1. Gears and Speed Introductory Presentation

2. Opening Activity In Get in Gear, we changed the gears on our robot to adjust its speed. If we want to change the speed more precisely however, we need to know exactly which gears to use.

3. Opening Activity What is the difference between the driving gear and the driven gear? What should you do to make the driven gear turn faster or slower? Explain :

4. Opening Activity Our driving gear is connected to our motor and is responsible for spinning the driven gear, which is connected to the wheel. What is the difference between the driving gear and the driven gear?

5. To make our robot move faster, we made our driving gear bigger and/or our driven gear smaller. To slow it down we swapped the two. Opening Activity What should you do to make the driven gear turn faster or slower?

6. Preview: Gear Ratio The relationship between the sizes of your driving gear and driven gear is called the Gear Ratio.

7. Preview: Gear Ratio A gear ratio is the number of turns your driving gear must make in order to turn your driven gear once. Gear Ratio Implies… 1:2 or ½ The driving gear must make ½ a turn to turn the driven gear once 1:1 or 1 The driving gear must turn once to turn the driven gear once 3:1 or 3 The driving gear must turn 3 times to turn the driven gear once

8. Preview: Gear Ratio Lets consider the following example for the rest of the presentation. Here we have an 8 tooth driving gear and a 40 tooth driven gear. 8 Teeth 40 Teeth Driven Gear Driving Gear

9. Preview: Gear Ratio Lets look at each tooth as a push. A 1-tooth push moves 1 tooth, and a 2-tooth push moves 2 teeth. If we rotate our 8-tooth gear once, which is an 8-tooth push, well push 8 teeth on the 40-tooth gear. 8-tooth push

10. Preview: Gear Ratio Suppose we want to turn the 40-tooth gear one entire revolution. We have to turn our 8-tooth gear enough times to create a 40-tooth push. Well, this is easy because: 5 x 8 = 40 So we just have to turn our 8-tooth gear five times to create a 40-tooth push. This is enough to turn the big gear once.

11. Preview: Gear Ratio Whats our definition of Gear Ratio?A Gear Ratio is the number of turns your driving gear must make in order to turn your driven gear once. Gear Ratio = 5 The Gear Ratio for the example was 5, so this means that our driving gear must turn 5 times to turn our driven gear once. What is our example Gear Ratio? Verbally explain what our example Gear Ratio implies.

12. Preview: Gear Ratio For our 8-tooth and 40-tooth gears the Gear Ratio is 5. Does this mean our Gear Ratio can also be written 8:40 ? 8:40 means 8/40, which equals 1/5. This implies that our driving gear has to turn 1/5 of a rotation to rotate our driven gear once. This is obviously wrong from what we know. NO it does NOT!

13. Preview: Gear Ratio We already discovered that our driving gear must turn 5 times to turn our driven gear once. So a Gear Ratio of 1/5 is clearly incorrect. 40:8 Because this means: 40/8 = 5 We can write our Gear Ratio like this:

14. Preview: Gear Ratio You can calculate Gear Ratio by dividing the number of teeth on the Driven Gear by the number of teeth on the Driving Gear. # teeth on Driven Gear # teeth on Driving Gear Gear Ratio =

15. Preview: Gear Ratio Now that weve cleared that up, it makes sense that our equations to calculate Gear Ratios would look like this: Gear Ratio = Driving axle turns Driven axle turns Gear Ratio = # of Driven Teeth # of Driving Teeth 8 Teeth 40 Teeth Driven GearDriving Gear

16. Preview: Gear Ratio From our example we get: Gear Ratio = # of Driven Teeth = 40 # of Driving Teeth = 8 Gear Ratio = Driving axle turns = 5 Driven axle turns = 1 = 5 8 Teeth 40 Teeth Driven Gear Driving Gear

17. Preview: Gear Ratio Find the Gear Ratios for these examples: 1.A 5-tooth gear driving a 45-tooth gear. 2.A 3-tooth gear driving a 12-tooth gear. 3.A 12-tooth gear driving a 3-tooth gear. Gear Ratio = 9 Gear Ratio = 4 Gear Ratio = 1/4

18. Preview Now you have the necessary knowledge to get started in the Gears and Speed Investigation. Good Luck!