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Five things to consider when choosing the best Geroler motor for your needs

When selecting a gerotor or Geroler motor there are many items to consider. Performance. Quality. Reliability. Support. Cost. Sounds pretty basic, but with the influx of new entrants into the market, it is clear not all manufacturers are the same. Choosing the wrong one could lead you down the wrong path of costly recalls and frustration. Before selecting your motor, let’s discuss what sets a gerotor or Geroler motor apart from the others on the market.

The gerotor motor, or generated rotor motor, has been around for decades. In fact, the first gerotor motor in Eaton’s Geroler® Portfolio was manufactured over 65 years ago. Soon after, Eaton invented the Geroler motor to meet the needs of the market and improve upon performance, reliability, quality and cost while still providing quality support.

geroter motor and Eaton Geroler motor comparison

Gerotor and Geroler motors use what is termed as the Orbit principle, which is what gives the motors their tremendous power density and compact size. A gerotor motor star has six teeth and seven lobes. The spaces among them are pressure chambers. Pump fluid flows into these pockets, creating high pressure in one chamber and low pressure in another. This creates an imbalance of forces, which causes the gerotor motor star to rotate, or orbit. A gerotor motor star orbits multiple times (image 1) – typically six to eight times depending on the specific star and ring geometry – for each complete single revolution within the outer ring. Eaton’s Geroler Portfolio uses the gerotor principle, but incorporate Eaton’s advanced Geroler technology (image 1). Geroler motors use rollers instead of lobes which reduce friction, wear, and improve low speed performance, extending the motors life.


Gerotor and Geroler motors deliver from 10 to 50,000 inch pounds of torque and can operate at speeds up to 2,000 RPM. Because of their simple design and compact size, they can be used in both mobile and industrial applications. However, they are ideal for mobile applications – especially agriculture, material handling and construction – because of their incredible power density.

Speed and torque requirements of the application will determine the size of a gerotor or Geroler motor. This will point users into what displacement (how much fluid is needed to turn one revolution) is needed. Speed and torque can be determined with the following basic motor equations. These are the starting points for finding the right sized motor.

Theoretical Torque (in-lbs) = CIR x Pressure differential/(2Pi)

Theoretical Speed (RPM) = GPM x 231 / CIR

So, when it comes to choosing which manufacturer’s gerotor or Geroler style motor to use in your machine, it’s just as simple as “Potato, pah-tato”, right?

Not really!

Five things to consider when deciding on the right gerotor and Geroler motor for your needs

1. Performance

It is always a good idea to ask for mechanical and volumetric efficiency data, but make sure the test data is over an extended period of time. Many manufacturers tune performance to peak in the first few hours of operation, but then degrade quickly. Performance that degrades quickly will not do your machine or your customer justice. Compare apples to apples. Hydraulic motor performance data is not standardized. Be wary of ratings and test data that do not include all the performance test parameters. “A performance rating without an oil viscosity is worthless.” Consider the performance of not just the product, but also the team of support. Will they deliver the product on-time? Will they provide support in critical times?

2. Quality 

Does the manufacturer have a history of consistent quality? Ask for the quality data and let the data speak. Some manufacturers do not have the process controls to ensure repeatable performance. Gerotor and Geroler motor grinding is not all the same. Grinding star profiles outside the capabilities of the form grinding machine will cause inconsistent results. What are the impacts of decreased product quality on your business’s reputation? Look for a manufacturer that focuses on using high-quality materials and follows industry standard manufacturing processes. Some manufacturers decrease the cost of their product by using inferior materials or speeding up processes like heat treating and form grinding. Consider warranty options. Does the manufacturer you choose have a 2-3 year standard warranty? If not, why?

3. Reliability

Reliability is quality over time.Your machine needs both. Look for a manufacturer that has a track record of being reputable. In this game it’s true that history is the best predictor of the future. Can you count on the manufacturer to be a leader in technological innovations? With the time, effort and resources you’re putting into developing your machine, make sure you’re partnering with a manufacturer that can help position your business as a leader in the industry. Consider where the motor is made. Is it American-made? Can you rely on the manufacturing materials used and standards practiced in the manufacturing location?

4. Support

Consider the long-term relationship of your business and the manufacturer. Will you get the support you need now and in the future? A product is only as good as the support system that surrounds it. Investigate the manufacturer’s options for additional support. Would you benefit from CAD modeling support or the creation of a custom solution? Remember custom solutions will differentiate your machine from the competitor. Do you just want a part or do you want a system of solutions? Some manufacturers have the know-how and resources to provide a custom system of solutions for your machine. Others can provide a singular part but may not have the capabilities to provide insight and recommendations on improving the machine’s design.

5. Cost

Obviously cost is very important. However cost is really a function of all the previous above items. Sacrificing the above items can provide a lower cost, but what will that do to your machine and your customer when issues arise? Some manufacturers try to keep costs low by having a “one size fits all” approach to their motor portfolio; however this compromise often leaves you with a solution that really does not work the way it should on your machine. Look for quality products that fits your application, rather than the cheapest option that will likely need to be replaced more frequently.


There’s certainly no shortage of things to consider when choosing the best gerotor and Geroler motor for your needs. As you consider your options, think of Eaton. With the broadest and most unique Geroler Motors portfolio in the industry as well as a team that provides unsurpassed support in modeling and custom solutions, Eaton is the manufacturer with the history and expertise you can feel proud to partner with.