# D28.1 UHV Stepper Motor

> 1.8°, two phase hybrid stepper motors (1 x 10-10 mBar)

Canonical product page: [https://arunmicro.com/products/D28-1_UHV_Compatible_Stepper_Motor/](https://arunmicro.com/products/D28-1_UHV_Compatible_Stepper_Motor/)

55 mNm, NEMA 11

## Product details

- Product code: `d28.1`
- Category: [Ultra High Vacuum Stepper Motors](https://arunmicro.com/products/category/uhv-stepper-motors/)
- Made in the UK
- UK-based support

## Best for

Compact ultra-high-vacuum motion applications where installation space is limited and relatively low motor torque is required.

The D28.1 is AML's smallest D-series UHV stepper motor, with a NEMA 11 frame size and 55 mNm holding torque. It is intended for low-speed, precision in-vacuum positioning and manipulation.

Choose the D28.1 when compact size is a priority and 55 mNm holding torque is sufficient.

Suitable for UHV systems operating below 1 × 10⁻¹⁰ mbar. Standard specification includes a 1.8° step angle, operating temperature range of -65 °C to +190 °C and bakeout capability to 200 °C. Cryogenic, radiation-hardened, PT100 and custom-shaft configurations are available.

## Not suitable when

Do not select the D28.1 where the application requires more than 55 mNm holding torque; consider a larger AML D-series motor.

Consider the D35.1 where a small increase in motor size is acceptable and up to 75 mNm holding torque is required. For substantially higher torque requirements, consider the D42 or D57 series.

The standard D28.1 is not suitable for operation below -65 °C; select the cryogenic D28.1-C version for operation down to -196 °C.

Applications involving unusually high speed, high duty cycle, significant axial or radial shaft loading, special shaft geometry or unusual environmental conditions should be reviewed with AML before selection.

## Selection guidance

Select the D28.1 primarily when minimum motor size is important and 55 mNm holding torque is sufficient.

Alternative D-series motors provide progressively greater torque:
- D35.1: 75 mNm, NEMA 14
- D42.1: 250 mNm, NEMA 17
- D42.2: 450 mNm, NEMA 17
- D42.3: 550 mNm, NEMA 17
- D57.1: 1,000 mNm, NEMA 23

Motor selection should consider required torque at the intended operating speed, duty cycle, motor temperature, mechanical loading and vacuum environment rather than holding torque alone.

## Compatibility and prerequisites

The D28.1 is a two-phase bipolar hybrid stepper motor designed for installation inside an ultra-high-vacuum system.

A compatible bipolar stepper motor drive is required. AML SMD3 and SMD4 drives are designed for use with AML D-series vacuum stepper motors.

The embedded motor temperature sensor should be used for motor protection because convection cooling is absent in vacuum. Standard motors use an embedded Type K thermocouple; a PT100 temperature sensor is available as an option.

Confirm that the mounting arrangement, shaft coupling, axial and radial loads, vacuum-compatible cabling, electrical feedthrough and motor drive are suitable for the application.

## Ordering guidance

Standard order code: D28.1 — 55 mNm UHV stepper motor.

Available configurations include:
- D28.1-C — cryogenic version, -196 °C to +190 °C
- D28.1-P — PT100 temperature sensor instead of the standard thermocouple
- D28.1-R — gamma-radiation-hardened version, rated to 1 × 10⁶ Gy
- D28.1-X — custom shaft modification

Before requesting a quotation, provide the required quantity and identify any cryogenic, radiation, temperature-sensor, bearing, shaft, connector or cabling requirements.

For custom shaft configurations, provide AML with a dimensional drawing or sketch.

If motor suitability is uncertain, provide the required operating pressure, temperature range, torque or load requirement, operating speed, duty cycle and mechanical interface.

## Order codes

| Order code | Description | Price |
| --- | --- | --- |
| D28.1 | 55 mNm UHV stepper motor | £841.00 |
| D28.1-C | D28.1, Cryogenic -196 °C to +190 °C | £934.00 |
| D28.1-P | D28.1 with PT100 temperature sensor in lieu of thermocouple | £900.00 |
| D28.1-R | D28.1, Gamma radiation hardened | £934.00 |
| D28.1-X | D28.1 with shaft modification | Price on request. Contact AML for a quotation. |

## Overview

New AML UHV stepper motor size.

Compact UHV stepper motor. Ideal for space restricted applications with low torque requirements.

