ALAR-LP Large Aperture Rotary Stages


Design Features

  • Low-profile form factor with overall stage height as short as 65 mm
  • Direct-drive torque motor delivers extremely precise, smooth, cog-free rotation
  • Generous axial- and radial-load capacity is suitable for linear/rotary stage combinations and certain gimbal configurations
  • Long service life and consistent performance over time
  • Engineered for easy integration into multi-axis systems and machines
Aerotech’s ALAR family of direct-drive rotary stages provides superior angular positioning and velocity control. ALAR-LP (low profile) offers a generous payload capacity with a short overall height, making it ideal for space- or weight-constrained applications that require a vertical axis of rotation. Other members of the ALAR family include the ALAR-SP, which offers a balance of load capability, torque, and form factor, and the ALARXP, which delivers the highest levels of torque.

Advantage: ALAR

ALAR-LP offers numerous advantages over worm-drive stages. Because ALAR stages use direct-drive torque motors, they are free from backlash, vibration, and excessive wear commonly associated with gear-driven stages, and they are also capable of much higher speeds and accelerations. These advantages translate to higher system accuracy, repeatability, and longevity, as well as greater throughput. Users can more precisely manufacture, inspect, or process more parts in less time, leading to lower operating costs and higher profits.

Brushless, Slotless Direct-Drive Motors

Aerotech’s brushless, direct-drive motors are featured in all ALAR stages. Because there are neither brushes to wear, nor gear trains or couplings to maintain, ALAR stages are capable of high speeds and accelerations, plus consistent, stable performance over time with zero backlash, windup, or hysteresis. Further, ALAR
motors are both slotless and ironless, thereby eliminating cogging and torque ripple to deliver exceptionally smooth motion. ALAR stages are ideal for applications requiring outstanding contoured motion, smooth scan velocities, and precise incremental steps.

Generous Payload Capacity with a Low Profile

Large-diameter angular contact bearings provide high axial- and radial-load capacities, maximizing positioning performance with respect to axis error motions, stiffness, and rotating friction. ALAR-LP is up to 40% shorter and up to 50% lighter than ALAR-SP, making this low-profile stage attractive in space- and weight constrained applications. ALAR-LP performs best when oriented with a vertical axis of rotation.

Flexible Configurations for Simplified Integration

ALAR-LP is offered with features and options that facilitate easy integration into multi-axis motion systems and subsystems. It is available with a range of clear aperture diameters from 100 mm to 325 mm, and also a variety of feedback options including analog 1 Vpp, digital RS422, and absolute encoders. Continuous
360-degree travel is standard, with available limited-travel options ranging from 10 degrees to 340 degrees. ALAR-LP stages can even be adapted for use in vacuum environments.


Common applications for ALAR-LP stages include single- and multi-axis sensor testing, missile seeker testing, antenna testing, inertial navigation device testing, photonic component alignment, high-accuracy laser machining, and precision wafer inspection. Due to their shorter height and lower mass, ALAR-LP stages are
well-suited for linear/rotary stage combinations, and they can also be used as the azimuth axis in gimbal arrangements. The large-diameter clear aperture and direct-drive motor make ALAR a better-performing alternative to more traditional worm-gear


ALAR-LP Specifications

Mechanical Specifications







Continuous (optional 340° max. limited travel)


100 mm

150 mm

200 mm

250 mm

325 mm

Resolution (Min. Incremental Motion)1

0.1 µrad

(0.02 arc sec)

0.09 µrad

(0.018 arc sec)

0.02 µrad

(0.014 arc sec)

0.05 µrad

(0.01 arc sec)

0.04 µrad

(0.009 arc sec)


± 9.7 µrad (± 2 arcsec)

Bidirectional Repeatability

± 2.4 µrad (± 0.5 arc sec)

Tilt-Error Motion

19.4 µrad (4.0 arc sec)

