Keep in mind that there are exactly a grand total of 4 moving parts in a quadrotor drone. This is the core reason for their success, robustness, ease of use and

Keep in mind that there are exactly a grand total of 4 moving parts in a quadrotor drone. This is the core reason for their success, robustness, ease of use and all. If all quadrotors needed oil, gas, vibrated like crazy (bad for IMUs), had 100+ moving parts (engine, servo gears, etc...), weighted at least 1-2kg, ran super hot and noisy... we would not have had the "drone revolution".