FA-87892 / Inverse kinematics solvers / Member archive

Joint wrap saturates at +/-180 instead of wrapping · case 02

Multi-turn heading requests yield wrist angles pinned at 180 or -180.

Member previewVariant 2 · 3 implementations · 7 checks per implementation

Case contract

Input [l1,l2,l3,px,py,phi,elbow]: planar three-link arm, phi is the required tool heading in degrees. Subtract l3 along phi to get the wrist centre, solve the two-link sub-chain (elbow "up" gives q2>=0), set q3=phi-q1-q2 and wrap each joint to [-180,180) in degrees rounded to 4 places. A wrist centre outside |l1-l2|..l1+l2 returns "unreachable".

Why this case matters

Inverse kinematics code turns task-space goals into joint commands; a wrong branch, sign, limit or update order sends a real arm to the wrong pose.

One recorded failure

Sample boundary fixture

This sample comes from the broken implementation of a controlled reproducer.

Boundary fixture	Actual	Expected	Outcome
multi-turn heading	`[32.3158, 101.7795, 180.0]`	`[32.3158, 101.7795, -89.0953]`	Failed

MEMBER ARCHIVE

The complete case is available to members.

This record includes three runnable implementations, regression fixtures, execution results, and source hashes.

Member access is invitation-based. Sign in with your invited account to inspect the sources.