B grade Authoritative secondary, traced to origin

"Open source" — which layer is actually open?

The most common phrase on a spec sheet, and in DIY circles it is read as "I can repair it, modify it and replicate it". But hardware has no agreed definition, and the same sentence can mean four entirely different things.

The claim: "This robot is open source." In a DIY context that gets read as: I can repair it, modify it, replicate it, even build a second one.
Reality: In robot hardware, "open source" covers at least four things: SDK and documentation only; open hardware (schematics and structural CAD); a published bill of materials with sourcing channels; and full-stack, including training data and policy weights. The same phrase lands on very different layers, and what you can do differs enormously between them. There is a subtler layer still: files are provided, but as read-only exports — a PCB as PDF with no project files, a 3D model as STL with no editable STEP. It looks complete and gives you almost no way to change anything structural.
Where the gap is: The marketing line says "open source" and the reader's default assumption is the top layer; most machines actually stop at layer one. This is not lying — it is what happens when a term gets used by each party in the sense most favourable to them. The reverse case exists on the same street: hardware that is entirely closed and clearly more expensive, such as Dynamixel servos, has had openly published protocol documentation, SDKs and simulation models for years. Closed hardware does not mean a closed ecosystem.
When it closes: The word only carries information when the publisher states which layer is open. Three operational tests: can you obtain editable engineering files rather than read-only exports; can you source every part from the published list yourself; does the licence permit commercial use and redistribution.

This site's call

Do not ask whether it is open source. Ask which layer is open. The first gets you a slogan; the second decides whether you can still change the thing after you have paid for it.

Four layers behind one word

Layer	What you get	What you can do
1. SDK and docs	APIs, sample code, partial protocol notes	Write programs. No changing structure or electronics; a broken part usually means support
2. Open hardware	Schematic, structural CAD	Modify structure and electronics; sourcing parts is your problem
3. Published BOM	Bill of materials and sourcing channels	Buy every part independently, build a second unit
4. Full stack	Plus training data and policy weights	Retrain, change behaviour, continue without the vendor

Judge by file format, not by the word: editable engineering files (STEP, PCB sources) or read-only exports (STL, PDF)? That single test is more useful than any "open" label.

A question you can use immediately

Ask the publisher three things: where the STEP files are, where the PCB project is, and what it costs to buy everything on their list yourself. If all three get an answer, you are at layer two or above.

Sources

licences and hardware directory notes in the official repositories of the projects concerned (checking file formats offered)
Crowdfunding and shipping pages for the same projects (comparing claimed openness with files actually published)

Objects in this entry

Last checked 2026-09-28