How do you select the right DC gear motor for an industrial machine, automation system or OEM product? Should you choose a 12V or 24V motor? How much torque do you need, which gear ratio is appropriate, and when is an encoder necessary?
Selecting a DC gear motor involves much more than matching a voltage rating or choosing a motor that appears powerful enough.
An incorrectly selected motor may fail to deliver the required speed under load, draw excessive current, overheat, experience premature mechanical wear or struggle to start the mechanism it was designed to operate.
For engineers developing industrial equipment, automated machinery and electromechanical systems, understanding the relationship between torque, speed, gearbox ratio, power consumption and duty cycle is essential.
This engineering guide explains the key principles of DC gear motor selection, including practical calculations, common design mistakes and real product examples from the GM20 planetary DC gear motor series, available through Amironic in Israel.
1. What Is a DC Gear Motor and Why Is a Gearbox Necessary?
A DC gear motor combines a direct-current electric motor with a mechanical gearbox.
The electric motor converts electrical energy into rotational motion, while the gearbox modifies the relationship between rotational speed and output torque.
A conventional DC motor often operates at relatively high rotational speeds. However, many industrial mechanisms require the opposite:
- Lower rotational speed.
- Higher output torque.
- Controlled mechanical movement.
- Compact installation dimensions.
- Reliable operation under varying loads.
A gearbox allows the motor’s rotational speed to be reduced while increasing the available torque at the output shaft, subject to the gearbox’s mechanical efficiency and operating limits.
Practical Example: Reducing Motor Speed
Consider a DC motor operating at 3,000 RPM.
If the motor is connected to a gearbox with a reduction ratio of 30:1:
Output Speed = 3,000 / 30 = 100 RPM
The theoretical output speed is approximately 100 RPM.
At the same time, the gearbox increases the available output torque, although the actual increase is reduced by mechanical losses.
This principle makes geared DC motors particularly useful in industrial automation, mechanical positioning, feeding systems, actuators and OEM equipment.
DC Motor vs. DC Gear Motor
| Feature | Standard DC Motor | DC Gear Motor |
|---|---|---|
| Output speed | Typically higher | Reduced by gearbox |
| Output torque | Direct motor torque | Increased through reduction |
| Mechanical configuration | Motor only | Motor and gearbox |
| Low-speed applications | May require additional transmission | Often suitable |
| Mechanical integration | External gearing may be required | Integrated transmission |
| Typical applications | Fans, pumps, high-speed mechanisms | Actuators, automation, positioning mechanisms |
The correct choice depends on the mechanical requirements of the application rather than on motor size alone.
2. How to Select a DC Gear Motor: The Essential Parameters
Before selecting a motor, engineers should define the operating requirements of the complete mechanical system.
The most important parameters include:
| Parameter | Engineering Consideration |
|---|---|
| Supply voltage | 12VDC, 24VDC or another available voltage |
| Output speed | Required shaft speed in RPM |
| Output torque | Continuous, starting and peak torque requirements |
| Gear ratio | Required reduction between motor and output shaft |
| Duty cycle | Continuous or intermittent operation |
| Starting current | Power supply and motor driver capability |
| Mechanical dimensions | Available installation space |
| Shaft loading | Radial and axial loads |
| Feedback | Speed, direction or position monitoring |
| Environmental conditions | Temperature, vibration, contamination and humidity |
| Service life | Expected operating hours and mechanical cycles |
One of the most common selection mistakes is choosing a motor based only on its no-load speed.
A motor capable of rotating at 100 RPM without a mechanical load may operate considerably slower once connected to a machine.
For this reason, the required torque and speed must always be evaluated together at the intended operating point.
3. How to Calculate DC Motor Torque
Torque represents the rotational force available at a motor shaft.
It is normally expressed in Newton-meters (Nm), although some manufacturers specify torque in Newton-centimeters (Ncm).
The fundamental relationship is:
T = F × r
Where:
- T = Torque (Nm)
- F = Applied force (N)
- r = Perpendicular distance from the rotational axis (m)
Example: Calculating Torque for a Mechanical Arm
Assume a mechanism must apply a force of 100 N at the end of a 50 mm lever arm.
