Lay the parts out, start the machine, and see whether it does the job.
Nothing on the bench yet.
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Nothing here is on rails. Every part you put down becomes a real body in a physics simulation — it has mass, friction and a bit of bounce, and it is under gravity from the moment the machine starts. A ramp does not carry the ball along a path; the ball rolls down it, and can hop off it, sit on the wrong side of it, or stop dead in a corner.
That means a layout which looks right can still fail, and the only way to find out is to start it. Put it back returns every part to exactly where you left it before the run, so a near miss can be nudged rather than rebuilt.
The bench is bigger than most screens. Zoom in with the controls in its corner, the scroll wheel, or two fingers; drag the bare paper to move about, and drag a part to move the part. Fit puts the whole bench back on screen. The keys work too: + and − zoom, 0 fits, [ and ] turn the selected part, the arrow keys nudge it and Delete takes it off.