What is a Stepper Motor Driver?
A Stepper Motor Driver is the driver circuit that enables the stepper motor to function the way it does. For example, stepper motors require sufficient and controlled energy for phases in a precise sequence. Due to this, stepper motors are considered more advanced than the typical DC motor.
Despite what may seem to be an uber complicated system, it can be built with a few transistors. By organizing their on and off functions in the proper manner, the system is able to sufficiently power the phases, and the motor is able to step through the process. A unipolar driver can be made within a decent budget. It is important to remember that this driver will only be able to power unipolar motors. If you wish to power a bipolar motor, you will need two full-bridges. This enables the system to return the current to the steps. These can prove to be more challenging to make, but you can purchase H-bridge chips to ease the process.
How Do Stepper Motor Drivers Work?
Stepper motor drivers rely on input from a separate source in order to function and create an output.
The following four signals control the motor:
- CLOCK: The clock signal gives the stepping command.
- RESET: Puts the final level signals in a defined start position.
- DIRECTION: Determines the sense of rotation of the motor axis.
- HALF/ FULL: Decides whether to operate in full or in half-step.
A cheap way to power a simple stepper motor is through a microcontroller. This is sufficient since these drivers only need a couple signals to operate. The first is a step signal and the second, a direction signal. The latter, when at logic high +5V, tells the motor the direction to work in. When the signal is low (GND) it goes in the opposite direction.
A full-step typically needs two rectangular signals in quadrature. Depending on the leading phase, the axis of the motor will either rotate clockwise or counter-clockwise. The rotation is proportional to the clock frequency, which controls the pulse on the line. This is the GND and +5V that was referred to earlier. So depending on the step resolution setting dip switches, the motor will go from one step position to the next. For example, if it is set in full-step mode, a full step will be taken, and a half a full step if the motor is set to half-step mode, and a quarter step for quarter mode, and so on.
Due to inertia, you must ramp pulses up and down in order to keep in sync with the magnetic field. Otherwise, the motor can stall. The ramp must also be smooth and have little to no movement in order to prevent the motor from stalling.
How Do You Pair Drivers with Motors?
It is crucial that you match the driver to the correct motor. If done incorrectly, the motor performance will not be sufficient, or it can even damage either portion or both.
When looking into matching motors and drivers be sure to consider voltage limits and the maximum current the driver can supply. Be sure to consider the “continuous” current rating and not the “peak” current rating, since they are not applicable to stepper motors. As for the motor, make sure that it can take the amps per phase and resistance per phase that the driver is providing. Also, the continuous current rating of the driver should be larger than the current rating of the motor.
Frequently, the voltage is stated but not always. You can use Ohm’s law to calculate it and ensure your process yields productive results. Multiply this by 20 to the get the max operating voltage of the motor driver. If the coil voltage is not provided, the square-root of the motor’s inductance (mH) can be multiplied by 32 to get the power supply voltage.
This is illustrated below.
For example, if the motor specifications shows the rated voltage is 3V, (3V* 20= 60V) it is safe to drive the motor with a driver of a maximum 60V operation voltage.
Example 2, if the motor specifications shows the phase current and resistance is 5A and 0.6ohms, (5A * 0.6ohms = 3V * 20 = 60V).
Example 3, if the motor specifications shows the inductance/phase is 2.5mH ((√2.5) * 32 = 50.6V), you are safe to use a motor with a 50V operating driver. Implementing an inductance value of the phases gives a conservative voltage rating, as it is a very accurate calculation of maximum power supply voltage.
Driving a Stepper Motor Does Not Have to be Complicated
Though the setup process for a stepper motor may seem complex, with patience and the right guide, the process can be fairly simple. Utilizing a microcontroller is an efficient way to drive a motor because a driver only needs a few signals to operate. Pairing motors with drivers can also be easy. By establishing the continuous current rating, the amps per phase, and by using Ohm’s law to calculate voltage, you can successfully pair your motor and driver.
By pairing a driver with a stepper motor, you will be able to send currents to the motor to ensure that it operates in the manner you wish. With this precision established, you can now complete projects that require strict speed control and accuracy.