Harmonic Drive Mounts are on the rise, due to their lightweight design, lack of counterweights, and improved connectivity as compared to classic German equatorial mounts. In the realm of affordability, the ZWO AM3 and the upcoming Sky-Watcher 100i (available from July 2024) stand out as the most budget-friendly harmonic drive mounts in 2024, priced at $1499 and $1695. The AM3, weighing 3.9 kg, offers portability advantage, while the 100i boasts enhanced payload capacity, supporting 10 kg without and 15 kg with a counterweight. For a mid-range investment around $2000, the ZWO AM5, the HAE29, and the Sky-Watcher 150i present compelling options, with varying weights and payload capacities. At the $3000 price point, the iOptron HAE43 and the Pegasus Astro NYX-101 offer high payload capacities. For premium high precision tracking, iOptron’s EC models with encoders and Rainbow Astro’s RST-135 and RST-300 mounts with DC motors stand out, albeit at a higher cost.
In this blog, I’ll begin by exploring the concept of harmonic drive mounts, also known as strain wave gear mounts. I’ll outline their key advantages and disadvantages to assist you in determining whether a harmonic drive mount is the right choice for you. Following that, I’ll conduct a comparison of harmonic drive mounts available in 2024, focusing on factors such as price, weight, payload capacity, motors, connectivity and, where applicable, their tracking and guiding accuracy. Finally, I’ll highlight the harmonic drive mounts worthy of your consideration in 2024, categorized by different price ranges.
The Pros and Cons of Harmonic Drive Telescope Mounts
Despite the branding hype around harmonic drive mounts, it’s fascinating to note that the underlying technology, based on strain wave gearing, has been around since 1957. The drive’s key advantages include zero backlash, high torque, accuracy, and reliability, making it useful in industries requiring precise motion control, such as Robotics, Aerospace, and Automotive, as well as in telescope mounts.
One significant advantage of Harmonic Drive Mounts over traditional German equatorial mounts is their compact design. These mounts are typically lighter and more portable, making them ideal for setups on the go. For instance, my ZWO AM5 mount weighs a little over 5.5 kg (12 lbs), allowing me to easily transport it to my preferred observation spots, unlike my bulky Sky-Watcher EQ6-R Pro mount, which weighs about 17 kg (37 lbs) without counterweights. Additionally, harmonic drive mounts don’t necessarily require counterweights due to their unique design. In a harmonic drive system, the output motion is achieved through the elastic deformation of a flexible spline and the interaction with a rigid circular spline. This design eliminates the need for counterweights because the drive system itself does not rely on gravitational forces for balance, unlike traditional mounts. That said, incorporating a counterweight to your harmonic drive telescope mount does improve stability, enabling a greater payload capacity.
Moreover, harmonic drive mounts offer minimal backlash, ensuring smooth and accurate tracking, particularly beneficial for long exposure astrophotography. However, while they provide impressive performance, they may not match the precision of some traditional mounts. For instance, my ZWO AM5 tracks at 0.5 to 0.7 arcseconds with auto-guiding, slightly less accurate than my Sky-Watcher EQ6R Pro, which averages 0.3 to 0.5 arcseconds. Additionally, the higher cost of harmonic drive mounts compared to traditional options may deter some users, especially considering their similar payload capacities. Despite this drawback, harmonic drive mounts like the ZWO AM5 have become my preferred choice for their portability, accuracy, and convenience. While traditional mounts still have their place, the versatility and performance of harmonic drive mounts make them a compelling option for many amateur astronomers and astrophotographers.
Harmonic Drive Telescope Mounts included in this overview
Now that you have a better understanding of harmonic drive telescope mounts, including their advantages and disadvantages, let’s delve into the range of telescope mounts available in 2024. This overview encompasses harmonic drive mounts from five different brands: ZWO’s AM3 and AM5; iOptron’s HAE29(EC), HAE43(EC), and HAE69(EC); Pegasus Astro’s NYX-101; Rainbow Astro’s RST-135 and RST-300; and SkyWatcher’s brand new 100i and 150i. In this overview, I will examine current pricing, telescope weight, payload capacities with and without counterweights, motor types, and tracking accuracy (if provided), culminating in a final conclusion. Additionally, I have created a comparison table detailing these characteristics and included links to reputable telescope retailers across the USA (Agena Astro and High Point Scientific) and the EU (Astroshop), which offer worldwide shipping, to aid you in your decision-making process.
