Video Transcript

Hello again, this is Janette and Joe with Groschopp and this is the ninth video in our “How to Choose an Electric Motor” series. We’re going to take everything we’ve discussed and apply it in three scenarios with varying levels of customized motors.

Any motor will work for most applications, but there’s usually only one or two types that are best. Sometimes the choice is clear, but other times you will need to weigh priorities.

First up is a cooling pump for an MRI machine.  The designers were looking for a minimum of 50,000 hours of operation with a goal of 100,000.

The pump was magnetically coupled to the motor, giving the motor a nice, smooth load with low vibration, but a standard motor was having trouble meeting the life specifications.

Let’s look at the motor reference chart.

Remember the importance of prioritizing your Application Criteria?  That’s what we’ve done here, highlighting the characteristics that meet the application requirements.  A brush-type DC motor wouldn’t meet the life requirements, but the AC and BLDC motors would meet or exceed all the criteria.  Since the application didn’t need the high starting torque or variable speed of a Brushless DC motor, the AC motor was the cost-competitive solution.

With the help of Groschopp engineers, a permanent split capacitor AC motor was chosen.  We worked with a bearing manufacturer to choose a lubricant and a method for securing the outer bearing race to increase its life and the life of the motor.  We also realized that capacitor life could be an issue. A low-cost solution was found by selecting a standard capacitor with a higher voltage rating.

Let’s move to the next example. A tool manufacturer was designing a Cellulose Insulation Blower that homeowners could use themselves.

This unit needed to be portable, compact, and lightweight.  The tool required a one-and-a-half horsepower motor to drive both the high speed blower fan and the insulation agitator.

The manufacturer had already designed the system around a standard motor, but was having failures because the motor couldn’t stand up to the high vibration levels.

An additional challenge of this application was to keep the motor operating within the 15 amp current limit so it could be plugged into an average household outlet.

Let’s look at the quick reference motor chart again.  

Occasionally we come across an application where none of the motor types meet all of the application criteria.  This is when prioritizing is essential.  In these situations we decide which criteria are most important, and go with the motor that will meet the highest priority items first.

Maintaining the required power and speed while keeping the package size small was critical to the success of this project.  This made a universal motor the clear choice.  Although the customer preferred a quieter motor style, other performance characteristics were more important.

A standard frame size was used by designing a housing and foot mount to make a drop-in replacement for the existing motor. A more robust commutator was also used to limit vibration.

The customer saw a sharp reduction in failure rates plus a good increase in service life with the new motor design.

These two applications are prime examples of this simple truth:  you don’t have to settle for an off-the-shelf motor to use in your product. Simple modifications can be made to a standard motor to create a custom design for a non-standard application.

Our final example comes from the automotive industry so you can be sure reliability is essential.  

The motor is used on a automatic transmission for motor coaches. Failure of this motor would leave the vehicle stranded causing a potentially dangerous situation for passengers.

The application required a high performance gear motor with a failsafe system built-in.  The customer envisioned a motor with a “back up” winding inside the armature that could be engaged in the event of a primary winding failure. In addition, the motor is exposed to grit, water, salt and other environmental factors, so it needed to be well protected.

If you look at the highlighted quick reference chart, you’ll see it looks like there’s only one motor that meets all the application criteria, but in this case the data is a bit deceptive.  The chart suggests that a brushless DC motor would be the ideal choice, and in terms of performance it was.  Brushless DC motors have high starting torque and naturally run on DC power, but the motor would’ve required a fairly expensive control that wasn’t appropriate for this application.

A significant factor that lead us to a DC motor solution was the intermittent run time of the motor with very short “on” times.  With the short duty cycle of the application, there were no concerns about the DC motor brushes wearing out, even in a long-life application.

The final solution was a DC right angle gearmotor with a two-commutator armature and custom designed gear housing.  This motor was tested extensively throughout the design cycle by both Groschopp and the manufacturer and it continues to be tested extensively throughout production.  There are hundreds of thousands of these motors on the road today with minimal failures.

This is a great example of a “blank sheet” custom design.  Although a standard frame size was still used, the IP rating, custom gear housing, and fail-safe requirements called for a fully custom design.

Coming up is the last video in our “How to Choose an Electric Motor” series. We’ll be discussing some of the engineering tools we’ve developed to help make motor selection less daunting. For more information about Groschopp, to read more case studies or find out about our products, check out our website at www.groschopp.com.