1. Power Transfer using GEARS Dean Celini Mentor FRC Team 1322 9/10/2016

2. A gear is a rotating part having teeth that can mesh with another toothed part. More than one gear in mesh can produce a mechanical advantage or ratio change. Gears in mesh can change the torque, speed and direction of an input power source such as an electric motor. What is a Gear?

3. Mechanical Advantage and Torque

4. Intpforum.com What is mechanical advantage? Archimedes recognized the power of mechanical advantage

5. Fulcrum Effort Load Effort Arm Load Arm 500 lbs 50 lbs If the teeter totter is centered on the fulcrum, the Effort Arm Length is the same length as the Load Arm. There is no mechanical advantage and the smaller bear will be lifted up because the big bear is 10X heavier in weight Big Bear weight Little Bear weight = 500 lbs 50 lbs = 10 times heavier Lever Principles A Teeter Totter is an example of a lever and mechanical advantage

6. Fulcrum Effort Load Effort Arm Load Arm If the effort arm length is longer than the Load arm, a mechanical advantage is created. Lever Principles A lever can be used to provide a mechanical advantage to lift heavy things

7. Lever Principles It the effort arm is long enough, the lighter object will be able to raise the heavier one This can be calculated using the lever rule: Load X Load Arm Length < Effort X Effort Arm Length 500 lbs X Load Arm < 50 lbs X Effort Arm 500 lbs < Effort Arm 50 lbs Load Arm If the effort arm more than 10 times longer than the load arm the small bear will lift the big one 10 < Effort Arm 1 Load Arm Fulcrum Effort Arm Load Arm

8. Lever Principles R1 R2 Gears can be thought of as levers, the size of the gears will effect the mechanical advantage R2R1 Load Gear 1 Load Gear 2 If R1 and R2 are the same size there is no mechanical advantage. When the gears are different sizes(R1 ≠ R2) it will effect the mechanical advantage of the gearset. Lever For example: Mechanical advantage can be used on a robot to increase its ability to push or lift heavier objects

9. Levers are used to create another type of mechanical advantage known as torque. Torque is the tendency of force to rotate an object about an axis. Torque can be thought of as a twist to an object, such as tightening a bolt. What is Torque

10. Torque is found by multiplying the force applied by the length of the lever. Torque= Force x Lever Length The amount of force needed to apply a given torque can be reduced by increasing the length of the lever Torque What is Torque

11. Gears and Torque Gears create torque similar to a lever Radius Torque Force Torque is found by multiplying the force applied by the radius of the gear. Torque= Force x Gear radius

12. Speed

13. Gears and Speed Typically gear rotational speed is expressed as RPM or revolutions per minute Revolution is one complete rotation of a gear What does RPM mean, it is the amount of time it takes the gear to rotate one complete revolution. The higher the RPM the faster the gear spins and the lower the RPM the slower the gear spins. For example: A gearset that increases the RPM can be used to make the robot move faster

14. More than one gear in mesh can produce a mechanical advantage or ratio change. Sizing of gears will provide ratio change between the driving and driven gear. When two gears are in mesh, direction of rotation will change Simple Geartrain Input(Driving) gear rotates clockwise Output(Driven) gear rotates counter clockwise

15. Gear Design Pitch Diameter Root Diameter Circular Pitch Center Distance Outside(Tip) Diameter The green circles are known as the pitch circles. The pitch circle of a gear is very important as it is used to determine the center distance between gear shafts and can be used to determine the gear ratio

16. Gear Ratio = Number of teeth on output gear Number of teeth on input gear Simple Geartrain When the input gear is smaller in diameter than the output gear, the geartrain will increase torque and lower speed This is called an under drive gear set On an under drive gear set the Gear Ratio will be > 1 input Output Speed Ratio = Number of teeth on input gear = 1 Number of teeth on output gear Gear Ratio For Example: A robot with under drive gearing will tend to move slower but be able to push objects easier

17. Gear ratio = Number of teeth on output gear = 100 = 5 Number of teeth on input gear 20 1 Simple Geartrain Calculate the Gear Ratio and Speed Ratio when a 20 tooth input gear drives a 100 tooth output gear input Output Speed ratio = Number of teeth on input gear = 20 = 1 Number of teeth on output gear 100 5 Ratios are more commonly expressed as Gear Ratio => 5:1 Speed Ratio => 1:5

18. Output Torque= Input torque X Gear Ratio Output Speed = Input speed X Speed Ratio Simple Geartrain Calculate the output torque and speed of a geartrain with a Gear Ratio of 10:1 when the input gear is connected to a motor that produces 10 NM of torque at 2500 RPM input Output Output Torque = 10 NM X 10 = 100 NM Output Speed = 2500 RPM X 1 = 250 RPM 10

19. Simple Geartrain When the input gear is larger in diameter than the output gear, the geartrain will reduce torque and increase speed This is called an over drive gear set On an over drive gear set the Gear Ratio will be < 1 input Output For Example: A robot with overdrive gearing will tend to move faster but not have as much pushing power

20. Simple Geartrain A gear that is inserted between two or more other gears is called an Idler Gear. The idler gear will change the direction of rotation of the output gear. Idler gears help can help with spacing of the input/output gears Input gear Idler gear Output gear Input and output gears rotate in the same direction

21. Simple Geartrain An idler gear does not affect the gear ratio between the input and output gears. Don’t believe it….Let’s do the math! Gear A (input)Gear B (idler)Gear C (output) 12 Teeth36 Teeth60 Teeth Ignoring the Idler(Gear B)

22. Input Gear Compound Gear Output Gear Compound Geartrain If two gears are mounted on a common shaft then it’s a Compound Gear train.

23. To find the overall ratio for the compound geartrain, you mulitiply each simple geartrain together. For example, for the blue geartrain the output gear had 21 teeth and the input gear has 7 teeth. So the ratio is 21/7 or 3:1. For the green geartrain, the output gear has 30 teeth and the input gear has 9 teeth. So the ratio is 30/9 or 3.33:1. The overall ratio is 3 X 3.33= 10 or 10:1 Compound Geartrain Input(Driver) Output(Driven) 7T 21T 9T 30T

24. Worm Geartrain This type of gear train allows smaller package space than spur gear arrangement The worm always drives spur gear otherwise it will tend lock and jam It also changes the axis of rotation 90˚ The gear ratio is simply the number of teeth on the spur gear divided by 1 How can a worm geartrain be used on a robot?? Worm and spur gear

25. The rack and pinion geartrain is used to convert between rotary and linear motion The linear distance travelled by the rack in one rotation of the pinion gear can be determined by multiplying the pitch diameter by π(3.14) How are rack and pinion geartrains used on a robot?? Rack and Pinion Geartrain Heavy Duty Car Jack

26. Bevel Gears Bevel Geartrain Bevel gears are used to transfer drive through an angle of 90˚

27. Bevel Geartrain

28. FTC Gear Chart A Gear Chart is a handy reference to determine the effects of combining gears to form a gear set Remember: Under drive => Ratios >1, Over drive => Ratios < 1 To calculate output torque: Select an input and output gear, look up the torque ratio Multiply the input torque of the motor X torque ratio Output Torque = Input torque X Torque Ratio To calculate output speed: Select an input and output gear, look up the speed ratio Multiply the input speed of the motor X speed ratio Output Speed = Input Speed X Speed Ratio

29. FTC Gear Chart

30. THANK YOU !!