STOBER Servo Gearmotors vs. AC Motors and Gearboxes: 6 Reasons to Make the Switch
Smaller, lighter and more precise. What's not to love?
When designing a machine, space matters. So do weight, speed, accuracy, and how quickly a machine can complete its work.
A traditional AC motor paired with a gearbox can get the job done. But a STOBER servo gearmotor may offer a better solution, especially when space is tight or your machine needs to start, stop, and change speed frequently.
A servo gearmotor combines a servo motor and gearbox into one compact unit. That can mean less space taken up by the drive, less weight to manage, and better control over how your machine moves.
Let's look at six reasons to consider making the switch.
1. Save space inside your machine
Space is often at a premium in machine design. A shorter drive can give you more room for other components or help you design a more compact machine.
STOBER compared two drive setups using the same K2-series gearbox: one with a servo gearmotor and one with a separate 2 HP AC motor.
Measurement | STOBER servo gearmotor | AC motor + gearbox |
Total length | 393 mm | 593 mm |
Difference in length | 200 mm shorter | 200 mm longer |
Length compared with the other option | About 34% shorter | About 51% longer |
That's 200 mm—nearly 8 inches—less length.
In this example, the servo gearmotor is about 34% shorter than the AC motor-and-gearbox setup.
That extra space could help you:
Build a more compact machine.
Fit components into a tight space.
Simplify your machine layout.
Make better use of the space you already have.
Actual savings will depend on the motor, gearbox, mounting setup, and other components.
2. Reduce motor weight
A lighter motor can be easier to handle, mount, and fit into your machine design.
Here's how two selected motors compare.
Measurement | 98 mm-frame servo motor | 2 HP AC motor |
Motor weight | 5.1 kg | About 15 kg |
Weight difference | 9.9 kg lighter | 9.9 kg heavier |
Relative weight | About one-third as heavy | About 2.9 times as heavy |
Percentage difference | About 66% lighter | About 194% heavier |
In this example, the servo motor weighs about 66% less than the AC motor.
That's nearly 10 kg less motor weight to work with.
For machine builders, a lighter motor can make installation easier and offer more flexibility when designing equipment with limited space or weight constraints.
Note: These figures compare the motors only, not the complete motor-and-gearbox assemblies.
3. Get more control over speed
Not every machine needs to run at one steady speed. Some need to speed up, slow down, or adjust their speed throughout the process.
That's where a servo motor can make a difference.
Performance | Servo motor | AC motor |
Speed range | 0–5,000 rpm | 0–1,800 rpm |
Maximum speed | 5,000 rpm | 1,800 rpm |
Difference in maximum speed | 3,200 rpm higher | 3,200 rpm lower |
Speed accuracy | ±0.001% | ±1–3% |
A servo system can give you more flexibility when setting speeds and help maintain more consistent motion.
This can be useful when your machine needs to move accurately, change speeds often, or repeat the same movement cycle after cycle.
Actual speed accuracy depends on the motor, drive, feedback system, setup, and operating conditions. Confirm the specifications for your selected system.
4. Help your machine work faster
If your machine starts and stops throughout the day, the time it takes to speed up and slow down can add up.
Servo motors can accelerate, decelerate, and change speed quickly. They can also be a good fit for applications that require frequent starts and stops.
Motion requirement | Servo motor | AC motor |
Frequent starts and stops | Supports demanding motion cycles | The example limit is 10 starts and stops per minute |
Acceleration | Can accelerate quickly | More limited acceleration |
Deceleration | Can slow down quickly | More limited deceleration |
Frequent speed changes | Offers flexible speed control | May be less suited to demanding speed changes |
The potential result? Shorter cycle times and more work completed in the same amount of time.
The actual improvement depends on your machine. If movement is slowing down your process, a servo system may help. If the process itself takes most of the time, changing the motor may make less difference.
The key is to look at how your machine moves and where time is being lost.
5. Use less energy
Energy efficiency matters, especially for machines that run for long hours.
The selected motor comparison lists 96% efficiency for the servo motor, compared with 88–93% for the AC motor.
Efficiency | Servo motor | AC motor |
Motor efficiency | 96% | 88–93% |
Difference in efficiency | 3–8 percentage points higher | 3–8 percentage points lower |
Energy lost as motor losses, based on these figures | About 4% | About 7–12% |
In simple terms, a more efficient motor loses less of its input energy as heat.
However, motor efficiency alone doesn't tell the whole story. The gearbox, drive electronics, machine load, operating speed, and hours of use all affect total energy consumption.
For the fairest comparison, look at how much energy each complete drive system uses under the same working conditions.
6. Simplify your drive setup
With a traditional arrangement, the motor and gearbox are separate components. With a servo gearmotor, the motor is integrated with the gearbox.
That can make a big difference when space is limited.
