FA-88134 / Inverse kinematics solvers / Member archive

Stewart legs exactly at a stroke end are flagged · case 04

A pose whose legs sit exactly at lmin or lmax is reported as a limit violation.

Member previewVariant 4 · 3 implementations · 7 checks per implementation

Case contract

Input [A,B,pose,lmin,lmax]: base anchors A and platform anchors B (platform frame), pose [x,y,z,roll,pitch,yaw] in degrees with R = Rz(yaw) Ry(pitch) Rx(roll). Leg i length is |p + R b_i - a_i|. Return lengths rounded to 4, or ["limit", i, length] for the first leg outside the inclusive range [lmin,lmax].

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
identity pose exact 13	`["limit", 0, 13.0]`	`[13.0, 13.0, 13.0]`	Failed

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