Check out the specifications, availability, and prices of the Harmonic Drive Telescope Mounts here!
Harmonic Drive Mounts: Price and Weight Variations
In the realm of harmonic drive mounts, there is a notable price difference among the various options available. Beginning with the most affordable, the ZWO AM3 is priced at $1,499, followed closely by the SkyWatcher 100i at $1,695 at the time of writing. Moving up slightly in price, the ZWO AM5 and iOptron HAE29 both come in at $1,999, and the SkyWatcher 150i is priced at $2,195. Venturing into the higher-end options, the iOptron HAE43 stands out at $2,898, followed by the Pegasus Astro NYX-101 at $2,960. Finally, options beyond $3000 include the iOptron HAE29EC at $3,348, Rainbow Astro RST-135 at $3,895, iOptron HAE69 at $4,208, iOptron HAE43EC at $4,248, iOptron HAE69EC at $5,318, Rainbow Astro RST-135E at $5,459, and the Rainbow Astro RST-300 at $8,490.
The telescopes, ranked from lightest to heaviest based on their harmonic drive mounts, are as follows: the Rainbow Astro RST-135 at 3.30 kg, followed by its variant, the Rainbow Astro RST-135E at 3.40 kg, are the lightest mounts in this overview. Next is the iOptron HAE29 and its EC version, both weighing in at 3.70 kg. Moving up the weight scale, we have the ZWO AM3 at 3.90 kg, followed by the SkyWatcher 100i at 4.30 kg. The ZWO AM5 weighs 5.50 kg, followed by a three-way tie between the SkyWatcher 150i, iOptron HAE43, and iOptron HAE43EC, all at 5.80 kg. Continuing upward, the Pegasus Astro NYX-101 weighs 6.40 kg, while the Rainbow Astro RST-300 is significantly heavier at 8.50 kg. Finally, tying for the heaviest positions, we have the iOptron HAE69 and its EC counterpart, both weighing 8.60 kg. It’s worth noting that all of these mounts are considerably lighter than the mount head of my classic German equatorial mount, the Sky-Watcher EQ6R Pro, which weighs 17 kg.
Most harmonic drive telescope mounts are typically sold separately from tripods, allowing users to choose a tripod that suits their specific needs. Carbon fiber tripods have gained popularity due to their lightweight nature, which complements the lightweight design of harmonic drive mounts. However, it’s essential to consider that these tripods may experience reduced tracking accuracy in strong winds. From personal observation, I’ve noticed a decline in tracking accuracy on my ZWO AM5 when paired with the TC40 carbon tripod in winds exceeding 3 Beaufort.
Payload Capacity Variations
In terms of payload capacity, there are significant differences among the telescope mounts. Starting with the lower payload capacities, the ZWO AM3 supports 8 kg without a counterweight and 13 kg with one, followed by the SkyWatcher 100i at 10 kg without a counterweight and 15 kg with one. Moving towards higher capacities, the iOptron HAE29(EC), and the Rainbow Astro RST-135(E) both support 14 kg without a counterweight and 18 kg with one.
Stepping into mid-range, the SkyWatcher 150i supports 15 kg without a counterweight and 25 kg with one, while the iOptron HAE43(EC), and ZWO AM5 both support 20 kg without a counterweight and 25 kg with one. The Pegasus Astro NYX-101 supports 20 kg without a counterweight and 30 kg with one.
Finally, the highest payload capacities include the iOptron HAE69(EC), supporting 31 kg without a counterweight and 36 kg with one, and the Rainbow Astro RST-300, supporting 30 kg without a counterweight and 50 kg with one.
Harmonic drive mounts: Motor Types and Reduction Ratio
Most harmonic drive mounts in this overview use stepper motors, paired with a synchronous belt to track the night sky. Stepper motors operate by dividing a full rotation into a precise number of steps, with each step corresponding to a specific angle of rotation. Stepper motors are known for their accuracy and ability to move in small, precise increments, making them well-suited for applications where precise positioning is crucial, such as in telescope mounts.
