Sounds easy, right? Lets see...
There are basically 3 different ways wind turbine are constructed to accomplish YAW. Two are passive (relatively simple) and one is active (very complex). There are pros and cons to each method and that gives KidWind teams something to think about and consider.
The first passive system is one that most people have seen and is the type used on old farm water pumping wind mills. They operate with a tail that is behind the tower and blades. The blades operate UP Wind of the tower and Nacelle. The tail acts like a weather vane and keeps the blades facing directly into the wind if it is the correct size and shape.
The problem is to engineer the attachment of this tail so that it can rotate the Nacelle that holds the blades, gears and generator. Good problems to solve and many options to choose from.
The second passive system is the Off Set Pivot. The blades operate DOWN Wind of the tower and Nacelle. In this system the wind force on the blades causes the Off Set to Pivot and rotate so the blades are facing against the wind direction (down wind of the tower). Some wind force is blocked due to the tower and Nacelle getting in the way. This is referred to as tower shadow. No tail or system to mount the tail is needed. However some weight balancing needs to be done to reduce the load of the blades and Nacelle that will be placed on the Pivot bearing.
Lastly in this discussion is the Active - Motor Driven system. All utility grade wind turbines use a system like this. It is very complex, expensive and good at providing YAW for maximum energy output. This requires two sub-systems. One that can determine the direction the wind is coming from. And another sub-system that can rotate the Nacelle and Blades (this is a VERY BIG job) and automatic communications between the two systems.
In my model, as a proof of concept I used the existing technology the runs your electric windows in your vehicle. At the bottom of the picture you have a wind vane between two micro switches. This determines which way the wind is coming from. If the wind is coming straight on the vane is in the middle and no switch is on. In the top part of the picture you have a large gear that can be rotated CW or CCW by the small gears driven by the three small DC motors when they receive a signal ( polarity + or - ) ( polarity - or + ) from the micro switches if pushed to the left of right (up or down in this picture) by the wind.
I will let the circuit drawing do the talking here on how it is wired to reverse the polarity and thus reverse the direction the motors turning the large yellow gear CW or CCW.
In my model I applied the Proof of Concept by fixing a ring gear to the stationary part of the tower mounted to the tower base. The green gear is glued to the white PVC and then set screwed to the 1" black pipe.
The wind direct "signal devise" (wind vane with two micro switches) is mounted to the top of the Nacelle behind the blades.
The circuitry, relays, battery and drive motors are mounted to a plate that is locked to the main
1 - 1/4" PVC pipe that slides over the 1" Black Pipe than the green gear is set screwed to so it cannot rotate. The 1 - 1/4" PVC rides on a thrust bearing and allows it to rotate. The small green gear on the left in the picture turns when it get a signal from the micro switch. Since the large green gear is fixed (set screwed) the motor and plate it is attached to rotates the 1 - 1/4" PVC, Nacelle and blades to keep the blades pointed facing the wind. YAW!
Everything you see here from the wooden plat up rotates around the green gear that is set screwed to the the 1" pipe screwed into the base.
Active YAW system model. It will be interesting to see what the different KidWind Teams come up with to solve this years YAW Challenge problem. Plenty of good stuff to learn and apply. YAW'al!
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