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gabymuino Newbie Joined: 25/02/2010 Location: United StatesPosts: 26
Posted: 05:05pm 24 Feb 2010
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Hello...
I am a new member here! I'm a middle school student. In one month I am going to my State Science Olympiad in Orlando FL, and I am competing in a wind power event. I have to construct previously of the event, a CD disk propeller. This will be testing for efficiency. It will be attached to a generator and a fan will be blown onto it. I must find a design to maximize the voltage output of the generator. The specifications are:
The only material that I cannot use is any kind of metal.
The CD can be modify, but not the hole that is going to used to attached to a generator.
The measure for the blades has to be between 20 and 24 cm.
I need to know:
The best material to use
Shape of the blades
Quantity of the blades
Is there anyone that can help?
Gaby Muino
gabymuino Newbie Joined: 25/02/2010 Location: United StatesPosts: 26
Posted: 05:41pm 24 Feb 2010
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Edited by gabymuino 2010-02-26Gaby Muino
turnymf Regular Member Joined: 04/10/2008 Location: AustraliaPosts: 84
Posted: 02:47am 25 Feb 2010
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I guess the cd will be the hub and be a hawt with a radius of 20cm
I would go will the lightest stiff plastic I could find
Such as poly carb roofing like laserlight
How will it be attached to the generator?
gabymuino Newbie Joined: 25/02/2010 Location: United StatesPosts: 26
Posted: 03:12am 25 Feb 2010
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Thanks to responded to me...
The diameter of the blade has to be between 20 to 24 cm.
It will be attached as it is attached in a CD player.
If you want you can check this web site
http://soinc.org/sites/default/files/uploaded_files/Physical ScienceLabSetup.pdf[/URL]
I'm waiting for your suggestions,
Thank you again!
GabyGaby Muino
KarlJ Guru Joined: 19/05/2008 Location: AustraliaPosts: 1178
Posted: 03:33am 25 Feb 2010
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If a fan is being used to blow on it I'd be going for
Keep it simple, go the maximum diameter you're allowed
Twist and taper are not required for this type of thing I wouldnt think.
Make sure its balanced and go with lollypop sticks
Luck favours the well prepared
Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333
Posted: 07:27am 25 Feb 2010
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Your link above is broken. Use the post a link button above next to the U with a underline.
Ok my turn to ask you some questions!!
What is the generator?? this is to run. This will effect the blade design greatly.
How do this attach to the generator, as i fail to see how a cd can work in a normal way (they have an arm over top that will get in the way)
What is measured in the test? rpm, power generated, or what??
Will the generator have any load on it...like a light globe or something.
Have you done any other research, like reading on this site.
What do you understand about windmills and blade design.
Like do you realize that the length of the blade will give more torque but less speed (rpm). This is why it is important to know what generator you will be running as the blade is normally designed to suit the generator.
Some generators will need a lot of torque to get started but once spinning will pick up speed ok.
Others will require little torque to start and there for the blade can be designed to reach higher speeds.
Some generators stop making more power after a certain speed others keep increasing.
Do you see now that the questions asked are rather unknown without more information from you.
Lots of things will work but its a matter of how well they work.
Pete.Edited by Downwind 2010-02-27Sometimes it just works
turnymf Regular Member Joined: 04/10/2008 Location: AustraliaPosts: 84
Posted: 08:50am 25 Feb 2010
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Ouch Downwind
Go easy on the kid
KarlJ Guru Joined: 19/05/2008 Location: AustraliaPosts: 1178
Posted: 09:41am 25 Feb 2010
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Luck favours the well prepared
Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333
Posted: 10:30am 25 Feb 2010
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Sorry if i trod on any toes, but was trying to cut to the chase and help the kid rather than sit on the fence.
I have been around this merry-go-round before with other young folk and given a lot of time and effort to them.
What is the use of giving advice without knowing all the facts.
I was told as a kid ...it is no harder doing it right than doing it wrong...
