Physics Lab B/C

Locked
Greg Doe
Member
Member
Posts: 81
Joined: December 13th, 2008, 4:49 pm
Has thanked: 0
Been thanked: 0

Re: Physics Lab B/C

Post by Greg Doe » January 8th, 2010, 9:31 am

Fleet 130
Excelent choice of a word! TURBINE works for me. Thanks, Greg

Greg Doe
Member
Member
Posts: 81
Joined: December 13th, 2008, 4:49 pm
Has thanked: 0
Been thanked: 0

Re: Physics Lab B/C

Post by Greg Doe » January 9th, 2010, 10:11 am

Fleet 130
Thanks for posting those links. A lot of good information. They should be required reading for
anyone doing this event, or coaching it. There was only one comment that I find fault with, and
that is the ability to light a light bulb with a small motor/generator like we are using. We easily
lit 3 volt bulbs. They weren't really bright, but they very visible in daylight conditions. Another parameter that could be checked came to mind after reading those articles. What are
the RPM's of our tubines? If I can, I will try to collect some data in this area. Thanks again.
Greg Doe
Smyrna, TN

fleet130
Staff Emeritus
Staff Emeritus
Posts: 433
Joined: November 10th, 2001, 3:06 pm
Location: Mare Tranquillitatis
Has thanked: 0
Been thanked: 0
Contact:

Re: Physics Lab B/C

Post by fleet130 » January 9th, 2010, 6:42 pm

Here's a suggestion I think would improve the event:

Instead of using both a high and low speed fan, only one speed would be used with voltage measurements be taken with first a 1.0 ohm and then a 1.0 megaohm resistor (load) connected across the generator output (If desired two speeds could be used, for a total of 4 voltage measurements). Simply put, this would show that the output voltage of the generator depends, to some extend, on the load connected to its output.

Another change might be to add a graph of the voltage vs load resistance and to predict the output with a third (previously unknown) load connected. ( Or to calculate the unknown load resistance from the voltage produced with it connected across the generator).

Pros? Cons? Suggestions?
Information expressed here is solely the opinion of the author. Any similarity to that of the management or any official instrument is purely coincidental! Doing Science Olympiad since 1987!

Greg Doe
Member
Member
Posts: 81
Joined: December 13th, 2008, 4:49 pm
Has thanked: 0
Been thanked: 0

Re: Physics Lab B/C

Post by Greg Doe » January 11th, 2010, 9:52 pm

Fleet130
I had to think about your suggestions for a couple of days before commenting. I believe they
should leave B division alone, but incorporate your suggestions (or something similar) in C
division. I think there is still a lot of room for improvement in blade design. B division would
continue to be a voltage challenge, and C would be a load challenge.
Another result from this format is that B and C blade design would be very different. Good idea.
Greg Doe
Smyrna, TN

fleet130
Staff Emeritus
Staff Emeritus
Posts: 433
Joined: November 10th, 2001, 3:06 pm
Location: Mare Tranquillitatis
Has thanked: 0
Been thanked: 0
Contact:

Re: Physics Lab B/C

Post by fleet130 » January 11th, 2010, 10:42 pm

My problem with the current rules is that they place emphasis on turbine design that is contrary to real world requirements. By measuring voltage with no load, the turbine must be designed to produce speed instead of torque. I believe this to be a major factor in why smaller diameter turbines have been found to outperform ones of larger diameter. By placing a load on the turbine, the emphasis would be on torque rather than speed.
Image
I realize that some of what I suggested may be beyond Div. B. I think both divisions need the load so the turbine makes sense and doesn't conflict with what is observed in the real world. The graphs are a toss-up, although they are currently part of many other Div. B events. Predictions and/or determining an unknown load are most likely for Div. C only.

All of this needs some experimenting to see what works and what doesn't. One of the reasons I brought it up was in hope some others would "check it out". It's too easy for one person to overlook important details.
Information expressed here is solely the opinion of the author. Any similarity to that of the management or any official instrument is purely coincidental! Doing Science Olympiad since 1987!

User avatar
georgexu316
Member
Member
Posts: 23
Joined: November 9th, 2009, 7:26 am
Division: C
State: NY
Has thanked: 0
Been thanked: 0

Re: Physics Lab B/C

Post by georgexu316 » January 12th, 2010, 5:25 pm

fleet130 wrote:My problem with the current rules is that they place emphasis on turbine design that is contrary to real world requirements.
I completely agree. The voltage generated by the wind turbine has almost nothing to do with how much energy it captures. In fact, commercial wind turbines mounted 150 meters high generates less voltage than the small ones we build. The commercial turbines actually have what's called a gearbox, which converts the slow moving blades into fast moving gears, which then hikes up the voltage for delivery to the powerhouse.
In real world, wind would not be that fast, and you can't always mount the blade anyway you'd like relative to wind vector, because wind direction is variable.
All of this needs some experimenting to see what works and what doesn't. One of the reasons I brought it up was in hope some others would "check it out". It's too easy for one person to overlook important details.
Honesty, building wind turbine doesn't isn't really about physical science, but rather more about optimization, engineering, and trying what works and what doesn't work. You really don't have to understand anything about turbine blades to build a good one. As long as you test enough blades and keep a record of what kind of design works the best, you'll probably be much better off than someone who spends hours trying to work out equations for a perfect design.
Last edited by georgexu316 on January 12th, 2010, 5:36 pm, edited 2 times in total.
Physics lab wind turbine videos:
http://www.youtube.com/user/georgexu316

User avatar
georgexu316
Member
Member
Posts: 23
Joined: November 9th, 2009, 7:26 am
Division: C
State: NY
Has thanked: 0
Been thanked: 0

Re: Physics Lab B/C

Post by georgexu316 » January 12th, 2010, 5:28 pm

E Edgar wrote:Thanks for your comment; that definitely agrees with my empirical observations.

