Within the kit of parts, FIRST provides each team with a number of such motors to be used in the construction and operation of their robot. Each motor features unique operating characteristics and behaviors that are governed by physics and understanding such characteristics is important for a team to choose the correct, most efficient motor to accomplish a given task.
For determining the efficacy of a motor in performing a certain task, there are certain values describing that motor that are necessary for performing some calculations.
- Stall torque is the maximum torque value a given motor can produce. When a motor is said to have stalled, that indicates that its rotary motion has stopped, having reached equilibrium with its environment. Stalling a motor is not positive because of its effect on current draw. This is measured in units such as Newton_meter (N_m), inch_lbs (in_lbs.), etc.
- Stall current is the value of electrical current drawn by a motor in a stall condition. This value often exceeds the limits on current use imposed by FIRST and can result in damage to the motor and other electrical components. This is measured in units of amperage (A).
- Free speed is the highest speed at which the shaft rotates, measured when the force acting upon said shaft is as close to zero as possible. Zero force acting upon a shaft is impossible, however, due to environmental factors such as gravity and friction. Free speed is measured in revolutions per minute (RPM) or radians per second (rad/s).
- Free current is a measurement of the current drawn to the motor under a minimum load condition, previously defined as its ‘free speed’. This is measured in units of amperage (A).