Additionally, a belt can act as a mechanical reduction mechanism, which reduces the backlash and improves the overall precision of the motor. The belt can help dampen vibrations and resonance, leading to smoother and more precise movements. Moreover, belts provide better torque transmission and can minimize gear-induced errors, contributing to enhanced accuracy.
The most expensive harmonic drive mounts use DC servo motors. These motors are often more accurate in tracking compared to stepper motors due to their closed-loop control system. DC servo motors incorporate feedback mechanisms, such as encoders, which continuously monitor the position of the motor shaft and make real-time adjustments to ensure accurate tracking. This feedback loop allows DC servo motors to compensate for errors and disturbances more effectively, resulting in smoother and more precise tracking performance. Additionally, DC servo motors generally offer higher torque and faster response times compared to stepper motors, further improving their tracking accuracy, especially in challenging conditions such as windy environments.
The majority of harmonic drive mounts utilize stepper motors paired with belt drives, including the ZWO AM3 and AM5, the SkyWatcher 100i and 150i, iOptron HAE29, HAE43, HAE69, and the NYX-101. In contrast, the Rainbow Astro RST-135, RST-135E, and RST-300 models feature DC servo motors, which promise improved tracking accuracy and smoother motion control. Notably, iOptron’s “EC” variants like the HAE29EC, HAE43EC, and HAE69EC are equipped with encoders (RPEC; Real-time Periodic Error Correction), providing more precise tracking accuracy compared to the same model counterparts that do not include encoders, at higher cost.
Reduction Ratio
In a harmonic drive or strainwave gear system, the reduction ratio refers to the ratio between the number of teeth on the flexspline (the input) and the number of teeth on the circular spline (the output). This ratio determines how much the output shaft rotates in relation to the input shaft for a given input rotation. A higher reduction ratio means that the output shaft rotates more slowly but with greater torque compared to the input shaft.
In the context of harmonic drive telescope mounts, a higher reduction ratio can be beneficial for several reasons. Firstly, it allows for finer control and smoother motion, which is crucial for precise tracking of celestial objects during astrophotography or observation. With a higher reduction ratio, the mount can make smaller adjustments to the position of the telescope, resulting in more accurate tracking and better image quality. Additionally, a higher reduction ratio helps to reduce backlash and minimize mechanical errors, leading to improved overall performance and stability of the telescope mount. Overall, a higher reduction ratio enhances the precision and reliability of harmonic drive telescope mounts, making them ideal for demanding astronomical applications.
The reduction ratios of various harmonic drive telescope mounts vary across different models, with some ratios being more clearly defined than others. For instance, the ZWO AM3, the AM5, and SkyWatcher 150i feature a 300:1 reduction ratio. iOptron’s HAE29 model specifies a reduction ratio of 480:1 for RA (Right Ascension) and 360:1 for DEC (Declination), whereas the HAE43 model offers ratios of 640:1 for RA and 480:1 for DEC. The “EC” variants of iOptron mounts, such as the HAE29EC, HAE43EC, and HAE69EC, maintain the same reduction ratios as their non-“EC” counterparts. The Pegasus Astro NYX-101 presents a reduction ratio of 500:1 for RA and 300:1 for DEC. However, specific ratios for some models like the SkyWatcher 100i and Rainbow Astro RST-135 and RST-135E are not clearly specified. Additionally, the Rainbow Astro RST-300 model also lacks a clear indication of its reduction ratio, it is labeled as “Model no. 25.”
