It's simple: if you've got a brushed motor, you'll want to break it in under controlled circumstances before taking it out into the world. Why break in your engine? The main idea of breaking in your engine is to wear down your engine's brush so as to maximize surface contact with the commutator, reducing resistance (and therefore waste energy) and thereby increasing power. For detailed instructions on breaking in your remote control vehicle's engine, watch this RC hobbyest how-to.
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