Export ASMT¶

In one sentence: Export the assembly's kinematic structure — parts, joint types, and placement data — to an XML-based ASMT file for use in external multi-body dynamics solvers.

Overview¶

Workbench: Assembly
Menu: Assembly → Export ASMT

Export ASMT writes the assembly structure to an ASMT file (Assembly Structure and Motion Transfer format) — an XML-based interchange format for kinematic assembly data. ASMT carries the structure and joint definitions; it does not embed part geometry.

Intuition¶

FreeCAD's assembly solver handles kinematics well for visualisation and mechanism checking. For force analysis, dynamics simulation, or interoperability with external engineering software, you may need to export the assembly structure to an external solver. ASMT is the format designed for this handoff.

Think of ASMT as the "bill of joints" — analogous to the Bill of Materials being the bill of parts. It describes how everything connects and moves, in a format that external tools can read.

When to use it¶

Feeding the assembly definition into an external multi-body dynamics (MBD) solver for force and motion analysis.
Exchanging assembly constraint data with other CAD systems that accept ASMT input.
Archiving the kinematic structure of an assembly in a human-readable XML format for documentation or version control.

When NOT to use it¶

Don't use ASMT to transfer geometry — it carries only structure and kinematics. Export part geometry separately as STEP or STL files.
Don't use ASMT as a general-purpose FreeCAD backup — save the .FCStd file for that.

What is exported¶

Data	Exported?
Part names and placements	✓ Yes
Joint types and references	✓ Yes
Joint parameters (offset, angle, pitch, etc.)	✓ Yes
Part geometry (B-rep, mesh)	✗ No
Bill of Materials / material data	✗ No
Simulation definitions	✗ No

Step-by-step¶

Confirm the assembly is solved and complete.
Choose Assembly → Export ASMT.
A file save dialog opens. Navigate to the output location.
Enter a filename — the .asmt extension is added automatically if not typed.
Click Save.

The resulting file is a plain XML file that can be opened in any text editor for inspection.

Parameters¶

Export ASMT has no task panel parameters — it writes the file immediately when you confirm the save dialog.

Python API¶

Minimal example¶

import FreeCAD as App
import FreeCADGui as Gui

# Trigger ASMT export via GUI command
Gui.doCommand('import CommandExportASMT')
Gui.doCommand('CommandExportASMT.CommandExportASMT().Activated()')

Direct API call¶

from ExportASMT import export_asmt

doc = App.ActiveDocument
asm = doc.getObject("Assembly")
export_asmt(asm, "/path/to/output.asmt")  # TODO: verify method signature

Common mistakes and pitfalls¶

ASMT does not include geometry

ASMT is not a stand-alone assembly file. The receiving solver needs the part geometry separately — typically exported as STEP or STL files alongside the ASMT. ASMT only carries kinematic structure.

Multiple assemblies: the active one is exported

The export operates on the active assembly. Double-click the correct assembly in the model tree before exporting if the document contains multiple assemblies.

External solver compatibility

ASMT support varies between external tools. Verify that the receiving solver accepts FreeCAD-generated ASMT before relying on this export for a production workflow.