Our Telescope Control Functionality page describes the functionality of our PrimeTCS-i controller.  This page describes the physical details of PrimeTCS-i.

Clean System Architecture

PrimeTCS-i is architected for optimal real world application.  From decades of experience installing telescope control solutions we have learned a great deal about implementing systems that are robust and reliable.  In particular, by far the leading cause of problems is cable or connector failures.  Because of this, PrimeTCS-i has been designed around two important principles best assuring system reliability:

  1. Electronic co-location: locate the TCS electronics near the “use point” thus minimizing cabling
  2. Exclusive use of quality components in the design
Electronic Co-Location

Our PrimeTCS products include two electronics modules, one for RA/Az and one for Dec/Alt.

PrimeTCS is designed to minimize wiring and cabling by co-locating the electronics modules with the motors and encoders.  As the adjacent diagram shows, with separate electronics modules mounted near their associated components (e.g., motors, encoders, guider, handpaddle), the cabling is localized and does not need to run back to the mount’s base or other central location.  To facilitate this electronics co-location a single high-flex and tough jacketed cable (of customer specified length) is used to connect the two electronics modules.  This cable, shown in green in the diagram, consolidates what would otherwise be many cables (e.g., motor signals, encoder, autoguider, limit switches, handpaddle) into one signaling interface.

Of course, the PrimeTCS electronics modules can be mounted centrally if one chooses.

Exclusive Use of Quality Components

See the adjacent diagram for a summary of PrimeTCS' quality attributes. PrimeTCS is backed by a 2 year warranty against defects in materials or workmanship.

 Visit the PrimeTCS-i spec sheet

Broad Spectrum of Motor Options

PrimeTCS-i is an “indexing” motor controller and as such outputs step and direction signals.  Commercially available motor drivers commonly accept step/dir controller inputs hence PrimeTCS-i can be used with a broad selection of motors and drivers.

Contact us for help in interfacing PrimeTCS-i to existing motors or in selecting new motors.

Complete PrimeTCS-i systems integrated with brushless servo motors

Astrometric offers PrimeTCS-i systems integrated with servo motors available in a variety of sizes.  Our motors include motor drive electronics attached directly to the servo motor.  There are no separate drive electronics modules.  All of our motors are high performance brushless servo motors providing smooth, accurate, efficient and trouble-free operation.

Our PrimeTCS-i integrated systems include everything needed to apply state of the art telescope control to virtually any instrument.  Systems include all the necessary cabling and power supplies and are configured, setup and tested at Astrometric prior to shipment.  Various gearbox options are available.  Contact us for help selecting a PrimeTCS-i integrated system.  A table of common configurations is provided below.

Motor Size
Face x L (in)
Motor Size
Face x L (mm)
Continuous Torque
Continuous Torque
Max rated RPM SKU
2.33 x 3.34 59 x 85 58 0.41 2880 MOTOR-5-01
2.33 x 4.84 59 x 123 124 0.88 2130 MOTOR-7-01
3.42 x 5.38 87 x 137 277 1.95 1380 MOTOR-4-01
3.42 x 5.38 87 x 137 478 3.38 730 MOTOR-8-01

Many other motor options are available.  Contact us to explore options.

Each of the above motors includes a 6400-count (built-in) encoder and is available with an integral planetary gearbox.  The following reduction ratios are available: 3:1, 4:1, 5:1,  7:1,  10:1,  15:1,  25:1,  30:1,  40:1,  50:1,  70:1 or 100:1.

View PrimeTCS-i integrated systems pricing

Telescope drive system options

Astrometric has extensive experience with selection of gearing, belts/pulleys and other drive system components that are uniquely suited to accommodating the twin needs of precise, smooth and stable low-speed tracking and high speed accurate slew for object acquisition.  Visit our Drive System Options page for more details.

Regardless of the type of drive system, and particularly for non-geared systems where, for example, a pinion-on-disk or belt reduction is used, tracking and pointing accuracy can be dramatically improved using optional high resolution axial encoders.

Diverse axial encoder options

While PrimeTCS can be operated "open loop" without high-resolution axial encoders, superior pointing and tracking performance can be achieved using optional encoders which accurately sense the real telescope axis angle of rotation.  With suitable encoders, system performance is largely unaffected by drive system errors such as periodic gear error or pulley/belt tooth “cogging”.  We have extensive experience using encoder options from many vendors; particularly Heidenhain and Renishaw.

Encoders are broadly available in two styles:

  • Incremental: requires initial alignment to find the axial “zero” point. This is commonly called “homing”.
  • Absolute: requires no initial alignment and will not lose alignment after being properly setup once at the time of system installation.

Astrometric provides support for both of these encoder styles.  Details follow...

Direct incremental encoder support

PrimeTCS-i directly interfaces to incremental quadrature encoders providing TTL or CMOS voltage levels with count rates up to 4MHz and count resolution up to 1 billion counts/rev.  A common solution is to use tape and readhead encoders such as the Renishaw Tonic units shown in the adjacent images.

HREM2: RS422/485 differential signaling interface

Most modern high-resolution incremental encoders provide quadrature and index outputs in a differential electrical format: either RS422 or RS485.  Astrometric provides the HREM2 RS422/485 to TTL converter to allow these types of encoders to be connected into PrimeTCS.

HRAM: absolute encoder support

As mentioned above, PrimeTCS directly supports standard incremental quadrature encoders or, with the HREM2 accessory, encoders which provide differential drive signals.  Incremental encoders have the disadvantage that they must be “zeroed” (or “indexed”) through an alignment process involving sky sighting or a homing operation.  Absolute encoders provide a fixed (or absolute) angle value at all times and, as such, remove the need for sky sighting or homing to align the telescope.  In addition to providing convenience for remote/autonomous operation, absolute encoders eliminate the complexity of alignment via homing or sky sighting and provide a more reliable system.

Our High Resolution Absolute encoder Module (HRAM) provides interfacing to absolute encoders.  The HRAM supports absolute encoders from Heidenhain, Renishaw and other vendors that use the EnDat, BiSS or SSI interfaces.

Other Interface Features

PrimeTCS provides the following additional features which are of particular value for remote/autonomous installations.

External “park” and “parked” signals

Often a telescope needs to be put into a safe position prior to closing the telescope’s enclosure (e.g., roll-off roof) in order to assure that the enclosure “clears” the telescope when it closes.  Additionally, for remote operation, roof closure is often signaled via a “weather safe” device. PrimeTCS provides a Park In input that allows a weather safe device to signal the telescope to park.  Once parked at its safe/pre-defined position, PrimeTCS asserts its Parked Out signal which can then be used to safely close the telescope enclosure.

Analog limit encoder input

PrimeTCS provides an analog input used to sense axial hard limit switches.  These switches can be assigned a particular angle providing absolute position re-set in the event a limit switch is struck.

General purpose digital output

Can be toggled from Maestro or ASCOM scripted interface.

Drive enable

An external drive enable is provided that de-asserts in the event of any fault or hard limit strike.