Wind Power C

[fleet130]

I was just hoping that I could get away with using a multimeter for the testing setup

Presumably, at the competition, probes will be set up, connected and operated by the event officials. There is no need for you to be familiar with them. When you are testing your turbines at home, you are looking for relative measurements (is this one better/worse than another)? I see no reason why you couldn't use a multimeter.

I recommend using a digital meter so that it doesn't load down the circuit & affect your measurements. In reality, this probably doesn’t matter much because the impedance of even a cheap analog multimeter is relatively high compared to the load resistor specified.

Using a 7.5 ohm resistor and a digital meter with 10 Mohm input, the total load resistance would be = 7.4999 ohms

For an analog (mechanical) meter with 1000 ohm input, the total resistance would be 7.4444 ohms.

This would be about .75% change in load. (unless I made a mistake)

[Flavorflav]

I was just hoping that I could get away with using a multimeter for the testing setup

Presumably, at the competition, probes will be set up, connected and operated by the event officials. There is no need for you to be familiar with them. When you are testing your turbines at home, you are looking for relative measurements (is this one better/worse than another)? I see no reason why you couldn't use a multimeter.

I recommend using a digital meter so that it doesn't load down the circuit & affect your measurements. In reality, this probably doesn’t matter much because the impedance of even a cheap analog multimeter is relatively high compared to the load resistor specified.

Using a 7.5 ohm resistor and a digital meter with 10 Mohm input, the total load resistance would be = 7.4999 ohms

For an analog (mechanical) meter with 1000 ohm input, the total resistance would be 7.4444 ohms.

This would be about .75% change in load. (unless I made a mistake)

Well, last year the event official who set up this event for the regional was me, so I actually do need to figure them out. Thus the question.

[ichaelm]

I did some math to scale down the measurements for a couple modern super-efficient commercial wind turbines, assuming the wind speed would become 2 mph and the diameter would be 28 cm (this year's maximum). I ended up with 75 milliwatts. This is not exactly feasible for our turbines, because we cannot control the torque of the CD motor / generator, and it will likely be very inefficient. I'd guesstimate that a reasonable goal might be somewhere around 50 milliwatts. Today, I made a setup using a CD motor from last year and a 7.5 ohm resistor. My turbine from last year, which won 8th place at nationals (B division) and has a diameter of 20 cm, generated 16.3 milliwatts. Obviously it was designed with speed in mind, and not actual power, so I think lots of improvement is possible. I expect that within a month or two, someone will post a result here that blows this one away!

[Flavorflav]

I'm also a little concerned about the new clearance specifications. Last year we just put out a blanket rule that for regionals and states, the blade assembly could not break the plane of the CD. Without having measured, I don't think that any of the setups I've seen (including the sample setup on soinc.org) would allow an assembly that used the full allowable backward sweep. To do so, I think you would have to remove the motor from the plastic housing, which I haven't wanted to do for fear of messing up the mounting clips. Has anyone done this successfully? If so, how did you then mount it to the support rod?

[ichaelm]

What I did, for our team's personal use, was I used my dremel drill with a cutting bit to cut off all the excess plastic around the motor and rotating CD mount. Then I used my dremel with a sanding bit to round off the edges and make it look shiny. Then I used duct tape to affix the motor to a wooden stick. For a real competition, you could use something like a ring stand instead. And perhaps use something more reliable than duct tape.

Also, I'm about to post an excel sheet with last year's results on the wiki. Unfortunately, I only have B division. It was really close at the top!

[j0llybear]

im glad they fixed the rule about what kind of motor they use for the generator. Last year i went undefeated until state where the event supervisor decided to take a motor out of a toy car and mount the blades on that , while not strictly against the rules, it still made our blade assembly, which was getting up and over 2V at competition completely worthless... needless to say, state was not a very happy time for me last year

[ichaelm]

Really? That's strange. How did they make it "adapted for CD attachment"?

[fleet130]

I've updated the circuit pictorial to depict a computer instead of a Multimeter!

[illusionist]

im glad they fixed the rule about what kind of motor they use for the generator. Last year i went undefeated until state where the event supervisor decided to take a motor out of a toy car and mount the blades on that , while not strictly against the rules, it still made our blade assembly, which was getting up and over 2V at competition completely worthless... needless to say, state was not a very happy time for me last year

That shouldn't have affected only your team though. All of the other teams will have the same situation, so it will still be fair as to who gets first and who gets second place. A similar thing happened at our states too, but it was fair since all the teams were affected.

[ichaelm]

Anyone have opinions on building materials? Two years ago I used styrofoam, which was good enough for regionals, but didn't do so well at states. It was pretty flimsy. Then last year I started with balsa and have never looked back