RST-135E: The best harmonic drive mount money can buy?

After a year with the Rainbow Astro RST-135E, how does it stack up? Find out what it's guiding capabilities and performance are like, if it's able to go unguided and what my two annoyances are with it.
Rainbow Astro RST-135E Initial Impressions: • Harmonic Drive Mount R...
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Timestamps:
0:00 Intro
2:00 General Thoughts
3:15 Guiding Performance
5:30 Periodic Error
6:50 Unguided Performance
7:40 Backlash & PHD2 Settings
8:24 Windows Bug
9:05 Altitude Lock
9:45 Is It Worth $10,000?
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[@josesalcedo5089]

Excellent video. I also have this mount and love it. I use it with an 18kg Takahashi TOA-130NFB and normally get guiding errors in the range 0.25" to 0.6" over many hours. The mount is a joy to use.

[@crm114.]

Excellent overview. Just bought this mount for my quick set-up option. I was struggling to get much under 1 “ RMS guiding on my first outing (when my other rig was getting 0.5). I might try your settings.

[@niraj_dave]

Heard good things about this mount and from another who's using it currently. His result matches yours as well - so that's astounding that two different users having same quality. Because most of the times, hardware build can differ a bit sometimes - but Rainbow Astro seems to have quality issue covered just fine. Now if they only lower price a bit, it would make others to do it even better. Even though other harmonic mounts are good, this one is a top notch.

[@deep_space_dave]

I heard a lot of good things about this mount but it is out of my price range. I settled for a iOptron HEM27EC. I can image unguided for up to 30 seconds as long as there is no wind or big trucks rolling by otherwise I have to guide. I also have to have almost perfect polar alignment or else I have perfectly consistent elongated stars 🙂 Considering that this mount is expensive too, it is still a lot cheaper and gives a lot of bang for the buck! Also there is no back driving so I can shut off the mount without worrying about my kit hitting the pier. I am also running it at it's max payload without a counterweight of 13.5kg and still have round stars unguided (RASA 8 with accessories, camera, and computer). Enjoy your gem of a mount. Clear Skies!

[@realmcerono]

What a nice setup with the mele pc and all! Congrats! Software looks like EQmod and as long the mount communicates with some app (phd2, nina, stellarium etc.) you are not able to close it.

[@mikei.6294]

Great video on this mount. I recently bought a 135E, in part based on your review. Thank you for having a screenshot of your PHD2 settings in the second video and your guiding results are impressive! Would you mind telling me what guide speed you are using in the mount. I've tried .5x and .9x sidereal. Thanks. Mike

[@derekbaker3279]

Rohan, you have absolutely made my day! You covered everything I needed to learn about the RST-135E. The only unknown left for me is how it operates in very cold conditions, during my Canadian winters, but that's something you never get. lol. As portability is very important to me & I also hope to use this as my travel mount with a RedCat 71, it seems to be nearly all good news (...I will need to really bite the bullet in terms of cost, but it seems like it's a keeper...). Thank you!

[@AstroWithRoRo]

Glad to hear it answered most of your questions Derek! Can't help with the cold temp testing though unfortunately. All the best with your decision and purchase!

[@Mandragara]

This is something I'm interested in. Astro imaging is something I only really do in conjunction with other activities (camping etc), so I really prioritise size and speed of setup. It is pricey though as I don't really image above 500mm FL

[@richness1644]

Try enlarging the EQMod software window. You should see an “OK” button at the bottom. Click that button and the window should close. Don’t ask me how I know. LOL

[@rossc383]

Out of curiosity, can a phd2 Predictive PEC algorithm help with PE? On this mount or non encoder version

[@jackthecat6225]

Seems like the value adds are convenience, ease of setup, weight and precision. Those things certainly have a price and it seems that makes the cost worth it. The only issue I have is the polar alignment issue with the lock. For that price level, that is not acceptable in my mind. Not that you can't work around it, I just think at that price point it is not excusable.

