Bigger propellers on octocopter at the same size of frame

Hi

I have quite big octocopter with flat frame cinenestar type with 16" propellers and t-motor u7 420kv motors. It has 120 cm frame size. I would like to change the propellers in it to 18" to have longer flight time. I can use longer booms but the copter will be too big for my car so I am wondering about using the same booms but 4 motors up and 4 motors down like in the picture in attachment. Is that setting is as efficient like flat octo or I will lost same flight time like on coax setup ?? What kind of mixer I should use for such setting ? I am using Mikrokopter FC but I think that will be similar in APM or Pixhawk.

a6299627-95-MK%200319-large.jpgregards

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  •  When I will have same free time I will do the test ...

  • Tested 7 years ago at the beginning of multirotor adventure, as I wrote : The overlapping will cause no problems but I doubt it will increase efficiency .

  • There was a research paper floating around on the net that showed with a ~10% overlap, there was a ~5% increase in efficiency. Don't hold me to those numbers. It was something like that. Unfortunately I don't have the link anymore.

    Luc Maximilien said:

    The overlapping will cause no problems but I doubt it will increase efficiency .

    You can change by software the motor direction if you have black MK Esc or last version MK Esc,  if you have the red MK Esc it is not possible and you have to switch two motor cables that arrives to Esc to change the rotation  direction.

    What is your AUW, payload and Flight Time ?

  • Why not do some testing with the original prop in the original configuration versus the "up/down" configuration, everything else being the same? Not only will you have your answer, but come back here and let us know what the results were. Nothing better than real world results versus theory.

  • Guess that 4 pair of good 18" propellers as T-motor are not cheap.

    Good Luck for your project !

  • Yes but that's bigger weight and much bigger price for batteries I think ??? Are they better than tattu ? Do you have any link ? Can I have 12000 or 15000 batt in the same weight as tattu lipo ?

  • In that case I suggest to switch to a different type of batteries , Sony Lion high C discharge , so you can go up to 20 minutes. 

  • hover is 70-80A

  • yes

  • I have done some maths , not with E-calc,  you should hover at 91,6A with a 6S setup .

    Are you using standard 20-30C Lipo batteries  with 3000 g of weight ?

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