- Suitable for use below 1 x 10-10 mBar (7.5 x 10-11 Torr)

- Continuous running in vacuum at high torque and step rates with AML drive

- Bakeable to 200 °C

- Step angle of 1.8°

- Step angle tolerance of ±5%

- Operational temperature range -65 °C to +190 °C

- Embedded thermocouple or PT100 sensor

- Open construction with all internal spaces vented

- Cryogenic extended operating temperature option available, range -196 °C to +190 °C

- Gamma radiation hard versions available 1 x 106 Gy

- Standard motors are fitted with open stainless steel bearings, lubricated with NyeTorr® 6300 ultra low outgassing UHV grease 

- Hybrid silicone nitride ceramic bearings option available, dry lubricated with tungsten disulfide

- Custom shaft modifications available

## Technical Data

##### Specifications

| Specification | Value |
| --- | --- |
| Motor type | Two-phase hybrid stepper motor |
| Vacuum compatibility | Below 1 × 10-10 mbar |
| Holding torque | 55 mNm |
| Detent torque | 6 mNm |
| Step angle | 1.8° |
| Step-angle tolerance | ±5% |
| Current per phase | 1.0 A |
| Phase resistance | 5.0 Ω |
| Phase inductance | 2.8 mH |
| Rotor inertia | 14 gcm² |
| Mass | 145 g |
| Maximum axial force | 5 N |
| Maximum radial force | 9 N |
| Operating temperature | −65 to +190 °C |
| Bakeout temperature | 200 °C |
| Temperature sensor | Type K thermocouple |
| Lead length | 1.5 m |
| Lead termination | 1.5 mm crimp sockets |
| Standard bearings | Open stainless steel |

##### Motor Dimensions

| Dimension | Value | Detail |
| --- | --- | --- |
| Frame width × height | 28 × 28 mm | NEMA 11 |
| Body length | 36 ±1 mm | As dimensioned in the drawing; excludes front shaft projection |
| Front shaft diameter | 5.00 mm h7 | Tolerance +0 / −0.012 mm |
| Front shaft projection | 20 ±1 mm | From front mounting face, as drawn |
| Mounting centres | 23 × 23 mm | Square pattern |
| Mounting threads | M2.5 | Use the extended mounting screws; do not adjust the factory assembly screws |
| Thread projection | 6.5 ±1.0 mm | As shown in the drawing |
| Front locating diameter | 21.90–22.00 mm | Locating feature projects 2.0 mm |
| Optional rear shaft | 9 ±1.0 mm | Option X; confirm the required shaft modification when ordering |

## Documentation and downloads

- [Application of UHV Stepper Motors](https://arunmicro.com/documentation/APN_Application_Notes_for_UHV_Stepper_Motors.pdf)
- [Axial & Radial Loads](https://bookstack.vps-da8d40f3.arunmicro.com/books/axial-and-radial-loads-on-aml-stepper-motor-bearings)
- [Datasheet](https://arunmicro.com/documentation/Datasheet_AML_UHV_Compatible_Stepper_Motor.pdf)
- [Magnetic Leakage Fields](https://arunmicro.com/documentation/APN_N28_Magnetic_leakage_fields.pdf)
- [Material Content](https://arunmicro.com/documentation/APN_Material_Content_of_AML_UHV_Stepper_Motors.pdf)
- [Operating Instructions](https://bookstack.vps-da8d40f3.arunmicro.com/books/d-series-uhv-stepper-motor-user-manual)
- [RoHS](https://arunmicro.com/documentation/CE_AML_UHV_Stepper_Motors.pdf)
- [Vacuum Performance](https://arunmicro.com/documentation/APN_Vacuum_Performance_of_AML_UHV_Stepper_Motors.pdf)
- [CAD Models (.STEP)](https://arunmicro.com/downloads/CAD_VCSM.zip)

## Related products

- [D35.1 UHV Stepper Motor](https://arunmicro.com/products/D35-1_UHV_Compatible_Stepper_Motor/): 75 mNm, NEMA 14
- [SMD4 Stepper Motor Drive](https://arunmicro.com/products/smd4-stepper-motor-drive/): Stepper motor drive optimised for use with AML UHV-compatible motors. Features advanced connectivity with USB, Ethernet and RS232/485 interfaces. Optional encoder module for incremental and absolute encoders
- [SMD3 Stepper Motor Drive](https://arunmicro.com/products/smd3-stepper-motor-drive/): Stepper motor drive optimised for use with AML UHV-compatible motors. Four operating modes including USB remote from a host PC and opto-isolated step and direction inputs. Continuous monitoring of motor temperature is provided with automatic shutdown to prevent motor damage.
- [MLF18F](https://arunmicro.com/products/electrical-feedthrough/): MLF18F 18-way feedthrough on a DN40 CF flange (70 mm OD). Individual glass compression seals and bakeable to 250°C.
- [MLF18 UHV Connectors](https://arunmicro.com/products/vacuum-side-connector/): UHV, 18-way Vacuum-Side Connectors.
- [D-sub UHV Connectors](https://arunmicro.com/products/d-sub-connectors/): UHV, bakeable D-sub connector. 9 and 15-way female connectors available for mating with the VFxxD-xxCF feedthroughs.