[@Dudleydogg]

this mount is fantastic, have you compare or review this to ZWO AM5, and the Sharpstar Mark III ? I can't get past that dangling wire on the sharpstar, and the clunky looking hand controller LOL

[@Evanturar]

Lifting my Bisque MyT is the only real negative. Not sure if the size and narrow mounting platform is worth the extra money, but It’s nice to see such a compact package. Guiding isn’t a thing Bisque users mess with using SkyX. Just a different approach.

[@scottrk4930]

Great Review , thanks ! With most existing Mounts we generally know where the failures or weaknesses are going to be . Worn belts , gummed rollers , bad bearings , old grease etc . Do we know yet where future maintenance issues might be on a Harmonic Drive Mount ? If there were any failures I can only imagine they would fairly expensive and not a do-it-yourself type of repair . Keep us posted on how this Mount behaves for you with more use . Cheers/SRK

[@derekbaker3279]

Hi Scott. I thought I would chime in with my take on your excellent question. First, Rainbow Astro is a labour of love from the engineers at a highly regarded manufacturer of robotic arms for mass-production manufacturing. The robotic arms use the same harmonic drive system, and they have to be super-durable & very accurate in their movements. Apparently the engineers at the company are amateur astronomers, and they decided to take the same technology & use it in telescope mounts. IMHO, this is a sign that Rainbow Astro's harmonic drive telescope mounts will be very strong, durable & virtually maintenance-free. Second, there are a few owners of Rainbow Astro mounts who have an astro-channel on YT, and some have had their mounts for a few years, and I have yet to hear of any problems. My guess is that any maintenance/repairs happen infrequently, so, even if the maintenance/repairs are expensive, when the cost is averaged over the time between fixes, the hit to one's wallet would not be more than the amounts associated with most traditional equatorial mounts. Furthermore, if one wants to have a permanent observatory (perhaps a remote observatory), and one does not want to risk an unreliable mount that needs frequent adjustments/repairs, the mounts available (Software Bisque, Astro-Physics, etc.) are at least as expensive as the Rainbow Astro mounts. Third, there is a Facebook forum dedicated to Rainbow Astro mounts, and there are a number of threads on Cloudy Nights, so you may want to do some research on those sites to find out what others have experienced. I hope my input has been helpful.

[@scottrk4930]

@@derekbaker3279 Hi Derek , thanks for the reply . I'll check out more Sources regarding this Mount . I see from comments below that you're somewhere in my backyard , LOL , I'm roughly at 43'36" N 80'8" W . Winters are cold here eh ?/SRK

[@Maranthas]

I am using RST-135E with Celestron EdgeHD 9.25 with a 0.7 focal reducer (effective FL 1667mm). Using OAG I get sustained RMS of 0.25 on windless nights, 0.35 on windy nights. Using the counterweight for the setup though as 9.25 is kinda heavy.

[@AstroWithRoRo]

That’s great guiding! What do you as a tripod for your setup? I agree the 9.25 + counterweight can become quite heavy.

[@nikanj]

Congrats on the new mount. I sounds great. Out of curiousity what would you get for the same budge if weight and size were not a factor? EQ8R? CEM120? Or something better quality but with a lower payload?

[@AstroWithRoRo]

For around the same price you could get the EQ8RH, CEM120EC or Paramount MYT if weight isn't a concern.

[@wolfgangkuechle9085]

Thank you for your great videos on this interesting mount. Do you have experience with dew building up and how the mount handles these conditions? Are you using any tools for polar alignment like the QHY Polemaster and how accurate does the polar alignment have to be for the mount to perform well?

[@AstroWithRoRo]

My mount has had no issues with dew. I use either the 3 point polar align in NINA or the polar align tool in SharpCap, both work well. I usually aim for a polar align under 1 arc minute, and that's what all my numbers are based off.

[@wolfgangkuechle9085]

@@AstroWithRoRo Thank you!

[@oristernberg5640]

What do you think about the 44 EC harmonic drive of ioptron. Will be great if you could review the mount, as the spects seem the same as the rainbow mount but at a fraction of the price. Great content, keep reviewing new gear.

