Why stepper motors needs stepper controller to drive it?

As the name implies “stepper”, these motors are different from regular brushed DC motors. Driving stepper motors are bit more complicated than driving regular brushed DC motor. These complexity comes through stepper motors winding mechanism. So steper motors needs to supply pulse current and this current is generated stepper motor driving board. Stepper motors require phased pulses of current to make them rotate by control steps. In order to do this, we need to send pulse current of varying polarity to its multiple windings. The speed of the motor is determined by the frequency of the pulses. The direction of motor motion is determined by the phasing between the pulses being applied to the various windings. Due to this multiple windings, stepper motors require stepper controllers to energize the phases in a timely sequence to make the motor rotate. With a computer controlled stepping we can achieve very precise positioning and/or speed control. For this reason, stepper motors are the motor of choice for many precision motion control applications including CNC machines.

Stepper motors windings energizing phases in a timely sequence process as shown below.

Positive voltages(+) represent by red
Negative / ground (-) represent by blue

energising-phases

Image source:  www.solarbotics.net

The simplest type of stepper motor driver can be built with a multiple transistors. These controller circuits are simply switched on and off current in sequence to energize the winding phases and step the motor.

simple-unipolar-driver

stepper-driver-transistor

stepper-driver

Small to medium entry level stepper motor controllers for stepper motors

I have been using prebuilt stepper motor controller breakout boards for my various projects. Most of the 3D printer makers know about these stepper motor drivers and it’s characteristics. These breakout boards are very small in size and relatively very cheap. I hope to write a separate blog post in the future by explaining in detail how to use these drivers in small level CNC machines.

  • DRV8825 Stepper Motor Driver Carrier, High Current
  • A4988 Stepper Motor Driver Carrier, Low Current

Advanced stepper motor controllers for small to medium level CNC machines

Some stepper motor controllers have been built to achieve industrial level stepper controller performance for small to medium level CNC machines. The gShield and TinyG CNC stepper controller boards are few examples. These boards feature constant-current drivers, that can be tuned to deliver maximum torque and speed from your motors.

The TinyG CNC features an on-board G-code interpreter and 4 motor outputs, making this a complete embedded solution for a small to medium sized 4-axis CNC machines.

These advanced, high-performance boards contains sensitive electronics and more complex to work with, it’s required some experience and must follow documentation from manufactures. Details of these boards and their operation can be found in the TinyG Wiki and the Synthetos Forums.

Before you start to work with stepper motors and stepper motor driver controllers, you should know the specifications of the motor and stepper controller board. These are most critical because you might damage your electrical component by exceeding it’s rated current or you might not get the best performance from your motors or controller board. Best place to follow these specifications are from manufactures web site or product data sheets.

Know the Motor Specifications

Stepper motor parameters

  • Amps per phase – This is the maximum current that the motor windings can handle without overheating.
  • Resistance per phase – This is the resistance of each phase.

A Voltage rating is often stated. It is usually calculated from the two above – but not always. “Peak” current ratings are not applicable to stepper motors. Always go by the “continuous” current rating. It’s better to calculate yourself from the above parameters using Ohm’s Law

Know the Driver Specifications

The two most important parameters in the driver specifications are:

  • Voltage – The maximum voltage that the driver can supply to the motor.
  • Continuous Current – The maximum current that the driver can supply to the motor

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