Simulate an existing open-source design

Most machines worth simulating already have source: an OpenSCAD design, a folder of STLs, a vendor STEP, a build123d project. Machinome does not ask for a rewrite. It adds a thin layer beside the design that reads it as it is, gives it a control surface, and proves what the design claims. The worked case is a RepRap printer authored in OpenSCAD, simulated without changing one .scad file and shown on machinome.org’s Foundry (see Examples).

The shape of the layer

Keep the design source untouched, under its own licence, and add one package beside it:

Printer/
    Printer.scad             the design, as published
    ...
    printer/                 the simulation layer
        __init__.py
        parts.py             leaves reading the design
        machine.py           the assembly, drivers, instructions
        test_machine.py      the contracts
    pyproject.toml           [tool.machinome] model = "printer.machine:Printer"

Read the parts as they are

Pick the leaf kind that reads the source without copying it:

• an OpenSCAD design: OpenScadNode per module, or Solid2Node with SolidPython’s import_scad reaching one module of the original file;

• published STLs: StlNode per part, body= for a print pack, adjust() for units and orientation (Reuse a vendor STEP or an STL);

• a vendor STEP: machinome import-step scaffolds a part per product and an assembly per assembly product at the document’s own placements;

• a Python CAD project: CadQueryNode or Build123dNode leaves that import the project’s own functions and return their solids.

Each leaf tracks its source, so editing the design rebuilds the parts that read it.

Size the control surface to the machine

Declare the inputs the machine actually has, on the assembly that owns each: an axis’s travel on the axis, the whole printer’s Home on the printer. A joint per moving body, a relation per mechanical link, a driver per handle, an instruction per operation a user performs. Do not add inputs the machine does not have; a simulation that can pose the design into states the real machine cannot reach proves less, not more. Pick the execution model by what the machine keeps (Three ways a machine runs).

A small demo set

Two or three instructions that show the machine doing its job, Rest, Home, Present the bed, are worth more than a slider per screw. They are what a reader presses first, and what a scenario triggers.

Prove what the design claims

Write the contracts the design implies and prove each one red first: parts that must not interfere at rest and through a move, pieces that must be one body, fits that must locate and still run free, an assembly that must stand under gravity, a sequence of inputs that must leave the machine where the design says. Where the design does not meet its own claim, say so in the test with a measured allowance rather than a silent tolerance, and record the finding beside the layer.

What the layer does not do

It does not certify the design. Simulation describes declared kinematics, state transitions and stops; it is not a dynamics solver, and geometric tests establish their stated contracts, not material strength, friction or manufacturability. It also does not relicense anything: the design keeps its licence, the layer carries its own, and a page or an export that shows the design says where it came from.