From DT Online
Multiple gears can be connected together with one or more Idler Gears.
If there are an odd number of gears, the output rotation will be the same direction as the input. If there are an even number, the output will rotate in the opposite direction to the input.
Features and Applications
Note 1: Neither the number of idler gears nor the number of teeth on each idler gear affect the overall Velocity Ratio or Mechanical Advantage which are both governed purely by the number of teeth on the first driver gear and last driven gear.
Note 2: If both first driver gear and last driven gear has the same number of teeth, they will rotate at the same speed, however if they have different numbers of teeth then the gear with fewer teeth will rotate more quickly - i.e. the Velocity Ratio (or ‘Gear Ratio’) of a pair of meshing gears is given as the Number of Teeth of the Driver Gear divided by the Number of Teeth of the Driven Gear. The Mechanical Advantage (or ‘Torque Ratio’) similarly is given as No. of Teeth on Driven divided by No. of Teeth on Driver.
|Windmill - the blue gear is driving and the orange one is driven. The two small gears are idlers. Use the pink arm to stop or reverse the orange gear's rotation.|
Click top left to enlarge