title_body: How do you figure out which motors to use for your UAV? There are a ton of electric motors on the market. Is there a mathematical formula or some other means of figuring out which size of motor you will need for your airplane, helicopter, or drone?
upvoted_answer: N.B.: This applies particularly to drones, and to a lesser extent to helicopters.  Airplanes are a totally different field and would require a separate answer.
  Obviously the more power per weight... the better.  But basically you want to be able to get enough energy out of the motor to be able to hover at around half throttle.  There's a good tutorial here which explains the full process, but basically you'll have to do the following:
  1. Make an estimation of the total weight
  Be sure to include the weight of your motors in this calculation.
  2. Multiply that weight by 2
  This compensates for the fact that the drone has not only to hover but also to move upwards through the air.  If you build your drone and find it's too sluggish for what you want, simply increase this factor.
  3. Find an engine that will generate 1/n thrust
  ...where n is the number of engines that you will have on the drone.  So for instance, if you calculated that the weight of your drone was going to be 800g, you'll want each motor to have roughly 400g of thrust.
  For most propellor motors designed for flight, you'll be able to find what is called a &quot;thrust table&quot; which will list propellor size (be sure your body is big enough to leave space for the propellors to spin independently!), the amount of current it burns, thrust (usually measured in grams), etc.
  Do the comparison, and you're set!