First, convert the lever length into meters:
50 mm = 0.05 m
Then calculate the required torque:
T = 100 × 0.05 = 5 Nm
The mechanism therefore requires 5 Nm under the specified conditions.
However, this is only the starting point.
Real applications must also account for friction, acceleration, mechanical efficiency, load variations and an appropriate design margin.
Starting Torque, Continuous Torque and Maximum Torque
These terms must not be confused.
Starting torque is the torque required to initiate movement, including overcoming static friction and accelerating the load.
Continuous torque is the torque a motor can deliver under specified operating and thermal conditions without exceeding its permitted limits.
Maximum torque is the highest torque specified for a particular motor or gearbox under defined conditions. It must not automatically be treated as a continuous operating rating.
A motor with a maximum torque rating of 9 Nm is not necessarily suitable for continuous operation at 9 Nm.
Engineers should verify the permissible operating torque, thermal limitations and duty cycle before finalizing the selection.
Converting Ncm to Nm
Manufacturers may specify torque using different units.
The conversion is:
1 Nm = 100 Ncm
Therefore:
- 100 Ncm = 1 Nm
- 250 Ncm = 2.5 Nm
- 600 Ncm = 6 Nm
- 900 Ncm = 9 Nm
These conversions are particularly useful when comparing gear motor specifications from different manufacturers.
4. How to Calculate Gear Ratio and Output RPM
The gearbox ratio determines how much the motor speed is reduced before reaching the output shaft.
The basic relationship is:
Output RPM = Motor RPM / Gear Ratio
For example, a motor rotating at 4,000 RPM with a 100:1 gearbox produces a theoretical output speed of:
4,000 / 100 = 40 RPM
Increasing the reduction ratio generally reduces output speed and increases the available output torque, subject to gearbox efficiency and mechanical limits.
Does a Higher Gear Ratio Always Mean a Better Motor?
No.
A higher reduction ratio may provide greater torque multiplication, but it also reduces output speed.
Depending on the gearbox design, it may also influence mechanical efficiency, backlash and the response of the mechanism when changing direction.
A lower ratio may deliver the desired speed but insufficient torque.
The correct ratio must therefore be selected according to the required operating point.
Torque Multiplication Through a Gearbox
A simplified relationship is:
Output Torque = Motor Torque × Gear Ratio × Gearbox Efficiency
For example, assume:
- Motor torque: 0.1 Nm
- Gear ratio: 50:1
- Assumed gearbox efficiency: 80%
The theoretical output torque is:
0.1 × 50 × 0.80 = 4 Nm
This example illustrates the calculation method. The actual efficiency must be obtained from the gearbox manufacturer or verified experimentally.
In addition, the calculated torque must remain within the gearbox’s permissible mechanical and thermal ratings.
5. 12V vs. 24V DC Gear Motors: Which Should You Choose?
Both 12V and 24V DC gear motors are widely used in electromechanical equipment.
A 12V motor may be suitable for battery-powered systems, portable equipment and products already designed around a 12V electrical architecture.
A 24V motor is frequently used in industrial automation, control panels, OEM machinery and systems with standardized 24VDC power supplies.
Why Are 24V Motors Common in Industrial Automation?
For a comparable electrical input power, a higher supply voltage generally allows lower current.
The basic electrical relationship is:
P = V × I
Where:
- P = Electrical power (W)
- V = Voltage (V)
- I = Current (A)
For example, a 60 W electrical load would theoretically draw:
- At 12V: 5 A
- At 24V: 2.5 A
Lower current can help reduce resistive losses in cables and electrical connections.
However, this does not mean that a 24V motor is automatically more powerful, more efficient or better suited to every application.
Motor performance depends on its electrical and mechanical design, gearbox ratio and operating conditions.
Choosing Between 12V and 24V
The decision should consider:
- Available system voltage.
- Required torque and output speed.
- Motor driver compatibility.
- Power supply capacity.
- Cable length and electrical losses.
- Starting current.
- Overall system architecture.
The GM20 series includes both 12V and 24V configurations, allowing engineers to select a suitable voltage according to the application.
6. What Is a Planetary Gearbox?
A planetary gearbox is a mechanical transmission consisting of a central sun gear, multiple planet gears and an outer ring gear.
The arrangement allows torque to be transmitted through multiple gear contacts within a relatively compact assembly.
