Name:____________________________                                                                                                            Student ID:___________________

Date:_____________________________

Gear ratios:

Gear ratio: Ratio of how many times gear 1 turns to how many times gear 2 turns.

i.e. a 1:2 ratio means is you spin gear one once, gear two spins twice.

[number of turns of the driver]:[number of turns of the follower]

Gear ratios can be expressed in two equivalent forms: 

a:b  where a and b are integers (whole number)

1:c   where c can be any rational(fraction) number

To convert from a:b  to 1:c,    c=b/a.

Example 1:   first gear has 10 teeth and second gear has 20 teeth

If you spin gear 1 once, gear 2 spins _______ times

Gear ratio is  ____:____

Scale to integer form 

Gear ratio is  ____:____

Example 2:  first gear has 15 teeth and the second gear has 10 teeth

If you spin gear 1 once, gear 2 spins _______ times

Gear ratio is  ____:____

Scale to integer form 

Gear ratio is  ____:____

Another Approach

Counting gear teeth

Gear one has A teeth and gear two had B teeth

Simplify the fraction

Then the ratio is  X:Y

Example 3:  first gear has 3 teeth and the second gear has 12 teeth

A=_______                                                                                            B=________

                                                                                                       simplify, =

Gear ratio is  ____:____

Convert to 1:?

Gear ratio is  ____:____

Example 4:  first gear has 40 teeth and the second gear has 30 teeth

A=_______                                                                                                B=________

                                                                                                           simplify , =

Gear ratio is  ____:____

Convert to 1:?

Gear ratio is  ____:____

Gearing Up and Gearing Down

Gearing up : increasing the number of revolutions per driver rotation

                        Also increases the rpm  (rotations per min)

                        Gearing up occurs when a<b in the gear ratio a:b

                        Use: gives more speed

Gearing down (Gear reduction): reducing the number of revolutions per driver rotation

                        Also reduces the rpm (rotations per min)                                              

                        Gearing down occurs when a>b in the gear ratio a:b

                        Use: gives more power

Questions:  Is it gearing up or gearing down? (circle one)

Ex 1:  gear ratio:____:____                                                                            up     or    down

Ex 2:  gear ratio:____:____                                                                            up     or    down

Ex 3:  gear ratio:____:____                                                                            up     or    down

Ex 4:  gear ratio:____:____                                                                            up     or    down

Gear trains

When 3 or more gears are connected in a row, it is referred to as a gear train.

Only the first and last gear contribute to the gear ratio. 

Therefore, calculating the gear ratio will the same, only using the first and last gear.

Gear Ratios Worksheet

 Using the gears in the kit answer the following the questions.

 You will need the 40 tooth, 24 tooth, 16 tooth, and 12 tooth gears.  

  Express the ratios in the form you prefer.

Challenge:

Build a motorized cart to complete an obstacle course using a maximum of four motors. 

• construct two motor generators

• use two motors to power and steer your cart

• use two motors for hand cranks

• choose gear ratios to optimize the speed and control, on your cart and hand crank

• do not use your RCX

• test your design

THE COMPETITION WILL BEGIN 10 MINS BEFORE THE END OF CLASS.