PPolySim OS

Inverse Kinematics

Point at where you want the hand, and solve for the joints. Inverse kinematics is the hard, essential direction behind every robot that reaches for something.

Inverse KinematicsLive

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Inverse kinematics is the hard direction: given where you want the tip, find the joint angles. For a 2-link arm the law of cosines gives a clean closed form — but with two solutions (elbow-up or elbow-down) and none at all when the target is out of reach. Drag the target, or click anywhere to move it there.

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Data Inspector

Joint 1-20.8°
Joint 291.4°
Target dist126
Total reach180
Reachableyes

Governing equation

Reading this result: This 2-link arm (segments 100 and 80, total reach 180) has a closed-form inverse: the law of cosines gives the joint angles that place the tip exactly on the target, with two branches — elbow-up and elbow-down. Iterative methods like CCD or the Jacobian transpose converge to one of them.

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How it works

Inverse kinematics finds the joint angles that place the end effector at a desired target. For a two-link arm the law of cosines gives a closed-form solution — but with a twist: there are usually two configurations (elbow-up and elbow-down), and none when the target lies outside the reachable workspace. Click to move the target.

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The math, the assumptions, real-world uses, or a code translation — explained for this exact simulation.

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Frequently asked questions

Is this inverse kinematics solver tool really free?
Yes. Inverse Kinematics runs entirely in your browser using your device's own compute, so local use is free forever. You only pay Compute Tokens if you scale a job to the cloud.
Do I need to install anything?
No. Everything runs client-side in a modern browser — no downloads, no license, no account required to start.
Can I save or share my simulation?
Create a free account to save projects, and use a shareable embed or minted DOI to publish a live, interactive version anywhere.
How accurate are the results?
The solver uses established numerical methods, but results are for research and educational purposes and should be validated against experiment or professional review before you rely on them.