Maximum Speed3

50 rpm

45 rpm

90 rpm

90 rpm

120 rpm

Maximum Torque

17.5 N•m

22.9 N•m

126.8 N•m

147.9 N•m

213.8 N•m

Continuous Torque

3.0 N•m

4.0 N•m

19.3 N•m

22.5 N•m

35.0 N•m

Axial Load

1175 N

1325 N

4350 N

4590 N

5825 N

Radial Load

950 N

1275 N

4125 N

5050 N

6450 N

Moment Load4

150 N•m

225 N•m

1075 N•m

1475 N•m

2200 N•m

Shaft Inertia

0.022 kg•m2

0.031 kg•m2

0.190 kg•m2

0.310 kg•m2

0.550 kg•m2

Shaft Inertia with Limits

0.026 kg•m2

0.042 kg•m2

0.229 kg•m2

0.383 kg•m2

0.675 kg•m2

Stage Mass

8.3 kg

9.8 kg

28.2 kg

35.0 kg

44.5 kg

Stage Mass with Limits

8.9 kg

10.8 kg

30.1 kg

37.4 kg

49.9 kg

  1. Resolution assumes 1 Vpp encoder with 2000x controller multiplication.
  2. Certified with each stage. Requires the use of an Aerotech controller.
  3. Square-wave digital encoder options will limit maximum speed below the listed value. Contact factory for specific stage and encoder speed combination.
  4. The ALAR-LP base must be fully supported by a rigid mounting surface to achieve the specified moment load.

Electrical Specifications

Electrical Specifications







Brushless Slotless

Continuous Current











Peak Current, Stall











Bus Voltage

Up to 340 VDC

Incremental Encoder Line Count

31,488 lines/rev

36,000 lines/rev

47,200 lines/rev

55,040 lines/rev

64,800 lines/rev

Limit Switches1

5 V, normally closed

  1. Limited travel options only.


Ordering Information

ALAR-LP Large-Aperature Rotary Stage

Option Description
ALAR100LP Mechanical-bearing, direct-drive rotary stage, low profile, 100 mm aperture
ALAR150LP Mechanical-bearing, direct-drive rotary stage, low profile, 150 mm aperture
ALAR200LP Mechanical-bearing, direct-drive rotary stage, low profile, 200 mm aperture
ALAR250LP Mechanical-bearing, direct-drive rotary stage, low profile, 250 mm aperture
ALAR325LP Mechanical-bearing, direct-drive rotary stage, low profile, 325 mm aperture

Travel (Required)

Option Description
  Continuous travel (standard)
-TR010 Limited travel, ±5 degrees
-TR020 Limited travel, ±10 degrees
-TR030 Limited travel, ±15 degrees
-TR060 Limited travel, ±30 degrees
-TR090 Limited travel, ±45 degrees
-TR120 Limited travel, ±60 degrees
-TR180 Limited travel, ±90 degrees
-TR240 Limited travel, ±120 degrees
-TR300 Limited travel, ±150 degrees
-TR340 Limited travel, ±170 degrees

Feedback (Required)

Option Description
-E1 Incremental encoder, 1 Vpp
-E2 Incremental encoder, digital RS422, x4 interpolation
-E3 Incremental encoder, digital RS422, x20 interpolation
-E4 Incremental encoder, digital RS422, x40 interpolation
-E5 Incremental encoder, digital RS422, x100 interpolation
-E6 Incremental encoder, digital RS422, x200 interpolation
-E7 Absolute encoder

Integration (Required)

Aerotech offers both standard and custom integration services to help you get your system fully operational as quickly as possible. The following standard integration options are available for this system. Please consult Aerotech if you are unsure what level of integration is required, or if you desire custom integration support with your system.

Option Description
-TAS Integration - Test as system
Testing, integration, and documentation of a group of components as a complete system that will be used together (ex: drive, controller, and stage). This includes parameter file generation, system tuning, and documentation of the system configuration.
-TAC Integration - Test as components
Testing and integration of individual items as discrete components that ship together. This is typically used for spare parts, replacement parts, or items that will not be used together. These components may or may not be part of a larger system.