Precision Instruments for Astronomy

Xerxes Scientific designs and produces precision astronomical instrumentation for scientific research.

Our primary area of focus is semi-custom telescope mounts and control systems for astronomical imaging. Our D11 and D21 direct drive modules are part of our modular telescope mount system, which can either be incorporated into custom telescope mounts or be provided with mounting hardware in kit form for ready assembly and installation at the customer's site. In addition to direct drive modules, also in development are modular friction drive components which can be used with telescopes ranging from small consumer telescopes to observatory class instruments weighing up to 1,000 lbs. Our design philosophy emphasizes the use of the latest generation of industry standard electronics and control protcols, which protects your investment by future-proofing the electronics, which are the least reliable part of a telescope control system.

Products coming in 2019

Drive Systems and Components

D11 & D21 Direct Drive Systems

D11 Drive design	D11 single axis on test platform	M77, stack of 15 five minute unguided exposures, 2500mm focal length SCT

screenshot of Astrometrica star profile from unguided five minute exposure>

The D11 Modular Direct Drive System comprises a custom-built high torque direct drive servomotor, precision 26 bit absolute encoder, and CANopen compatible electronic controller. Two D11 modules can be combined to create a custom equatorial, alt-alt, or alt-azimuth telescope mount. Direct drive systems are ideal for telescope pointing and control as they completely eliminate backlash and nagging worm gear adjustment and alignment. Direct drive systems also automatically compensate for disturbances to the telesope such as wind gusts.

Design characteristics

• 210mm OD (150mm ID) high rigidity crossed roller bearing eliminates preload adjustments and is fully rigid in all axes
• 11 N-m (D11) to 21 N-m (D21) continuous torque output easily accomodates common imbalance issues
• 34 N-m (D11) to 64 N-m (D21) peak torque
• 200mm Renishaw precision code ring provides higher precision than competitors with 150mm code rings
• 26 bit industry-standard absolute BiSS encoder
• CANopen interface compatible with all Modular Direct Drive Components and many other industrial control products
• NexStar emulation
• ASCOM over ethernet interface for common astronomical control software (using host PC)
• Overall dimensions of motor: appx. 250mm x 145mm
• Unit weight: 45 lbs
• Servo Drive (per axis): 115VAC power, 6A continuous, 18A peak, plus 24VDC 1A auxiliary supply in NEC electrical enclosure
• Servo drive safety approvals: IEC 61010-1:2001, UL 61010-1

Example of a GEM-style equatorial mount made from two D11 drive units, counterweight plate, plus mounting hardware:

Why CANopen?

CAN (Controller Area Network) was originally developed by Bosch for use in automobiles, but is now the de facto standard for industrial control systems. CAN data buses provide two-way communication between nodes, using an eight byte message payload, and provides speeds up to 1Mbit/sec. CANopen is an open standard protocol for industrial control systems using the underlying CAN phyical and logical layers. CANopen servo drives are widely available and constantly being improved which provides future-proofing to the system designer and customer. Multiple drive axes, sensors, and control end points (such as a hand controller, ST-4 guide port, tilt and temperature sensors) can be attached onto the common bus, and the Xerxes Modular Drive system provides a simple cable interface for all equipment, using only four wires. CANopen control has been proved out in our traditional DC servo drive system currently installed at our observatory in Eastern Washington, which carries a Meade 16" f/10 SCT on a custom offset axis equatorial mount.

Copyright (c) 2018 Xerxes Scientific, LLC

For more information write to bruce@xerxesscientific.com.

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