This project has been featured in HACKADAY.

I have recently assembled an ultra-portable tracker setup. The intention is to build a simple yet fairly accurate sky tracker capable of capturing wide-field targets, particularly, the Milky Way.

To head directly to the Arduino controller page, click here.

Why use a tracker?

Due to Earth’s rotation, objects in the sky appear to move from east to west. Taking a long-exposure photo of stars using a non-tracking camera will produce trails. To overcome this (and minimize trailing), a robotic tracker as simple as a geared stepper controlled by an Arduino, can be used.

The tracker was built so that I could still capture the Milky Way (for exposures longer than 30 seconds) from remote locations where traveling with a heavy telescope mount is not an option.

tracker_eteny (1)

Ultra-portable tracker built from a geared stepper motor. Click here for another photo (side view).

Any geared stepper motor with sufficient torque can be used as a drive mechanism. For this project, I used a Sanryusha P43G geared stepper motor (a stepper motor with a built-in 1:500 gearbox).

tracker_eteny-3

Sanryusha P43G geared stepper motor

I simply attached an aluminum plate to the end shaft of the P43G stepper. A ball head mount was then used to connect a DSLR to the plate. The photo below shows how the parts are connected together.

tracker_eteny-4

Motor drive, some metal connectors, aluminum plate, and ball head mount.

This tracker is small enough to sit lightly on a tabletop, and all the components can fit easily on a small camera bag. It is designed to carry only a very light payload such as a DSLR with a wide-field lens.

tracker_eteny (3)

Components of the setup: tripod, tracker with controller, ball head mount, power supply, and a DSLR with lens.

To test the accuracy of the tracker, I tried to capture the Milky Way using an 18-55 mm lens, set at 18 mm (wide field). The point of the test is to determine if the tracker is capable of producing pin-point stars. Note that the test was conducted from a location with a considerable amount of light pollution.

18 mm at 90 sec (animation)

Milky Way captured with an 18 mm lens at 90 seconds exposure, with and without tracking. To view the image at full resolution, click here.

To test it further, I also tried it with a more demanding lens: 55 mm. Without tracking, stars appear as streaks, but with tracking, stars remain as fixed points.

55 mm at 120 sec (animation)

Milky Way captured with a 55 mm lens at 120 seconds exposure, with and without tracking. To view the image at full resolution, click here.

Even with a 55 mm lens, the tracker is capable of accurate tracking up to 120 seconds, which should be more than enough for Milky Way shots.

Picture saved with settings embedded.

Milky Way captured on April 17, 2016, using the ultra-portable tracker setup. A total of 5 images, each having an exposure of 90 seconds, were stacked together in DeepSkyStacker to produce this final image. Taken with a Canon 1100D DSLR, 18 mm f/3.5 lens, at ISO 400. To view the image at full resolution, click here. Cavite, Philippines. Photo Credit: Anthony Urbano

Like with all equatorial trackers, proper speed calibration and polar alignment are needed to achieve best results. For information on how to setup this tracker or any other sky tracker for that matter–even the commercially available ones, click here.

For an advanced application of the project (using what is called an automatic guider), click here.

Updated October  15, 2016.

Related article: Arduino Stepper Motor Controller

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© Anthony Urbano (Manila, Philippines)

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