Open Telescope Controllers: OnStep and AstroEQ

I ran across two telescope automation projects recently.

OnStep Telescope

One is called: OnStep by Howard Dutton. Basically, it is a Do It Yourself (DIY) conversion of theoretically any mount to become a GOTO that can be controlled from a computer, or optionally via WiFi or Bluetooth, from a smart phone or tablet. Howard even created a free Android app for controlling the mount.

Open Telescope Control

What is different about OnStep is that it is an open solution for telescope control, and it implements the Meade LX200 command set, making it compatible with various Planetarium software, including the following:

There is also an INDI, device driver for OnStep that provides support for the few extensions that Howard made to the LX200 protocol. This allows things like using any OnStep mount with the excellent Ekos imaging automation platform that comes with KStars.

Versions Of OnStep

There are basically two designs for OnStep.

The older one, based on ArduinoMega 2650 board as the brains, with A4988 or DRV8825 stepper drivers.

The newer one is based on Teensy 3.2, which has more processing power and memory than the Mega, and the based on the Trinamic TMC2130 stepper driver.

The latter, as Howard explains, is far superior, providing more precision, and quieter operation. His findings are confirmed by emails in the Yahoo Group, and on Cloudy Nights.

Here is an article that explains how the why the Trinamic TMC2130 is superior, using microstepping.

How To Build Your Own OnStep

There are several ways to build your own OnStep:

Using a plain Perboard

For this option, the components are all put on a plain piece of perfboard, and wires are jumpered all over the place to make the right connections. This would be error prone for someone inexperienced, like myself.

User benula on CloudyNights shared pictures of his specific build. The motors are connected using DIN connectors for robustness.

Using Teensy Shield Board

This option relies on the Teensy shield board which comes with a 12 volt barrel socket, DC to DC converter for 5 volt power, and pin headers. Also needed is another perfboard shield that the stepper drivers and WiFi module will go on. The drawback of this solution is that it still requires jumper soldering.

User TonyStar shared the details of his build on Cloudy Nights.

The following are the main components needed for Tony's version.

Sparkfun parts

DigiKey Canada Parts

DigiKey provides the same items as Sparkfun, but can be more economical and/or offer free shipping. DigiKey has a Canadian store, and free shipping for orders over $100. If you are in the USA, the same URL will work if you change '.ca' in the domain name to '.com'.

There are lots of additional pieces needed, such as a perfboard to build the project on, an RJ type connector if you want an ST4 port, sockets for connecting the motors, and capacitors.

Ready Printed Circut Boards for OnStep

There are a couple of designs for Printed Circuit Boards (PCBs), but they are hard to find at first.

Although these PCBs require soldering, but it is all straight down through the board, with no need to do any jumper cables, and that minimizes errors.

The cost of printing the boards is not cheap, each costing $40 to $45 in quantities ranging from a minimum of 3 to 5 at most providers. At Fritzing, the cost seems to be cheaper: 51.30 Euro for 3 PCBs, VAT and shipping included (~ $75 CAD).

Howard's OnStep Mini PCB

Howard Howard Dutton designed an OnStep Mini PCB board, and posted its details on Cloudy Nights. This is a vertical build, meaning all the power, USB and ST4 connections are at a right angle to the board's plane.

Christian Kampf CKScope

There is another design by Christian Kampf, called CKScope, based on the Teensy 3.5 based. It lacks an ST4 autoguiding port.

In order to get the above two designs, you have to first join the OnStep Telescope Yahoo Group, which is a restricted group, wait until you are approved, then go the files section, and after some searching, you will find two designs. As an open source contributers for the best part of two decades, I never understood why there are such barriers put in place. This hinders collaboration by adding barriers for potential adopters or contributors. If spam is the problem, then make the group read only, and still require people to be approved if they want to post messages.

DragonLost94 On Fritzing

Yet another design based on Teensy 3.2 by dragonlost94 at Fritzing. Fritzing is an open source application, and a web site where you can share designs and even order a PCB manufactured.

More Resources About OnStep

Here are more links to people who have implemented OnStep by themselves:

  • A project for converting an old CG-11 mount to Goto, using direct coupling of the motors to the worm gear. This way, he avoids Non-Periodic Error (NPE) from the gear reduction.
  • A post by Howard noting that the Teensy + TMC2130 are superior to Mega2650 and DRV8825.
  • A post by Howard Dutton from 2015 on StarGazersLounge.
  • A video by Howard Dutton of his modified Losmandy G11 mount slewing using OnStep.
  • Another OnStep Project
  • Kai Wicker modified a Vixen GPD2 mount to work with OnStep. His solution is a Teensy board, and RAPS128 stepper drivers.
  • A picture of a 3D printed OnStep case based on Teensy and TMC2130. Very compact and functional.
  • Christoph Reinhardt, in German, (Google translation) modified a Vixen Super Polaris to work with OnStep. He provides detailed schematics on what he did. His version is AdruPilot Mega
  • A video of a custom mount using Onstep.
  • An EQ5 mount using OnStep, controlled from a smart phone.
  • Another mount using OnStep and a tablet.
  • Hackaday article

AstroEQ: EQMOD Emulation

Another telescope GOTO project is AstroEQ, from the UK.

Basically, he was a univesity student when he started this project, to convert a non-GOTO motorized mount into a GOTO mount.

A ready made AstroEQ controller is available for purchase. It has USB on one side, and two connectors for steppers on the other.

You buy your own stepper motors (e.g. this motor), and find a way to install them on the mount, after sourcing pulleys, belts, and custom brackets. Spur transfer gears are also possible. But if pulleys are used, there is zero backlash.

The strong point of this project/controller is that it fully emulates a Synscan EQ6/EQ5 using EQMOD, and is therefore compatible with many software planetariums.

It is therefore usable out of the box with KStars/INDI, just like any EQMOD mount. See this video, and writeup (Italian) for an example. The person even added Bluetooth!

There are some limitations for AstroEQ though:

  • It is meant to be driven from a computer only, so there is no hand controller included, but one is available at extra cost.
  • It does not provide Bluetooth or WiFi on the pre-made controller, although it can be added if you build the board yourself.
  • It uses the older DVR8825 stepper drivers, and does not have TMC2100/TMC2130 by default. This limits the microstepping that can be done, which can be sub arc second if using the latter.

The above translate into advantages for OnStep:

  • Have Bluetooth and WiFi support baked in.
  • Free OnStep App available in Google Play Store, so the mount can be controlled from an Android device. No hand controller needed.
  • Supports higher resolution options when using the TMC2130 controller by microstepping and can go down to a tiny fraction of an arc second that way.

Too bad OnStep does not sell a pre-made controller ...

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