Nothing is fixed down
No part is anchored to the ground, so the whole assembly drops.
Comparison demo
Do public CAD assemblies actually work?
One rigid-body simulator, the same two tests for every assembly: stand still under gravity for 4 s, then take a small push on the first joint.
Falls apartStands, won't moveWorks
Fusion 360 Gallery8 assemblies
AutoMate8 assemblies
Articraft8 assemblies
FunCAD packages3 designs
Public assemblies were sampled from mechanism types that our tasks also cover, such as gear trains, hinges, sliders and linkages.
Can't even stand
8 of 24 public assemblies fall apart under gravity alone.
Parts with no joint
Washers and a bushing sit in place but belong to no joint, so they drop out of the pump.
Joints that hold nothing
Its joints turn freely and nothing holds them, so the arm folds under its own weight.
Stands, but won't move
15 of 24 hold still, then don't move under the test push.
Touching faces lock the joint
The hinge is right, but door and frame touch with zero clearance. Contact holds it shut; even a 10× push barely moves it.
Only a much bigger push turns it
The gears mesh with zero backlash. The ring gear ignores the test push and turns only at ten times the load.
Ours: built to be tested
Same simulator, same push: 3 of 3 stand, then turn their first joint.
Mechanical alarm clock
The push on the barrel turns the gear train, and the hands move.
Four-bar windshield wiper
The crank drives the coupler, and the arm sweeps.
Rigid-body simulation in PyChrono with identical settings for every assembly. Gravity test: fails if any part moves more than 10 mm in 4 s. Push test: a load scaled to the driven part's weight on the first movable joint; passes at 10° or 10 mm of travel. Files are only translated: no joints, anchors or limits are added. Gear and rack meshing is not modelled, so our third design, a rack-and-pinion gate, passes on its pinion alone.