OpenAstroTracker (OAT) is an open-source DIY star tracker which can be build from simple, affordable and 3D printed parts. The main intention behind this device is to provide an affordable possibility to enter the world of astrophotography.
¶ How it works
OpenAstroTracker is an equatorial mount which "compensates for Earth's rotation by having one rotational axis parallel to the Earth's axis of rotation". You can mount a camera (mostly a DLSR or DSLM) on top of it and it rotates with the same speed as our earth rotation in order to remove stars movement relatively to the camera and allow longer exposures this way. The mount is being controlled by an Arduino. The Arduino is controlling multiple stepper motors which in turn rotate the camera mount. The mount provides multiple options for control: LCD Keypad, USB Serial connection, WiFi. Latter two enable remote control with special astrophotography software based either on the LX200 protocol, ASCOM or INDI platforms.
Since the second version of OAT (aluminium base) it is very easy to extend the tracker by various add-ons:
- OpenAstroGuider, a DIY camera and lens which tracks movements of the tracker and allows the controller software to correct tracking issues thus drastically increasing maximal exposure time and image quality.
- Built in GPS module automates several setup steps by parsing current location and time from GPS satellites.
- Digital Level allows a very convenient way of leveling your tracker in order to improve polar alignment, tracking precision and GoTo precision.
- AutoPA is a bigger add-on which is able to automate the polar alignment process by moving whole tracker and using plate solving to align the tracker to the celestial pole.
- Many others to come...
¶ Features
Even thought the project is still under development, OpenAstroTracker already provides a lot of features which can be otherwise found only on very expensive mounts which can cost you thousands of dollars.
¶ LCD and Keypad
The mount has a LCD Keypad module which allows manual control. Most of the core features and some add-ons are supported.
¶ WiFi
Builds based on an ESP32 board allow wireless control of the mount while keeping support for serial connection over a USB cable.
ESP32 is not the primary platform. While it is officialy supported and functional, it is not tested as much as Arduino Mega. Also we don't recommend starting with it if you are a complete beginner. WiFi requires additional setup and adds potential issues.
¶ Remote Control
OpenAstroTracker firmware implements the Meade LX200 protocol. This allows you to use nearly each popular astrophotography software out there to control the mount remotely. In general this enriches the feature set of the standalone tracker by many other features which were implemented into tools like Sequence Generator Pro, Stellarium, KStars etc. If you use the ESP32 board, you can connect and control the tracker from your mobile devices via SkySafari Plus (check the App store).
¶ GoTo
With the help of the GoTo feature you can let the mount point on the celestial object of your interest automatically. Without GoTo you would need to make multiple photos of the night sky and step by step approach your target. With GoTo you can simply enter your target in the LCD menu or control software and the mount will align itself to point towards this target.
¶ Polar alignment helpers
The quality of your images will be mostly dependent on the quality of your polar alignment. In order to help you, OpenAstroTracker already includes several procedures to assist you with rough or precise polar alignment procedure.
¶ Add-ons
There are already some awesome and very helpful add-ons out there which improve the tracking quality or just make usage of this tracker much more convenient. But there is still a lot to come!
¶ Before You Start
The tracker can be built in a few variations, some are due to older ways things were done, some are budget-dependent, etc. Some depend on your targeted usage.
¶ The Frame
There are variations of the frame that you can choose from, depending on budget and requirements.
- Printed base, printed camera mount - all parts are 3D printed. This causes the tracker to have a lot of play and flex, which means tracking is better suited for wide field shots.
- Printed base, Aluminium camera mount - the camera mount is made stiffer by using 2020 aluminium extrusion and easier to mount the camera to (supports a quick release plate, for example).
- Aluminium/printed mix base, Aluminium camera mount - the base shape is a aluminium extrusion triangle with printed connecting parts. This version is the most stable and has the least flex.
We strongly recommend you choose the third option, the rigidity and precision achievable with this frame is much better than the other two.
