The first port of call is to understand what torque and speed you require. This will immediately give you a clear idea of what is possible. As a quick example, most stepper motors do not exceed 1000rpm. Therefore if you need to go above this you will need a brushed DC or brushless DC motor. Equally if you require positional accuracy or easy monitoring of number of revolutions for an application such as dosing or pumps, then a stepper will perform much better.
The second port of call is to understand what you require from the motor for it to work successfully in your application? For example, ask yourself the following questions;
If you require high positional accuracy stepper motors are by far the best choice as they can be micro-controlled to rotate 1/100th of a degree (or more) if required. If energy efficiency are more important to your project than positional accuracy then it is likely that a brushless DC motor will be best as these offer much greater lifespan than brushed DC motors and are more efficient than stepper motors. Once you have prioritised the most important characteristics required from the motor you can then make a decision. Below is a simple table with the pros and cons of each type of motor to help you further.
|Stepper (requires a stepper motor driver or stepper motor controller to operate)
|High positional accuracyVery fine control of speed and position.Relatively low cost and widely available.
|Not the most energy efficient.Max speed is typically 1000rpm. Not suitable for applications requiring higher speeds.As turning a stepper motor involves taking ‘steps’ around the 360 degree rotation (typically 200 steps per 360 degrees) they are not the smoothest. This can be improved using microstepping but a brushed DC or brushless DC motor will typically be smoother.
|Brushless DC (BLDC) (requires a brushless motor driver, sometimes known as brushless electronic speed controller (Brushless ESC) to operate.)
|Lightweight and energy efficient.Able to achieve speeds of well in excess of 10000rpm.Can be operated to maintain a constant speed under variable load.Exceptional lifespan due to no wearable parts (except bearings).
|Depending on your application and torque/speed/physical requirements, BLDC motors can be quite expensive. Prices are reducing all the time as more companies adopt them.Sensorless brushless motors can be difficult to start. This can be offset by using an intelligent controller with an inbuilt startup acceleration programme such as the Zikodrive ZDBL15.
|This is the traditional form of DC motor and has been around a long time.Typically very smooth to operate.Low costCan reach high speeds.Maintaining constant speed is possible if using an encoder.
|Lifespan is often poor as the brushes used to affect commutation can wear or burn out. This can also lead to a drop in performance over the life of the motor as brushes start to wear out and the motor operates less efficiently.Depending on the anticipated use cycle of the motor and the intended lifespan it can often be lower cost to use BLDC motors as these will require less maintenance and will maintain performance across lifespan. Positional control is virtually impossible.
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