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26:1 sub-micro plastic planetary gearmotor next to a micro metal gearmotor and a LEGO Minifigure for size reference. |
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Sub-micro plastic planetary gearmotors. Gear ratios from top to bottom: 700:1, 136:1, 26:1. |
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Overview
These tiny brushed DC gearmotors have a diameter of just 6 mm and weigh just over a gram, which makes them great actuators for miniature robots and very small mechanisms. They consist of a coreless motor fastened to a planetary gearbox by a small clip. The gears are made from liquid crystal polymers (LCPs), and gearbox’s nylon output shaft is compatible with our 14 mm wheels. Three gear ratios are available:
- 26:1, which has a free run speed of 2500 RPM and stall torque of 1.5 oz-in (110 g-cm) at 6 V
- 136:1, which has a free run speed of 500 RPM and stall torque of 8 oz-in (550 g-cm) at 6 V
- 700:1, which has a free run speed of 90 RPM and stall torque of 12 oz-in (900 g-cm) at 6 V
Note: Stalling or overloading gearmotors can greatly decrease their lifetimes and even result in immediate damage. For these gearboxes, the recommended upper limit for instantaneous torque is 3.5 oz-in (250 g-cm); we strongly advise keeping applied loads well under this limit. Stalls can also result in rapid (potentially on the order of seconds) thermal damage to the motor windings and brushes; a general recommendation for brushed DC motor operation is 25% or less of the stall current.
The intended nominal operating voltage for these motors is 3 V to 6 V, though in general, these kinds of motors can be used at voltages outside this range (rotation typically starts between 0.2 V and 0.3 V). Lower voltages might not be practical, and higher voltages could start negatively affecting the life of the motor. When operating at 3 V, the free-run speed, stall torque, and stall current will all be approximately half of what they are at 6 V as these specifications scale roughly linearly with voltage.
Since the gearmotor’s output shaft is nylon, there can be small variances in the diameter from unit to unit. These variations might cause press-fit attachments like our 14 mm wheel to fit loosely in some instances. If you experience a loose fit, you could try swapping wheels or using a small dab of glue to help hold the wheel on.
Gearmotor dimensions
The following diagram shows the micro plastic gearmotor dimensions in mm. The planetary gearbox has a D-shaped plastic output shaft, which is 2 mm in diameter with a section that is flattened by 0.5 mm. The “D” portion of the shaft is 2.5 mm long. The motor measures 6 mm in diameter and 9.3 mm in length, and the gearbox length, labeled “L” in the diagram below, depends on the gear ratio.
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Dimensions of the Sub-Micro Plastic Planetary Gearmotors. Units are mm over [inches]. |
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This dimension diagram is also available as a downloadable PDF (92k pdf).
These motors originally shipped with leads that extended approximately 2 cm (0.8″) from the back of the motor, but we began transitioning to shipping units with much longer leads (approximately 12.5 cm, or 5″) in January, 2017. All units shipping now have the new, longer leads. These leads are pre-stripped and unterminated (i.e. they do not end in a connector).
Motor accessories
The micro plastic gearmotor’s output shaft is compatible with our 14 mm wheels. We do not have any brackets for this gearmotor, and it does not have any mounting holes, but its compact size makes it easy to fasten with tape or glue. Alternatively, since this gearmotor is nearly the same size as a 1/4″ fuse, it can be mounted using standard 1/4″ (6 mm) fuse clips, which can be found at places like Radio Shack and Digi-Key.
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