This gearmotor consists of a low-power, 6 V brushed DC motor combined with a 498.87:1 metal spur gearbox. The gearmotor is cylindrical, with a diameter just under 25 mm, and the D-shaped output shaft is 4 mm in diameter and extends 12.5 mm from the face plate of the gearbox. Key specs at 6 V: 12 RPM and 150 mA free-run, 300 oz-in (22 kg-cm) and 2.4 A stall.
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Our Code: MEC-30203
Supplier Link: [Pololu MPN:1591]
These motors are intended for use at 6 V. In general, these kinds of motors can run at voltages above and below this nominal voltage, so they should comfortably operate in the 3 – 9 V range, though they can begin rotating at voltages as low as 1 V. Higher voltages could start negatively affecting the life of the motor.
These gearmotors have output shafts with a diameter of 4 mm. The Pololu universal aluminum mounting hub for 4mm shafts can be used to mount our larger Pololu wheels (60mm-, 80mm -diameter) or custom wheels and mechanisms to the gearmotor’s output shaft (see the left picture below).
We also stock Pololu's 25D Metal Gearmotor Bracket Pair that fits these motors.
The gearbox’s output shaft works directly with the 120mm-diameter Wild Thumper wheels.
The face plate has two mounting holes threaded for M3 screws.
The diagram below shows the dimensions (in mm) of the 25D mm line of gearmotors. The value of 'L' is 27mm for this motor.
| Size: | 25D x 58L mm |
|---|---|
| Weight: | 96 g |
| Shaft diameter: | 4 mm |
| Gear ratio: | 498.87:1 |
|---|---|
| Free-run speed @ 6V: | 12 rpm |
| Free-run current @ 6V: | 150 mA1 |
| Stall current @ 6V: | 2400 mA |
| Stall torque @ 6V: | 300 oz·in2 |
| Motor type: | 2.4A stall @ 6V (LP 6V) |
No; the information Polou have available for this motor can be found on its product page. However, you can approximate various additional motor parameters from the information found in the “Specs” tab.
The electrical resistance of the motor can be approximated by dividing the rated voltage by the stall current (at the rated voltage). The electromotive force constant (Ke) can be approximated by dividing the rated voltage by the free-run speed (at the rated voltage). To approximate the motor torque constant (Kt), you can divide the stall torque by the stall current.
For pretty much any DC motor, the current, speed, power, and efficiency curves as a function of torque will look like those in the graph below (assuming motor voltage and temperature are constant):
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The current and speed curves are approximately linear, and the product pages for Polou's motors provide the approximate end points for these lines: (0 torque, no-load current) and (stall torque, stall current) for the red line, and (0 torque, no-load speed) and (stall torque, 0 speed) for the blue line.
The orange output power curve is the product of the speed and the torque, which results in an inverted parabola with its peak at 50% of the stall torque.
The green efficiency curve is the output power divided by the input power, where the input power is current times voltage. The voltage is constant, so you can divide the output power curve by the current line to get the general shape of the efficiency curve, which in turn lets you identify the torque, speed, and current that correspond to max efficiency.
Note: A good general rule of thumb is to keep the continuous load on a DC motor from exceeding approximately 20% to 30% of the stall torque. Stalling gearmotors can greatly decrease their lifetimes, occasionally resulting in immediate damage to the gearbox or thermal damage to the motor windings or brushes. Do not expect to be able to safely operate a brushed DC gearmotor all the way to stall. The safe operating range will depend on the specifics of the gearmotor itself.
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