6 01 Spring Semester 2008 Design Lab 9 Issued Tuesday April 8 1 MASSACHVSETTS INSTITVTE OF TECHNOLOGY Department of Electrical Engineering and Computer Science 6 01 Introduction to EECS I Spring Semester 2008 Design Lab 9 Issued Tuesday April 8 All questions in this lab must be written up and handed in as part of problem set 9 Homework due In Design Lab Question 9 Design and draw the circuit diagram for an op amp circuit to compute v1 v2 where v1 and v2 are the voltages coming out of the two potentiometers refer to revised design lab 8 handout for details Design Lab Finish your position controller See revised design lab 8 for a detailed explanation Question 10 Construct your circuit for computing v1 v2 Turn the potentiometers and measure the change in output voltage that is produced Can you set the potentiometers so that the output is 6 So that it is 6 Question 11 Connect up the motor so that the feedback system drives the motor angle to equal d Does the motor turn to a stable position when you turn on power Change the angle of potentiometer 1 d Does the motor position change accordingly Checkpoint 60 minutes Show the potentiometer controlling your motor The head should move smoothly and have a symmetric range of motion to the left and right Explain how this system is different from the way you were controlling a motor with a pot in the previous checkpoints The Eyes Have It Our goal for the rest of this week s lab is to design and build a system that causes the robot s head to look in the direction of a strong light We will do this by mounting two photo resistors on the top face board of the robot head and then designing a circuit that will cause the head to rotate so that the two photo resistors are seeing or are exposed to the same light level It will also be necessary to add some mechanism that puts one of them in a shadow when the board is not pointed directly at the light source Here is the pin out diagram for the KA 334 package again 6 01 Spring Semester 2008 Design Lab 9 Issued Tuesday April 8 2 Question 12 Design a circuit for controlling the robot head based on the photo resistors There are many very complex ways to approach this but there is also a simple solution just involving your virtual ground and an amplifier It should satisfy the constraint that you use only three wires going to between the face where you add only the photo resistors and the board below Draw the circuit Question 13 Arrange for there to be a shadow on a photo resistor so that the board can be made to rotate toward the light Ask an LA for ideas about how to do this Question 14 Now build up the photo sensing circuit and connect it to the motor It should rotate the head toward the side of the photo resistor measuring the highest light level Demonstrate that the head does indeed turn toward a bright light You might need to experiment with the nose device for shadowing the photo sensors or the placement of the photo resistors to get it to work well Checkpoint 120 minutes Show your robot head turning toward the light Gainfully Employed Now we re interested in understanding what happens when we change the gain in this control system We have some new potentiometers which look just like our old potentiometers except that they have a red mark on them and behave like our old potentiometers except they have a maximum resistance of 50K instead of 5K Question 15 Find a way to put one of these new potentiometers into your control circuit without adding any additional op amps and add or change an existing resistor so that by turning the potentiometer you can generate gains that span at least the range 0 2 to 10 Draw the schematic Determine what resistance in the pot will generate an overall system gain of 0 5 Determine what resistance in the pot will generate an overall system gain of 10 Question 16 Build the circuit Test and describe its behavior for a gain of 0 5 and of 10 Question 17 At what gain does the motor stop responding Intuitively why does that happen At what gain does the system become unstable Intuitively why does that happen You may need to go outside the range of gains suggested above in order to push the system to these limits if you have to do more than turn the potentiometer to do so please describe what changes you made to your circuit 6 01 Spring Semester 2008 Design Lab 9 Issued Tuesday April 8 3 Checkpoint End of lab Show your robot head behaving in three noticeably different ways with three different gains Post lab Homework Question 18 Show what resistors you would have to add or change in your answer to question 9 in order to compute K v1 v2 for K 2 How about for K 10 Question 19 There are two errors that would have been easy to make in your design for question 9 The first would have been to turn the head to the left when you turn the control pot to the right and vice versa What error in your circuit would have caused that to happen Draw a circuit diagram showing a small change to your circuit that would have made it exhibit this problem Question 20 The other error is to generate positive feedback instead of negative feedback that is to send a larger correction to the motor when the error gets smaller What error in your circuit would have caused that to happen Draw a circuit diagram showing a small change to your circuit that would have made it exhibit this problem Concepts covered in this lab Design of simple buffers and differential amplifiers Closed loop sensory motor control of a system
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