However, wouldn't the weight of the blade only affect the rotational inertia and therefore acceleration? A heavier blade should theoretically take longer to accelerate but (I think) should spin with the same angular velocity. Considering a linear analogy, if one pushes a 1 pound brick with the same force as a 2 pound brick, only their acceleration is affected, not their velocity. The 2 pound brick would take longer to get the same velocity as the lighter brick but it eventually would. Now, the heavier brick would create a larger frictional force and so its maximum velocity would be less. However, with "fan" blades, since there is very little contact surface with the CD player, I don't see how friction could affect a heavy blade significantly differently to a lighter one.

Perhaps the observed superior performance of the lighter blades is due to some other factor (like, is it harder to balance a heavy blade?)?

The ideas presented in your last post may very well be correct, I just want to think it through a bit so that I can convince myself I'm not jumping to premature conclusions.
This is theoretically true, but I have tested that by placing extra mass on the back of the blades (as not to hinder airflow), and my experiment shows that heavier blades do in fact produce less voltage. I really can't explain it, but maybe it shifts the drag and lift equilibrium somehow.

btw, I don't know if maybe my fan is really fast or my motor is good (i took it out of a standard CD player), but I've been hitting over 1000 mV pretty easily on high, and over 800mV on low.
Physics lab wind turbine videos:
http://www.youtube.com/user/georgexu316

Juce7
Member
Member
Posts: 19
Joined: May 13th, 2009, 2:30 pm
Division: C
State: TX
Has thanked: 0
Been thanked: 0

Re: Physics Lab B/C

Post by Juce7 » January 17th, 2010, 7:43 am

georgexu316 wrote:
andrewwski wrote:Looking at the blades, I'd go with something narrower that tapers as you go toward the tip.
Narrower blades are for slower wind speed. At slower wind speed, the extra mass just adds to the moment of inertia. At high speeds, however, it captures wind energy efficiently, while adding relatively few moments of inertia.
That’s why if you look at a normal windmill, it will have narrow blades because wind speed isn’t very high. But in this competition, the fan produces enormous amount of wind speed (relatively), thus a big fat blade works much better.

I’ll probably cannibalize my old CD player to get a motor to measure voltage this week.
I’m also trying foam blades. I’ll post up the voltage measurement results.
sry, this is kind of late, but i was wondering if anybody who used andrewwski's line of thinking and has made their blades fat, and if so, the voltage. I've been using thinner blades that taper on the end and ive been getting 1.164 V on high and 660 mV on low.( on a relatively weak 20 inch box fan....and whenever i test the blades on higher powered fans the blades just give out higher and higher voltages)
The only difference between genius and stupidity is that genius has limits
~Albert Einstien

To be in Science Olympiad, you have to posess both

Sanity is something no proper Science Olympian has

Glacierguy1
Member
Member
Posts: 162
Joined: March 16th, 2006, 5:08 am
Division: Grad
State: NY
Location: LI,NY
Has thanked: 0
Been thanked: 0

Re: Physics Lab B/C

Post by Glacierguy1 » January 17th, 2010, 12:00 pm

At athens, the setup the Event supervisor used was weird (I only heard this, I wasn't there to see it.) It was not only the center of the CD player that you put the CD on, but also the backing. My Blade assembly wobbled a little but it didn't matter on my setup, but when it wobbled on this one,it hit the back numerous times and in a few seconds, a blade broke off.

Did this setup violate any rules, or should I redesign my propeller to fit that?
SAVE OUR GLACIERS.

rockhound
Member
Member
Posts: 109
Joined: February 14th, 2009, 11:00 pm
Division: Grad
State: FL
Has thanked: 0
Been thanked: 0

Re: Physics Lab B/C

Post by rockhound » January 17th, 2010, 1:06 pm

Glacierguy1 wrote:At athens, the setup the Event supervisor used was weird (I only heard this, I wasn't there to see it.) It was not only the center of the CD player that you put the CD on, but also the backing. My Blade assembly wobbled a little but it didn't matter on my setup, but when it wobbled on this one,it hit the back numerous times and in a few seconds, a blade broke off.

Did this setup violate any rules, or should I redesign my propeller to fit that?
Unfortunately, no. The rules say that the mount must be able to move in three dimensions, a 20" fan must be used that is at least 15cm above the table (surface), and must be able to have a CD attached to it. Besides that the rules say nothing about how the set up is to be. :roll:

Locked

Return to “2010 Lab Events”

Who is online

Users browsing this forum: No registered users and 1 guest