KidWind Blade Pitching

 The learning opportunities continue to pile up as I work to design a blade pitching system for KidWind teams to study and learn from. After seeing what the College Wind Challenge teams put together for the 2022 challenge in San Antonio, TX my wheels began to turn. 

The Darlington and Mauston KidWind teams continue to learn and grow finishing among the top 3 high school teams again this year. So it is my hope that they will take on the task of designing, building and testing a wind turbine for the 2023 KidWind Challenge year that will have blades that change pitch as the speed of the rotor picks up. 

The goal here is to provide the teams with a proof of concept to study and improve upon. Words just cannot do these ideas justice. Like the saying goes, "I hear it I forget. I see it I remember. I do it I understand."

DESIGN #1 Basic mechanical system 101

First up is this model. The design is made to have the blades start with a 45 degree pitch to get maximum starting torque to start turning the rotor. In operation the wind tunnel fan is started and when up to speed a switch is closed to start the blades on their cycle to pitch the blades to 3-5 degrees and run at optimum speed.

Each blade is pitched by a worm gear drive system as shown here. Limit switches are used to stop the blades by opening the circuit to the individual drive motors. Got to 3D print a worm gear and some mounting brackets that would have been a real killer to machine out of steel.

The system drive motors are 12 volt and the power to run them comes from 3 sets of AA batteries held in PVC tubes. There are some complicated DPDT relays and switches needed to be able to reverse the polarity to run the motors backwards to get the blades to return to the 45 degree pitch. Overall the self contained system proved it's self when placed in the wind tunnel with blades held at 45 degree pitch the maximum rpm was about 150. When the system was placed in the wind tunnel and operated so the pitch changed the rpm went up to 400. Very happy with this first design. The major problem was that the DC gear motors turned at slightly different speeds and this caused the pitch from blade to blade to vary. Plus no way to attach a generator.

DESIGN #2 The NEMA Stepper Motor control with Arduino and Rotary Encoder. 

This was going to be a trimmed down model with the center threaded rod bring turned causing the nut on the end of the rod to move toward the front of the turbine and change the pitch of the blades. The linkage to get the blades to change pitch was a real head scratcher. After several failures these linkage rods seemed to do the trick. 

At first I tried to drive the 1/2 - 13 NC rod directly with the stepper motor but there was not enough power.  My fix was to attach a 32 tooth KidWind gear to the shaft and drive it with an 8 tooth pinion that I 3D printed to fit the stepper motor shaft. You can see the stepper motor at the bottom of the Nacelle. The drive mechanics worked well.

Now the plan was that I wanted to place all the electronics and power supply into the Nacelle for one nice neat package. I did manage to place the Arduino board, Stepper Motor Control board and Rotary Encoder in the Nacelle. However the 5 volt power for the Arduino board and 12 volt power for the Stepper motor would not fit. Also there was no way to attach a generator to this system. But the system worked well. The blades would be placed at a 3-5 degree pitch angle. Then the system turned on and the Rotary Encoder turned the correct number of turns to make the stepper motor rotate the threaded rod and move the nut until the blades were at a 45 degree pitch. Now the wind tunnel would be turned on and when up to speed the Rotary Encoder button be pushed sending a signal to the Arduino board to return the stepper motor to the position it started at. This would be the 3-5 degree pitch for highest rpm. Took a bit of new learning to get the Arduino and programming code to work but all is good. Now to just solve the problem of being able to  get it to drive a generator and produce some electricity.

DESIGN #3 Thinking like the real 2MW Vestas 

OK so the stepper motor needed to be in the nose of the rotor. And the linkage rods reversed. A 1/2 - 20 NF threaded rod with a nut was used as before to provide the motion to the linkage arms. The blades are mounted to the white gear (just used the gear I had instead of cutting a blank disk) and allowed to rotate to change their pitch. Now just behind the white gear is the slip ring assembly where the 2 signal and 2 power lead connections are made. All of this rotates at the speed of the blade rotor, just like a Vestas turbine!

Now this 1/2 - 20 NF rod is held in some nice bearings for support (not like the piece of 2x4 in the model). Then a coupler does the job between the rotor and the 1:25 gearbox and 20 watt generator. Using a 5" diameter PVC pipe for the Nacelle the electronics and power supplies should fit nicely.

So now the next step is to learn how to get the data from the rpm sensor to be used to determine the pitch of the blades and control rotor speed and electrical output. No small task but a good learning opportunity for KidWind teams that want to blow away the judges in 2023.