This NEMA 17-size hybrid bipolar stepping motor has an integrated 28 cm (11″) threaded rod as its output shaft, turning it into a linear actuator capable of precision open-loop positioning.
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The lead screw built into this stepper motor extends 28 cm (11″) from the face of the stepper motor and weighs 385 g (13.5 oz). We also carry versions of this stepper motor with an 18 cm and 38 cm lead screw, and we also have the stepper motor available without a lead screw.
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| Stepper motor with 28cm lead screw: bipolar, 200 steps/rev, 42×38mm, 2.8V, 1.7 A/phase. |
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| When the nut is prevented from rotating, it travels up or down the rod as the motor rotates. |
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This linear positioning drive consists of our 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 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. This stepper motor comes in three versions with different length lead screws built in: 18 cm, 28 cm, and 38 cm.
NEMA 17-size stepper motors with 18, 28, and 38cm lead 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. We recommend the DRV8825 stepper motor driver carrier or AMIS-30543 stepper motor driver carrier for use with this stepper motor, which allow 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. Extra traveling nuts are also available for purchase separately.
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), we were able to achieve speeds close to 30 cm/s (12 in/s) with the 28 cm lead screw version.
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 colour-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 we recommend using a bipolar stepper motor driver.
The JST XHP-4 connector that terminates the leads of the NEMA 17 stepper motor with 28cm lead screw |
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Our NEMA 17 aluminium 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: We can customise 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 we advise against since the manufacturer specially treats the end of the lead screw to protect the nut.
More specifications are available in the datasheet (63k pdf). Note that while the datasheet is for the stepper motor with 28 cm lead screw, the only difference between the three versions is the length of the lead screw.
The following diagram shows the stepper motor, lead screw, and traveling nut dimensions in mm. The value of L is 182 mm for the stepper motor with 18cm lead screw, 282 mm for the stepper motor with 28cm lead screw, and 382 mm for the stepper motor with 38cm lead screw. Note that the datasheet incorrectly labels the threaded rod as “TR8×3”; it is really a Tr8×8(P2) leadscrew, which is the ISO designation for a trapezoidal metric thread with an 8 mm nominal diameter, 8 mm lead, and 2 mm pitch. (Put more simply, the rod has four independent threads spaced 2 mm apart, so the carriage nut advances 8 mm for each full revolution of the rod.)
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The inside of a bipolar stepper motor
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:
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Note: This stepper motor is SOYO part number SY42STH38-1684A.
| Size: |
42.3 mm square × 38 mm (NEMA 17)1 |
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| NEMA size: | 17 |
| Weight: | 385 g2 |
| Shaft diameter: | 8 mm |
| Shaft type: | 28 cm threaded rod3 |
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| Steps per revolution: | 200 |
| Current rating: | 1680 mA4 |
| Voltage rating: | 2.8 V |
| Holding torque: | 51 oz·in |
| Resistance: | 1.65 Ohm4 |
| Inductance per phase: | 3.2 mH |
| Number of leads: | 4 |
| Lead length: | 16 cm5 |
Yes. To avoid damaging your stepper motor, you want to avoid exceeding the rated current, which is 600 mA in this instance. The DRV8825 stepper motor drivers let you limit the maximum current, so as long as you set the limit below the rated current, you will be within spec for your motor, even if the voltage exceeds the rated voltage. The voltage rating is just the voltage at which each coil draws the rated current, so the coils of your stepper motor will draw 600 mA at 3.9 V. By using a higher voltage along with active current limiting, the current is able to ramp up faster, which lets you achieve higher step rates than you could using the rated voltage.
If you do want to use a lower motor supply voltage (under 8 V) for other reasons, consider using our DRV8834 low-voltage stepper motor driver carrier.
The answer to this question depends on the type of stepper motor you have. When working with stepper motors, you will typically encounter two types: unipolar stepper motors and bipolar stepper motors. Unipolar motors have two windings per phase, allowing the magnetic field to be reversed without having to reverse the direction of current in a coil, which makes unipolar motors easier to control than bipolar stepper motors. The drawback is that only half of the phase is carrying current at any given time, which decreases the torque you can get out of the stepper motor. However, if you have the appropriate control circuitry, you can increase the stepper motor torque by using the unipolar stepper motor as a bipolar stepper motor (note: this is only possible with 6- or 8-lead unipolar stepper motors, not with 5-lead unipolar stepper motors). Unipolar stepper motors typically have five, six, or eight leads.
Bipolar steppers have a single coil per phase and require more complicated control circuitry (typically an H-bridge for each phase). The DRV8824/DRV8825 has the circuitry necessary to control a bipolar stepper motor. Bipolar stepper motors typically have four leads, two for each coil.
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| Two-phase bipolar stepper motor with four leads. |
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The above diagram shows a standard bipolar stepper motor. To control this with the DRV8824/DRV8825, connect stepper lead A to board output A1, stepper lead C to board output A2, stepper lead B to board output B1, and stepper lead D to board output B2. See the DRV8824 or DRV8825 datasheet for more information.
If you have a six-lead unipolar stepper motor as shown in the diagram below:
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| Two-phase unipolar stepper motor with six leads. |
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you can connect it to the DRV8824/DRV8825 as a bipolar stepper motor by making the bipolar connections described in the section above and leaving stepper leads A’ and B’ disconnected. These leads are centre taps to the two coils and are not used for bipolar operation.
If you have an eight-lead unipolar stepper motor as shown in the diagram below:
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| Two-phase unipolar stepper motor with eight leads. |
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you have several connection options. An eight-lead unipolar stepper motor has two coils per phase, and it gives you access to all of the coil leads (in a six-lead unipolar motor, lead A’ is internally connected to C’ and lead B’ is internally connected to D’). When operating this as a bipolar stepper, you have the option of using the two coils for each phase in parallel or in series. When using them in parallel, you decrease coil inductance, which can lead to increased performance if you have the ability to deliver more current. However, since the DRV8824/DRV8825 actively limits the output current per phase, you will only get half the phase current flowing through each of the two parallel coils. When using them in series, it’s like having a single coil per phase (like in four-lead bipolar steppers or six-lead unipolar steppers used as bipolar steppers). We recommend you use a series connection.
To connect the phase coils in parallel, connect stepper leads A and C’ to board output A1, stepper leads A’ and C to board output A2, stepper leads B and D’ to board output B1, and stepper leads B’ and D to board output B2.
To connect the phase coils in series, connect stepper lead A’ to C’ and stepper lead B’ to D’. Stepper leads A, C, B, and D should be connected to the stepper motor driver as normal for a bipolar stepper motor (see the bipolar stepper connections above).
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