Gear ratio
From Combat Robot
Typical motors used for robot propulsion,servos, or weapon drive do not produce sufficient torque to perform their function efficiently. A mechanical drivetrain involving gears, sprockets and chains, or belts and pulleys is used to multiply torque while reducing RPM proportionally. Note that since power is the product of torque and RPM, the overall power of the output is not effected, except for frictional losses.
Calculating the Ratio
For a single-stage gear reduction, divide the number of teeth on the output gear or sprocket by the number of teeth on the input gear or sprocket. For belt/pulley systems without teeth, the effective diameters of the pulleys are used.
Example: a 12 tooth input sprocket on the motor drives a 60 tooth output sprocket on the axle shaft. The gear ratio is 60:12, or (60/12):(12/12), equals 5:1. The left part of the gear ratio is the gear reduction factor.
Multiple stage reduction requires that you calculate each stage and multiply the grear reduction factors together. Two 4:1 reductions in series equals a (4*4):1 = 16:1 overall ratio.
If the gearbox is sealed, you may simply see how many turns of the input shaft are required to produce one turn of the output shaft. Seven and a half turns of the input for one turn of the output equals a 7.5:1 ratio.
See also: Optimum gearing.
