Gears and Speed

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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
Explain

• 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?

4
Opening Activity
What is the difference between the driving gear
and the driven gear?

• Our driving gear is connected to our motor and is
  responsible for spinning the driven gear, which
  is connected to the wheel.

5
Opening Activity
What should you do to make the driven gear turn
faster or slower?
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.
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
12 or ½ The driving gear must make ½ a turn to turn the driven gear once
11 or 1 The driving gear must turn once to turn the driven gear once
31 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.

Driving Gear
8 Teeth
Driven Gear
40 Teeth
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
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.
What is our example Gear Ratio?
Gear Ratio 5
Verbally explain what our example Gear Ratio
implies.
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.
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 840 ?
NO it does NOT!

840 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.
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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.
We can write our Gear Ratio like this
408 Because this means 40/8 5
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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
Gear Ratio
teeth on Driving Gear
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
16
Preview Gear Ratio

• From our example we get

Gear Ratio Driving axle turns 5
Driven axle turns 1
5
Gear Ratio of Driven Teeth 40
of Driving Teeth 8
5
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Preview Gear Ratio

• Find the Gear Ratios for these examples
• A 5-tooth gear driving a 45-tooth gear.
• A 3-tooth gear driving a 12-tooth gear.
• A 12-tooth gear driving a 3-tooth gear.

Gear Ratio 9
Gear Ratio 4
Gear Ratio 1/4
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Good Luck!

• Now you have the necessary knowledge to get
  started in the Gears and Speed Activity.