In the K2-series example, the servo gearmotor creates a shorter, more compact assembly than the separate AC motor-and-gearbox setup.
Design consideration | STOBER servo gearmotor | AC motor + gearbox |
Motor and gearbox arrangement | Integrated into one compact drive | Separate motor and gearbox |
Overall length in the example | 393 mm | 593 mm — 200 mm longer |
Motor weight in the example | 5.1 kg | About 15 kg — 9.9 kg heavier |
Motion control | Servo-based speed and motion control | Depends on the motor and control system selected |
An integrated servo gearmotor may help you reduce the space needed for your drive, make installation simpler, reduce motor weight, and design a more compact machine.
The best choice still depends on what your machine needs to do, including its speed, torque, workload, and budget.
A real-world example: Same output, different drive setup
What happens when both options need to deliver the same speed and torque?
Consider an application requiring an output speed of 85 rpm and an output torque of 133 Nm.
Design requirement | Servo solution | AC solution |
Required output speed | 85 rpm | 85 rpm |
Required output torque | 133 Nm | 133 Nm |
Gearbox efficiency assumption | 96% | 96% |
Motor speed | 3,000 rpm | 1,700 rpm |
Difference in motor speed | 1,300 rpm higher | 1,300 rpm lower |
Gearbox ratio | 35:1 | 20:1 |
Motor torque | 3.96 Nm | 6.93 Nm |
Difference in motor torque | 2.97 Nm lower | 2.97 Nm higher |
Motor size | 98 mm frame | 2 HP motor |
Both setups are designed to meet the same output requirements, but they use different motor speeds and gearbox ratios.
The takeaway is simple: choosing a motor isn't just about horsepower. It's about finding the right combination of speed, torque, size, weight, and motion control for your machine.
Young Mechatronics can help you compare options and choose a drive that fits your application.
Frequently asked questions
What is a servo gearmotor?
A servo gearmotor combines a servo motor and a gearbox into one unit. It provides controlled motion at the speed and torque your machine needs.
What are the main advantages of a servo gearmotor over an AC motor and gearbox?
A servo gearmotor can be smaller, lighter, and more precise. It can also offer more speed flexibility and faster acceleration and deceleration. The benefits depend on the specific products and application.
How much space can a STOBER servo gearmotor save?
In the K2-series example, the servo gearmotor measures approximately 393 mm long, compared with 593 mm for the AC motor-and-gearbox setup. That's about 200 mm, or 8 inches, shorter.
Is a servo motor lighter than an AC motor?
It can be. In the selected comparison, the 98 mm-frame servo motor weighs 5.1 kg, compared with approximately 15 kg for the 2 HP AC motor. That's about 9.9 kg less, or approximately 66% lighter.
Can a servo gearmotor make my machine faster?
It may. Servo motors can accelerate, slow down, and change speeds quickly. If movement is limiting your machine's cycle time, a servo system may help reduce it. Actual results depend on the application.
Can a servo gearmotor save energy?
It may, depending on how the machine operates. The selected motor comparison lists 96% efficiency for the servo motor and 88–93% for the AC motor. Comparing total system energy use under the same operating conditions gives a more accurate picture of potential savings.
Should I replace my AC motor with a servo gearmotor?
A servo gearmotor is worth considering if you need to save space, reduce motor weight, improve speed control, or handle frequent starts and stops. If your machine runs at a steady speed and doesn't need precise motion control, an AC motor may still be the right choice.
The best way to decide is to compare both options against your machine's actual requirements.
Quick summary: STOBER servo gearmotors vs. AC motors
Here's how the two drive options stack up across key performance and design considerations.
What you're comparing | STOBER servo gearmotor | AC motor + gearbox |
Overall drive length | 393 mm | 593 mm — 200 mm longer |
Motor weight | 5.1 kg | About 15 kg — 9.9 kg heavier |
Motor size | Can be up to 50% smaller | Can be up to twice the size |
Speed range | 0–5,000 rpm | 0–1,800 rpm |
Speed accuracy | ±0.001% | ±1–3% |
Acceleration and deceleration | Can speed up and slow down quickly | More limited acceleration and deceleration |
Frequent starts and stops | Supports demanding motion cycles | Example limit of 10 starts and stops per minute |
Motor efficiency | 96% | 88–93% |
Drive arrangement | Motor integrated with gearbox | Separate motor and gearbox |
Technical note: Specifications and dimensions are based on selected motor and gearbox combinations. Actual performance varies by model, drive configuration, and operating conditions. Confirm specifications for your application with Young Mechatronics.
Let's find the right drive for your machine
Your motor choice affects more than how the machine runs. It can affect the space you need, the weight you have to mount, and how quickly your machine can do its job.
A STOBER servo gearmotor may help you build a smaller, lighter, more responsive machine.
Have a machine design or drive application to work through?
Contact Young Mechatronics to discuss your speed, torque, space, and motion requirements.