Pete.Sometimes it just works
gabymuino Newbie Joined: 25/02/2010 Location: United StatesPosts: 26
Posted: 01:51pm 25 Feb 2010
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Any advice and help is welcome…
Don’t worry; I understand what you’re saying…
Sorry but I’m new in this and my knowledge about this matter is not too much, that is reason than I’m asking for help!!!
I’m going to try to explain better what I need:
I have to design a Turbine, rotor, windmill, fan or whatever name you want to give it.
I have to create a wind turbine-like object using a CD and other materials. During competition, they will attach your device to a CD motor. You will then place a fan in front of your device and turn it on. Your blade will spin therefore creating voltage. The higher your voltage, the better your score. I must include a standard CD in my wind turbine.
I have to use a CD that can be modify, but not the hole because this has to be attached to a device (CD motor) that the Science Olympiad is going to provide to the teams at the time of the event (I made mine to test my windmill with a CD player parts).
The size of the blades on the windmill has to be measure between 20 to 24 cm and the only material that I cannot use is any metal or derivate.
So I have to design a windmill that has to be attached to the Olympiad device. I can play with the high and angles of the device to adjust my windmill. I’m not allowed to move the fan.
The velocity is going to be measure in mV. They are going to measure low velocity and high velocity and the sum of the two is going to be your score. Last year winner score at National was 600mV.
I understand that I have to have in mind:
Blade Width
Curve of the Blade
Blade Pitch
Number of Blades
Blade Material
Alteration of CD or not
I hope that you can help me & Thanks
Gaby Muino
gabymuino Newbie Joined: 25/02/2010 Location: United StatesPosts: 26
Posted: 02:26pm 25 Feb 2010
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Here you have some pictures
Gaby Muino
Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333
Posted: 03:09pm 25 Feb 2010
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I take it the 20-24 cm is the dia.and not the length of 1 blade from centre.
Are you able to use screws to attach the blade to the cd or is that counted as metal used?
As far as i am aware a cd motor is a 3 phase motor and will give 3 x ac outputs, do you know if the voltage is going to be read as dc with the combined total of all 3 phases.
In other words each phase will have 2 diodes attached to it to rectifier it to dc and the 3 + outputs will be joined together and the same for the - outputs.
It is good you have got a test motot to try some blades on.
I should point out i am not the expert here on blade design, but will try to get you started with the hope that others will jump in with more advice and correct me if i am incorrect.
A 3 phase motor like this will have what we call cogging, you can feel this when you turn the shaft and it will feel slightly knotchy, albeit in this small motor only very little cogging.
Cogging will effect the start up and is why i asked about the gererator used, as you will need a bit of torque to get the thing to start to spin.
If you look at some blade designs (big or small) you might notice that they have a bigger profile in near the hub (cd in your case) this is to give some torque at startup but not to effect the blade speed to much.
Out near the tip it is thin so not to cause to much drag at higher speed.
2 blades will on average spin faster than 3 or more, but the torque will be less.
The longer the blade the slower the speed but the greater the torque.
So all this is a balancing act to gain the best result for the generator being used in the wind speed available.
I think for starters you will get a reasonable blade from a piece of round pvc pipe (the white plastic pipe a plumber uses.) I am not sure what you have in the states but here we have what is called stormwater pipe that is used to connect the gutters on your house out to the street or to a water tank.
This is pvc and comes in 2 sizes 75mm and 90mm.
It is a rather thin wall thickness compared to sewer pipe etc. (its lighter)
I would try the 75mm and cut a double blade out of this.
This should give a reasonabale starting point and then you can make some changes from there.
The other option is to hand carve some blades out of wood but is not an easy job.
Do you have someone to assist you with the cutting out of the pvc pipe etc. and a few tools to work with.
Let me know what your thoughts of this method is.
Pete.
>>> edited to remove link should others in the same project try to gleem off gabys efforts.<<<<Edited by Downwind 2010-02-27Sometimes it just works
gabymuino Newbie Joined: 25/02/2010 Location: United StatesPosts: 26
Posted: 03:23pm 25 Feb 2010
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I cannot use any kind of metal so screws are not allowed.
