Lesson 23

Today's Concept:
IK gives you one value for θ₂. But there are two physical configurations that reach the same tip position: elbow-up (θ₂ negative) and elbow-down (θ₂ positive). The math is identical; the physical result is different.

The configuration you choose depends on the environment. Obstacles below the arm? Use elbow-up. Obstacles above? Use elbow-down. The calculation doesn't make that decision for you — the engineer does, based on the physical constraints of the task. Today, you run both configurations for your user's target, measure both results, and justify which one actually works for your design.