Learn how Harmonic Drive mounts differ from traditional worm gear mounts, their impact on astrophotography performance, and an overview of popular models from ZWO, Sky-Watcher, Pegasus Astro, and more.
Harmonic Drive mounts, also known as Strain Wave Gear mounts, have been gaining traction in the astrophotography community due to their unique design and performance advantages over traditional worm gear mounts. In this guide, we'll explore the distinctions between these two types of mounts and highlight some notable Harmonic Drive mounts from manufacturers like ZWO, Sky-Watcher, Pegasus Astro, and others.
Understanding the Difference: Harmonic Drive vs. Worm Gear Mounts
Traditional worm gear mounts utilize a worm screw meshing with a worm wheel to achieve the necessary gear reduction for precise tracking. While effective, this design can suffer from backlash—a slight lag when reversing direction—due to the inherent gaps between the meshing gears. Backlash can affect tracking accuracy, especially during long-exposure astrophotography.
In contrast, Harmonic Drive mounts employ a strain wave gearing system comprising three main components: a wave generator, a flexspline, and a circular spline. The wave generator deforms the flexspline, causing it to engage with the circular spline in a manner that ensures a large number of teeth are in contact at any given time. This design virtually eliminates backlash, offering smoother and more precise tracking. Additionally, Harmonic Drive mounts are typically more compact and lightweight, often eliminating the need for counterweights, which enhances portability—a significant advantage for field astrophotographers.
Impact on Performance
The zero-backlash characteristic of Harmonic Drive mounts leads to improved tracking accuracy, which is crucial for capturing sharp images during long exposures. The high torque capacity of strain wave gears allows these mounts to handle substantial payloads relative to their size, further contributing to their appeal among astrophotographers seeking a balance between portability and performance. However, it's worth noting that while Harmonic Drive mounts offer these advantages, they may exhibit higher periodic error compared to well-tuned worm gear mounts. This periodic error can be mitigated through autoguiding techniques, but it's an important consideration for users aiming for the utmost precision in their imaging.
Popular Harmonic Drive Mounts
Here are some notable Harmonic Drive mounts from various manufacturers:
ZWO AM5: The ZWO AM5 is a compact and lightweight mount that supports up to 13 kg without a counterweight and 20 kg with one. It operates in both equatorial and alt-azimuth modes, providing versatility for different observational needs. The mount integrates seamlessly with ZWO's ASIAIR system, allowing for wireless control and an intuitive user interface.
Sky-Watcher 100i: The Sky-Watcher 100i is an affordable Harmonic Drive mount priced at $1,695. It offers a payload capacity of 10 kg without a counterweight and 15 kg with one, making it a compelling option for those seeking a balance between cost and performance.
Pegasus Astro NYX-101: The NYX-101 is designed for astrophotographers requiring advanced tracking capabilities and remote operation features. It boasts a payload capacity of up to 20 kg without counterweights and 30 kg with them, positioning it as one of the more powerful Harmonic Drive mounts available.
Rainbow Astro RST-135: Weighing only 3.3 kg, the RST-135 is one of the lightest Harmonic Drive mounts on the market. Despite its lightweight design, it can support up to 13.5 kg without a counterweight and 18 kg with one. Its exceptional tracking accuracy and portability make it an excellent choice for astrophotographers on the move.
iOptron HEM27: The iOptron HEM27 is a budget-friendly hybrid Harmonic Drive mount that combines a strain-wave drive system with traditional worm gears for added stability. It supports a payload capacity of 13.5 kg without a counterweight and 20 kg with one, offering a good balance between performance and affordability.
Conclusion
Harmonic Drive mounts present a compelling alternative to traditional worm gear mounts, especially for astrophotographers prioritizing portability and reduced backlash. While they come at a higher price point and may require considerations for periodic error correction, their advantages make them worthy of consideration for both amateur and seasoned astrophotographers.
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