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Think PhaseOverviewThis phase describes how to calculate the gearing for a robot drivetrain. It focuses on two mainmethods: calculating based on output speed, and calculating based on motor load.Phase ObjectivesAfter completing this phase, you will be able to:■■Determine how fast a wheel is rolling based on its rotational speed.Calculate the load on a motor based on wheel traction.Prerequisites and ResourcesRelated phase resources are:■■■Unit 5: Speed, Power, Torque, and DC Motors.Unit 6: Gears, Chains, and Sprockets.Unit 8: Friction and Traction.■Unit 9: Drivetrain Design 1.■A basic understanding of unit analysis.Required Supplies and SoftwareThe following supplies are used in this phase.SuppliesNotebook and penWork surface6■Unit 10: Drivetrain Design 2
Research and ActivityDrivetrain DesignIn Unit 9: Drivetrain Design 1, we discussed the factors that affect what makes a Drivetrain turn. Thisunit describes the Geartrain or Powertrain of the Drivetrain. The Geartrain represents the part of theDrivetrain that transmits power from the Motor to the ground.Wheel SpeedThe first concept to understand is figuring out how fast the robot moves across the floor based on howfast the wheel is spinning. For each time the wheel makes a full revolution, it rolls forward a distanceequal to its circumference. So if we calculate the circumference of the wheel, we know exactly how farthe robot goes per revolution.The circumference of a wheel is equal to its diameter multiplied by Pi (about 3.14).Once we know the circumference of the wheel, we can calculate how fast it is rolling based on itsrotational speed. In the example below, we assume the wheel diameter is 4 inches, and the wheel isspinning at 50 RPM. Let’s calculate how fast the wheel is rolling in inches per second. First, we calculatethe circumference:After we calculate the circumference, we can determine the ground speed based on the wheel RPM.Most of the following is just unit analysis and cancellation:Now we know the way to calculate ground speed from wheel RPM. If we know the <strong>VEX</strong> Motor has anoutput of approximately 100 RPM, and we know what reduction we want our wheel to spin at, we cancalculate the approximate gear reduction needed.Think Phase■7
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Page 4 and 5: PhaseCreateBuildStandardScience (NS
Page 8 and 9: Let’s say we have a 5 inch diamet
Page 10 and 11: Drivetrain DesignThe two methods li
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Page 14 and 15: Bevel Gear OptionsThe following opt
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