This is a high-power 6V brushed DC gearmotor with a 98.78:1 metal spur gearbox, designed to deliver high torque at low speed in a compact 25mm body. With a no-load speed of ~99 RPM and a chunky stall torque of 15 kg·cm, it’s a solid choice for small robots and mechanisms that need to push, lift, or drive heavier loads than typical hobby motors.
Compatibility-wise, it runs from a 6V DC supply and is best driven through a proper DC motor driver—it can draw up to 6.0A at stall, which is far beyond what microcontroller pins or small H-bridges can handle directly. The output is a 4mm D-shaped shaft (12.5mm long), so you’ll want wheels, hubs, couplers or pulleys that match a 4mm D-shaft. It’s a brushed motor (not stepper/servo), so speed control is typically via PWM from a motor driver; for precise speed/position control, consider the encoder-equipped version.
Practical uses include 2WD/4WD rover drive trains, compact winches and linear actuators (via leadscrew), motorised doors/arms, and classroom robotics where durability matters. Compared with lower gear ratios (e.g., ~30:1), this 99:1 version trades top speed for much higher torque and better load handling; compared with plastic gearmotors, the metal gearbox is tougher under repeated starts/stops and higher loads.
Suggested add-ons include a suitable high-current motor driver (e.g., Dual Motor Driver), a 6V battery pack or regulated supply (e.g., 6V Battery Pack), and 4mm D-shaft mechanical hardware like wheel hubs or couplers (e.g., 4mm D-Shaft Hub).
Key Features
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Pololu
99:1 Metal Gearmotor 25Dx54L mm HP 6V
A high-power 6V brushed DC gearmotor with a 98.78:1 metal spur gearbox. The cylindrical motor body measures just under 25mm in diameter, and the D-shaped out...
A high-power 6V brushed DC gearmotor with a 98.78:1 metal spur gearbox. The cylindrical motor body measures just under 25mm in diameter, and the D-shaped output shaft is 4mm in diameter, extending 12.5mm from the gearbox face plate. Also available with an integrated encoder for closed-loop control.
Specifications
- Gear Ratio – 98.78:1
- Voltage – 6V
- No-Load Speed – 99 RPM
- No-Load Current – 420mA
- Stall Torque – 15 kg·cm (210 oz·in)
- Stall Current – 6.0A
- Motor Diameter – ~25mm
- Output Shaft – 4mm D-shaped, 12.5mm length
- Gearbox – Metal spur gears
- Dimensions – 25D × 54L mm
Ideal For
- Robotics drive systems
- Motorised mechanisms and actuators
- Projects requiring high torque in a compact form factor
Package Contents
- 1× 99:1 Metal Gearmotor 25D×54L mm HP 6V
Jargon buster
Plain-language definitions for the technical terms used above.
- closed-loop control
- Closed-loop control means the system uses feedback, such as motor position or speed, to adjust its output automatically. This matters because it can keep a motor moving accurately even when the load changes, unlike simple open-loop control.
- encoder
- A device attached to a motor or shaft that reports movement, such as rotation steps or position. In a pump system, an encoder can help measure or control how much the motor has turned, which affects how repeatable the watering amount can be.
- kg·cm
- A torque unit often used for hobby servos, meaning how many kilograms of force the servo can hold at a 1 cm arm length. A higher kg·cm rating means the servo can move or hold heavier loads, but power supply current needs may also increase.
- Torque
- A twisting force that causes something to rotate, usually measured in newton-metres or kilogram-centimetres. It matters when choosing motors, servos, gears, and tools because higher torque is needed to lift heavier loads, turn larger wheels, or move mechanisms without stalling.
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Brands
Robotics & Motion
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