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EvaluationChallengeIn this challenge, you measure the speed of the drivetrain you built in Unit 10: DrivetrainDesign 2 > Build Phase.Instructions Figure 11. Place two strips of masking tape on the floor, 20’ apartfrom each other. (If you do not have 20’ of open space,use whatever space you have, and carefully measure thedistance between the tape lines.)2. Place your robot approximately 5’ behind one of thetape lines.3. Turn your robot and receiver on.4. Drive your robot at full speed towards the two tape lines.Start timing when the front of the robot passes the firsttape line, and stop timing when the robot passes thesecond tape line. See Figure 1.5. Record the time in your engineering notebook.6. Repeat this test 10 times.7. Calculating Average Speed: 1. Calculate the average timeof your trial. 2. Using the average time, calculate theaverage speed of your robot. Remember, the equationfor speed is: Speed = Distance / Time 3. Record thesecalculations in your notebook.Engineering NotebookUsing the equations from the Unit 10: Drivetrain 2 > Think Phase, and lessons on gearing from theUnit 6: Gears, Chains, and Sprockets > Think Phase, calculate the theoretical speed of your drivetrainin feet per second. Use 100 rpm as the free speed of a <strong>VEX</strong> motor. Be sure to show all your calculations.Remember, the free speed of a wheel is equal to the free speed of the motor, multiplied by thereduction ratio of the gearing. Be sure to convert the free speed of the wheel from revolutions perminute to revolutions per second.Now that you know how many times your wheel turns in one second, by multiplying this value by thecircumference of the wheel, you can calculate how far your robot moves in one second.Compare the values of your measured and theoretical speeds.■■Why are they different? List at least five factors that may have caused the difference.Why do you think you were asked to start the timing only after the robot had driven for a distance?PresentationPresent your findings on the differences between measured and theoretical speeds to the class.28■Unit 10: Drivetrain Design 2
STEM ConnectionsBackgroundA pitching machine works by using a spinning wheel to shoot a ball towards the plate at a given speed.The wheel’s direction of rotation is towards the batter. A ball is dropped though a tube and when itmakes contact with the surface of the spinning rubber wheel it is hurled forward. The speed of thepitch is controlled by changing the RPMs of the motor.Science1. What material should the spinning wheel be made of to grip and fling a baseball most effectively?2. Would you change this material based on the type of ball you are pitching?Technology1. You have to make a pitching machine with a motor that runs at only one speed.2. What other parts of the machine can you adjust to change the velocity of the pitch?3. How can you calculate the speed of the pitch before you put the ball in the machine?Engineering1. What scientific forces are involved in the pitching motion of the machine?2. Consider the motion of the wheel and the interaction of the wheel with the ball.STEM Connections■29
Page 1: 10:Unit10Drivetrain Design 2 UnitIn
Page 4 and 5: PhaseCreateBuildStandardScience (NS
Page 6 and 7: Think PhaseOverviewThis phase descr
Page 8 and 9: Let’s say we have a 5 inch diamet
Page 10 and 11: Drivetrain DesignThe two methods li
Page 12 and 13: Technical OverviewThe following Aut
Page 14 and 15: Bevel Gear OptionsThe following opt
Page 16 and 17: Create the Bevel GearsIn this secti
Page 18 and 19: 5. Press E to start the Extrude too
Page 20: Reduce the Weight of the GearIn thi
Page 23 and 24: 16. Click Circular Pattern.17. To c
Page 25 and 26: ActivityIn this activity, you desig
Page 27: Amaze PhaseOverviewIn this phase, y

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