Y6B Pusher Motors Running Hot

Not sure if this has been discussed, but I've conducted 6 test flights of my Y6B and after running for 10 minutes in Loiter each flight I've felt the motors and observed the upper motors are relatively cool and the lower ones hot enough to fry eggs on it.  Why are the lower motors running hard than the upper one?  Is there something I can do to ensure I don't burn up the lower motors?  Uppers are running 10 x 4.7, lowers are running 11 x 4.7 propellers.

Appreciate some insights and recommendations on this topic.

Doug W.

You need to be a member of diydrones to add comments!

Join diydrones

Email me when people reply –


  • all this has been discussed over and over again, here and all around RCGroups for a long time,,,,if you want official answers,they simply does not exists bcs it is very complicate....best you can do is to ask Leonard Thall, developer,who did all this testing again and again in Autotuning  blog...but in fact is simple....if you want simplicity use same props...if you want to gain minute or two fly time and efficiency, do your tests or find existing tests what is best for your setup...the reason I used big letters before is that I never saw somebody flying bigger props on top.....

  • Just run the same props on the top and bottom.  Then see if that helps. 

    • I plan to do two different configurations to see if my Y6B handles (a) differently, (b) all motors heat evenly, and (c) which configuration gives me the balance of stability vs run time.  

      The two setups will be, larger prop on top and smaller on bottom. The second config will test, all props of the same size.  I will use 10x4.7 to start with, then swap them for 11x4.7 to see what I get.

      More to follow.

    • ...and you will not use most recommended solution bigger props(or better bigger pitch only) bottom..??

    • I took my Y6B up for a few flights today and I noticed that when I ran 11 inch on bottom and 10 inch on top my Y6 seemed a bit more difficult to maintain a decent stable flight.  Landed it and replaced the lowers with 10x4.7 and took off again.  BIG different in handling and stabilization.  After landing I also noted the lower motors were warm but not hot as they were when running with 11 inch props.

      So my first series of tests from a stabilization and handling point indicates 10 inch props top and bottom is a better configuration than running 11x4.7 bottoms, and 10x4.7 tops.

      Next test with be to run 11x4.7 tops and keep 10x4.7 on bottoms and I will report what I discovered.

    • +1

  • I have read a wide variety of opinions on this matter, including the NTP 3675.  I have built quite a few coaxial setups, and I have gotten better "overall" results with using the same props all around.  I have a number of videos of me demonstrating this on my youtube channel with the various coaxial setups I have made.

     In instances where I have used a combination of larger and smaller I got better results with mounting the larger props on top with smaller diameter props on bottom, but with a higher pitch.  One of the links Emin cited eluded to this setup as being preferable as well.  It can be found on a number of commercial setups.  

    • ok...you convince me..i will delete caps lock

  • Regarding larger bottom rotor, I agree it is correct.

    From NASA tech paper 3675 "A Survey of Theoretical and Experimental Coaxial Rotor Aerodynamic Research "

    see image (the second green text, first is for rotor separation distance)

    3701736104?profile=originalbut in saying that one should do what they want to do based on their own analysis of information at hand...

    • Once I read somewhere for best efficiency that distance between top and bottom should be Pitch value of propellers used....in practical for prop 15x5.5 you make distance of 14cm(5.5 inch)

This reply was deleted.