Unit Step Response to Plant Dynamics?

Discussion in 'Homework Help' started by woodmark75, Dec 15, 2014.

  1. woodmark75

    Thread Starter Member

    Dec 11, 2014
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    I have plotted a unit step response to G(s) which is a transfer function representing an remotely operated vehicle (ROV).
    The issue is that I'm trying to interpret the result. I would have expected the line to drop, showing the ROV dropping due to gravity etc. It doesn't, it climbs?

    G(s)= -0.125(s+0.452)/(s+1.25)(s^2+0.234s+0.0163)
    Unit Step Response : https://app.box.com/s/sxpd9boxnqm3qhokptrl

    Could anyone explain why the plot rises the way it does?
     
  2. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    your mathmatical expression does indeed return negative values.

    could the problem be in the graphing applications interpretation of the expression. (are you sure it is entered the way it should be for that application)
     
  3. woodmark75

    Thread Starter Member

    Dec 11, 2014
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    I'm using Simulink. I used a step input block, entered G(s) as a transfer function block & then put the output to scope?
     
  4. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    not familar with simulink...whatever it is doing, it is not performing the calculations correctly. try simplifying your function just to see the output is correct then add more elements until you get the problem portion isolated
     
  5. t_n_k

    AAC Fanatic!

    Mar 6, 2009
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    This is the unit step response I obtained....
    G(s) step response.jpg
    No issues as far as I can see. Kermit has probably indicated your likely source of error.
     
  6. woodmark75

    Thread Starter Member

    Dec 11, 2014
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