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Texas Two Step: A dual axis motor controller for equatorial telescope mounts

![Texas Two Step breadboard prototype controlling an unloaded Orion Astroview] (https://github.com/dadap/tx2step/raw/master/img/tx2step-breadboard-proto.jpg)

Introduction

The Texas Two Step is a replacement hand controller for the Synta Dual-Axis motor kit for EQ-3 and EQ-5 type equatorial mounts (it can probably be adapted to other mount designs utilizing stepper motors as well), with the following improvements:

  • Faster setting rates (original HC is limited to 8x sidereal)
  • Analog 2-axis joystick to control setting rates (instead of rate slider switch combined with directional pad)
  • ST-4 support with independent guiding (ST-4) and setting (joystick) rates.
  • Main unit attaches to mount; RA, DEC, ST-4 cables move with telescope, and a single cable connects the control unit to a handheld joystick unit.
  • Integrated rechargeable battery (to replace 4x D-cell pack, and eliminate the additional cable for power)
  • All LEDs are dim and red to preserve dark adaptation
  • Additional tracking rates (solar, lunar)
  • Smaller and lighter
  • Lower power draw (current prototype draws about .5 W for tracking)

The Texas Two Step is powered by an Atmel AVR microprocessor (currently an Atmega328P on a breadboarded prototype circuit) and the stepper motors are driven by dual TI DRV8834 low-voltage stepper driver ICs. The DRV8834 is selected to allow a common power source (5V, boosted up from the output of a single 18650 LiIon cell) for the logic and the motors.

TODO

A schematic and PCB layout should eventually be added to this repository.

The following features are not yet implemented:

  • Directional switching not implemented; RA tracking direction is dependent on the order of stepper motor wiring to the driver boards. The final design is intended to allow switching between northern and southern hemisphere operation via a DIP switch or jumper setting.

The following features may or may not eventually be implemented:

  • Backlash compensation (probably in the declination axis only; RA guiding at less than 1x tracking rate requires no backlash compensation.)
  • Periodic error correction: implementing this will probably require some form of persistent storage, as the available EEPROM storage on the microcontroller is likely insufficient.