Fundamentals of gearmotors

These A and F Series helical parallel shaft gearmotors and speed reducers from DieQua feature torque capacities up to 2,800 Nm (2,065 ft lb) for Series A, and up to 14,000 Nm (10,325 ft lb) for series F.

Gearmotors are combinations of an electric motor (either ac ordc) with a gear reducer integrated together into one unit. They can bebought direct from manufacturers as integrated units, saving designersthe effort of integrating separately purchased motors with gear reducers.

There are as many gearmotor types as there are combinations of electric motors and gears.

Motor type – these can be ac or dc, brushed or brushless, or permanent magnet. Often times the application will determine which motor is best suited for that particular task. In general, brushless dc gearmotors have really good speed regulation properties, so they’re usually preferred in applications requiring tight variable speed control. However, ac gearmotors have gotten better at speed control and they are now competitive with many dc gearmotors.

Gear type – here again, the application demands can help determine the best gear type. Is efficiency the most important parameter? Torque? For instance, planetary gears have high power density and are more compact than other arrangements. They also tend to cost more than other gear types. On the other hand, worm gears are prevalent in many gearmotors, especially right-angle gearmotors, but their efficiency ratings are lower than other gear types.

Another way to classify gearmotors is according to their horsepower rating; as either fractional or integral. An integral horsepower gearmotor is any motor with a horsepower of 1 and above, as opposed to fractional horsepower motors that are less than 1 hp. The design considerations for integral horsepower motors are fairly similar to fractional horsepower motors because the same types of parameters are important. So for instance, torque and speed matter in all cases.

Gearmotors are also differentiated by the output shaft orientation, with two standard types being parallel and right-angle arrangements. Beyond shaft configuration itself, other factors such as the type of gears used in the gearmotor determine performance.

Generally speaking, a right-angle gearmotor is less efficient than a parallel configuration. A typical right-angle gearmotor arrangement includes a worm gear assembly, which serves to translate the rotary motion of the motor by 90 degrees. In parallel-shaft gearmotors, the gear setup can take any number of forms, from helical and spur gears to complex planetary gear systems. In terms of gear efficiency, spiral bevel gears tend to have the greatest efficiency, followed closely by helical and spur gear types, all of which are in the range of 93 to 99%.

More demand for compact machine designs means that space considerations are an important design priority. So if the application calls for a right-angle gearmotor as the only one that will fit the design requirements without having to redesign the entire machine, then that’s the one to go with. Even if it sacrifices some efficiency, compactness and fit may be the more relevant design factors.

Other factors to consider include environmental factors such as temperature, IP rating for washdown or debris or spray etc., mounting configurations, as well as lubrication needs, among others.

Gearmotors can be designed specifically for particular applications. For instance, the Conveyor Series from Brother Gearmotors are double-sealed with an O-ring and feature high-grade grease for lifetime lubrication and a durable e-coat paint to withstand tough environments.

CONTINUOUS VS. INTERMITTENT DUTY

The classification of a motor as either continuous or intermittent duty revolves around the idea of duty cycle. That is, how long the motor is on and off. So the basic decision for determining continuous vs. intermittent duty is fairly straightforward. If the motor is switched on and runs continuously then the motor should be rated for continuous duty. If the motor is switched on for a short time or has a cyclic operation, then the motor can be rated intermittent operation and the motor has no efficiency requirement. As a rule of thumb, if the motor is running more than one hour continuously with no switching on or off during that time, then, in general, the application is continuous. If the motor runs for less than an hour continuously, then the application can be considered intermittent.

One reason this is so important is that if the wrong motor is selected (intermittent instead of continuous, for instance), the risk is that the motor could overheat, damaging the motor and/or other devices.

Some of the most common examples of intermittent applications include packaging equipment, metering pumps, palletizers and winders and coilers. Typical continuous applications range from bulk material handling conveyors to continuous flow pumps and continuous mixers.

A properly sized gearmotor with the right combination of motor and gearing can prolong operating life and boost overall design efficiency. Gearmotors also eliminate the need for couplings and potential alignment problems that come with those components. Such problems are common when a design includes the connection of a separate motor and gear reducer — which in turn increases the potential for misalignment and bearing failure, and ultimately reduces useful life.