Contra-rotating props/fans: How to build the smallest possible?

[saute]

Hi all! I have been reading and watching videos about building contra-rotating props by using tandem brushless outrunners, and was wondering: How small can you go with this? if the thrust advantages are to be believed, a big amount of thrust could be available from very small motors.
I saw this example on HK website:
https://hobbyking.com/en_us/ldpower-mt1306-3100kv-brushless-multicopter-motor-cw.html
Is it possible to do this with something the size of the power pack A motors?
Is it possible to do this with edfs?

 

[Morgan]

it should be doable with any motors but you do have to have two esc . I tried it and it didn't work with one esc.

 

[quorneng]

The issue with tandem contra rotating motors is the shaft of the rear motor has run inside the shaft of the front one. Small motors use small shafts (3 mm or less) so it will probably require the front motor to be re-engineered to have a larger hollow shaft but you need some engineering expertise and equipment to be do that.
It is technically a bit easier to create contra rotation shafts using geared motors.

You are mistaken in thinking a contra rotating prop is more efficient than the same power going through a single. It isn't.

 

[Morgan]

sorry I misunderstood you .I thought you ment a twin engine.

 

[saute]

punt
current plans are to mount two a pack motors opposed with the appropriate rotations and props, in a shroud, or as a " prop-in-slot " design.

 

[quorneng]

There is nothing wrong with a pull/push arrangement using counter rotating props.
You still have zero torque with the benefit the props are then some distance apart so there is less "siren" prop noise.

Basically a pusher design but using small, light high kV motors driving 5x3 CW and CCW props.
It needed zero motor torque as with big double section flaps it can fly very slowly resulting in very limited aileron effect.

 

[willsonman]

You may find my article useful for this...
https://www.flitetest.com/articles/bugatti-100p-the-contra-rotating-motor