OK, I have most of the DIY FBL done.  Now, a question.  should the main blades be leading edge or trailing edge controlled?  I keep looking at this and thinking, I have a choice, I think.  I had to redo a couple of things because I did not have the geometery in my head.  

billm's picture

leading edge

My name is Billm and I'm a Heli Holic

jbeech's picture

Show us what you've done Rick, we need pictures!

Are you pursuing either of the RNFBL set ups (v1 or v2) we spoke of?


RNFBL Rotor Head v1


Remove all of the components associated with the flybar.   



Remove the Mixer Arms and attach them to the main shaft as seen below. You can also reuse the main blade grip linkages.  



You will need to create the “Follower” .  See below.  Remove the slip pins and replace with threaded bolts. I used M2.5x25 bolts, however, M2.5x30 will give you more adjustment and will have increased grip. I drilled out the top part to M3, this allows easy assembly and adjustment. Because the bolts can now slip, I placed nuts on them to prevent this from occurring. The bottom part was drilled and tapped for M2.5, however, you may get by without tapping this hole. Notice that I elected to remove the unused arm. Removal is not necessary; however, I found that it does need to be shortened somewhat because in certain cases that arm can contact the swash. I adjusted the position of the follower so that the levers were horizontal when the swash was at its' midpoint, representing 0 degrees of pitch on the blades. Upon reflection, I believe this is not too critical, but you need to be close so that you can achieve equal positive and negative blade angles without the arms becoming locked. Upon full extension of the swash, the levers are at close to 180 degrees to each other and can reverse, causing a lock up of the swash. The follower is the same for v1 and v2 of the RNFBL head.





Below is the v2 head. There is simply no mixer arms. The linkage goes straight from the blade grips to the swash.   



There are now two issues that some say need to be resolved.

  1. Now that the intermediate arms are gone, you lose mechanical advantage. With the servo arms in their stock position, to obtain full pitch range, the servos only need to move about 30 degrees. In all of the purpose built FBL heads, this is corrected by moving the grip ball to a position of about 30 mm from the main shaft axis. JB suggests that we can improve the situation by moving the servo arm link to around 13mm from center.

  2. The Delta is not good. What is Delta? First, Delta is simple a math notation meaning “difference”. In our case, this is the distance from the center of the grip ball to the center of the shaft. See below.


You can correct this using a Century Long steel ball, part # CNLR1021.


See Below.




Note: I was not exactly perpendicular to the head when I took this photo.

You will need to drill and tap for M3 threads.

This modification is also valid for the v1 version.


JB suggests that the Delta correction is not necessary, at least for the type of flying that the RNFBL will be used. I believe that depends upon having strong links and strong digital servos that can resist the forces imposed by the Delta.


Revisiting the RNFBL v1


The following is probably not at all necessary. However, I noticed that it could be done, so why not?


As describe above, the grip link will not be parallel to the main shaft. This can be mostly corrected by using the optional spacer provided in the kit.   


Move ball-spacer-screw indicated by the red arrow, to the arm, indicated by the green arrow.

This is probably not only optional, but can probably be classified as ….........anal.


OK, the above is subject to editing, enhancement, and correction, by JB and others.

Rick Harms




My post showing how to do the RNFBL was my first of this nature.  I think the pictures are too small.  

So, another experiment.  Go to the attached link for a closer look at the pictures.  Maybe this will work.

Rick Harms

Hmmmm,    no comments or suggestions.  I guess there is no interest.  

Oh well.