[@derekbaker3279]

Hi Ori. One difference I will point out is that the iOptron harmonic drive mount does not use a harmonic drive gear system on the Declination Axis. While the RA uses the kind of harmonic gear system that the Rainbow Astro 135/135E/800 uses (also the ZWO AM5, etc), the DEC Axis uses a traditional stepper motor & pulley system. On the other hand, the smaller of the two iOptron harmonic mounts (27EC?) has provision for a through-the-mount cable, which the 44EC & other harmonic mounts do not offer.

[@oristernberg5640]

@@derekbaker3279 Thanks for your input. The interesting thing is, will it perform as well as the rainbow. The previous EC models were so precise, you didn't had to have guiding system. You could image subs for 5 minutes straight with no problem according to people who had it. Will the hybrid harmonic drive perform the same as there predecessore ? If so the rainbow does not worth the money

[@derekbaker3279]

@@oristernberg5640 Hi Ori. Yes, you are absolutely correct when you say that the iOptron EC mounts have a periodic error that is similar to the Rainbow Astro 135E. The only difference in tracking & guiding from the iOptron EC German Equatorial Mounts is that the Rainbow Astro 135E has virtually no backlash, while the iOptron EC mounts have a lot more backlash, which requires adjustments & compensation. And, as Rohan says, a good German Equatorial Mount will be the better option if portability is not a crucial issue. In fact, some German Equatorial Mounts with encoders (e.g. Astrophysics Mach2, 11000AE, etc) have around 0.2 or even 0.1 arc second of periodic error! However, if portability, low periodic error & low drift rate are high priorities then the substantial cost of the RST-135E may be justified. 🙂

[@cdh79]

I'm currently looking into the non-E version as a possible option. How do you power it in the field? To my understanding the recommendation is 15V and not 12V and I have read that if the voltage drops below 12V the mount "crashes" or was this exaggerated information?

[@AstroWithRoRo]

I power it with a Jackery battery unit, usually through a Pegasus Astro PowerBoxAdvance (but sometimes with the PBA). This usually delivers somewhere around the 13v mark and the mount works great with that for me. Recently when I travelled for a solar eclipse I powered it directly through a 100WH battery pack that's unregulated and it worked fine around the 12v mark (but I wouldn't want to let the voltage drop too low and risk any potential damage).

[@phillipjones4743]

What is the backlash program you used? Great review. I may order it this month.

[@derekbaker3279]

I think he used the guiding analysis that is part of the free PHD2 guiding application.

[@AstroDenny]

It looks like EQMOD, and if it is, there is a separate installed icon to kill the process.

[@borovikmotion]

so if 1 turn of the motor is 7 arc minutes, then the ratio in the harmonic drive is 1:206. Well, I'm thinking it is possible to 3d print such a device 😄 will be almost free comparing to the 10k$. There are a lot of 3d printed harmonic drives examples on youtube, but the issue is size, lets say 1 3d printed tooth is 4 mm, 1:206 ratio will require 412 teeth, then the diameter of such a gear will be 524 mm, which is huge 😁. But photopolymer printers provide better accuracy, like 0.05 mm, so gear can be smaller and the whole thing is theoretically possible

[@cosmicmark]

Have you ever used the RST-135 (non encoder) mount? Does the 135E out perform the 135 when guiding? I don't usually ever go unguided, but if the guiding performance with the encoder (and from my understanding only helps unguided performance?) improves, then I would get this in a heartbeat.

[@derekbaker3279]