Planetary gearboxes are frequently selected when a mechanical system requires a useful combination of torque density, compact dimensions and coaxial input/output shaft geometry.
Advantages of Planetary Gear Motors
Depending on the specific design, planetary gearboxes may offer:
- High torque density.
- Compact mechanical construction.
- Multiple available reduction ratios.
- Coaxial input and output.
- Suitable load distribution between gear elements.
- Convenient integration into industrial mechanisms.
Planetary Gearbox vs. Conventional Gearbox
A planetary gearbox is not necessarily superior in every application.
Spur gearboxes, worm gearboxes and other transmission designs may be preferable depending on cost, packaging, efficiency, noise, backlash and load requirements.
For example, a worm gearbox may be considered where the mechanical arrangement requires a right-angle transmission.
A planetary gearbox may be attractive when compact axial construction and torque density are important.
The selection should always be based on the requirements of the complete mechanism.
7. GM20 Planetary DC Gear Motor: A Practical Industrial Solution
The GM20 series is a family of brushed DC motors with integrated planetary gearboxes.
The series is designed for applications requiring different combinations of output speed and torque within a compact electromechanical assembly.
Available configurations include 12V and 24V motors, multiple gearbox ratios and an optional two-phase Hall-effect encoder.
GM20 Technical Specifications
| Parameter | GM20 Series |
|---|---|
| Motor type | Brushed DC gear motor |
| Gearbox | Planetary |
| Nominal voltage | 12VDC / 24VDC |
| Gear ratios | 4:1 to 625:1 |
| Maximum specified torque | Up to 900 Ncm (9 Nm) |
| No-load output speed | Approximately 6.7–1,024 RPM |
| Output shaft diameter | Nominal 10 mm |
| Shaft support | Two ball bearings |
| Maximum radial shaft load | 300 N |
| Radial load reference position | 10 mm from mounting flange |
| Maximum axial shaft load | 150 N |
| Operating temperature | -20°C to +60°C |
| Approximate weight | 700–900 g |
| Encoder option | Two-phase Hall-effect encoder |
The listed values are based on the available GM20 technical documentation.
Maximum torque values should not be interpreted as continuous-duty ratings without further verification.
GM20 Gear Ratio and Speed Comparison
The following table presents selected GM20 configurations using the 24V motor version.
| Model | Gear Ratio | Maximum Specified Torque | Speed at Specified Maximum Torque |
|---|---|---|---|
| GM20-4-24 | 4:1 | 0.5 Nm | 640 RPM |
| GM20-16-24 | 16:1 | 1.5 Nm | 186 RPM |
| GM20-25-24 | 25:1 | 2.5 Nm | 116 RPM |
| GM20-64-24 | 64:1 | 6 Nm | 45 RPM |
| GM20-100-24 | 100:1 | 7 Nm | 32.4 RPM |
| GM20-244-24 | 244.14:1 | 9 Nm | 14.9 RPM |
| GM20-625-24 | 625:1 | 9 Nm | 6.3 RPM |
Values are typical catalog figures. Actual performance depends on operating conditions and the specific motor configuration.
How to Interpret the GM20 Selection Table
Consider two different applications.
Application A: Higher-speed mechanical movement
A mechanism requiring relatively high output speed may benefit from a lower gear ratio, provided the available torque is sufficient.
Application B: Low-speed, higher-torque movement
A mechanism requiring slow rotation and greater torque may benefit from a higher reduction ratio.
In both cases, the motor must be evaluated against the actual torque-speed operating point, not simply the maximum values shown in the table.
The GM20 series provides several configurations that can be evaluated according to these requirements.
8. DC Gear Motor with Encoder: Speed and Position Feedback
In many automation systems, commanding a motor to rotate is not enough.
The controller may also need to determine:
- Whether the motor is rotating.
- The direction of rotation.
- The rotational speed.
- The amount of relative movement.
- Whether the commanded motion has been completed.
An encoder provides electrical signals representing shaft movement.
These signals can be processed by a motor controller, PLC or embedded control system.
What Is a Two-Phase Hall-Effect Encoder?
A Hall-effect encoder uses magnetic sensing elements to detect changes in a magnetic field.
In a two-phase quadrature encoder, two signals—commonly designated A and B—are generated with a nominal 90° electrical phase difference.
