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FAQ (Frequently Asked Questions)
Category:
CDS 101/110 Fall 2004
Identifiers: H0 H1 H2 H3 H4 H5 H6 H7 H8 L0.0 L1.1 L1.2 L2.1 L2.2 L2.3 L3.1 L3.2 L4.1 L4.2 L5.1 L5.2 L6.1 L7.1 L9.1
- What is the sentence fragment on the fourth bullet of problem 4 supposed to say?
- My frequency response for problem 4 isn't very interesting - the amplitude is constant across the given range.
- There is a mixing of units in problem 2, since the reference is in mph and the model is in SI. Do we need to put in a conversion factor somewhere?
- On problem 3, part b, can we assume a11 is not equal to a22?
- Lastly, is rise time defined as the amount of time for which the signal reaches 95% of its final value, REGARDLESS if it has overshoot and oscillating effects which may bring it back below 95% of the final value ?
- For number 1, when is a block dynamic?
- What initial conditions should we use for the velocity and engine in problem 2?
- What exactly is transient and steady state response?
- Simulink: I have constants such as m, g, angle, etc. Is there a way to associate them to parameters that I can change whenever I want?
- For question 2d, what is the rise time for the hill?
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What is the sentence fragment on the fourth bullet of problem 4 supposed to say?
Submitted by: waydo
Submitted on: October 5, 2004
Identifier:
H2
Nothing - it was left over from an earlier draft of the problem. The homework on the web site has been updated.
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My frequency response for problem 4 isn't very interesting - the amplitude is constant across the given range.
Submitted by: waydo
Submitted on: October 5, 2004
Identifier:
H2
There was an error in the frequency range you were given. You should do the frequency response for 1 to 100 rad/s. The homework on the web site has been updated.
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There is a mixing of units in problem 2, since the reference is in mph and the model is in SI. Do we need to put in a conversion factor somewhere?
Submitted by: haomiao
Submitted on: October 5, 2004
Identifier:
H2
You DO in fact need to do a conversion gain from SI to english/english to SI. You just need to convert the reference input from mph to m/s.
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On problem 3, part b, can we assume a11 is not equal to a22?
Submitted by: waydo
Submitted on: October 10, 2004
Identifier:
H2
Yes. If a11 and a22 are equal the solution becomes somewhat more complicated (although the answer is the same).
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Lastly, is rise time defined as the amount of time for which the signal reaches 95% of its final value, REGARDLESS if it has overshoot and oscillating effects which may bring it back below 95% of the final value ?
Submitted by: haomiao
Submitted on: October 5, 2004
Identifier:
H2
Rise time is ALWAYS the time it takes the system to go to 95% for the
FIRST time. It is a measure of how fast the system reacts to a
change in reference input, so you always want to know how quickly the
system initially gets near to the reference, even if it
overshoots/undershoots away.
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For number 1, when is a block dynamic?
Submitted by: haomiao
Submitted on: October 5, 2004
Identifier:
H2
Whether or not a system is dynamic stems from the lack or presence of
internal states. In the case of a static map, the input is mapped
directly to the output, so in terms of A,B,C,D form the A, B, and C
matrices are 0-matrices, with y = Du being the only equation needed to
describe the system. Thus there is nothing dynamic or changing within the
system/block.
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What initial conditions should we use for the velocity and engine in problem 2?
Submitted by: haomiao
Submitted on: October 8, 2004
Identifier:
H2
For parts a & b just use zero since you're getting open loop response. It doesn't actually matter too much what initial values are used for parts c & d. Since the system is closed-loop, the controller will eventually settle system to the appropriate configuration for whatever the reference speed is. v0 can be whatever your initial reference is, and make a guess at what the inital engine force should be. Just make sure that you set the hill and step inputs to occur after any initial oscillations have damped out.
From Asa: Regarding the torque for parts c and d, you can pick an initial speed, and then use equations (1) and (2) to solve for the steady state (all derivatives = 0) torque needed to maintain that speed.
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What exactly is transient and steady state response?
Submitted by: haomiao
Submitted on: October 8, 2004
Identifier:
H2
The transient response is the inital fluctuations a system undergoes when external forcing first occurs, and the steady state response is the behavior the system settles into after a long period of time has passed. Basically, the transient response is the natural response of the system to an initial condition and corresponds to the homogenous solution to whatever differential equation defines the system, and usually dies down to 0. The steady state response corresponds to the nonhomogenous solution caused by the forcing, and does not die down as t -> infinity.
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Simulink: I have constants such as m, g, angle, etc. Is there a way to associate them to parameters that I can change whenever I want?
Submitted by: asa
Submitted on: October 8, 2004
Identifier:
H2
You should be able to use variable names for parameters in the simulink blocks. For example, if you want to have a variable for the initial velocity of the car, you can put "k" in the "initial conditions" section of that block's parameter window, and then set the value of k (eg. "k=55;") in the workspace.
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For question 2d, what is the rise time for the hill?
Submitted by: haomiao
Submitted on: October 9, 2004
Identifier:
H2
There isn't one. The hill is a disturbance, not a reference input. Rise time is a measure of how fast a system responds to a reference input, so it doesn't really apply in this case. Yes, this is a silly question, and yes, we will be taking it out.
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