Here Comes the Sun - Lego

Here Comes the SunThe ChallengeInvent a car that finds the optimal light conditions for charging a capacitor from asolar panel. After the solar panel charges the capacitor, the capacitor must beable to run the car for a least a few seconds. Recharge the capacitor while thecar is parked. How can you make sure the solar panel is facing the sunwhenever it stops?This activity requires:ü ROBOLAB 2.0 or higherü The Infrared Transmitter with serial cable #9713ü RCX® #9709,ü eLAB set #9684What to DoHere is one way to solve the problem using a touch sensor and a light sensor.Program the car to drive forward until you press the touch sensor, indicating youwish to park. When the touch sensor is pressed, the car stops and rotates slowlyas it searches for the brightest light. Once the car has found which direction hasthe brightest light, it turns facing that way, then halts.Building IdeasBuild a car that can turn in a circle. Mount the solar panel securely on top. Add atouch sensor to tell it when to park and a light sensor for finding the brightestlight.Programming IdeasIn your computer program, you will need to give your car a set of instructions fordetermining the direction with the brightest light and for stopping at the optimallight level. This set of instructions for doing a task is called an algorithm.©2002 The LEGO Group. LEGO, Invent & Investigate and RCX are trademarks of The LEGO Group.This page may be photocopied for non-commercial educational use. All other rights reserved.1

Here is one possible algorithm: Make the car turn as long as the light sensorvalues are increasing (that is, the light is getting brighter). As soon as the lightsensor values decrease, the car returns to its previous position and stops. Theadvantage of this algorithm is that it is fairly simple but it has disadvantages, too.Can you think of any?What other algorithms can you think of for finding the brightest parking position?Before you start programming, brainstorm methods that you could use fordetermining the direction with the brightest light as your car rotates, thenreturning to this position after the rotation is complete.Choose the algorithm that you would like to use for your computer program. Youmay use the simple algorithm described above or your own idea.JournalUse Import JPEG to create a Journal page showing your solar panel car.Create a page using the Describe template and write an explanation of thealgorithm you will use for finding the brightest parking position.ProgramUse Level 4 or 5 to write the program. You can use a container to store thevalue of the light sensor reading. To compare the current value of the lightsensor to an earlier one, use the Light Sensor Fork, wiring the container holdingthe earlier value into Compare.Download the program to your car and run it. If your program did not work asyou expected, modify it and try again.UploadOnce your car and program are working to your satisfaction, upload the data tothe computer.ProgramWrite a simple Pilot program that takes a light sensor reading every hundredth ofa second while the car turns a circle. Run the program to collect additional data.©2002 The LEGO Group. LEGO, Invent & Investigate and RCX are trademarks of The LEGO Group.This page may be photocopied for non-commercial educational use. All other rights reserved.2

UploadAdd a new page and upload the data from the Pilot program as well. Examiningthis data allows you to check that your car found the brightest light.Note: If you used an algorithm in which your car made a complete rotation, thenreturned to the brightest spot, you can just compare the data from your first andsecond rotations to see if your car found the brightest light.©2002 The LEGO Group. LEGO, Invent & Investigate and RCX are trademarks of The LEGO Group.This page may be photocopied for non-commercial educational use. All other rights reserved.3

ViewUse Compare in the View area to examine the data from your car and from thePilot program. Look at the maximum value of each line. Did your car find thebrightest spot?JournalUsing the Describe template to write a conclusion to your experiment. Developanswers to these questions:1) Did your system optimize the available light?2) How could you improve your car and program if you had more time?PresentCreate a presentation of your experiment containing the following pages: Journalpage describing the car and algorithm, Program page, Data page(s), Journalpage of conclusions.©2002 The LEGO Group. LEGO, Invent & Investigate and RCX are trademarks of The LEGO Group.This page may be photocopied for non-commercial educational use. All other rights reserved.4

Teacher’s Notes for Here Comes the SunLEARNING OBJECTIVES________________________________________________________________Students will understand:ü How to write a computer program that includes sensors.ü What an algorithm is and why it is useful.ü That, through experimentation, a value (such as light intensity) can beoptimized.ü That sensor readings provide feedback to control the behavior of a device.DISCUSSION________________________________________________________________This activity can be used in a number of different ways. For example, thestudents could be given plans for building the car and could concentrate onprogramming it. Or, students could be given one or more algorithms to programand test, rather than inventing their own.Building IdeasThe car can be built using one or two motors. The student handout assumes thatthe students will build their own two-motor cars. Alternatively, they can be givenbuilding plans for single-motor cars. This design will allow the car to go forwardor turn using just one motor.Sample building idea for a one-motor car:©2002 The LEGO Group. LEGO, Invent & Investigate and RCX are trademarks of The LEGO Group.This page may be photocopied for non-commercial educational use. All other rights reserved.5

If extra motors are available, the students can design their own two-motor cars.One possible car is shown below.Sample building idea for a two-motor car:Programming IdeasThe simple algorithm outlined in the student worksheet should be understandablefor students. However, it may cause the car to stop in a bright area which is notthe brightest possible position because this algorithm has no way of checkingwhether the bright spot it has found is just a local maximum.Here is a more sophisticated algorithm: The car rotates 360 degrees, finding andstoring the highest light value on its first rotation. Then it rotates a second time,stopping when the light sensor reaches this value again.If you choose to have students develop their own algorithms, you may want tobrainstorm ideas as a class and discuss each algorithm’s viability before thestudents begin programming.©2002 The LEGO Group. LEGO, Invent & Investigate and RCX are trademarks of The LEGO Group.This page may be photocopied for non-commercial educational use. All other rights reserved.6

Sample ProgramsHere is one possible solution for the simple algorithm: The car turns until the lightdims. Then the car returns to the location of the previous reading.Here are two possible solutions for the more complex algorithm: The car rotates360 degrees, finding and storing the highest light value. The car rotates asecond time, stopping when the light sensor reaches this value.Version 1. This solution uses the Timer Fork, which is only available inROBOLAB 2.0 Investigator Program Level 5.©2002 The LEGO Group. LEGO, Invent & Investigate and RCX are trademarks of The LEGO Group.This page may be photocopied for non-commercial educational use. All other rights reserved.7

Version 2. This version uses a Loop instead of the Timer Fork. This program canbe written in Level 4. This program is harder to understand and use than Version1. The number of loops needed for the car to complete one rotation must befound by trial and error.Here is program for capturing light sensor readings every hundredth of onesecond.©2002 The LEGO Group. LEGO, Invent & Investigate and RCX are trademarks of The LEGO Group.This page may be photocopied for non-commercial educational use. All other rights reserved.8

Testing the carsThe more complex algorithm works well in a wide range of settings as long as thelight conditions remain constant while the car is turning. The simple algorithm, byit very nature, is much more sensitive to shadows, glare, and other problems withthe lighting. It works best in a dim room with a single light source near the car,such as a reading lamp or a powerful flashlight.ExtensionThe position of the sun changes during the day. Modify the car so that if the lightshifts while it is parked, it will rotate to find the new brightest spot.Add just three commands to the original program for a solution to the extensionAt the end, right before Stop Data Logging, add a Wait for Dark icon followed bya Jump. Place the corresponding Land near the beginning, right after Start DataLogging.©2002 The LEGO Group. LEGO, Invent & Investigate and RCX are trademarks of The LEGO Group.This page may be photocopied for non-commercial educational use. All other rights reserved.9