By evaluating the sequence of these signals, the controller can determine rotational direction.
Counting signal transitions allows the controller to measure relative movement and calculate rotational speed.
GM20 with Two-Phase Hall Encoder
The GM20-2PHE configuration incorporates a two-phase Hall-effect encoder.
According to the supplied encoder documentation, the system uses a six-pole magnet and provides three pulse cycles per motor revolution on each channel.
The effective number of counts depends on whether the controller uses single-edge, double-edge or quadrature decoding.
Because the encoder measures motor rotation before the gearbox, the number of encoder counts per output-shaft revolution depends on the gearbox ratio.
For example, with a 100:1 reduction ratio:
3 encoder cycles × 100 = 300 cycles per output-shaft revolution per channel
With four-edge quadrature decoding, this corresponds theoretically to 1,200 counts per output-shaft revolution.
The actual relationship should be confirmed for the selected gearbox ratio and controller configuration.
When Is an Encoder Necessary?
A DC gear motor with an encoder may be appropriate for:
- Closed-loop speed regulation.
- Relative position monitoring.
- Motion verification.
- Direction detection.
- Repetitive mechanical movement.
- Automated positioning mechanisms.
However, an incremental encoder does not automatically provide absolute position after power-up.
Mechanical backlash, gearbox compliance and other transmission effects can also influence the accuracy of the final mechanism.
Applications requiring high positioning accuracy may benefit from additional feedback directly at the output shaft or load.
9. Where Are DC Gear Motors Used?
DC gear motors are found in a wide range of industrial and electromechanical applications.
Their suitability depends on the required torque, speed, operating cycle and environmental conditions.
Industrial Automation
Geared DC motors can drive feeding mechanisms, mechanical adjustments, small conveyors and automated movement systems.
Packaging and Dispensing Equipment
Packaging and dispensing mechanisms may require repeatable movement at controlled speeds, with sufficient torque to overcome process loads.
Test Equipment and Fixtures
Motorized test fixtures may use DC gear motors for clamping, positioning, opening, closing and controlled mechanical movement.
Electric Actuators and Valve Mechanisms
A DC gear motor can drive a mechanical actuator where the gearbox provides the required relationship between rotational speed and output torque.
OEM Equipment
Original equipment manufacturers often integrate DC gear motors into larger systems containing motor drivers, sensors, power supplies and mechanical transmissions.
In these applications, motor selection must be coordinated with the overall system design.
Low-Speed, High-Torque Mechanisms
Applications requiring relatively slow movement and significant rotational force may benefit from a geared DC motor with an appropriately selected reduction ratio.
The GM20 series offers several configurations for evaluating such requirements.
10. Five Common DC Gear Motor Selection Mistakes
Mistake 1: Selecting a Motor by No-Load RPM
No-load speed does not represent the speed available under operating load.
Always evaluate the motor at the required torque-speed point.
Mistake 2: Treating Maximum Torque as Continuous Torque
A maximum torque specification does not necessarily indicate the torque available during continuous operation.
Verify thermal limits, permissible operating torque and duty cycle.
Mistake 3: Ignoring Starting and Stall Current
Starting current can be considerably higher than normal running current.
The motor driver, power supply and protection circuitry must be selected accordingly.
Mistake 4: Ignoring Radial and Axial Shaft Loads
A gearbox may provide sufficient output torque but still be unsuitable for the mechanical loads applied directly to its output shaft.
Always verify the permitted radial and axial loads.
Mistake 5: Selecting the Motor Without Considering the Controller
A mechanically suitable motor does not automatically provide the required speed regulation or positioning performance.
The motor, driver, encoder and control strategy should be considered as a complete system.
11. Frequently Asked Questions About DC Gear Motors
What is the difference between a DC motor and a DC gear motor?
A standard DC motor delivers rotational motion directly from its shaft. A DC gear motor incorporates a gearbox that reduces output speed and increases available output torque, subject to efficiency and mechanical limits.
Which DC motor is suitable for high torque at low RPM?
A DC motor with an appropriately selected reduction gearbox is often suitable. Planetary gear motors are one possible solution, particularly when compact construction is important.
Is a 24V DC gear motor more powerful than a 12V motor?
