In the past we have seen the rise of stepper motors - small, compact motors that used low speeds at higher torque for a lower load capacity. Nowadays, servo motors run the industrial world, thanks to their high speeds, large load capacity, and better positional control.
Thus, picking between stepper vs. servo motors is as confusing as understanding their operation. The good thing is that we have got you covered as the following guide covers all about stepper motors vs. servo motors!
Stick around until the end to find more about how stepper and servo motors work, their benefits and cons, a grand comparison table, and a guide to choosing the right motor type according to your robotic needs! In the end, we'll also include some common FAQs to help you with your decision!
How do Stepper & Servo Motors work? The Quick Overview
The following is a quick overview of stepper and servo motors, including their advantages and disadvantages.
How Does A Stepper Motor Work?
The working of a stepper motor is carried out by an open loop system which, powered by alternating currents, causes the motor to "step" through a number of intervals. The resulting movement then creates a pre-programmed rotational motion and positioning.
The primary parts of a stepper motor are a rotor, magnet, and stator. Other parts include front and rear endcap, winding, ball bearing, and shaft.
The stator, acting on the rotor, creates a magnetic force that determines the rotational motion and static motor position. The permanent magnet also plays its role in turning the motor rotor in discrete intervals. This allows the motor to carry a load, a feature that makes them suitable for applications requiring good position and loading.
The best thing about a stepper motor is its simple design and easy operation. The motor also features a good low-speed torque which facilitates towing things from a standstill, as a greater horsepower generates with high torque.
Because the high torque at low-speed results in smooth motor working, the motor can get timely commands and its motion becomes synchronized accordingly. This feature makes stepper motors a better choice than servo motors in which incoming commands delay the motion.
However, when integrated into long movements, the same torque speed is a disadvantage in stepper motors. It limits the duty cycle and withholds the motor from reaching a peak torque value.
Yet, stepper motors have other features over servo motors, including quick responses when it starts. The low-speed torque results in a good low-speed workflow, and the function requires no prior tuning.
The compact size of the motor also makes it possible for the machine to save more energy, thanks to its simple, lightweight design. The motor's reduction of self-weight further impacts the overall cost, making stepper motors cost much less than servo motors.
However, because the motor runs in an open loop, the constant current flow sometimes becomes a problem when the operational requirements need a variable current voltage. The torque value also gets lower with the increase in speed, which limits the stepper motor's function to light loads only.
Pros & Cons of Stepper Motors
Let's look at the benefits and disadvantages of stepper motors.
A stepper motor may be the best solution to your robotic needs due to the following benefits:
- It has a simple design.
- It has a lightweight body.
- It is easy to control.
- It starts quickly without any delays.
- It uses low-speed torque that results in horsepower.
- The low-speed torque contributes to a good low-speed workflow.
- The motor's functioning requires no prior tuning.
- The compact design of the motors helps save more power.
- The lightweight body decreased the overall motor cost.
- The motion of stepper motors gets synchronized with commands.
A stepper motor may not be the best solution to your robotic needs due to the following cons:
- The motor runs on low-speed torque.
- The torque generated is not suitable for long movements.
- It has a limited duty cycle.
- The low-speed torque fails to reach a peak value.
- The current flows at a constant rate, making it challenging when a variable current voltage is required.
- The value of torque gets lower as speed increases.
How Does A Servo Motor Work?
Servo motors contrast with stepper motors and are well-known in robotics due to their capability to facilitate heavier loads. However, the true power of a servo motor lies in its position control which requires more than a DC motor.
Like stepper motors, servo motors have permanent magnets, a rotor, and a stator. They are structured in three-phase windings, augmented feedback, bearing, shaft, encoder, encoder cable, and motor cable.
Thus, a servo motor is designed with a combination of a motor, unlike a stepper motor, which makes it excellent for implementing positional control. However, the same structure makes it more complex to understand and install than a stepper motor with a simple design and easy operation.
Moreover, servo motors have closed-loops systems, which reduce downtime, improve speed control, and allow the system to experience robust control. Because the torque speed is high, it can achieve a peak value, resulting in a continuous duty cycle, unlike servo motors, where the peak value cannot be obtained due to low-speed torque.
However, such a high-speed torque also means timely tuning. Still, a servo motor may be a better option for various load systems due to its exceptional features and constant workflow.
The motor can also carry a higher load without catching much heat. That is, the machine has a higher resistance to heat even during heavy work, something you don't get with stepper motors prone to heat in case of overloading.
