PYTHON · NUMPY

Martial Arts: Forms and Timing

Compose a martial-arts form from timed keyframe poses, hitting each on time while keeping the center of mass over the support base.

01Challenge

The form's motion is flat because the poses are not sequenced. Interpolate between the keyframes so the body flows through each pose on time, and keep the center of mass balanced over its base the whole way through.

02Model

A martial-arts form, a kata, is a sequence of poses held in time: a library of motion primitives chained into a whole. Building one is the same skill behind any dexterous behavior, sequencing primitives and blending smoothly between them, and it forces the two constraints a humanoid always lives under: hit the pose on time, and never let the center of mass leave the support base, or you fall. You compose the form by interpolating between keyframes, the same keyframing that animates a character, then check that the trajectory both reaches every pose and stays balanced throughout. Master this and you have the grammar for combos, gestures, and reach.

03Guided practice

1. Interpolate. Fill com_at(t) with np.interp(t, [k[0] for k in keys], [k[1] for k in keys]), piecewise-linear between keyframes. 2. Hit the poses. Interpolation passes exactly through each keyframe at its time. 3. Stay balanced. The keyframes are within +/-0.15 m, inside the 0.20 m base, so a smooth blend never tips. 4. Confirm all keyframes are hit and the max center-of-mass stays under the base half-width.

04Feedback

PASS WHEN PASS when the form hits every keyframe on time AND the center of mass stays over the support base throughout.

If your run fails, check:

keyframes hit=False: `com_at` still returns 0. Interpolate with `np.interp` over the keyframe times and values.
Not balanced: if you scaled the poses up, keep |CoM| under the 0.20 m base half-width.
Hits keyframes but jerky: linear interpolation is fine here; the check is on positions, not smoothness.

05Retrieve & space

What is a motion primitive, and how does a form chain them? (a reusable pose/segment; sequenced with timing).
What is the support base (support polygon), and why must the CoM stay over it? (static balance; else it tips).
How does keyframing produce continuous motion from discrete poses? (interpolation between them).

06Mastery & project

Sequence timed keyframe poses into a balanced form: the grammar of composed, dynamic movement.

The primitive-sequencing skill that underlies dexterous manipulation and expressive gesture alike.

← Dance: Style and the Beat Play: The Drive That Expands the Body →

PYTHON · NUMPY

Martial Arts: Forms and Timing

Compose a martial-arts form by interpolating timed keyframe poses, keeping the center of mass balanced.

You read

the arrays and values already in scope

You change

the code you write in each cell

Fixed

the dataset and the checks that grade you