Short Answer:

The step angle in a stepper motor is the angle the rotor moves per pulse received by the motor. It is calculated by dividing 360° (a full rotation) by the number of steps the motor takes to complete one full revolution. For example, if the motor has 200 steps per revolution, the step angle would be 360° divided by 200, which equals 1.8° per step.

The step angle is a critical factor in determining the motor’s precision and resolution. Smaller step angles allow for finer positioning but may require more pulses to complete a revolution.

Detailed Explanation:

Step angle calculation in a stepper motor

In a stepper motor, the step angle is defined as the angular displacement the rotor makes with each electrical pulse. Each pulse corresponds to a fixed mechanical movement, and the motor’s rotor shifts by a certain angle, which is determined by the number of steps per revolution. Understanding how to calculate the step angle is important for determining the precision of the motor’s movement and for controlling its motion in various applications.

1. Step Angle Formula:

The step angle (θ) is calculated using the following formula:

Step Angle (θ) = 360° / Number of Steps per Revolution

Where:

• 360° represents a full revolution (one complete turn).
• Number of Steps per Revolution is the number of discrete positions the rotor can take during a full revolution.

For example, if a stepper motor has 200 steps per revolution, the step angle would be:

Step Angle (θ) = 360° / 200 = 1.8° per step

This means that for every pulse sent to the motor, the rotor will move by 1.8°.

2. Types of Stepper Motors and Their Step Angles:

Different types of stepper motors have varying step angles, which influence their precision and application.

• Permanent Magnet (PM) Stepper Motors: Typically have a step angle of 1.8° or 0.9° (for higher precision).
• Variable Reluctance (VR) Stepper Motors: Often have a smaller step angle, such as 7.5° or 15°.
• Hybrid Stepper Motors: These combine PM and VR designs and can have even finer step angles like 0.9°, 1.8°, or even 0.45°.

Note: Step angles like 0.9° and 0.45° are achieved by using microstepping techniques, where the motor is driven in intermediate steps to provide smoother motion.

3. Microstepping:

Microstepping is a technique used to divide the step angle further. In this method, the motor receives more pulses than the typical step count. For example, in a motor with a 1.8° step angle, microstepping can divide this angle into smaller increments like 0.9°, 0.45°, or even smaller.

• Full Step: The rotor moves one full step per pulse (e.g., 1.8° per step).
• Half Step: The rotor moves halfway between two full steps (e.g., 0.9° per step).
• Microstep: The motor moves in very small steps (e.g., 0.45° per step), providing smoother motion.

Microstepping is typically used to achieve smoother motion, higher precision, and better control over the motor’s speed.

4. Factors Affecting Step Angle:

The step angle depends on several factors:

• Number of poles: The number of poles in the stator and rotor windings affects the step angle.
• Motor design: The construction and design of the motor, including the rotor and stator, determine the number of steps and step angle.
• Control method: Microstepping or half-stepping reduces the step angle and increases precision.
• Drive circuitry: The drive electronics also play a role in how finely the motor can be controlled.

Conclusion:

The step angle in a stepper motor is the angle the rotor moves per step and is calculated by dividing 360° by the number of steps per revolution. Smaller step angles provide finer positioning accuracy, which is important for precision applications. The step angle can be further divided using microstepping to achieve even finer control over the motor’s movement. Understanding how to calculate and control the step angle is crucial for applications requiring precise rotational control, such as robotics, CNC machines, and 3D printers.