¶ The Stepper Motors
You have two (officially supported) choices for the motors themselves.
¶ NEMA17 steppers
The tracker moved onto these steppers because they are more powerful and do not have a gearbox, but achieve slightly smaller steps by using microstepping. They are more expensive and they require more power and they require holding power (so even when nothing is moving, the motor draws power to stay in position). They also require a driver board and there are more variations. We recommend the TMC2209 UART board. This board requires 5V-9V power and 3 signals. 4 wires connect the driver board to the stepper. There is no backlash or periodic error (or negligible) since there's no gears).
¶ 28BYJ-48 steppers
Originally the tracker was built with these very cheap steppers. These steppers are very low cost and use an internal gearbox to get reasonably small steps without using microstepping. They use very little power and do not require much holding power (since the gearbox essentially does not allow the motor to turn). They require a driver board (that is also quite cheap, usually the steppers and driver boards come bundled) which needs 5V and 4 signal wires, so 6 wires altogether. 4 wires connect the driver board to the stepper. The gearbox does introduce some inaccuracies like periodic error (gear inaccuracies) and backlash (gear play/slop which is significant when changing direction (or during a weight transfer while tracking).
¶ The Electronics
We support two main Arduino boards (with a third all-in-one board in the works). Which one you choose depends mainly on how you want to use the tracker. Also, if you prefer not to solder and do cable management, the MKS board will be a better solution. Coming Soon.
¶ Arduino Mega 2560 with LCD shield
This option is suited for standalone operation and laptop operation. The LCD shield provides a simple menu system and display and 5 buttons with which to interact with it. It allows you to control the tracker, polar or drift align it, slew it to coordinates or a few objects, calibrate it, etc. without needing a laptop (although you will still need to be able to figure out Polaris HA, unless you also get the GPS addon).
Connectivity is via USB only.
¶ ESP32
This option is suited for laptop and iPad/iPhone/Android operation (sometimes with commercial products). The ESP32 is visible as a Wifi device and must be on the same network as the device you want to use to control it.
Connectivity is via USB or WiFi.
¶ The Controlling Software
The Arduinos that are part of the tracker you can think of as the firmware for the device. You now have the choice of software to control the tracker. You can use:
- A PC laptop running OATControl connected via USB
- A PC laptop running Stellarium using (supplied) ASCOM drivers connected via USB
- An iOS/Android device running SkySafari+ connected via Wifi (ESP32 only)
- A Raspberry Pi running Astroberry connected via USB to the tracker and controlled from a web browser on the same network.
- others....
¶ The Image Capture Software
In addition to controlling the mount, you also need to control your camera. Although you could also use an intervalometer without anything else....
The options open to you depend on the camera you wish to use. Some cameras are supported by special proprietary software packages and you might be forced to use those. For the two major DSLR producers, you have way more options, as many program support these two out of the box.
For beginners, the BackyardNIKON or BackyardEOS programs on PC are great. They allow you to control all aspects of your camera and stream the view to your laptop screen, which is particularly useful for polar alignment (part of setup you need to do every session). They also allow you to plan an imaging session (take n pics with these camera params, then take m pics with these etc.)
Sequence Generator Pro is another more advanced PC program that allows you to control all your gear from one place, plan complete imaging sessions over multiple nights, etc. Very full featured and well supported.
¶ The Image Processing Software
After you've captured all your pictures, you'll need to process them. There are quite a few options available to you.
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PixInsight - The Rolls-Royce of image processors, both in features and price. Very steep learning curve. Best results.
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AutoStakkert & Registaxx - These are programs used for processing images of planets. As the achievable focal length for OpenAstroTracker is quite short for planets, use one of the other options.
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DeepSkyStacker - Free, but capable program. Processes Darks, Flats, Lights, etc. Stacking only, no editing.
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Siril - Free and Cross-platform, can stack and edit.