Com Cutting!!!!
You would be surprised to see how long you can go without having to cut the com as long as you maintain your motors. What I mean by this is taking them apart about every 5-8 runs/batteries and cleaning the com, brushes, bearings, etc... I use a com stick to do mild cleaning, and occasionally take a scotch brite pad to the com. I do this very lightly by wrapping the scotch brite loosely around the com, then spinning the rotor by hand. This will remove very little material from the com and keep the com clean. It also allows a better visual of the com surface once you have it all cleaned off. Replace your brushes about every 15-20, or sooner depending on usage and softness of brushes, runs and your motors will wear out bearings before the rotor needs replacing.