Real Life results with auto guiding
Most of us will probably use autoguiding gear in combination with one of the harmonic drive mounts in this overview. Unfortunately, auto guiding results are not often reported by manufacturers , but let me give you some indications from personal experience and reports in the field from astrophotographers. My ZWO AM5 demonstrates a tracking accuracy ranging from 0.5 to 0.8 arcseconds across imaging nights, when guiding at 1-second intervals with a quadruplet apo refractor at 600mm focal length. Unfortunately, specific information regarding the periodic errors of iOptron’s harmonic drive mounts while guiding in real-world conditions remains elusive at present. Pegasus Astro has provided insightful data on their website, offering three PHD2 graphs for their NYX-101 model. These graphs, based on telescopes with approximately a 500mm focal length, indicate an average deviation of 0.3 to 0.6 arcseconds per pixel when employing off-axis guiding set at a 1.5-second tracking interval. In contrast, when utilizing a telescope with a 2800mm focal length, one of the PHD2 graphs illustrates deviations of approximately 0.8 to 1 arcseconds per pixel in both RA and DEC, employing off-axis guiding at 2-second intervals. Additionally, Rainbow Astro has shared a live PHD2 graph featuring the Rainbow Astro RST-135 paired with an 8” SCT, displaying deviations of 0.5 to 0.6 arcseconds while guiding at 0.5-second intervals.
Connectivity, Latitude, EQ/Alt-Az mode, and other options
The ZWO AM3, AM5, SkyWatcher 100i, 150i, iOptron HAE29, HAE43, HAE29EC, HAE69, HAE43EC, and HAE69EC models all provide connectivity options including WiFi, Hand Controller (HC), and USB. Moreover, these mounts support autoguiding and are compatible with ASCOM protocol, enabling remote control via software that utilizes ASCOM. Additionally, the Pegasus Astro NYX-101, Rainbow Astro RST-135, RST-135E, and RST-300 mounts offer similar connectivity options such as WiFi, HC, and USB, along with autoguiding and ASCOM compatibility.
All mounts are adaptable for use within a latitude range spanning from 0 to 90 degrees and are operable in both Equatorial (EQ) and Altitude-Azimuth (Alt-Az) modes. An advantage of Alt-Az mode is its elimination of the need for polar alignment, allowing tracking across the meridian without requiring telescope flipping. However, due to inherent tracking inaccuracies, prolonged exposure astrophotography in Alt-Az mode leads to field rotation and the appearance of elongated stars or star trails. Additionally, nearly all harmonic drive mounts featured in this overview offer dual saddle options, accommodating both Vixen and Losmandy style telescope connections. One exception is Rainbow Astro, which does not include a dual saddle for the RST-135, RST-135E, and RST-300 models, necessitating a separate purchase at an additional cost.
Check out the comparison table here!
Conclusion
Top Value, lightweight Mounts ($1500)
In the realm of affordability, the ZWO AM3 and the forthcoming Sky-Watcher 100i (available from July 2024) emerge as the most budget-friendly harmonic drive mounts in 2024, priced at $1499 and $1695, respectively. If prioritizing portability, the AM3 edges out as the lighter option at 3.9 kg compared to the 100i at 4.3 kg, with a $200 difference. However, the 100i boasts an enhanced payload capacity of 10 kg without and 15 kg with a counterweight, compared to the AM3’s 8 kg to 13 kg range.
The ZWO AM3 is available at Agena Astro (USA/WW), High Point Scientific (USA/WW), and Astroshop (EU/WW).
The SkyWatcher 100i is available at Agena Astro (USA/WW), and High Point Scientific (USA/WW).
Mid-Range Excellence ($2000):
For those willing to invest a bit more, the ZWO AM5, the HAE29, both priced at $1999, or the Sky-Watcher 150i at $2195 (available from July 2024), offer compelling price-to-quality ratios. The HAE29 stands out as the lightest mount, weighing merely 3.7 kg, while the AM5 at 5.5 kg and the 150i at 5.8 kg are approximately 2 kg heavier. Both the AM5 and HAE29 boast similar payload capacities of 13 kg and 14 kg without, and 20 kg and 18 kg with a counterweight, respectively, while the Sky-Watcher 150i offers a higher payload capacity of 15 kg without to 25 kg with a counterweight.
The ZWO AM5 is available at Agena Astro (USA/WW), High Point Scientific (USA/WW), and Astroshop (EU/WW).
The iOptron HAE29 is available at Agena Astro (USA/WW), High Point Scientific (USA/WW), and Astroshop (EU/WW).
