land inside the polygon formed by those contact points.

A creature reaching up to a new hold may briefly let the COM drift toward an edge of the base, creating a sense of risk or strain.

2.2 Climbing on Ceilings

Ceiling climbing (insects, geckos, alien creatures) feels especially uncanny, but the COM rules still hold.

  • The COM still points toward the ground due to gravity.
  • The support base is now overhead; limbs must compensate with strong grips.

To make it believable:

  • Keep the COM directly under a cluster of supports—e.g., four legs around a central torso, or multiple sticky pads near the COM.
  • Limbs often bend inward, pulling the body toward the ceiling.

If you draw a ceiling climber with COM off to one side, it should clearly be swinging or slipping, not resting neutrally.

2.3 Climbing Gaits and Footfalls

Climbing has its own “footfall” patterns:

  • Slow, cautious climbers often keep three or more points of contact at all times.
  • Faster climbers may briefly go down to two points of contact, especially in jumps between holds.

When concepting:

  • Show one limb at a time searching for the next hold while others support.
  • For production, a simple contact diagram (which limbs are attached when) helps animators choreograph the climb cycle.

3. Brachation: Swinging from the Arms

Brachation is a type of locomotion where a creature swings from branch to branch using its arms (or equivalent limbs). Gibbons are a classic example, but it’s a powerful reference for any arm‑dominant creature—jungle beasts, ruin‑dwellers, canopy predators.

3.1 COM as a Pendulum

In brachiation, the COM behaves like a swinging pendulum beneath the handhold.

  • At the bottom of the swing, the COM is directly below the grip and moves fastest.
  • As the creature swings forward, the COM rises, converting kinetic energy into potential energy.

This creates a graceful arc that you can exploit for dynamic posing.

3.2 Single‑Arm vs Double‑Arm Brachation

Double‑arm brachiation:

  • Both arms grip the same branch or bar.
  • The COM hangs between them; the body swings as a single unit.
  • Good for heavy creatures or those with huge torsos.

Single‑arm brachiation:

  • One arm at a time supports the COM.
  • The COM hangs directly under the supporting hand.
  • The free arm reaches forward to the next support.

In both cases, the arms must be long enough and the shoulders strong enough to support full body weight.

3.3 Drawing Brachation Poses

Key poses in a swing sequence:

  1. Hang / bottom:
    • Arms extended overhead.
    • COM directly below hands.
    • Legs trailing slightly backward.
  2. Forward swing:
    • COM moving forward and upward.
    • Torso and legs angled forward.
    • Free arm reaching out.
  3. Release and catch:
    • Old hand releasing; COM in mid‑flight, still following an arc.
    • New hand grabbing ahead; body stretches between holds.

When sketching, draw the pendulum arc the COM follows, then hang the body from it. This ensures the swing looks physically grounded even when stylized.

3.4 Integrating Brachation with Other Modes

Brachating creatures often also:

  • Climb vertically using both arms and legs.
  • Leap between gaps in the canopy.

Design limb proportions with this in mind:

  • Long arms for reach and swinging.
  • Grasping hands or hooked claws.
  • Torso and COM shape that facilitate swinging (not excessively bulky in ways that contradict the motion).

For production, show a few swing phases and how the creature transitions from brachiation to climbing or landing on a branch or ground.

4. Burrowing: COM and Directional Force Underground

Burrowing creatures live in or move through a resisting medium (soil, sand, debris). Their locomotion centers around pushing material aside or compressing it.

4.1 COM and Direction of Travel

In burrowing, the COM is usually:

  • Positioned close to the head or front of the body if the creature digs forward.
  • Supported by body segments that press outwards to maintain traction.

The creature must balance:

  • Forward thrust into the material.
  • Lateral pressure against the tunnel walls.

