Wind Power B/C

[ASingh]

There are some REALLY good insights and comments in this thread so far. Instead of replying to each of them, I'd like to share some general comments to hopefully steer the conversation. I'd also like to request suggestions on specific, concrete changes to the rules wording.

1. This is a Physics committee event. Hence our general philosophy is that the theoretical and practical portions of the event should contribute equally to the score. What that specifically means is that we don't do tiering in Physics events (as that would make the practical portion outweigh the theoretical portion).

I think the way the event played out, this balance between the theoretical and practical portions was not realized in practice. I am OK with using Power (square function of Voltage) as the metric, but I think normalizing the score with the top team getting a 50 causes a distortion. Most turbine designs are only capturing a very small amount of the energy in the wind, and small differences (compared to the amount of available energy) in their performance are getting exaggerated. So a team may be capturing 2% (score of 50) of the energy and another 1.5% (score of 37.5) of the energy. There is no such scaling on the written part, and even achieving a 5 pt difference would be hard.

A couple of options:
1) An easy thing to do would be to normalize the written score also. So if the top team had a 35/50 and the next team had a 30/50, the scored would be 50 and 42.85. This would make it a little more balanced.
2) Instead of normalizing wrt to max power score in the event, normalize to some target power level (Betz limit, or best turbine power generated at this year's national, etc.). So then as in the written part, no one may get a 50 and your score would be dependent on how good your performance is compared to best possible performance.

Another thing that might help is if the equipment was standardized...box fan type, motor/generator...so that designs can be optimized to known conditions.

[soyuppy]

Has anyone seen inconsistency in the test stand voltage results, specifically the Ward Science stand ?

I have been using a test stand based on a CD motor taken from a used portable CD player as my main test stand at all of the invitationals, regionals and state final and it has been consistent in that my reference blade assembly has always returned the same voltage range (305 to 315 mV) all season.

I have also been using a Ward Science test stand as a backup and a comparison. When the test stand first arrived it was reporting approximately 30% higher voltages (430 mV) than my CD motor based stand. Recently I have noticed that the voltages reported by the Ward stand are dropping:
a) The initial high voltage is getting a little lower
b) While a blade assembly is being tested it initially peaks and then the voltage slowly drifts down by 20 to 50% over 5 minutes of continuous running
c) After testing a number of other blade assemblies and then going back to the original reference the voltage reading is significantly (10% to 20%) lower than it measured at the beginning of the test session.
d) If the test stand is left until the next day it seemed to recover but not to the original 30% higher results I used to get with it.

I have tried with two different fans and swapped out the volt meter and power cables and am still seeing the same behavior. The resistor does not seem to be warming up so I don't think that is the problem (but I didn't measure it very scientifically), and I was not able to measure the motor windings temperature.

I am particularly concerned about observation (c) that the voltages are reducing throughout a test session because it could give teams competing later in the day a disadvantage. I am still investigating but in the mean time was wondering if anyone else has seen this test stand behavior.

We had same issue with the CD motor that we extracted from a CD player. When motor was test initially, reading was consistent. Then over time, the reading start to fluctuate by large amount. Then we got these set of motor from Amazon.
http://www.amazon.com/Water-RC300-FT-08 ... ge_o07_s00. They work much better and has been consistent. Just use the mounting hub from the old motor.

[soyuppy]

There are some REALLY good insights and comments in this thread so far. Instead of replying to each of them, I'd like to share some general comments to hopefully steer the conversation. I'd also like to request suggestions on specific, concrete changes to the rules wording.

1. This is a Physics committee event. Hence our general philosophy is that the theoretical and practical portions of the event should contribute equally to the score. What that specifically means is that we don't do tiering in Physics events (as that would make the practical portion outweigh the theoretical portion).

I think the way the event played out, this balance between the theoretical and practical portions was not realized in practice. I am OK with using Power (square function of Voltage) as the metric, but I think normalizing the score with the top team getting a 50 causes a distortion. Most turbine designs are only capturing a very small amount of the energy in the wind, and small differences (compared to the amount of available energy) in their performance are getting exaggerated. So a team may be capturing 2% (score of 50) of the energy and another 1.5% (score of 37.5) of the energy. There is no such scaling on the written part, and even achieving a 5 pt difference would be hard.

A couple of options:
1) An easy thing to do would be to normalize the written score also. So if the top team had a 35/50 and the next team had a 30/50, the scored would be 50 and 42.85. This would make it a little more balanced.
2) Instead of normalizing wrt to max power score in the event, normalize to some target power level (Betz limit, or best turbine power generated at this year's national, etc.). So then as in the written part, no one may get a 50 and your score would be dependent on how good your performance is compared to best possible performance.

Another thing that might help is if the equipment was standardized...box fan type, motor/generator...so that designs can be optimized to known conditions.