The Sky-Watcher 150i is available at Agena Astro (USA/WW), and High Point Scientific (USA/WW).
High Payload Powerhouses ($3000):
In the $3000 price range, options like the iOptron HAE43 at $2898 and the Pegasus Astro NYX-101 at $2960 present themselves as formidable choices. The HAE43 weighs 5.8 kg compared to the NYX-101 at 6.4 kg. Both mounts offer a payload capacity of 20 kg without a counterweight, with the NYX-101 leading at 30 kg with a counterweight, compared to the HAE43’s 25 kg.
The iOptron HAE43 is available at Agena Astro (USA/WW), High Point Scientific (USA/WW), and Astroshop (EU/WW).
The Pegasus Astro NYX-101 is available at Agena Astro (USA/WW), High Point Scientific (USA/WW), and Astroshop (EU/WW).
Premium High Payload Mounts (>$4000):
For those seeking top-tier performance and payload capacity, the iOptron HAE69 at 31 to 36 kg, priced at $4208, and the Rainbow Astro RST-300 with a 30 to 50 kg payload capacity stand out. Moreover, for those prioritizing enhanced accuracy in (unguided) tracking, iOptron’s EC models with encoders and Rainbow Astro’s RST-135 and RST-300 mounts with DC motors offer premium options, albeit at a higher cost.
The iOptron HAE69 is available at Agena Astro (USA/WW), High Point Scientific (USA/WW), and Astroshop (EU/WW).
The Rainbow Astro RST-135 is available at Astroshop (EU/WW).
The Rainbow Astro RST-300 is available at Astroshop (EU/WW).
iOptron’s Premium tracking mounts:
iOptron’s harmonic drive mounts with enocoders (EC) and real-time periodic error correction (RPEC) are available here:
The iOptron HAE29EC is available at Agena Astro (USA/WW), High Point Scientific (USA/WW), and Astroshop (EU/WW).
The iOptron HAE43EC is available at Agena Astro (USA/WW), High Point Scientific (USA/WW), and Astroshop (EU/WW).
The iOptron HAE69EC is available at Agena Astro (USA/WW), High Point Scientific (USA/WW), and Astroshop (EU/WW).
Clear skies!
Very good review. I was leaning towards buying one. This article convinced me to wait fro another 6mnths to a year to see field results.
Nice post! Thank a lot for the comparison.
For no particular reason other than better be safe than sorry I have set the Ioptron CEM70 as the baseline. Do you think any of those harmonic mounts in your review can match or even outperform the CEM70 when it comes to guiding. Let’s take a C8 Edge HD with a reducer and OAG guiding using a ASI2600mm pro plus filter wheel
Hi Gert, I’m not sure yet. I will be testing out the AM5 with my Celestron Edge HD 8″ with a focal length of 2000mm. I’m really curious about the guiding results – if they are about 0.5 arcseconds I’ll be happy. Stay tuned.
Any results using the C8 EdgeHD? I’m curious as I’m thinking of using this combination of scope and mount.
I had the HAE29 for about two weeks, and immediately had problems. The key problem is the HandControlls poor communication with 2 Android 11 Tablets and NO communication with a Smartphone. I posted a review on AgenaAstro and it was pulled about 36 hours later, I also posted a review on iOptrons own site. It was not untill I told iOptron that I was going to find a YouTube maker and post it that I was quickly notified that iOptron was going to refund me.
I own about 3 of those harmonic mounts (ZWO AM5, iOptron HEM 27EC and Sharpstar MK III) and they all perform very well. I have used them mainly with a 600mm and a 1300mm scopes, no OAG but a 200mm William Optics guidescope.
All of them deliver constantly well under 1″ total error guiding and the stars were nice and round.
Communication wise, never had any troubles either connecting to the mounts directly or connecting them to AsiAir.
The Sharpstar MK III is a true workhorse moving my 15kg scope around with ease.
All those mounts are lighweight and the absence of counterweights makes them perfect travel companions.
I got my HAE43 last week. After 2 short nights I‘m still not heavily impressed about the guiding results using my ASIAIR.
