6 01 Spring Semester 2008 Exploration 10 Due Thursday May 1 1 MASSACHVSETTS INSTITVTE OF TECHNOLOGY Department of Electrical Engineering and Computer Science 6 01 Introduction to EECS I Spring Semester 2008 Exploration 10 Due Thursday May 1 Exploration 10 designing better heads In design lab 9 question 15 we studied the effects of gain on the stability of a head orientation controller In that lab we modified the gain by changing the gain of a circuit In design lab 10 we studied the effect of delays on stability when head orientation was controlled by the computer There is still one other aspect of the design that will have an important impact on the system stability the physical design of the head itself The way that you position the two photo resistors on the head how they are oriented and the shape of the nose that you build may have very important implications for how the final system will behave For example for some designs the output of the photoresistors varies smoothly with head rotation while in others it is not even monotonic Nonlinearities can be problematic especially when they effect the error signals that are generated when the head angle is close to the target In the previous labs design choices that affect these non linearities were made arbitrarily In this exploration we will study the effect of those choices This exploration is divided into three parts In the first part we will build the basic infrastructure for testing and calibrating the sensors In the second part we will explore several head designs and we will see how they affect the function relating the output of the photo resistors with the angle of the head In the third part you can study the effect of your design choices on the stability of the angle controller Can you propose an optimal head design Question 1 Write a Python program to sweep the head back and forth The head should first rotate so that it is looking directly forward 0 It should then sweep uniformly to the left When it reaches 3 not quite full left which would be 2 it should reverse direction and sweep uniformly to the right till it reaches 3 It should then return uniformly to 0 This whole sequence should take approximately 5 seconds Question 2 To build an optimal feedback controller for light tracking we must quantify the performance of the photosensors Measure and plot how the computer s representation of the left and right photosensor depend on the angle of the head when the light which is stationary is coming from a point that is 1 foot directly in front of the head 6 01 Spring Semester 2008 Exploration 10 Due Thursday May 1 2 Question 3 Change the distance between the two photo resistors and remeasure the relations between the photosensor outputs and head angle Compare results for the two different distances and explain any differences Question 4 Change the length of the nose or remove the nose entirely and remeasure the relations between the photosensor outputs and head angle Compare results before and after the change and explain any differences Question 5 Suggest some other change to the physical layout of the head that will affect the relation between photosensor outputs and head angle Compare results before and after the change and explain any differences Question 6 Describe features of the relations that were measured in the last three questions that are desirable and undesirable Design a physical layout of the head that is optimized in the sense that the desirable features are maximized and the undesirable features are minimized Describe the resulting layout Question 7 Test your optimized design from the last part for two different locations of the lamp one at one foot as before and one at four feet Describe the effect of changing the lamp distance Question 8 Generally we expect better performance if the error signal that we generate from the photoresistors varies linearly with head angle and does not depend on distance to the lamp Optimize your head design and the way you compute the error signal from the photoresistor voltages Measure and plot the resulting error signal as a function of head angle and lamp distance Question 9 Test the effects of your optimizations on the stability of the system for light tracking Determine the highest stable gain for the optimized system and for your original system In what ways if any has the system been improved Explain
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