I have never freighted a 100 kg heavyweight to San Francisco so I can't say.

I have gone with 2 bags, one containing a 60 pound lightweight robot and the other containing a total of 7 one pound and three pound robots, tools, spares and batteries and have had no problems with American customs. The bags always get opened for inspection (this is done out of my sight, I know because they put a card inside saying the bag has been opened for inspection) and I always include a large notice, right on the top, which says that the suitcase contains robots for competition at Robogames, the date and place of the event, and the fact that there are no wet cell or lithium batteries and that all batteries have been disconnected and terminals taped over. I don't say combat robots. I run my Robogames robots on NiMH batteries to avoid lithium batteries - the airlines all forbid them in luggage.