The hub for WinDIY initially gave me a real headache. As a pretty central part, the hub is super important and should be as stable as possible, but light and symmetrical at the same time (without an imbalance or something similar).

In addition, it has to absorb the force of the wind in the axial direction, the centrifugal force of the rotating blades and of course the rotation of the blades should be as smooth as possible. Obviously, it must also bear the static weight of the wings.

In addition, I had also considered to include a mechanism to adjust the wing's angle of attack (during rotation). This principle is also known from large wind turbines.

This has two advantages. 

• The wings can be adapted to the "apparent wind" (ie the combination of "true wind" and "wind due to the rotation"). As a result, you should always be able to extract the maximum energy from the wind.
• The main advantage in my opinion, however, is that if strong winds occur, the turbine can be protected from self-destruction caused by high rotational forces.

When high winds occur, the angle of attack of the blades can be adjusted so that the blades are aligned unfavorable to the "true wind". The turbine does not stop rotating, but will definitely lose speed of rotation. :)

Well, long story short: The hub has to enable the control of the blade angle while the hub itself rotates.

I have worked on this problem for a long time. You can see the result in the video. :)