4.2 Burrowing Strategies

Common burrowing styles to reference and stylize:

  • Scratch diggers (moles, certain lizards):
    • Large forelimbs with claws excavate soil.
    • COM stays low and forward; hindlimbs and tail stabilize.
  • Head‑first wedge burrowers (worms, some snakes):
    • Compact, wedge‑shaped heads.
    • COM moves as body segments telescopically contract and expand.
  • Whole‑body burrowers (sand swimmers):
    • Entire body undulates to fluidize sand.
    • COM shifts in small increments as waves propagate.

4.3 Drawing Burrowing Motion

In side view:

  • Show the creature at an angle pushing into the substrate.
  • The COM should be just behind or near the region doing the most work (forelimbs, wedge head).

In cutaway or X‑ray views (useful for concept sheets):

  • Draw the tunnel profile.
  • Place the COM inside the tunnel cross‑section and show how limbs or segments press against walls to move forward.

Design cues:

  • Stout, reinforced front sections for diggers.
  • Strong spine and rib structures.
  • Reduced or modified eyes, ears, or wings if they interfere with burrowing.

Production note:

  • If burrowing is a gameplay mechanic, include entry, mid‑burrow, and exit poses. Clarify how much earth is displaced and how quickly.

5. Leaping: Ballistic Arcs and Impact

Leaping is a dramatic, high‑energy locomotion mode that shows up constantly in creature design—predators pouncing, mounts clearing gaps, dragons launching into flight.

5.1 COM Path in a Leap

A leap can be treated as a projectile motion:

  • Once in the air (neglecting wing flaps or external forces), the COM follows a parabolic arc.
  • The shape of the arc depends on takeoff speed and angle.

Important: limb motion in mid‑air does not change the COM path (unless wings or jets provide new forces). Limbs can change the creature’s orientation, but the COM still follows the same ballistic curve.

For dynamic compositions:

  • Sketch the COM arc first.
  • Pose the body along that arc at different points: crouch, launch, mid‑air, landing.

5.2 Takeoff: Loading and Release

At takeoff, the COM moves from behind the support base to ahead of it.

  • The creature often crouches, bringing COM lower and backward.
  • Hindlimbs (or equivalent) compress like springs.
  • During push‑off, hindlimbs extend, driving the COM forward and up.

Drawing takeoff:

  • Emphasize compressed poses with bent joints and tight body lines.
  • Show the COM just ahead of the hindfeet when leaving the ground.

5.3 Flight Pose and Orientation

In mid‑air, limb positions affect attitude but not the COM arc (again, unless wings or jets are active).

  • Creatures may tuck legs under or stretch them forward in anticipation of landing.
  • The spine may curve based on pose (defensive coil, aggressive extension).

Concepting tip:

  • Use contrast: one frame with a drawn‑in, compact creature at launch, and another fully stretched in mid‑air for drama.

5.4 Landing and Impact

Landing is where the COM must return to a supported base safely.

  • Forelimbs often contact first, then distribute load to hindlimbs.
  • Joints flex to absorb impact, compressing the body.

Place the COM:

  • Directly above or just slightly ahead of the landing support base.
  • Inside a polygon formed by landing limbs.

If you want a stumble or crash, push the COM beyond the support base and show limbs failing to catch it.

Production note:

  • For creatures that leap often, include a 4‑pose sequence: crouch, takeoff, mid‑air, landing.
  • This helps animators design a reusable jump cycle.

6. Center of Mass Across Modes: Walk, Climb, Swim, Fly

Creatures often switch between locomotion types; your COM thinking should travel with them.

6.1 Walk ↔ Climb

On a slope or wall:

  • The COM shifts closer to the surface.
  • Limb contact patterns maintain a stable support base against gravity.

In design:

  • Show a gradual change: from upright walk to diagonal climb to full vertical scaling.
  • COM placement should migrate from above the feet to almost between hands and feet on the wall.

6.2 Leap ↔ Flight

For winged leapers (dragons, gryphons):

  • Initial leap sets the COM arc.
  • Early wingbeats alter the arc by adding lift.