Thus, a servo motor is a multi-functional machine packed with features and advanced functionality. The only concerning points are its complex design and operation, timely required tuning, and working limited to augmented feedback only (it works only with feedback).
Besides, the movement of servo motors often gets delayed with the command; it doesn't get synchronized properly, which can be a problem in some load systems where timely commands are mandatory.
Another thing to note about servo motors is their high-end price, which can cost much higher than stepper motors. Features like complex encoder feedback devices (located in servo drive hardware) and the complex algorithms that provide the motor with the required control signals add to the cost of servo motors.
However, it wouldn't be wrong to say that servo motors are worth every penny, given they are structured with a closed-loop system that provides better current control. Thus, servo motors are most suitable for variable load systems and improve performance and efficiency.
Pros & Cons of Stepper Motors
Let's look at the benefits and disadvantages of stepper motors.
A servo motor may be the best solution to your robotic needs due to the following benefits:
- A servo motor implements better positional control.
- It can facilitate heavier loads.
- It has a closed-loop system.
- It has lower risks of downtime.
- The torque is high in servo motors.
- Higher torque can achieve a peak value.
- The motor exercises better speed control because of higher torque.
- It is resistant to higher temperatures (it doesn't heat up easily, even during heavy work).
A servo motor may not be the best solution to your robotic needs due to the following cons:
- A servo motor has a complex design.
- It is hard to operate a servo motor.
- Due to higher torque and speed requires more tuning.
- Its working is limited to augmented feedback.
- Its motion gets delayed with the command.
- Servo motors are expensive.
Stepper Vs. Servo - Their Comparison
The following is a quick chart to help you remember the features of stepper and servo motors and their functionality.
|Features||Stepper Motors||Servo Motors|
|System||Open-loop system||Closed-loop system|
|Torque-speed relation||High torque at low speed||High torque at high speed|
|Torque peak value||Not achievable||Achievable|
|Torque-control / speed-control mode||Absent||Present|
|Torque & speed relation||Indirect (the value of torque gets lower as speed increases)||Direct (the value of torque gets higher as speed increases)|
|Largest torque and speed range||Absent||Present|
|Highest torque density||Present||Absent|
|Low speed ( < 1000 RPM)||Present||Present|
|Medium speed (1000 - 3000 RPM)||Possible||Present|
|High speed ( > 3000 RPM)||Not Possible||Present|
|High torque at low speed||Present||Present|
|High torque at high speed||Not Possible||Present|
|Highest input voltage range||Absent||Present|
|Current flow||Constant rate||Variable current voltage|
|Tuning||No tuning required||Prior tuning required|
|Power||Consumes less power||Consumes high power|
|Motion & commands||Motion synchronizes with commands||Motion delays with commands|
|Responsiveness||Gives quick response||Delays when starting (it waits for settling before the next move)|
|Suitable for||Short moves||Long moves|
|Heavier loads||Not possible||Possible|
|Holding torque/position keeping||A natural stop provided by magnet teeth||Electrical servo lock|
|Payload||Generally lower (in the same envelope)||Generally higher|
|Repeatability||Lower||Higher (because of closed feedback)|
|Velocity (and/or path repeatability)||Lower||Higher|
|Position holding without hunting||Possible||Not possible|
|Better positional control||NO||YES|
|Highest acceleration/deceleration achievable||Not possible||Possible|
|High BW (bandwidth) response time||NO||YES|
|Duty cycle||Limited||Not limited|
|Functionality||Doesn’t require feedback (it can work without it)||Limited to feedback (works only with feedback)|
Stepper Vs. Servo - How to Choose the Right Motor for Your Robotic Needs
Whether stepper or servo, the suitable motor for your robotic needs depends on the requirements. The comparison mentioned above in the table covers in detail the differences between servo motors vs. stepper motors.
However, if deciding between stepper or servo still feels confusing, you can start by understanding your priorities. The most important factors in a motor integrated into a robot (/cobot) are as follows:
- Structure (size, weight, etc.)
- Capability (load)
Thus, you can start by answering the following questions:
1. Torque Requirement
What is your torque requirement? How high is the torque value needed? Remember that the functionality of a motor depends on the relation between torque and speed, so think wisely.
