Me again... 

I appreciate the patience and help that several of you have put out in my cries for FNG help.

I can't find any good info on why I was told that a IC engine quad rotor with collective pitch rotors would not be able to respond quickly enough to keep it stable.  If I configure the APMs ESC wires to control the digital servos for the swashplates instead of DCBMs and have separate throttle control for IC engine RPM, would the change in pitch be so slow that the bird would be hard to stabilize?  I don't want to do any crazy 3D or monkey flip flying, just stable.

I realize that the ESC DCBM combo is way fast, but I can't see the blade pitch changes being that far behind.

How long does it take the airflow/thrust to change with the blade pitch changes vs DCBM speed changes?

Thanks for input and any links to data or personal experiences.


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It will be fast/responsive enough, You do not even need gyros.... (not me).

However more parts = less reliable not to mention dealing with vibration.

Always pro vs cons, for most here it is not worth it.







Collective pitch changes will be more than adequate.  Have you seen RC helicopter 3D aerobatics....  It is simply a question of complexity, vibration, etc....  In general the 4 motor electric setup is far simpler to deal with, but there should be no problem with control of a properly designed IC airframe using collective pitch control.
Pitch only no cyclic, pinion or worm gear scissor jack type lever under the swashplate to move it up and down.  KISS

Do you guys think that the T-Rex 700 blades can be modified (shortened) so as to keep the blade width?  I want to try 24 - 26 inch diameters.

Are the symmetrical blades exactly that?  The same on both sides?  If they are I can reverse them and have the CCW pair that is needed.

I want to try the three blade T-Rex 700 Flybarless rotor heads for the 12mm shaft size and machine the necessary swashplates/bearings.  Ican keep lower weight with 450s but robustness is key.

Opinions, ideas, tips, guides?...anything but please let it be constructive.

Hi William

"Do you guys think that the T-Rex 700 blades can be modified (shortened) so as to keep the blade width?  I want to try 24 - 26 inch diameters"

NO, you must not modify any composite baldes. You need a dynamically balanced bladeset. Thats how they are sold. If you prefer woodblades, you can play with them to a certain degree depending on the manufacterer. But you would have to balance them dynamically (same weight, same CG) before use.  


For the beginning I would start with an unmodified setup. As I mentioned earlier, the 450 flybarless is a good choice. You do not need more stability than the system provides. And if you should crash the copter, you are most likely better off with parts that can deform. To go with a rex 700 head just adds more weight and whats more important more mass to deal with. I proposed the standard rex 450 blades because they are cheap and symetrical. So you can use them for CW and CCW. Maybe you can have a look at the 500 and build some adapters for 450 blades.


Maybe have a look at the construction of heli rear rotors. Thats what you need in big. 


You could use 4 emotors with a governor mode esc and use collective pitch. That could be a very stable system.


The central combustion engine with the complicated drivetrain and its vibrations is maybe not the most promissing start.


good luck


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