When designing transitions:

  • Show the leap as a normal ballistic move at first.
  • Then transition into wing deployment, bending the COM path upward if needed.

6.3 Swim ↔ Climb or Walk

Leaving water:

  • COM changes from nearly neutrally buoyant to fully affected by gravity.
  • Creatures must quickly adjust stance and limb contact to support weight.

In staging:

  • Show a low, sprawled stance as the creature drags itself from water, COM close to support points.
  • Gradually raise the COM as more of the body emerges and legs take over.

7. Concepting vs. Production: Using COM Differently

7.1 On the Concepting Side

In early concepts, emotion and rhythm are priority, but COM still guides you.

  • Use a quick “COM dot + support base” check on your thumbnails. If they don’t line up, decide whether you’re implying motion (fall, slip, lunge) or need to adjust.
  • For cinematic frames (a leap, a swing, a burrow erupt), exaggerate the arc of the COM to enhance drama while keeping underlying physics legible.

You can stylize anatomy heavily—long limbs, tiny torsos, giant tails—as long as you place and move the COM sensibly.

7.2 On the Production Side

Production requires repeatable, rig‑friendly logic.

  • Provide side‑view or 3/4 diagrams showing COM path for key actions: climb cycle, brachiation swing, burrow progress, jump arc.
  • Annotate which limbs are supporting the COM at major moments.
  • Ensure joint placement and limb lengths match the implied COM dynamics across views.

This gives animators a clear blueprint, reducing guesswork and keeping movement consistent with your design intent.

8. Practical Exercises for Center‑of‑Mass Thinking

8.1 COM Dot Practice

  • Take existing creature art (yours or others’).
  • On a layer above, mark where you think the COM is.
  • Draw a line straight down (gravity) and check whether it falls within the support base.

Do this until you can estimate COM intuitively.

8.2 Climb and Hang Thumbnails

  • Draw a page of small creature thumbnails on walls and ceilings.
  • For each, place the COM and draw the polygon of contact points.
  • Adjust poses so the COM is inside the polygon unless you want a slip or swing.

8.3 Brachation Arc Sheet

  • Draw a simple arc representing the COM swing path.
  • Place the creature at 3–4 positions along the arc and hang it from different branches.
  • Focus on pendulum behavior rather than detail.

8.4 Jump Arc Planning

  • Sketch a simple parabolic line from takeoff to landing.
  • Place COM dots at several points along the arc.
  • Pose your creature at each point—crouch, launch, mid‑air, landing—keeping the COM dot consistent.

This will tighten your sense of how bodies move through space under gravity.

9. Bringing It All Together

Climbing, brachiating, burrowing, and leaping all look very different on the surface, but underneath, they share the same logic: where is the center of mass, and how is the body supporting or redirecting it?

  • Climb: COM stays close to the surface; multiple contact points form a stable base.
  • Brachiate: COM swings like a pendulum below handholds; arms and shoulders bear the load.
  • Burrow: COM pushes forward into resisting material; front segments and limbs drive progress.
  • Leap: COM follows a ballistic arc from push‑off to impact; limbs control orientation and support at key moments.

For both concepting and production creature artists, center‑of‑mass thinking turns wild designs into believable movers. It helps you:

  • Pose creatures in ways that feel heavy, agile, or precarious on purpose.
  • Communicate clearly with animation about where weight and support really are.
  • Integrate land gaits, flight, swim, and climb into a coherent movement language.

Whenever a pose feels off, ask:

  1. Where is this creature’s center of mass? Did I actually place it in my mind or on the page?
  2. Is the COM supported by the current contacts, or should this be a moment of imbalance and motion?
  3. Does the COM path make sense over time—from climb to leap to landing, from swing to catch, from burrow to erupt?

If you build the habit of checking these questions, your climb, brachiate, burrow, and leap designs will stop feeling arbitrary and start feeling like they obey a believable internal physics—making your worlds more immersive and your creatures more alive.