Unit Step Response to Plant Dynamics?

Thread Starter


Joined Dec 11, 2014
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?


Joined Feb 5, 2010
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)


Joined Feb 5, 2010
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


Joined Mar 6, 2009
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.