Bevel Gears
Bevel gears turn rotary motion through 90 degrees. Remember, you don't have to draw the gears in detail you can represent them using simple diagrams as shown.

One of the main reasons for having gears and pulleys other than to change the way in which things move is to change the speed at which they move. One of the wheels is always connected to a power source such as a motor and this is referred to as the DRIVER. The one which is connected to the driver, either by a belt or teeth is called the DRIVEN.
Once we know which is the driver and which is the driven and if we know how big the wheels are (if it is a pulley) or how many teeth they have ( if they are gears) we can begin to work out the GEAR RATIO or the VELOCITY RATIO.
Look at the formula :
                                     DRIVEN (size of wheel for a pulley, No. of teeth for a gear)
VELOCITY RATIO =--------
                                      DRIVER (size of wheel for a pulley, No. of teeth for a gear)
                                                                 DRIVEN
This formula can be shortened to  VR= --------
                                                                 DRIVER

When you make the calculation you are left with a fraction which is then converted into a ratio.