title_body: What is the most thrust dense copter configuration? I need to make a compact drone that does not need to be fast, nor very power efficient*. I wanted to know what is the most mass I can lift with the smallest footprint**. 
  
  To make this question more answerable: which is more compact for the same amount of payload (say 50g), a helicopter, a quadcopter, a quadcopter with duct-fans, or another strange configuration like: the dronut, the rollocopter or the ball drone?
  
  Are there any resources out there that have made such comparisons?
  
  * Not exactly true.
  
  ** Footprint - in case it was not completely obvious what I meant - is the transversal area of the drone. Or consider it a volume and assign it the volume of the smallest sphere that can contain the whole drone while flying.
upvoted_answer: Assuming you can only use up to four motors (because if you used six, eight, or even more you could just lift something with brute force) the most thrust dense configuration would probably be a ducted fan quadcopter. 
  
  The reason for that is ducted fans essentially stop a lot of air from being propelled sideways and more air goes down. Ducted fans can provide more lift and are more efficient than open-prop designs. 
  
  A helicopter would only have one motor and would need to be much larger to provide the same thrust as a quadcopter. Those other configurations mentioned would also not have nearly the thrust of a quadcopter of a similar size. 
  
  So, the best option would be a ducted-fan quadcopter (or hexacopter/octocopter if you can use lots of motors) with oversized motors. A good propeller would be a large prop as it gives more thrust at the expense of maneuverability and acceleration. Wider motors give you more torque but taller motors give you more RPMs so that depends on the prop. (A heavy aggressive prop should go with a wide motor and a lighter prop should be paired with a taller motor)
  
  If you don't really care about longevity, get a powerful ESC, high cell-count battery (probably 6s), and get a motor that is higher than normal KV for maximum thrust and power at the expense of the motor's longevity. But be careful to not go too crazy with the high KV as it could potentially burn out an ESC or destroy the motor.
  
  Also, as durability is not really that important for the purpose of this specific build, make it as light as physically possible (but still rigid, you don't want vibrations or flex) so that it can lift as much weight as possible. 
  
  Hopefully, this helps, as I'm not really sure what all of the requirements of this drone are.