Gear Ratios

Calculations

The most used drive system on a first robot uses sprockets and chains. It is vital to the success of a robot to properly adjust the size of sprockets in order to obtain the maximum speed and power. Balancing speed versus power can be daunting but with a few basic guidelines it can be made easy. Let ‘s examine a couple things to keep in mind while choosing the right gear ratio . . .

Two Broad Types of

Sprocketsa)Driver Sprockets are

directly driven by a motorb)Driven Sprockets mesh

with the driven sprocket

Gear Ratio VelocityFirst, notice which sprocket has the

most teeth. This will be the sprocket that completes one revolution. Take the number of teeth on the driven sprocket and divide that number by the amount of teeth on the driver sprocket.

Driver Sprocket: 30 Teeth

Driven Sprocket: 10 Teeth

30/10 = 3:1 Ratio

Revolutions per MinuteTo

calculate the RPM output of a given gear ratio, take the velocity ratio and multiply that number by the RPM output of the motor source.

Ex. 1: Motor RPM (60 rpm) x gear ratio (3:1) = 120 rpm

Ex. 2: Motor RPM (100 rpm) x gear ratio (1:4) = 400 rpm

RPM with a Compound Gear

The easiest way to calculate RPM on a compound system is to split up the problem into two equations or pairs depending on the amount of gears

involved. After finding the ratio for each pair, multiply them together with the

motor RPM to get your final RPM. (see next slide for examples)

Ex. 1: This example involves 4 gears. Gear A- Driver Sprocket, Gear B and Gear C are Fixed, and Gear D. The motor RPM in this example will be 100 RPM.

Driver Sprocket-Gear A (30 teeth) / Gear B (10 teeth) = 3:1 Ratio

Gear C (20 teeth) / Gear D(50 teeth) = 2:5 Ratio

3:1 Ratio x 2:5 Ratio x 100rpm = 120 rpm

Ex. 2: This example also involves 4 gears. Gear A- Driver Sprocket, Gear B and Gear C are Fixed, and Gear D. The motor RPM in this example will be 60 RPM.

Driver Sprocket-Gear A (20 teeth) / Gear B (15 teeth) = 4:3 RatioGear C (50 teeth) / Gear D (10 teeth) = 5:1 Ratio

4:3 Ratio x 5:1 Ratio x 60rpm = 400 rpm