Not sure I agree with with either 1 or 2. The score are always compare among those team that compete in the event for that day. All events in SO follow this scheme. Regardless of what baseline, the placement of your score doesn't change. If you actually score 20/50 or 30/50 and this happen to be the best score for that event for that day, it doesn't matter what normalization takes place, your are still in 1st place.

[soyuppy]

Resistance in the setup
In my setup, I have a 5 Ohm Resistor(verified by Multi-Meter), but when connected to CD motor, resistance drop to 3.5 Ohm.
How do you measure resistance in the setup? Is the 5-7.5 ohm measure on the entire circuit, including the CD motor connect or CD motor disconnect?

[daydreamer0023]

This is very urgent: I just got put on Wind Power for Nationals and I have no idea where to start. My partner has done it before and I can probably study my way through it somewhat (since it's similar to the format of Simple Machines last year), but what I really need help with is building the turbine blades, since we're thinking of remodeling them from what we previously used for states.

Can someone please share some design ideas that have worked well for them (I understand if you all don't want to give away team secrets), or at least some starting points for thoughts on building the device? Thanks in advance!

[PHXcoach]

Resistance in the setup
In my setup, I have a 5 Ohm Resistor(verified by Multi-Meter), but when connected to CD motor, resistance drop to 3.5 Ohm.
How do you measure resistance in the setup? Is the 5-7.5 ohm measure on the entire circuit, including the CD motor connect or CD motor disconnect?

The resistance of 5 to 7.5 ohms only applies to the load resistor (rule 2.d.iv). The resistance of the rest of the circuit (motor and wire) is not specified.
Just measure the resistance across the resistor without the motor in parallel or series with it.

[HandsFreeCookieDunk]

This is very urgent: I just got put on Wind Power for Nationals and I have no idea where to start. My partner has done it before and I can probably study my way through it somewhat (since it's similar to the format of Simple Machines last year), but what I really need help with is building the turbine blades, since we're thinking of remodeling them from what we previously used for states.

Can someone please share some design ideas that have worked well for them (I understand if you all don't want to give away team secrets), or at least some starting points for thoughts on building the device? Thanks in advance!

This late in the season, you might be better off just keeping the States blades, especially if they got you this far. If you do decide to change them, I've found that cereal box cardboard works well, although the blades have to be pretty big to drive the weight of the entire CD.

[dragonfruit35]

This is very urgent: I just got put on Wind Power for Nationals and I have no idea where to start. My partner has done it before and I can probably study my way through it somewhat (since it's similar to the format of Simple Machines last year), but what I really need help with is building the turbine blades, since we're thinking of remodeling them from what we previously used for states.

Can someone please share some design ideas that have worked well for them (I understand if you all don't want to give away team secrets), or at least some starting points for thoughts on building the device? Thanks in advance!

This late in the season, you might be better off just keeping the States blades, especially if they got you this far. If you do decide to change them, I've found that cereal box cardboard works well, although the blades have to be pretty big to drive the weight of the entire CD.

Balsa wood also works well, or at least it did for my blades. Drag type blades are definitely better in my experience.

[calvin102111]

This is very urgent: I just got put on Wind Power for Nationals and I have no idea where to start. My partner has done it before and I can probably study my way through it somewhat (since it's similar to the format of Simple Machines last year), but what I really need help with is building the turbine blades, since we're thinking of remodeling them from what we previously used for states.

Can someone please share some design ideas that have worked well for them (I understand if you all don't want to give away team secrets), or at least some starting points for thoughts on building the device? Thanks in advance!

This late in the season, you might be better off just keeping the States blades, especially if they got you this far. If you do decide to change them, I've found that cereal box cardboard works well, although the blades have to be pretty big to drive the weight of the entire CD.

Balsa wood also works well, or at least it did for my blades. Drag type blades are definitely better in my experience.

Work with balsa wood if possible. With my setup, using 4 blades, we were able to generate about 700 mV on low speed and 900 mV on high speed (however this is all relative). Personally, we used a design with a very precise airfoil, but this late in the season I wouldn't worry about that unless you have worked with them before. As previously stated, drag designs seem to be the best performance wise and in consistency.

In my opinion, one of the factors you have to worry about the most is balance. A poorly balanced assembly can really harm your power output. I use clay to balance my assembly, and I do so by placing it on the mount and rotating it so each blade is facing up and balancing it so it no longer falls towards one side. Repeat that for all of the blades. If it comes down to it and you cannot create a better design, just stick with the state design. Don't stress out over this event specifically, worry about doing your best in the events that you were in at state.

Best of luck to you!
-Calvin

[fl0w]

How is it that you guys have been finding drag type designs to be the best? Aren't those typically for vertical axis wind turbines?