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To supplement another answer - You mention a "main mechanism". A critical point before drafting a patent application is to determine what you think that the invention is. If you have invented a new carburetor you do not need to show a whole car and you might discuss variations of the carburetor that make it suitable for a lawnmower.
An invention ...
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I'm not an attorney, but generally you submit drawings that illustrate just the specific mechanism involved in the invention with enough context to explain how it works. Ordinary elements like motors and gears can be illustrated generically. You can get a pretty good idea of what patent drawings look for by looking at other patents. You can use Google ...
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