1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Rotating motion of a D.C motor

  1. Nov 29, 2007 #1
    I am doing this project to check how the number of baldes of a turbine affects its output. So I used a D.C motor which can be used as a dynamo. I attached a blade to it and forced water on to it and as a result of the rotation motion of the D.C motor/dynamo current was produced. Then I attached two blades to the motor and noticed that more current was produced. There will be a certain point after which there will be so many blades that their mass will be too much and hence the current would drop. Can anyone tell me how I can find the optimum number of baldes at which the "turbine" will give maximum output current?

    Mass of one blade = 4.5 grams
    Force of water (flow rate) = 50 ml per sec

    And apart from that question above can someone tell me how i can analyse my results the best and draw up a good conclusion?
  2. jcsd
  3. Nov 29, 2007 #2
    Is there a formula I could use for any calculations?
  4. Nov 29, 2007 #3


    User Avatar
    Science Advisor

    There's no way to answer that in a general sense. There's too many things that are particular to your system.

    Have you done any research on Pelton Wheels?
  5. Nov 29, 2007 #4
    No What are they? What are too many things particular to my system. If that is the case then how can I analyse my results?
  6. Dec 4, 2007 #5
    Atleast can anyone give me a link to results for experiments carried out by other people to see the effect of number of blades on the current output? That will help me get secondary research for my project.
  7. Dec 4, 2007 #6


    User Avatar
    Gold Member

    Hi Advait,

    you need a mathematical model of your system. This is not a trivial thing to do, because you have to write equations between your observables. For example, you know that the current output 'I' is related to the number of blades, 'N'.
    If you plot a graph of I vs N ( I is the y, N is the x) you might be able to guess the equation between I and N. If your theory is correct, you should see a rising I, then a peak and then I falling.

    You're in new territory here, just try and get as many data points as you can.
  8. Dec 5, 2007 #7
    I already did that. And yes I do get a parabolic graph and I also calculated the equation for that graph using my GDC (TI-84). It seems to work. I mean I get an equation and from that I can find optimum number of blades with maximum output. Thanks.

    And now I just need Secondary Sources to compare with my own results as a conclusion to my essay. Can anyone provide me links where someone has stated how many blades they use and what is their output or something like that. For example, tell me if there is any site which tells us the number of blades to the Niagara Dam and its output. Then using my graph and estimating the water flow rate I can theoretically calculate its output and check.
  9. Dec 5, 2007 #8


    User Avatar
    Gold Member

    OK. The theory of turbines and water-wheels looks difficult, as are most things involving fluid flow. I did a google search with 'Turbine theory' and 'water-wheel theory and go a lot of hits.

    I can't help further than that, not knowing much about hydrodynamics.
  10. Dec 5, 2007 #9


    User Avatar
    Science Advisor

  11. Dec 8, 2007 #10
    Yes. I did. but now I just need secondary sources to back up my results. For example if anyone can provide a site where someone has already shown there results to varying number of blades then I could compare my results with his/her and make my project better.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook