Hello everyone,
I’m a bit surprised that this solution, or rather this motor controller, hasn’t appeared in the astro-DIY community yet—or have I missed something?
The motor focuser is based on the Pololu Tic Motor Controller, in my case the Tic T500, with the following specifications:
• USB connection: Direct control without a COM port
• Operating voltage: 4.5 - 35 V
• Microstepping resolutions: Full, 1/2, 1/4, 1/8
• Phase current: Digitally adjustable up to 1.5 A (without cooling)
• Configurable step speed and acceleration
Additionally, the controller offers practical features such as homing, low input voltage detection and much more. Other models in the Tic series even support microstepping resolutions up to 1/256.
The T500 variant costs around $30 in the US (€35 in EU) from electronics distributors.
The connection setup is straightforward: depending on the variant, screw terminals are integrated, so you only need to connect the four phases of a bipolar stepper motor and the power supply (12 V).
An Arduino or separate microcontroller is not required, as the controller independently handles command processing and communication over USB.
Two Potential “limitations”, however these aren’t limitations for me personally, but want to mention:
- the controller loses its position after a restart
- there no integrated temperature sensor
ASCOM Driver
I have developed a fully compliant ASCOM driver for the Tic T500.
You can find the repository with the installer on GitHub:
https://github.com/a...olu-Tic-Focuser
Thanks to the use of LibUsbDotNet, the controller can be addressed directly via USB, eliminating the need for “messing around” with COM ports. It’s basically plug&play.
Currently, the ASCOM driver is “hardcoded” for the Tic T500. To operate it, you only need to install the Pololu USB driver available on the Pololu website, which also includes the Tic Controller configuration program.
Using the Tic Control Center, parameters such as phase current, step speed, direction of motion, and more can be configured. It is only important to disable the “command timeout” feature in the Tic Control Center. Step speed, acceleration, and step mode (full step or microstep) can be individually adjusted based on your equipment.
Planned additional features for the ASCOM Driver in a following version:
• Automatic detection of other Tic models
• Integration of additional functions (e.g., selection of microstepping resolution, adjustment of phase current, direction control) directly in the ASCOM setup dialog
• Customizable step range to set movement limits as needed
• Homing function
Low input voltage detection (VIN_LOW) is already integrated into the driver.
For everything else, the Tic Control Center can be used.
The configured values are permanently stored in the controller.
Functionality
Since the controller loses its position after being powered off, the driver starts with a preset position of 25,000 (out of a total of 50,000 steps), ensuring sufficient movement range in both directions.
The limitation caused by the lack of a temperature sensor can, if necessary, be bypassed with the ASCOM Deepsky Geek Virtual Focuser. This connects the Pololu ASCOM driver (or other motor focusers without temperature sensors) to an alternative temperature source, such as a Pegasus box.
The motor controller and ASCOM driver run stably with a simple bipolar stepper motor and have been extensively tested.
I am currently using a Baader Steeldrive II motor (Baader kindly publishes the motor’s pin configuration in its manual) with the Tic Controller. Thanks to the integrated Hall sensor of the Steeldrive II, I can also use the homing feature of the Tic Controller. I am just waiting for a panel-mount LAN socket with screw terminals to continue.
I hope I’ve sparked your interest!
Best regards,
Alexander
Edited by astro_alex80, 11 January 2025 - 02:48 AM.
