I struggled for hours with that generator too!
But finally found a way, so I decided it was quite a good puzzle.
Re Bob's problem with the non-breaking box, this happened to me one time in about 20 tests. I'd send the steel box over the tramp to smash on the ice cube, and box boxes always smashed except that one time when the steel box remained intact.
No idea why this happened. Does anyone else have any idea?