Not necessarily. Supply voltage alone does not determine mechanical power or torque. The motor’s design, current capability, gearbox ratio and operating point must be considered.
Can a DC gear motor operate in both directions?
Many brushed DC motors can reverse direction by reversing the applied voltage polarity. The GM20 series supports direction reversal through polarity reversal.
Can DC motor speed be controlled using PWM?
Yes. PWM control is commonly used with brushed DC motors and suitable motor drivers. Closed-loop control with encoder feedback may be required when accurate speed regulation under changing loads is important.
What is the difference between torque and RPM?
Torque describes rotational force, while RPM describes rotational speed. Both must be evaluated together when selecting a motor.
Does a higher gear ratio always provide more usable torque?
Not necessarily. Although a higher ratio generally increases torque multiplication, the actual usable torque is limited by gearbox efficiency, mechanical strength, thermal conditions and the motor’s operating characteristics.
Can a DC gear motor with an encoder be used for positioning?
Yes. An encoder can provide relative movement feedback for a positioning controller. Final positioning accuracy depends on encoder resolution, backlash, mechanical compliance and the control system.
What is the difference between a planetary gear motor and a worm gear motor?
A planetary gearbox typically provides coaxial input and output shafts and can offer high torque density. A worm gearbox uses a different gear arrangement, often providing right-angle transmission. The appropriate choice depends on the application.
Where can I buy a DC gear motor in Israel?
Amironic Ltd. supplies DC gear motors in Israel, including the GM20 planetary gear motor series in 12V and 24V configurations.
Engineers and purchasing teams can contact Amironic with their required voltage, torque, speed, dimensions and quantities to discuss suitable motor configurations and request a quotation.
12. How to Specify a DC Gear Motor for Your Project
Before requesting a quotation, it is useful to prepare a clear technical specification.
The following information can significantly simplify the selection process:
- Supply voltage: 12VDC, 24VDC or another voltage.
- Required output speed: RPM under operating load.
- Required torque: Continuous, starting and peak values.
- Duty cycle: Operating time, rest time and number of cycles.
- Mechanical dimensions: Available installation space and mounting requirements.
- Output shaft requirements: Diameter, geometry and shaft loads.
- Feedback requirements: Encoder, speed monitoring or positioning.
- Environmental conditions: Temperature, humidity, contamination and vibration.
- Estimated quantities: Prototype, pilot production and annual requirements.
A well-defined specification helps reduce selection errors and simplifies communication between the design team and motor supplier.
13. DC Gear Motors in Israel – Engineering Support and Local Supply
For Israeli manufacturers and engineering teams, sourcing a DC gear motor involves more than finding a component with the correct voltage and shaft diameter.
A suitable supplier should help customers identify motor configurations that match the mechanical and electrical requirements of the application.
This becomes particularly important when developing OEM products, integrating a motor into an existing mechanism or planning repeat production.
Amironic Ltd. supplies DC gear motors and electromechanical components to the Israeli market, including the GM20 planetary gear motor series.
The GM20 family offers multiple gear ratios, 12V and 24V motor configurations and optional Hall-effect encoder feedback.
Customers can provide their technical requirements to discuss suitable configurations and obtain commercial information.
Conclusion: The Right DC Gear Motor Starts with the Right Engineering Requirements
Choosing a DC gear motor requires a clear understanding of the relationship between torque, speed, gear ratio, voltage and mechanical loading.
A motor that meets the required RPM but cannot deliver sufficient torque will not perform correctly.
Similarly, a motor with a high maximum torque rating may still be unsuitable for continuous operation or for a system requiring accurate motion feedback.
The best selection considers the complete operating conditions of the machine.
The GM20 planetary DC gear motor series provides a range of 12V and 24V configurations, multiple reduction ratios and optional Hall-effect encoder feedback for industrial and OEM applications.
Looking for a DC Gear Motor in Israel?
Whether you are developing a new machine, upgrading an existing mechanism or selecting a motor for an OEM product, Amironic can help you evaluate suitable DC gear motor configurations.
Send us your required voltage, output speed, torque and estimated quantity to request technical information and a quotation.
Amironic Ltd. – DC Gear Motors, Planetary Gear Motors and Electromechanical Solutions
Tel: +972-3-9047744
Email: office@amironic.co.il
Website: https://www.amironic.co.il