|Stepper motor with 28cm lead screw: bipolar, 200 steps/rev, 42×38mm, 2.8V, 1.7 A/phase.|
|When the nut is prevented from rotating, it travels up or down the rod as the motor rotates.|
This linear positioning drive consists of Pololu's 42×38 mm NEMA17 stepper motor with a built-in lead screw in place of the normal output shaft, which makes it easy to move an object or platform in a linear motion with the precision of a stepper motor. Motors like this are especially popular for use in home-built 3D printers (e.g. RepRap) and CNC machines. The stainless steel threaded rod extends 28 cm (11″) from the face of the stepper motor, and since it is integrated into the motor itself, you do not have to deal with bulky shaft couplers or loose set screws.
The included copper alloy traveling nut (also known as a carriage nut) features a mounting flange with four holes threaded for M3 screws. The nut moves 8.0 mm per full revolution of the lead screw, which allows for a linear resolution of 0.040 mm per full step of the stepper motor. Even smaller step sizes can be achieved through microstepping, which is a feature of many bipolar stepper motor drivers. Pololu recommend the DRV8825 stepper motor driver carrier for use with this stepper motor, which allows for a linear resolution of 1.25 µm per 1/32 microstep. However, please note that the nut is not spring loaded, so changes in direction will result in loss of positioning precision due to backlash.
The maximum achievable linear speed depends a lot on the details of the system, including the load and motor supply voltage. Under ideal conditions (e.g. with gradual ramping up of the step rate, a high supply voltage, and no load), Pololu were able to achieve speeds close to 30 cm/s (12 in/s).
The stepper motor has a 1.8° step angle (200 steps/revolution) and each phase draws 1.7 A at 2.8 V, allowing for a holding torque of 3.7 kg-cm (51 oz-in). The motor has four color-coded wires terminated with a JST XHP-4 connector with 0.1" spacing: black and green connect to one coil; red and blue connect to the other. It can be controlled by a pair of suitable H-bridges (one for each coil), but Pololu recommend using a bipolar stepper motor driver.
Pololu's NEMA 17 aluminum bracket offers a variety of options for mounting this stepper motor in your project:
|NEMA 17 stepper motor with lead screw mounted with a stamped aluminum L-bracket.|
Note: Pololu can customize the shaft length for volume orders (at least a few dozen units). Please contact us for more information. While you might be tempted to cut the lead screw to shorter lengths yourself, this is something Pololu advise against since the manufacturer specially treats the end of the lead screw to protect the nut.
- Size: 42.3 mm square × 38 mm, not including the shaft (NEMA 17)
- Weight: 385 g (13.5 oz)
- Shaft diameter: 8 mm threaded rod
- Shaft length: 28 cm (11″)
- Steps per revolution: 200
- Linear step size: 40 µm (1.6 mil) per full step
- Current rating: 1.68 A per coil
- Voltage rating: 2.8 V
- Resistance: 1.65 Ω per coil
- Holding torque: 3.7 kg-cm (51 oz-in)
- Inductance: 3.2 mH per coil
- Lead length: 16 cm (6.5″)
More specifications are available in the datasheet (63k pdf).
The following diagram shows the stepper motor, lead screw, and traveling nut dimensions in mm. Note that the datasheet and diagram below incorrectly label the threaded rod as “TR8×3”; it is really a TR8×2 rod (the threading has a 2 mm pitch).
|The inside of a bipolar stepper motor.|
Stepper Motor Applications
Stepper motors are generally used in a variety of applications where precise position control is desirable and the cost or complexity of a feedback control system is unwarranted. Here are a few applications where stepper motors are often found:
- CNC machines
- 3D printer/prototyping machines (e.g. RepRap)
- Laser cutters
- Pick and place machines
- Linear actuators
- Hard drives
Note: This stepper motor is SOYO part number SY42STH38-1684A.
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Documentation and Resources:
- The Maker Revolution
The Maker Revolution celebrates the creation of new devices and the modification of existing ones - the transition from a consumer buying goods to eventually having a major part in their creation. The Maker Revolution places strong emphasis on free (...
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