I am a bit of a beginner, so I don't fully understand the way the air flows around the rotors in a quadcopter. My question is in the title, and I am basically wondering if something can be mounted adjacent to the motor, and directly beneath a part of the rotor, or if it will cause poor performance on that rotor. I have a very long camera which I can mount to the front of my drone body, but the edges of the camera lie directly underneath two of rotors. Will this cause performance problems/is it a better idea to mount it above them? Thanks!
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1$\begingroup$ Any obstructions protruding into the volume of air directly above or below the propellers isn't ideal because it disturbs the airflow through the propeller disc. This is one of the reasons why quadcopter frames try to minimize the width of motor arms. Is there some kind of more elaborate setup that you have in mind? $\endgroup$– ifconfig ♦Feb 23, 2021 at 6:14
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If you block the airflow into or out of a rotor, you reduce the lift it can generate (approximately) in proportion to the area you block. That means the motors will have to work harder, and your flight time will be reduced.
Work out what percentage of the total rotor area your camera will block. If it's more than about 20% you should probably look for a larger frame.
Obstructions above the rotors are less critical when hovering (as the rotors are sucking in stationary air from all sides) but in forward flight the airflow is more linear - and rotors don't like working in disturbed air so it's worse for high speed flight.
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$\begingroup$ Ok, thank you. My camera will block about 7-8% of the rotor area on two or the four rotors. From what you said it seems like I can continue to use this frame with only minor performance hits. However, do you have any recommendations for how far below the rotor to mount this camera to maximize flight time? (e.g. is there some sort of recommended threshold for obstructions or does flight time just scale with the rotors distance from the obstruction?) $\endgroup$– figbarFeb 23, 2021 at 20:24
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$\begingroup$ The further the better, but you can feel the down-draught from a quadcopter several feet away, so I doubt it will make a lot of difference. Interestingly for obstructions above a prop within a couple of inches there's noticeably more noise (and presumably a reduction of efficiency) $\endgroup$ Feb 24, 2021 at 8:57