Keyframes, curves, and timing

Keyframes describe destinations

A keyframe stores a value at a time. Two keys might say “head yaw is zero at 0 seconds” and “head yaw is 8 degrees at 1 second.” Interpolation fills the values between them. A graph editor plots time horizontally and value vertically; steep slopes mean fast changes.

In our studio, each preset contains intentional poses and holds. Duration stretches the whole clip; gesture size scales its angle offsets. Export writes a sample every 1/60 second. These samples describe semantic head channels, not calibrated encoder readings.

Hold, linear, and eased motion

Hold mode stays at a pose until the next key and then jumps. It helps block a performance before refining it. Linear mode moves with a constant slope inside each segment, but changes velocity abruptly at many keys. The eased mode uses a quintic curve with zero endpoint velocity and acceleration for each segment.

Smooth-looking curves still require checks. This particular easing makes the robot pause at each key; it is useful for a first gesture, not a universal animation recipe. A later spline may flow through keys, but overshoot and derivative limits must then be checked.

Timing is also an engineering decision

If you double the duration of the same path, its speed halves and its acceleration becomes one quarter. Halving the angular amplitude halves both as well. The supplied analyzer estimates derivatives from neighboring samples. It does not check torque, jerk, unmodeled peaks between samples or physical clearances.

This is why a tiny motion can be demanding when performed abruptly. Never interpret a successful CSV parse or a finite derivative as approval for a motor command. The mapping and physical tests come later.

Optional: learn the same idea in Blender

Blender is an animation and modeling application; CAD remains useful for dimensioned mechanical design. Download Blender from blender.org/download and open a new General file. For this exercise, use the default cube as a motion stand-in so you can learn the interface before importing robot geometry.

Select the cube. In its Transform panel choose XYZ Euler rotation. Set the frame rate to 24 fps, the timeline to frames 1–145, and place keys on Rotation using the field context menu. Use frame 1 = 0°, frame 49 = 10° on Z, frame 97 = 10°, and frame 145 = 0°. Open the Graph Editor, select the Z rotation curve, and compare Linear with Bezier and Auto Clamped handles. Blender shortcuts vary by version; the property context menu is a reliable starting point.

A Blender file is not a motor script. Preserve the authoring file, record axes and units, and bake/sample the intended channels before using a robot adapter. This optional cube study does not export automatically into our kit.