When your project needs more torque than a bare DC motor can provide, a gear motor is the answer. By adding a gear reduction stage between the motor and the output shaft, gear motors trade speed for torque — giving you the slow, powerful rotation needed for robot wheels, conveyor belts, and automated mechanisms. This guide compares three popular gear motor families available in India: the tiny N20, the workhorse JGB37 (25GA-370), and planetary gearmotors.
Why Use Gear Motors
A typical small DC motor spins at 10,000-30,000 RPM but produces very little torque. For most applications (robot wheels, actuators, automation), you need 50-300 RPM with much higher torque. Gear reduction achieves this through a set of meshing gears that reduce output speed while multiplying torque proportionally.
Gear ratio example: A 30:1 gear ratio on a 12,000 RPM motor gives 400 RPM output with 30x the torque (minus friction losses).
N20 Micro Gear Motors
The N20 (also called GA12-N20) is a 12mm diameter micro gear motor popular in small robots, mecanum wheel platforms, and precision mechanisms. Available in voltages from 3V to 12V and speeds from 15 to 4000 RPM.
Key features:
- Ultra-compact: 12mm diameter, 10-25mm gearbox length
- Available with encoder for closed-loop control
- Metal gear options for durability
- 3mm or 4mm D-shaft output
Best for: Mecanum wheel robots, small precision mechanisms, camera sliders, miniature actuators.
JGB37 / 25GA-370 Gear Motors
The 25GA-370 (also sold as JGB37) is a 25mm diameter gear motor that has become the standard for medium-duty robotics. It is the step up from BO motors for projects needing more torque, durability, and precision.
Key features:
- 25mm diameter, robust metal gearbox
- Available from 12 to 1360 RPM at 12V or 24V
- Encoder variants available for PID control
- 6mm D-shaft output with flat
- Mounting bracket available
Best for: Robot platforms, sumo robots, AGVs, conveyor belts, automated gates.
Planetary Gear Motors
Planetary gear motors use a sun-and-planet gear arrangement that distributes load across multiple gears simultaneously. This design handles higher torques in a more compact package compared to spur gear motors.
Key features:
- Higher torque density (more torque per size)
- Lower backlash than spur gear motors
- Better efficiency at high reduction ratios
- More expensive than spur gear options
Best for: High-torque applications, precision robotics, industrial automation, linear actuators.
Comparison Table
| Feature | N20 (GA12) | 25GA-370 (JGB37) | Planetary |
|---|---|---|---|
| Diameter | 12mm | 25mm | 25-42mm |
| Torque Range | 0.1-1.5 kg-cm | 1-15 kg-cm | 5-50+ kg-cm |
| RPM Range | 15-4000 | 12-1360 | 10-500 |
| Encoder Option | Yes | Yes | Some models |
| Price (India) | ₹150-400 | ₹200-600 | ₹500-3000 |
| Best For | Small robots | Medium robots | Heavy duty |
Selection Guide
- Calculate required torque: Torque = Force x Radius. For a robot wheel: Torque = Robot weight x Wheel radius / Number of driven wheels.
- Choose RPM: For robot wheels, RPM = (Desired speed in m/s x 60) / (Wheel circumference in m). Typical: 100-300 RPM for small robots.
- Select voltage: 6V for battery-constrained builds, 12V for standard, 24V for higher-power applications.
- Encoder needed? Yes for PID speed control, odometry, and position control. No for simple on/off applications.
Frequently Asked Questions
N20 vs BO motor: which is better for robots?
N20 motors have metal gears, higher torque, and encoder options. BO motors are cheaper but use plastic gears that strip under load. For any project beyond basic learning, N20 motors are the better investment.
Can I change the gear ratio of a gear motor?
Not easily. Gear motors come with a fixed gear ratio. If you need a different speed/torque balance, buy a motor with the appropriate ratio. External gear stages (timing belt and pulleys) can provide additional reduction.
What is gear backlash and does it matter?
Backlash is the small amount of play between meshing gears. It means the output shaft can rotate slightly without the motor shaft turning. For position-critical applications (robot arms, CNC), low backlash is important. For wheel drives, backlash is usually not a concern.
Conclusion
The right gear motor depends on your size, torque, and precision requirements. N20 motors are perfect for compact builds, 25GA-370 motors handle medium-duty robotics, and planetary motors deliver when you need maximum torque in a compact package. Always calculate your torque requirements before selecting a motor.
Shop gear motors at Zbotic.in.
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