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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
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What is the definition of "overshoot" for question 5?
Submitted by: asa
Submitted on: September 29, 2004
Identifier:
H1
The homework assignment itself defines overshoot in context as "the maximum amount by which the ball goes past the desired resting point, expressed as a percentage of the commanded position." However, it is unclear whether this might mean the first peak, the first valley (which may be larger in magnitude than any of the peaks) or simply the highest peak, regardless of whether it's the first.
Upon further consultation with a later chapter of the textbook, it gets a little more clear: In Chapter 3, overshoot is defined as the percentage by which the value initially rises above the final value. The book then continues to say that in cases where the first is not the largest, the term is ambiguous. For linear systems, this initial rise will always be the largest deviation from the desired value, so there's no ambiguity. The example in problem 5 is nonlinear, so we enter the gray zone.
From a practical standpoint as you do your homework, please consider the TAs. The best policy when there is ambiguity about definitions is to state clearly what definition you are using, and be consistent in that definition.
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Is it OK to use non-physical systems (like behavioral systems) for our examples on problem #1?
Submitted by: waydo
Submitted on: September 29, 2004
Identifier:
H1
This is just great. You need to be sure you can address all aspects of the question with the systems you choose, but feel free to be inventive.
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Do we measure settling time on #2 from time 0, or from when the step starts?
Submitted by: waydo
Submitted on: September 29, 2004
Identifier:
H1
You should measure setting time from when the input starts. For example, if the step time is at 13 seconds and you find the system has settled after 42 seconds, the settling time would be 29 seconds.
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What are the units of gain?
Submitted by: waydo
Submitted on: October 1, 2004
Identifier:
H1
For example, you need to plot gain on a graph - what units should you use?
The units of gain vary depending on application. For example, if you have a servo control mechanism, you may have gain in units of volts/degree, i.e. the number of volts applied to the motor per degree of error. In other cases gain is a ratio of magnitudes and is truly unitless. In general we don't worry about specifying the units on plots, etc.
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When I press the button to start the hw1cruise.mdl it just beeps at me.
Submitted by: waydo
Submitted on: October 1, 2004
Identifier:
H1
Simulink beeps when it's finished with a simulation, which is probably pretty fast for this model. The model doesn't give you any visible output, but the "To Workspace" blocks log the data to the MATLAB workspace. If you type "who" in the MATLAB command window after running the model you will see the logged variables. At this point you can, for example, "plot(time,vel)" to get a plot of velocity vs. time for the simulation.
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How do I access the data in the ballbeam structure, saved in the MATLAB workspace?
Submitted by: asa
Submitted on: October 1, 2004
Identifier:
H1
To burrow into the structure, use a "dot" syntax. That is, if you just type "ballbeam" in the workspace, it tells you that the structure is made up of "time", "signals" and a name. "ballbeam.signals" is made up of "values" and a dimension (4). If you look at the Simulink model, you can see that the first of the "values" is what's going to the scope; the other three are trashed. So, the data you want is in the first column of the vector "ballbeam.signals.values".
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How do you set the parameters of a Simulink simulation?
Submitted by: waydo
Submitted on: October 4, 2004
Identifier:
H1
This depends on what you mean by "parameters." There is a menu found under the "Simulation" menu called "Simulation parameters..." that lets you set things like the simulation duration as well as control some of the details of the integrator.
If you mean things like gains and other block parameters, you can access them by double-clicking on the block you want to change.
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How much was each problem worth?
Submitted by: waydo
Submitted on: October 12, 2004
Identifier:
H1
Each problem was worth 10 points, which will generally be the case. Occasionally we may decide to assign 20 points to a particularly hard problem. Regardless of the total number of points, all assignments will be weighted equally when calculating grades.
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Who do we talk to if we have questions about graded homework?
Submitted by: waydo
Submitted on: October 13, 2004
Identifier:
L3.2
, H1
You should send an email to the ta list (cds101-tas@cds), so the TA who graded the problem you have a question on can respond.
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