Geometry of the linkages

Basicly all throws, travels, linkages and lever arms had to be optimized for a flybarless (rigid) head. Additional are there some things to consider for conversion of a flybar head.

The target of the conversion is to get a really stiff and free from play linkage to the head under use of the complete servo travel and getting rational zyclic and collective pitch throws.

As first you have to convert the head for getting the linkage balls in 90° to the blade shaft axis in the center of the main shaft axis (look at the original mikado head drawing). Some helis might have very narrow linkage balls near the main shaft axis. In this case it is necessary to do some craftsman changes to get more distance for better performance in the throws. The Mikado heads have a distance between the linkage balls of about 62 mm.



For the conversion of the head and correct VStabi working it will be necessary to use the hardest dampeners you gan get for the head. Soft dampeners will be unrequested play in the whole regulator circuit. To fix the inner circle of the swashplate to the main shaft you have to use a swashplate driver instead of the pitch compensator. Using the Mikado head it will also be possible to get the connection with the included conduct. But this way will be only for short linkages in cause of the torsional play here.

If your heli has a push-pull with boost factor (lever at the servoside is shorter than at the swashplate side) you had to chek out if you can get other levers without boost.



A few basic thoughts about geometry:

As described in this article above we have the goal to use all the servo travel as best as we can. Unfortunatelly we have some helis with a perfect geometry as a Logo 500/600 and some with a not so perfect geometry for flybarless. Some helis will have mechanical limitations for converting and so we have to work out a compromise.

At VStabi we can adjust values in useful ranges to allow some compromises in geometry. In general it will always be the best to work out a perfect geometry because changing the values for the cyclic adaption is always a negative effect to our control travles / force and resolution.


How to figure out geometry ok / not ok:

Lets have a look on the complete process in example of the collective starting from stick, RX, Stabi, servo, arms, linkages, swash, linkages, blade grip and at least the blade.

Adjust a collective value with 80 in VStabi PC soft. Then switch into setup mode and measure the collective angles at 0% collective in live bar and at 100% collective in live bar. Calculate the complete collective throw at 100% stick throw. Using a 3D heli with 0deg in mid stick position it will be enough to measure the full collective angle at 100% stick input in live.

If you will get a collective angel abou 14 deg and more you should think to do some work on your geometry first here. In most cases unuseful collective travels are depending on translation ratios from PP levers, too long servo horns, to less distance between the blade grip linkage balls and main shaft at the main head.

With this procedure we have measured the complete collective chain form stick to blade. Now the only thing is to measure the cyclic ratio of our swashplate. Therfore measure the distances between the mid of the linkage balls to the mid of main shaft at the outer (A) and inner (B) swash ring in mm.



If we take this measure into our tool the correct cyclic gain will be shown as result.

In general we can say that a useful range for the CG is about 80 ... 110.

Will the result be lower than this we should improve the geometry of our heli. To improve the cyclic ratio use shorter ball links at the inner or longer ball links at the outer swash ring. Will a low CG shown together with a high collective (approx. more than 12 deg.) read about the collective improvement because this will have effect on cyclic also.

If the CG is more than 110 calculated do vice versa, especially on scale helis we need this travel for coorect working of our control loops.

Link to our online
geometry tool.

Download geometry tool as excel file.