Inverse kinematics

Teleop and planning both lean on ssik, the lab's analytical IK solver, which I didn't write, and on the OpenArm it kept failing. I traced it to a singularity in the solver itself: the OpenArm's joint axes meet at shared points, so its link lengths are zero and every twist is a right angle, and that exact geometry breaks the Raghavan–Roth elimination the solver uses. My fix nudges those zero lengths by a tiny fraction of the arm's size, so the solver works on an arm a hair off the real one, then, since forward kinematics is cheap, refines the answer against the true arm's FK, step after step, until it's an exact solution again. The maintainer confirmed the fix would have worked while landing the same one upstream.

For demonstrations and live driving, I built teleop with a Meta Quest. The apps I tried had no passthrough and left me dizzy, so I wrote my own: instead of an app on the headset, the robot serves a page the Quest's browser opens in AR, so the operator still sees the room, and the page streams both controllers' poses, grip and trigger to the robot over a websocket. Holding a grip engages its arm, and the trigger works the gripper. The headset's page goes dark once it enters AR, so the robot also broadcasts that live telemetry to any other browser pointed at it, and someone at a laptop can watch exactly what the operator is sending. It matches the old SDK's interface, so switching was a one-line change. I built it against the arms in MuJoCo first; at first the loop couldn't keep up, and the bottleneck turned out to be publishing the sim viewer over the network, not the control.