The DC Planetary Gear Motor Vs. Spur Gear Motors

Two of the most common types of gear motors are the DC planetary gear motor and the spur gear motor. If you're unfamiliar with these two types of motors, it can be confusing to know which one to choose for your application, but choosing the right motor is crucial to getting the right performance from your application. Below is a brief overview of each type to help guide your decision.

Differences And Similarities Between The DC Planetary Gear Motor And The Spur Gear Motor

A spur gear motor will generally be simpler and less expensive than a DC planetary gear motor. Spur gear motors work best in low-torque applications. Torque is limited in these gears since each gear bears the entire load.

A DC planetary gear motor, on the other hand, shares the torsional load over multiple planet gears so it can works well when higher torque is needed. In a planetary gear motor, the input shaft drives the central (sun) gear, which then turns the surrounding (planet) gears. This arrangement allows each of the planet gears to deliver torque in perfect synchronization with the others, which leads to greater output capacity and takes the pressure off of each individual gear.

Both types of gears are made from a variety of metals including steel, brass and nickel-steel. Some planetary gear motors are even made of plastic. Steel cut gears are the most durable, making them ideal for high-torque applications, while nickel-steel gears are more porous and better at holding lubricant than other materials.

Lubrication is important regardless of gear material, especially at high speeds and loads. Planetary gears are best at retaining lubrication because the planet gears recapture any oil that escapes the sun gear. This helps them operate at higher speeds. Spur gear motors are limited to lower speeds because oil tends to fly off and away from the gears. Higher speed uses tend to burn out the gear before its time because of inadequate lubrication.

Suitable Applications For Each Type Of Gear

Sometimes your gear choice is going to be limited by physical constraints, but more often than not, you'll engineer your gear before you develop housing for it. Still, each type of gear has specific design criteria.

Spur Gear Motors are usually made from steel or brass. These are straight-toothed gears that connect parallel shafts delivering high torque at low speeds. Important design factors include the size of the gears and the number of teeth on each of those gears. This determines the gear ratios for output torque and the shaft speed. Spur gear motors are usually cylindrical in shape, but they can be other shapes. The gears can be noisy, especially if lubrication is inadequate. Inadequate lubrication also leads to damaged teeth, which can lead to gear slippage or stress and ultimately failure of the gear motor. Spur gear motors are less expensive to produce than planetary gear motors, mainly because they use fewer gears than planetary motors and are simpler to manufacture.

DC Planetary Gear Motors come in many power levels and sizes. Also cylindrical in shape, a DC planetary gear motor is typically made of steel, brass and plastic. With so many gears and teeth, there is less worry about wear and stress making it easier to achieve large amounts of power transfer without damaging the gears.

Planetary gear motors are more expensive to produce because they require a sun gear, several planet gears, an outer gear and a moveable arm or carrier to hold the planet gears. While this configuration results in lower gear noise and higher efficiencies, it is also complex and parts can be inaccessible making repairs complicated. 

In short, spur gears are best for low-torque, low-speed applications. A DC planetary gear motor is a better choice if you need high torque and high speed.

The picture shows Planet gear motor system

Still not sure which gear motor is right for you? 
Contact Twirl Motor now. Our engineers will gladly help you figure out the right gear or even design a custom gear to meet your needs!

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