Motor Technology Selection: Evaluation Factors

Motors are usually an indispensable element of an application’s motion system. However, selecting the motor is rarely straightforward. Motor technologies all have characteristics that can impact a design in different ways, and  will determine whether you choose a brushless DC, coreless DC or stepper motor. Here are some key considerations to help you choose an optimal motor for your application.

A Case Study for Infusion Systems: Coreless Brush DC Motor Controls Nutrient Flow for Medical Feeding Pumps

Enteral feeding pumps are medical devices with a built-in tube used to deliver nutrients directly to the stomach of patients who are unable to safely consume food by mouth. The motor systems in these small, lightweight devices must also deliver sufficient torque to ensure continuous flow. The pumps also must be able to adjust flow rates — depending on the nutrition formula and patient needs — with accuracy and precision.

Portescap E-Store – Mini Motor Purchasing Available On-Line

Portescap has opened our new E-Store where you can find and purchase miniature motion technologies to suit any configuration, environment, or envelope. All Portescap motor technologies are available for review including Brushless DC, Coreless Brush DC, and Stepper (Can Stack, Disc Magnet, and Linear Actuator). You can view all motors within a technology and drive down to an individual motor page for a deeper evaluation. Once your selection is ready, you can purchase directly in the store if available or submit a request for a quote on the product.

Miniature Motor Selection on Demand

Portescap has released the MotionCompass™, a virtual environment that allows users to configure specific motion needs, compare performance across motor technologies and select an optimal mini motor solution. By inputting the basic application parameters (speed and torque), the MotionCompass generates motor recommendations for Brushless and Coreless Brush DC motors. All data is dynamically generated in real-time based on the product specifications. Users can compare performance metrics (Speed, Efficiency, Power and Current) and confirm the optimum solution for their application.

Precision Motors for Medical Infusion Systems

Overview

Portescap offers a range of motor technologies and accessories that enable innovation for Medical Infusion Systems. Whether it is a DC Coreless solution that utilizes its high efficiency to extend battery life or a stepper linear actuator that applies its mechanical precision for accurate dosing, Portescap marries the desired patient benefits to the infusion system requirements to create the optimum design. The addition of gearboxes and encoders provide flexibility in size, weight, and feedback for the motion solution.

As this series has shown, there are many factors to consider when choosing the optimum motion technology for your application.  Your application may have one or more primary factors, which would provide a starting point based on the best technology for that factor or factors.  But reviewing all the factors and how they impact the final product output will enable the ideal performance of our product.  Below is a summary table for the factors and the three motor technologies:

The type of application being designed will dictate different factors be considered for the motion solution.  Will the product be stationary?  Is the product mobile - being moved by an apparatus or on a person?  The typical usage of the product brings forth different factors to prioritize for your motion solution.

The next factor to review is the duty cycle for the motion solution in the application.  The duty cycle is defined as the ratio of the time the motor operates divided by the amount of total time for the cycle.  Typically, the motor does not run continuously but rather operates for a period (on-time) and then rests for a period (off-time).  The duty cycle affects the selection of the optimum motion solution, so it is important to understand the details and factors to consider.

Another factor to review is the accuracy required from the motion system in the application.  Is the motion continuous or incremental?  What is the resolution needed from the motor during incremental operation?  Does the motor need to have different resolutions for different points in the operation?

The next factor for consideration is the mechanical envelope for the motion system.  What is the space in the product that is dedicated to the motion system?  Is there flexibility on the diameter or length?

The next factor we will consider is the lifetime requirement of the motion system.  How many cycles must the motion system execute within the life of the product?  How many hours does that require from the motion system?

The next factor we will consider is the output torque requirement of the motion system.  What is the continuous torque requirement during operation?  Is there a peak torque for a limited time that needs to be considered?  Is the safety margin enough to compensate for the other factors in the application? 

One of the first factors to consider in your new product development is the output speed requirement of the motion system.  How fast does the motor need to rotate to drive the mechanism in the application?  And are there various speeds that need to be accommodated?  There are some general guidelines that will help you narrow down the technologies to consider:

As a design engineer, there is always excitement when you get to work on new product development. But when you get to the motion portion of the design, there are several technologies to consider, primarily Brushless DC, Coreless DC and Stepper. Which technology is best and where do you start? The challenge can be difficult as there are several factors to consider including output speed, torque, lifetime, mechanical envelope, noise, weight, cost and precision. It is not practical to analyze, purchase and test multiple technologies as this would be expensive and time consuming. Fortunately, there are guidelines that can assist in the initial review of the different technologies to narrow the selection.  

Portescap invites you to learn about the Ultra EC Brushless DC motors, which contain three optimizations to meet all application requirements. These two videos from Design World cover the 16ECP, balanced performance between torque and speed, and the 22ECS, optimized for speed and responsiveness.

In our blog post DC Coreless Speed vs Torque Curves, we talked about how to read speed vs torque curves and the linear relationship of speed and torque for a DC motor.  When comparing speed vs torque curves for various motors, the range of torque required in the application should be identified to ensure a proper comparison.  The curves will show the torque capability of the motor over the entire speed range, but the application torque range is typically limited to a narrow band.

Power density is the amount of power (time rate of energy transfer) generated per unit volume of the motor. The more powerful the motor in a smaller envelope, the higher the power density. Volume power density is an important consideration where space is constrained or where maximum output is needed in a fixed space. High power density enables miniaturization of applications and end devices or higher capability in current devices.

When selecting a motor for your application, one piece of reference information that can be used to make your selection is the speed vs torque curve.

As discussed in our collaboration post, early engagement leads to customized motors that are optimized for your application, but additional benefits can be realized utilizing Portescap’s Engineering expertise. Discussions will focus on the motor solution but routinely extend to the sub-assembly where the motor will reside. These early meetings can resolve challenges an Engineer may face around material selection and additional mechanical components.

Motor efficiency is the ratio between power output, which is mechanical, and power input, which is electrical.  Losses exist in all motors due to friction, heat, and materials, to name a few factors, so minimizing these losses is critical for applications that run off a battery.  The higher the efficiency of the motor, the longer the battery life during operation which results in longer time between charging.