I have to use glue or any other kind of scotch tape.
I understand that the windmill have to be the lighter that I can make, because has to be move just with the air produced by the fan, so the PVC, I think is heavy and is not easy to cut what do you think?
You mention wood... what about balsa wood? Is lighter and easy to cut
What about the number of blades and the angles?
Thank you for take your time in help me!!! Gaby Muino
Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333
Posted: 03:38pm 25 Feb 2010
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Pvc is not that heavy if you get a thin wall thickness.
It cuts with a saw rather easy and if you can find some one with a jig saw it would be an easy job.
Balsa would work but then you will need to find a profile to give a good result.
I would go for 2 blades and high speed.
Dont copy a aircraft prop as this is back to front to what you will need.
You could try something like a plastic bottle that might cut with some sissors and make the blades in 2 sections but will be harder to line up.
It will need to be a round cylinder type bottle.
A few quick tests will give a good idea of which way to head with the project.
I know the round pipe blades work quite well and have been used on small and big mills with good results.
Pete.Sometimes it just works
gabymuino Newbie Joined: 25/02/2010 Location: United StatesPosts: 26
Posted: 03:43pm 25 Feb 2010
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What about plastic cups or Styrofoam cups?
Anyway I'm going to try with the PVC
Thanks Gaby Muino
Downwind Guru Joined: 09/09/2009 Location: AustraliaPosts: 2333
Posted: 04:51pm 25 Feb 2010
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There needs to be enough rigidity in the material to hold shape and not fly to bits as it might reach some high speeds.
With the generator you have is it stiff to turn?
like if you give it a spin will it stop almost straight away.
The one i found in a junk box here is rather stiff or tight to turn.
Mine is 3 phase but not sure about all other types.
Can you post a close up photo of the back of your generator setup.
Will check back tomorrow as late here now.
Pete.Sometimes it just works
gabymuino Newbie Joined: 25/02/2010 Location: United StatesPosts: 26
Posted: 07:29pm 25 Feb 2010
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Mine is just the same as a standard CD player...
I just took a part an old CD player and I connected the two wires (black & red) to the voltmeter, to measure the voltage that the CD windmill generates.
Gaby Muino
neil0mac Senior Member Joined: 26/12/2009 Location: AustraliaPosts: 210
Posted: 09:58pm 25 Feb 2010
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More things to think about?
What is the range of air velocities generated by the 'driving fan'? Affects speed versus torque considerations? (No point in designing for speeds higher than that given out.)
The distance between the two? Loss of pressure is (inversely, or something?) poportional to the space between the two? Closer could have a miniscule 'pulse' effect you can harness?
Presumably the blade design of the driving fan could produce uneven air flow (pressure) from its centre to the periphery?
Or you can discard these!
On the question of attaching the blades ... If using two (as suggested above, or four?) blades cut them out as one piece with a clearance hole to clear the CD motor drive mechanism, attach them with small bolts (in holes with clearances) to allow for balancing, and then epoxy resin them to the CD when running true/evenly? Remove the 'metal' when done.
Perhaps there is a lighter tubular material you can find to use - or a thermo (not thermo setting) plastic sheet that you can form over (or between) two moulds? Even the plumber's pipe wall could be stronger/heavier than necessary - increasing inertia problems?Edited by neil0mac 2010-02-27
gabymuino Newbie Joined: 25/02/2010 Location: United StatesPosts: 26
Posted: 10:33pm 25 Feb 2010
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The velocity generated by the fan can vary, it's depend of the one that they have at that moment. At Regional they have a small one. I'm sending you a picture of the one that they probably going to use at my state competition.
About the distance between the fan and the windmill also can vary is depends on the judges at the moment of the competition.
So, I have to work based on the best material to use, Shape of the blades and angels and quantity of the blades.
Gaby Muino
neil0mac Senior Member Joined: 26/12/2009 Location: AustraliaPosts: 210
Posted: 11:57pm 25 Feb 2010
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The best of luck! That sounds very much like buying a lottery ticket! Here's hoping that each competition has the distance fixed, at least.
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Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.
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