I came across this interesting video:

As you can see in the video they have managed to control the coaxial design without using a swash plate and all the complicated mechanisms required for that. It looks like this is an excellent concept for very light weight systems. I do wonder how easy this can be scaled up into a device that can actually carry any additional equipment. This could be useful to obtain the under 2 kg UAV weight for the Canadian regulations.

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Comment by gsenroc on December 14, 2014 at 8:22am

awesome. one difficulty of small uav in this case I can imagine is the relatively small space to fit the equipments between these two motors, and how to put the antenna vertically.

Comment by Giovanni Esposito on December 14, 2014 at 8:22am

It's a grea idea, that can be clearly very useful where lighter, simpler and cheaper is better (like in toys or very small uas). But i'll bet it won't scale very well and never have the same autority of a real swashplate controlled variable pitch blade, making it very difficult to use outside or in any real world condition.  

Comment by Mark on December 14, 2014 at 9:12am

Could you explain in more details the idea of pitch change, please? I am not getting it in whole.

Regards,

Mark

Comment by Greg Nuspel on December 14, 2014 at 10:00am

Going to their website may help you with understanding the system http://modlabupenn.org/underactuated-rotor/ 

Comment by Mark on December 14, 2014 at 10:09am

Got it Greg! Thank you! I missed the point that blades are actually hinged in two opposing positions on the video.

That makes sense. There is something new you can learn each day.

Cheers

Comment by MarcS on December 14, 2014 at 10:55am

Hi, interesting idea.

Back in my head I did remember something similar. After some search it turnes out it actually was long ago. It is called Keyence Revolutor by a japanese company, which actually also sold mini quadcopter over 20 years ago!!

The idea sound similar, by well timed motor pulses impose a blade deformation. Was done by a brushed motor and an optical encoder. If I remember correctly I read a report back then saying the motor did not last long because of the pulse load. Was a unique thing at the time!

Here are some links for all interested in a little history:

http://www.acuvance.co.jp/english/heli.html  (this has the most technical information)

http://www.myhelicopters.com/keyence_revolutor.html

https://www.youtube.com/watch?v=a7bkuS8zk_s

https://www.youtube.com/watch?v=CEjNej4JXUE

Comment by Giovanni Esposito on December 14, 2014 at 11:45am

Great link MarcS!

Very impressive, and that is in 1991!

Comment by Rob_Lefebvre on December 14, 2014 at 5:03pm

Pretty interesting concept.  I'm also interested in real-world usability.  

Comment by technicus acityone on December 15, 2014 at 11:45am

Very interesting experiment!
But IMHO this sheme need more tests, sinusoidal shift rotating speed may cause unballancing and additional vibration, automatic set AoA have some inertia and may lead to troubles in control for dynamic flyghts regimes. .
There still needs  a large number of tests in different conditions. Good Luck! =)

Comment by Harry on December 15, 2014 at 12:33pm

I also went to the site and still have a little trouble understanding how they control it.  The blades are hinged at an angle which means it will pitch as it swivels on the hinge - I get that part just looking at it.  To control the pitch of the blade, they dork the motor signal which causes the blade to pitch?  How do they know where the blade is located in 360 degrees?

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