Open Hardware · CERN OHL

Turn, one back

A real 3D model of a 360° ball-and-socket robotic joint connecting two robot arms — with integrated visual sensors and backlash detection that identify where the spherical bearing is wearing, then redistribute the contact zone to extend service life up to ~10×. A grease port keeps the bearing serviceable for longer. Designed for joints, not gears. No magnetic coupling. Minimal added weight. Just the model.

360° ball-and-socket joint Connects two robot arms Visual sensors Backlash detection No magnetic coupling Minimal added weight Up to ×ばつ lifespan CERN OHL · Open Hardware

Original concept & design: Viktor Brunclík

Interactive model

Turn it over in your hands

A live 3D model built in your browser from the published design file. The output arm makes the small repetitive motion of a real robot joint — watch a single contact patch on the ball wear and redden. Turn, one back then shifts the load to a fresh patch; spread across the whole sphere, that's up to ×ばつ the service life. Drag to orbit, scroll or pinch to zoom.

Output arm (rotates 360°) Ball Wear patch Socket (transparent) Base link Lube port Backlash sensors Visual wear sensors

Drag to rotate · scroll / pinch to zoom · rendered from turn-one-back.scad

Overview

What is it?

Turn, one back is a system for 360° ball-and-socket robotic joints — the spherical bearing that connects two robot arms, where a ball rotates inside a socket through a full 360°. Not for gears. The bearing surface is the direct contact between ball and socket, and that is exactly what this system monitors and protects.

Most such joints fail because the same small patch of the ball takes all the repeated load. An arm that swings back and forth through the same arc always wears exactly the same spot on the sphere, while the rest of the surface remains untouched.

Turn, one back changes this. It uses visual sensors and backlash measurement to continuously monitor where wear is accumulating on the ball's spherical surface. Backlash here means the play that develops between ball and socket as the surface wears — not gear tooth clearance. The joint does its small repetitive motion on one spot of the bearing; when that spot wears, both ends rotate together — then one returns. The arm's working position stays exactly the same, but that same small motion now lands on a fresh patch of the sphere. No magnetic coupling. Negligible added weight.

Note: the index marks and sensor ring around the socket are a measurement tool only — they let the optical sensors track the ball's position and detect bearing play. They transmit no force and are not a gear.

The result: the entire spherical surface is used evenly, and the joint lasts dramatically longer — up to 10 times the original service life.

And it stays serviceable. A grease port feeds the ball-socket interface — re-lubricating refreshes the bearing film and clears debris, extending the service interval. It reduces friction, not lost material, so it stretches life rather than resetting it: the joint is maintained, not scrapped.

×ばつ

lifespan (wear redistributed)

360°

full surface utilisation

changes to normal operation

Mechanism

How it works

Turn, one back operates transparently alongside the existing motion — the joint keeps doing its normal job while wear is silently managed in the background.

Continuous wear monitoring

Visual sensors observe the joint surface in real time. Backlash measurement provides a quantitative signal of how much play has developed — and precisely where on the joint circumference it is worst.

Wear zone identification

The system builds a wear map: it knows exactly which angular sectors of the joint have taken the most damage and which remain fresh. This map is updated continuously as the joint operates.

Coordinated redistribution

When a sector reaches a wear threshold, both sides of the joint (upper and lower) rotate together to a new angular offset. Then one side (the lower / follower) returns to its previous position. The net working position is unchanged — but the contact zone has shifted to a fresh part of the surface.

Transparent continuation

Normal operation resumes immediately. The repetitive motion that was previously destroying one spot now happens elsewhere on the joint. Over time, every sector is used — and worn — evenly, maximising total service life.

Technical features

What the Turn, one back design includes

Two independent sensor systems

Visual wear sensors look directly at the ball's spherical bearing surface through windows in the socket, detecting scoring and material loss. Separate backlash sensors measure the play between ball and socket. Both systems operate continuously, no disassembly needed.

Serviceable — re-lubrication port

A grease port feeds the spherical bearing. Re-lubricate to refresh the film and clear debris, extending the service interval — the joint is maintained, not scrapped. No disassembly.

Backlash quantification

Precise measurement of mechanical play per angular sector, forming a full 360° wear profile.

Two-axis redistribution

Coordinated rotation of both joint sides shifts the active contact zone without disturbing the output position.

Full 3D model

Complete hardware design — ready to manufacture, adapt, and build upon under the CERN Open Hardware Licence.

Drop-in integration

Works alongside existing motion control with no changes to normal operating logic. No magnetic coupling — minimal added weight.

Open & royalty-free

CERN OHL — free for personal, research, and commercial use. Extend it, modify it, ship it.

Applications

Where it makes a difference

Any rotary sleeve-bearing joint with repetitive or limited-range motion stands to benefit — the more concentrated the normal wear pattern, the greater the gain.

🤖 Robotic joints & arms

⚙️ CNC axis drives

🏭 Industrial actuators

🖨️ 3D printer axes

🔭 Precision telescope mounts

🦾 Prosthetic mechanisms

Licence

CERN Open Hardware Licence

Turn, one back is released under the CERN Open Hardware Licence (CERN OHL) — the standard for open hardware, used and recognised worldwide.

CERN OHL

What this means for you

✅Use freely — for any purpose, including commercial products and manufacturing.

✅Modify & extend — adapt the design, improve it, combine it with other work.

✅Distribute — share the original or your modified version freely.

📌Preserve the licence — any distributed version (original or derivative) must carry the same CERN OHL licence and retain attribution to the original author.

The copyleft requirement ensures that improvements to this design remain in the open hardware commons — benefiting everyone.

Authorship note: Viktor Brunclík is the original author of this concept and the sole licensed author of this hardware design. No legal claim is asserted over the underlying idea — it is contributed freely to the world. The CERN OHL applies to the design files and documentation distributed here.

Attribution to the original author is required by the licence and appreciated in any derivative work or product.

Download the design files

The full parametric 3D model — open, editable, ready to render or manufacture. Released under CERN OHL.

Download .scad → Back to Bruncsoft

OpenSCAD format — free open source tool, renders to STL/STEP. Text-based, version-control friendly.