Guiding was around 1“ but on a low target. (Orion from 30degree down to 15degree)
Sometime a bit under 1“ sometimes a bit higher. Max guiding curves relatively constant swinging from +2“ to -2“ at 1second guiding exposure.
Have to test it more to the zenith for final results.
On problem is that the usb connection from the mount to the ASIAIR does not work. Can’t tell the reason.
Wi-Fi works but not super stable. Had some failed connections.
I have a question about the capacity of these types of mounts in general. For German Equatorial mounts like the Sky-Watcher EQ6r Pro we are warned about not exceeding above “50%, 60%, 40% etc.” of the capacity when used for astrophotography. Does that also apply to these mounts or can they truly hold our gear up to the rated capacity? For the AM5 will I be limited to about 50% of the 20 kg when I use it for astrophotography? Thanks.
Hi Don,
Good question. I’m testing the AM5 right now and the first couple of nights were great. I was able to get tracking below 1 arcsecond per pixel with my Edge HD 8″ with a filter wheel, camera, and guide scope. As the Harmonic Drive technique is very different, I do think these mounts cannot be compared to the same “rules of thumb” as german equatorial mounts. I have a new b/vlog where I talk about my first experiences with the mount – you can find it here: https://astroforumspace.com/zwo-am5-mount-review/
Clear skies!
You replied to this comment.
Hi Adam, thanks. Just as a follow up: I’v tested my ZWO AM5 now on 6 nights with gear varying from a lightweight APO refractor to my heavier 8″ Edge HD SCT Telescope with camera, guidcam, filterwheel etc. My ZWO doesn’t seem to mind the extra weight. Guiding is always below one arcsecond, mostly around .5 to .7 in RA and DEC. Cheers.
Got my AM5 end of April. Got 12 nights of guiding. Then on Monday June 19 AISAir app reported “USB serial disconnected” for the mount. Tried my older ASIAir Plus (non 256G version) same message. Plugged the AM5 in my Windows 11 PC and it reports device descriptor request failed and my MacBook Pro 2019 doesn’t see it at all. Opened a ticket with ZWO that day.
Today, Thursday, got a response I should still be able to use it with WiFi and was asked if the hand controller worked. I tried the HC and nothing. The LED next to the USB port is dark. The power button lights up. But nothing. I reported back but looks like I have a $2300 brick. No offer from them to fix or replace it at this point. Someone on the FB AM5/AM3 page reported their AM5 USB died about a month before mine. They obviously have some kind of teething problem and that is a shame. Maybe I’ll try a ZWO mount again in about 5 years or so.
Oddly enough I was going to buy a 2nd AM5 for my rig on the SkyGuider Pro. That is not happening now. Colleagues at work recommend the RST-135. Although it seems hard to find here in the USA I may go that route. Rainbow also has been doing this longer so hopefully they have better quality.
I’m sorry to hear that, Alex. You’re well within the warranty period I think? I’d ask for a replacement if I were you. Good luck. I hope this gets solved soon.
They said they will send a new mother board. I still do not have a tracking number.
In the meantime, I’ve sprung for the RST-135E more expensive version. I’m also waiting on that to arrive.
I have the NYX-101 since April and all I can say is that it is a great mount in terms of tracking
I have only used it with my 200/620 Sharpstar Newt (12kg fully loaded), w/o CW, but I have also loaded my big RC250 (~ 20kgs in total with computer, guidescope…), with a 5kg CW, and the mount operated flawlessly (I have not done any imaging with this set-up yet).
Another point worth mentioning, is the quality of their customer support; I’ve had several teething issues, mostly coming from problems generated by my lack of experience with the mount (which has been flawless since day one), and the communication by mail with them was extremely fast (they even helped me on a Friday at 9PM!).
I strongly recommend this mount which is superb in terms of build quality and tracking performance
Thanks for your personal review Massi!
Someone must be nuts to pay for those mounts $8500.
Yes, you can use the mount in alt-az mode for tracking
Thanks!
Well, recently i upgrade my old SW EQ5 mount with OnStep mount kit, and with my Quattro 150p on it, i achieve almost always guiding under 1″ – mostly around 0.45″ – 0.65″ per pixel.