What is a direct current (DC) motor?
A DC motor is a rotating electrical device that converts DC electrical energy into mechanical energy. An inductor (coil) in the DC motor generates a magnetic field that produces rotary motion when DC voltage is applied to its terminal. Inside the motor is an iron shaft wrapped with a wire winding. This shaft contains two fixed north and south magnets on either side, which cause both a repulsive and an attractive force, which in turn produces torque.
What is a DC gearmotor?
A gearmotor is an all-in-one combination of motor and gearbox. Adding a gearhead to a motor decreases the speed while increasing the torque output. The key parameters for gearmotors are speed (rpm), torque (lb-in) and efficiency (%). To select the most suitable gearmotor for your application, you must first calculate the load, speed and torque requirements for your application.
How do I find the right gearmotor - motor selection process?
The motor selection process in the design phase can be challenging. The following key points can help you identify and select the most appropriate motor or gearmotor for our application.
- Design Requirements - A design evaluation phase that examines product development requirements, design parameters, device features, and product optimization.
- Design Calcul ations - Calculations used to determine which motor is the best solution for your application. Design calculations determine gear ratio, torque, rotating mass, service factor, overload and test analysis.
- Types of DC motors / gearmotors - Most commonly used electric motors convert electrical energy into mechanical energy. These types of motors operate on direct current (DC).
- Brushed
- Brushless (BLDC)
- Planetary Gear Motors
- Helical Gear Motors
- Stepper Motor
- Coreless & Coreless Brushless
- Servo Motors
- Motor Specifications - Once the design calculations have been performed and the application parameters have been defined, you can use this data to determine which motor or gearmotor best fits your application. Some of the most common specifications to consider when selecting a motor or gearmotor are:
- Voltage
- Current
- Power
- Torque
- RPM (speed)
- Life expectancy/service cycle
- Rotation (CW or CCW)
- Shaft diameter and length
- Housing limitations
Performance curves of gearmotors?
The performance of a motor and the performance of a gearbox are combined into one graph by displaying three specific parameters. These three parameters are speed, torque and efficiency. These performance curves are important when selecting a gearmotor for your application.
Speed / revolutions (N) - (unit: U / min), given as a straight line showing the relationship between torque and speed of the gearmotor. This line is shifted laterally depending on the voltage increase or decrease.
Current (I) - (unit: A), indicated by a straight line, from no-load to full motor stall. This shows the relationship between current and torque.
Torque (T) - (unit: gf-cm) This is the load represented by the motor shaft on the X axis.
Efficiency (η) - (unit:%) is calculated using the input and output values represented by the dashed line. To maximize the potential of the gearmotor, it should be used near its peak efficiency.
Output (P) - (unit: W) is the amount of mechanical energy output by the gearmotor.
For example, consider the power curve (Figure 5) for a DC motor.
- The maximum operating efficiency (70%) of this motor would be 2,100 rpm (3.75 lb-in).
- As torque increases, speed and efficiency decrease. The result of increased torque is poor output power, and the unit may not operate once the motor reaches its stall torque (18 lb-in).
Gear motor performance curves are helpful when selecting a motor for your application. To make the best use of the performance curves, you need to know exactly what your application requirements are. You can use your load and speed requirements to determine the torque you need. Most DC motor and gearmotor manufacturers offer power curves upon request.
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