Precise, stable gearbox from the 3D printer - cost-effective components for astrophotography

• What was needed: a gearbox that rotates a device with a camera and lens 360° in 24 hours
• Manufacturing process: Filament extrusion (FDM)
• Requirements: cost-effective, different but precise rotation speeds, high stability of the device
• Material: iglidur® i150
• Industry: Astrophotography
• Success through cooperation: high precision, stability and abrasion resistance, low friction due to thrust washers

The application at a glance:
In astrophotography, different celestial bodies are imaged using long exposure and saved on a suitable medium. Anyone who has ever changed the exposure time on their own digital or mobile phone camera will know that photos taken with a long exposure time can be "blurred" by minimal changes. As the earth rotates around its own axis, this rotation is also a problem for the long exposure times used in astrophotography. Mr van Hove of vhw Digitalart has developed a device that compensates for the earth's rotation in order to be able to depict the motifs in the sky in their real form. The requirements for the plastic gearbox were a rotation of 360 degrees in exactly 24 hours, sufficient load-bearing capacity for the camera and lens, as well as high stability and abrasion resistance of the individual components. It should also be possible to set different rotation speeds, depending on which object is to be tracked in the sky. The gearbox and all brackets for the motor and electronics were manufactured using 3D printing with the tribofilament® iglidur® i150. In addition to the cost advantage of the 3D-printed components, the high abrasion resistance and suitability for rotation and swivelling applications of the igus® high-performance plastic also played a major role in the selection of the material and the manufacturing process.

The Earth's rotation must be compensated for so that long exposures can be made over several hours. The device that ensures that the celestial body to be imaged does not move from the camera's perspective and must move it and the lens or telescope so that it is stable. This includes precise and even rotation. A controller and an externally mounted control panel must also set different rotation speeds as the tracking times vary by object.

Mr van Hove worked closely with igus® to find the right materials for his project. The load capacity and precision are guaranteed by the RL-D-20 pivot bearing with a reduction ratio of 1:38. The high stability and abrasion resistance of the 3D-printed gears and mounts is achieved by the tribologically optimised iglidur ® i150 filament, as the material is particularly suitable for applications with low sliding speeds. The gearbox has a reduction ratio of 1:243. The friction of the 3D-printed gear is reduced by two thrust washers between the components, ensuring loss-free rotation. Mr van Hove rates the collaboration as "very good as usual".

In astrophotography, celestial bodies, nebulae and other objects in the night sky are imaged in visible light and stored on various media. The camera is oriented on the geographic North Pole parallel to the Earth's axis. The inclination of the camera corresponds to the latitude. The exposure time for such photographs is several hours, which is why the camera must be adapted to the Earth's daily rotation. Otherwise only lines will be visible instead of the objects' actual shapes. An appropriate device, a tracker compensates for the Earth's rotation if the rotation speed corresponds exactly to one revolution per day. There are also different rotation speeds depending on the object to be tracked. For stars, one revolution takes 23 hours, 56 minutes and 4 seconds. The moon requires a revolution time of 24 hours, 52 minutes and 28 seconds, while the sun requires exactly 24 hours.

The device must be able to support the entire weight of the camera and lens or the telescope throughout 360° rotation over 24 hours . Depending on the size, model, and equipment, this can be up to 4kg. The high precision of the rotation is achieved with a pivot bearing with a gear reduction of 1:38. A mechanical service life of at least 1,000,000 cycles also guarantees a long service life for the overall system. The 3D printed gear with a reduction ratio of 1:243 enhances strength and also has a long service life thanks to the thrust washers used and the abrasion-resistant iglidur i150 plastic.

The tribologically optimized iglidur i150 filament is easy to process and suitable for all 3D printers in the FDM process. In addition to the high abrasion resistance at low glide speeds and the good mechanical properties of the high-performance polymer, iglidur i150 is also suitable for contact with foodstuffs according to EU Regulation 10/2011. The integrated solid lubricants ensures it is maintenance-free and most applications benefit from its strength and layer adhesion.