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How to make a mirrored rotor spin in the opposite direction?


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Hi, I have two rotors on both sides of my aircraft and would like to make them rotate in opposite directions. But they were placed using mirror symmetry, so I can't change the orientation of a rotor independently from its mirror copy. What should I do?
 
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The end goal is to achieve hovering flight without creating a net torque about the centroid of my four rotors (there are two at the back in a similar arrangement). It's not a quadcopter since rotors are placed using mirror symmetry, and not central symmetry.
 
I also do not want to remove each blade from symmetry separately. If there is a way to remove one of the rotors (and all the blades attached to it) in one go, I'm all for it.
Thanks.
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If it's a quadcopter, you could maybe achieve the effect by having the rear pair counter-rotating? I can't say I've experimented with quad-copters: the only helicopter I've tried so far was a pair of stacked, counter-rotating rotors.

Which was fun, though those rotor blades made the descent through Eve's atmosphere painfully slow.

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O7lT9Ba.jpgAt the risk of confusing things, maybe you noticed the option "Invert Direction" on the rotors.  This does let you make rotors in a symmetric pair rotate in opposite directions, leaving the rotors linked by symmetry.   The rotor labelled 'clockwise' and 'inverted' actually rotates anti-clockwise.

However,  there is no similar 'invert' option on the propeller blades, so I see no practical use for inverting one rotor when using them with propellers. 

The simplest way I have found is to build one fan assembly (with the propeller blades in 4-way or 8-way symmetry around the rotor) and then alt-click to copy the assembly and paste in the other locations -- as Vanamonde said above.

Edit: There is another approach that you might like.  Let both forward rotors rotate clockwise, and both rear rotors rotate anticlockwise.  Then you do not fight with KSP's method of placing parts in symmetry, and the four rotors have zero net torque.   If you load the front rotors to pitch up quickly, torques will be imbalanced and you might yaw left, but those torques are small with KSP's propellers so you might not notice the yaw.

Edited by OHara
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If you have Advanced Tweakables activated, there is an option to “remove from symmetry” added to the right click menu. This stops them being linked after you’ve placed them allowing for individual changes. 

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