Hi @cosmicmark ! IMHO, the key difference between the 135E and 135 is that the encoder version does not require guiding corrections twice per second. That means (a) it is far easier to find a sufficient number of stars for PHD2, which can be a challenge when using off-axis guiding, on-axis guiding with narrow band filters (e.g. ASI2600MC-pro Duo), or guiding with a longer focal length guidescope/a higher f-ratio, (b) it enables one to use longer guide exposures & less frequent guiding corrections, which reduces the likelihood of erratic guiding due to 'chasing the seeing'. So, the questions to consider are (a) What method of guiding are you using? (b) At what focal length are you using your main (imaging) camera? (i.e. what pixel scale>) (c) At what f-ratio are you guiding? FWIW, I have seen a lot of awesome images taken with a scope on the RST135 on Astrobin, so the RST135 is a great option in a lot of situations. Of course, the RST135 is a lot more expensive than the AM5 & HAE29, which have very similar capacities & have a brake to prevent back-driving (if the power is interrupted). On the plus side, the company that makes the RST135, is a long-established south Korean manufacturer of 'harmonic motors'/'strain wave gear motors' in the robotics industry, and they do use servo motors instead of stepper motors, which is reflected in the fact that I have never heard of quality control or durability issues with Rainbow Astro mounts. Finally, I have an RST135E, and I can vouch for its fundamentally sound design & high level of machining (..even if it's not red in colour...lol).

[@sreeshab4093]

How does the standard 135 mount perfrom compared to 135E?

[@AstroWithRoRo]

I have no used the non encoder version. Build wise it should be the same as this, but with tracking similar to the AM5.

[@sreeshab4093]

can we use a 8 inch Edge without autoguiding and without counter weights? will it track accurately good enough for imaging deepsky?

[@AstroWithRoRo]

You will need to guide with a 8" SCT, anything over ~500mm FL will need guiding. I regularly use my 9.25" Edge without counterweights though.

[@sreeshab4093]

@@AstroWithRoRo got it thanks. how is ur guiding for 9.25? are u using OAG or guiding scope? can u pls share specifics.

[@AstroWithRoRo]

I use an OAG when shooting at f/7 or f/10 and a guide scope when using the hyperstar. In general the 135 is very consistant. I am usually seeing limited from where I live. Under decent skies I usually get sub 0.5 total RMS and the best I've seen is 0.24.

[@sreeshab4093]

@@AstroWithRoRo which OAG is best suited for C8 and C9.25? The celeston one or Askar one or zwo one?

[@AstroWithRoRo]

I use the ZWO OAG-L, but this will only connect with a ZWO filter wheel so depends what the rest of your setup is like. I haven't used the Askar or Celestron OAG's.

[@davepastern]

did something happen to your channel? I was subscribed. Looked for some videos on harmonic drives and found yours and clicked on it and found out that I'm no longer subscribed. Weird.

[@billallen275]

Not a bad price, either!

[@billallen275]

(I mean, it is more than my car, but you know... )

[@celestromel]

You purchased yourself? You’re nutz!

[@derekbaker3279]

Everyone who does astro-imaging is a bit nuts. lol

[@kajouman]

10 K ? i would buy a EQ8 pro for that money,that can hold a 100 lbs scope.

[@derekbaker3279]

When is the last time you took your EQ8 Pro backpacking with a RedCat 51? 😉😁😂

[@kajouman]

@@derekbaker3279 i dont need to backpack,i live in a dark place with 360 view.

[@1966wasp]

Why would anyone make that kind of financial investment for at best 5 strong nebula targets to image? And once imaged then what, you image them again and again. Save your cash or have a great holiday...

[@wolfgangkuechle9085]

Sorry, but this is an utterly stupid comment. First of all it's everyones own decision how much money to invest in his/her hobby. And then there are countless targets to aim at. What's your problem with other people taking different decisions than you?

[@AstroWithRoRo]

Sorry if I gave off the impression this mount is only useful if imaging nebulae, but that's not at all the case. This mount is capable of imaging at any focal length. I have used it for visual, planetary, nebulae, satellite and solar imaging so far and it has been excellent at all of it. Of course, many mounts can do that too, so the advantage of this is how lightweight it is, and the fact you don't need to balance it. It is perfect for someone who wants an accurate mount that also travels a lot. There's also plenty more than 5 good nebulae to image (especially under my southern hemisphere skies)!

[@realmcerono]

Why would anyone take the time to make such an ignorant comment?

[@thomasmastrocinque7132]

@@realmcerono lol

[@UNLKYHNTR]

You've lost me at "ten thousand dollarydoos"....