Multiple Gear Ratios for KidWind Nacelles

 Did you ever design a set of blades, attach them to your turbine hub, place it in the wind tunnel and not have the blades turn?  Could the resistance in the gear ratio be to high? What to do? Read on...

Here is a picture of my first modification to the original KidWind Nacelle. Drilling holes for two brass tubes through which axles are ran so a two step gear ratio could be built.  This two step ratio allows for ratios of 1:16 and 1:32 using the existing KW 16 T, 32 T, 64 T and 8 T generator pinion. The purpose if this was to increase the rpm to the KW generator and produce more electricity. Mission accomplished!

Then I thought, what if...

I sawed off the bottom section on one side of the Nacelle and mounted a couple of metal guide rods. On these guide rods would slide an Upper and Lower Guide with set screws to lock them in place. The adjustable Upper Guide would hold the axle for the middle set of gears. The adjustable Lower Guide would hold the KW generator.  The first step, green gears  (8 T pinion and 64 T ) would be a 1:8 ratio and always stay this way. The yellow 16 tooth gear would always be stacked on the middle axle shaft but the white top gear would be changed out to get any different gear ration between 1:8 and 1:32. The idea here being that perhaps there would be some value in being able to more finely adjust the gear ratio between the blades and the KW generator and get more electrical output?

So I went to work with my 3D printer and proceeded to make gears with 56,  48 and 40 teeth to fill in some of the ratio gap between the now possible 1:16 and 1:32 ratios using the green KW 64 and 32 tooth gears. 

Note: I also printed off gears with 28, 24, and 20 teeth to fill in the gaps between the now possible 1:8 and 1:16 ratio)

So hear is a picture showing the set up for a 1:32 ratio ( 8:64 x 16:64 reduced to 1:8 x 1:4 then to 8 x 4 = 32 for the final two step ratio 1:32) which is now possible. Note: the Nacelle needs to be modified plus you need the two rods and Upper and Lower Guides. Changing out the top main shaft gear connected to the rotor blades with any of the new gears now gives you 6 new ratios.

Here is the wind tunnel setup for 4 m/s. The shroud for high speed is hinged on the right side and open.

I decided to test out the new adjustable gear ratio design and to see if it would hold up and if changing the ratios would result in more electricity output from the 2 watt KW generator. I would test two different rotors. One with 3 blades and one with 6 blades. The size of the blades (NACA 2024   400 mm long with a 70 mm chord) would be the same for both. The pitch of the blades was set at 15 degrees. The rotors would be tested in wind speeds of 4 m/s and 7 m/s. And electricity output from the 2 watt KW generator would be measured in Joules with a 30 ohm load for 30 seconds.

With the shroud swung shut the wind speed increases to 7 m/s and makes a significant difference in wind speed and force on the blades and gear train. Good test of turbine component strength.

Here is the data that I collected over the tests under these conditions with 9 different gear ratios.

Note: The data in yellow can now be produced in one step with the present Nacelle

The data in pink could be produced now with present KW gears and the New Nacelle with Up Grade Kit.

Conclusion: Changing gears to get multiple gear ratios is made possible and easier with this design change and additional parts. However, the impact to the electrical output with the 2 watt KW generator did not seem of value when compared to the existing 1:8 , 1:16 and 1:32 gear ratios. More testing will follow with longer blades and higher wattage generators.

Comments and feedback is appreciated.

Dick Anderson