At which speed are you willing to run your loads? Remember that the speed in servo/stepper motors can be classified into three categories:
- Low speed (up to 1000 RPM)
- Medium speed (1000 - 3000 RPM)
- High speed (above 3000 RPM)
As mentioned before, stepper motors mostly run on low speed (but they can achieve medium speed). On the other hand, servo motors run at higher speeds whose value can be increased from low to high.
Thus, your choice is between:
- High torque and slow speed
- High torque and high speed
3. Variable Loads
Will your load be fixed or vary as it moves? Stepper motors are most suitable for fixed loads, while servo motors go well for variable loads.
4. Power Consumption
How much power consumption are you willing to use in your future projects? Stepper motors save more battery than servo motors.
5. Additional Functions
Do you need any additional functional features in your required motor (such as holding torque; stepper motors are good at that)?
With operation comes staff training; the more complex a system, the more time and money will be spent on training. Stepper motors have a simple design and are easy to operate, unlike servo motors which have an intricate design and are more technical to operate.
7. Operating Conditions
What is the workspace atmosphere in which you will install your motor? Does your production line deal with extreme temperatures? Stepper motors have lower resistance to heat, while servo motors are good at enduring high temperatures.
How much space is available for motor integration? Is there enough room for a servo motor that is heavy and large, or are you looking for a small, compact stepper motor?
How much is your budget? How much have you planned to spend on timely maintenance? Stepper motors are much more cost-effective than servo motors but cannot do heavy work. Servo motors, on the other hand, are popular for their heavy loading but require proper maintenance and are expensive.
By answering these questions, you'll get a fair idea of the right motor type for your robotic needs!
Stepper vs. servo is a confusing and complex decision, but not when you know the functionality of both motors and their appropriate jobs.
Stepper motors are small, lightweight, and easy to integrate/operate. Servo motors are the opposite; they are large, heavy, and have a more complex and technical integration/operation.
Both motors use high torque, but stepper motors run at low speeds, while servo motors have no limit for speed. Also, stepper motors save more power than servo motors which consume high power.
The cost of the motors also plays a significant role; stepper motors are fairly cost-effective and don't require much maintenance or staff training. However, servo motors are expensive and need proper maintenance, not to forget the additional cost of staff training to operate servo motors.
So, in the end, it all depends on your working requirements. Choose a stepper motor if you need a small motor for light loads, or go for a servo motor if the loading is heavier.
Commonly Asked Questions - Stepper VS Servo
What are Some Similarities Between Servo and Stepper Motors?
Servo and stepper motors are powerful machines that convert electrical energy to mechanical energy. In robotics applications, both the motors source reliable power to systems (cobots, automotive, hoists, lifts, cranes, etc.). Though the two motors have different functioning and components, their functionality meets the following features:
- They both possess higher positional accuracy.
- Regardless of design and working, both motors facilitate quiet operation.
- They work with smooth velocity.
- They are used for motion control.
Servo Vs. Stepper Motors: Which is More Efficient?
Both servo and stepper motors are suitable for different robotic systems. However, servo motors are superior to stepper motors since they are more efficient. It is because servo motors are designed with a closed-loop structure, allowing them to implement better positional control.
Because the current flow is constant throughout the process, the motor only uses the voltage needed, unlike stepper motors. This improves overall efficiency, allowing the motor to experience lower downtime risks, making it suitable for variable load systems.
What are the Key Differences Between Servo and Stepper Motors?
Stepper motors use open loop structures, while servo motors are designed with a closed loop structure. Also, stepper motors have low torque speed, which results in low-speed workflow, while servo motors have higher torque speeds, allowing them to reach a peak torque value.
Moreover, stepper motors have a simple design, an easy operation, and are cost-effective compared to servo motors with a complex design, are hard to operate, and require a heavy investment.
When to Use a Stepper Motor Over Servo?
Though servo motors are more popular than stepper motors in today's world due to their higher functionality, a stepper motor should be employed in robotics when the application requires a small, simple motor with an easy operation.
Furthermore, if the requirements are a quick start without delays, low torque value with low speed, and no prior tuning, a stepper motor will win over servo motors. Lastly, cost also plays a role here, as small businesses may want to consider stepper motors due to their low cost and long-term functionality.
When to Use a Servo Motor Over a Stepper?
Servo motors are the demand of the modern era but should be employed in robotics when the application requires better positional control, lower risks of downtimes, and heavier load lifting.
The working atmosphere is an important factor here as servo motors are resistant to higher temperatures and would work best in heavy production lines. However, note that servo motors have a complex design and should only be handled by properly trained staff.