Upload the parts too. The zip file has assembly only.
currently i have the same problem too. it seem that when i use contact (either group contact or not) the part is still hitting each other. hopefully someone can help
Some like this
Not to directly answer your question but your assemply will not animate no matter what you do. Your first part is ALWAYS stationary / fixed. Since your first part is the cog it will not move no matter what you do. If you want motion add a part as a pivot and load it first. Then put your cog on it.
What you are looking for is Interfecrence Detection. You can find it in the help menu.
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