Vex Robotics Design System's Inventor's Guide

Speed vs. Torque

A motor can generate a set amount of power; that is, it can provide a specifi c amount of energy every second?this energy is most commonly used to make a wheel spin. Since there is only so much energy to go around, however, there is an inherent trade-off between Torque—the force with which the motor can turn the wheel—and Speed—the rate at which the motor can turn the wheel.

The exact confi guration of torque and speed is usually set using gears. By putting different combinations of gears between the motor and the wheel, the speed-torque balance will shift.

Gears

Gear Ratio
You can think of gear ratio as a “multiplier” on torque and a “divider” on speed. If you have a gear ratio of 2:1, you have twice as much torque as you would if you had a gear ratio of 1:1, but only half as much speed.

Calculating the gear ratio between a pair of gears is simple. First, identify which gear is the “driving” gear, and which is the “driven” gear. The “driving” gear is the one that is providing force to turn the other one. Often, this gear is attached directly to the motor axle. The other gear, the one that the driving gear is turning, is called the “driven” gear.

To fi nd gear ratio, you just need to count the number of teeth on the “driven” gear, and divide it by the number of teeth on the “driving” gear.