What is your opinion on harmonic drive mounts?

May 25, 2022

I own a RST-135. I have few images in gallery yet with that setup. Mostly because I didn‘t get a lot of opportunity to travel and put a lot of work into my „semi-permanent“ one.

My take on it:
For small to smallish (say up to 4“ refractor/6“ newt), it is awesome: No counterweight needed, works well with photo tripod. I have a „flying“ setup with an FSQ-85 that fits into carry-on luggage. If you can guide with a guidescope you can use a cheap guiding cam and are fine. If you have an IMX174 or Ultrastar, use an OAG. Short guiding exposures are neccessary, combined with tight guiding parameters - although I don‘t see the 0.5s that are thrown around as optimal for my setups, usually 1-2s are better. Due to the short exposures, guiding is more seeing dependent than with other mounts. I have not seen any problems with this in my images, I assume the image deteriorates before guiding does. With a sturdy (Berlebach Planet) tripod, the RST-135 carries an 8“ f/6 Newtonian or 5“ refractor. It can actually carry a RASA 11 - but that needs care during setup and supervision. You need to be aware that on power loss the mount can start to move the unbalanced setup. This is not a „fall“, the mount drive acts as a break. So for unsupervised imaging I always balance well and do use counterweights. The polar wedge is serviceable but could be both sturdier and easier to adjust precisely. The rest of the mount is built extremely well. The drivers have been rock-solid except in combination with the ASIAir: There are frequent guiding hickups, random slews and strange problems with meridian flips. Under Windows (NINA, Voyager), no problem. If you can manage, it guides better at about 15V than at the minimum 12V.

Getting good guiding needs some experimentation, and the optimal parameters change depending on the load. So for that reason I‘m not sure I would recommend it for a beginner. Also, you pay a hefty premium for what is, basically, a mount with barely the same weight capacity and guiding accuracy as an EQ-6R.

RainbowAstro is a subsidy (or owned by the same people as - not sure which) very experienced robotics manufacturer. The RST is nice, but quirky. If that‘s the best they can do, I‘ld wait until some reviews pop up for the other ones. Preferably made by people not paid by the manufacturers. Of the brands listed, I have the highest confidence in Pegasus to pull it off.

Btw, for hiking I use a 80mm lens, DSLM and a tripod, If I feel luxurious, an AZ-GTi. That‘s even lighter and even more quirky.

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May 25, 2022

Torben van Hees:
I own a RST-135. I have few images in gallery yet with that setup. Mostly because I didn‘t get a lot of opportunity to travel and put a lot of work into my „semi-permanent“ one.

So 4 (UK) grands for a quirky little mount. I know where I'd spend that much (mount wise) and ain't it.

May 25, 2022 · Edited: May 25, 2022

andrea tasselli:
Torben van Hees:
I own a RST-135. I have few images in gallery yet with that setup. Mostly because I didn‘t get a lot of opportunity to travel and put a lot of work into my „semi-permanent“ one.

So 4 (UK) grands for a quirky little mount. I know where I'd spend that much (mount wise) and ain't it.

What AP capable mount that fits into carry-on luggage with a capacity for a 4“ refractor would you recommend instead?

The quirks of the mount can be worked around if you know them. As always, you pay a premium for miniaturization. I agree it‘s the wrong mount if size/weight does not play a major role in the decision. 10Micron, AP and SBig make great ones for those use cases, I hear.

The problems with the ASIAir are not limited to the RST: I haven‘t been able to finish a full night session with the ASIAir without an interruption of some kind, no matter which mount (10Micron, Heq-5, G111, RST, AZ-GTi, Omegon Goto Dobson). It really needs babysitting.

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Topic starter

May 25, 2022

Thank you Björn, thank you Torben.

The fact that harmonic drives are known since 1955 but only recently get used in astro mounts is actually one of the facts which I find a bit suspicious. Did they only recently get into an affordable price range or did just nobody come up with the idea? (Or am I ignorant and just not aware that they were used earlier?).

I'm not completely surprised that the RST has some quirks - thank you for the honest statement. In some sense this is what I expect for the 1st generation of these mounts and what makes me somewhat reluctant to buy one given the price. I would not be surprised to find similar "surprises" for the other products. I share your opinion that Pegasus has a reputation of delivering quality and is most likely the best bet. Unfortunately their mount is one of the biggest and heaviest among the announced models - which may actually tell us something …

I'm not really "hiking", it's just a 20 minute uphill walk, so I consider up to 30 kg / 60 lbs "portable". I still won't carry a RASA 11 with me :-)
On the other hand each kg/lbs hurts and getting lighter is worth the money. I won't get younger over the years anyway. Admittedly the weight of the photographer is a bigger issue, but that's a totally different story …

I currently take my first steps with the AZ-GTI and can confirm its quirkiness - one of my motivations to look for another mount. Short term I may be better served with one of the announced new Trackers (StarAdventurer GTI or iOptron SkyHunter) but their maximum load of 5 kg is a bit underwhelming and in combination with their required counterweights they weigh in almost as much as the harmonic drive mounts.

Except for the occasional use of my Maksutovs 90 and 127 for moon and planets I usually image above 2 arcsec image scale, so Björn is most likely right that I'm not pushing the guiding limits.

To make a long story short, minimum weight for a maximum of around 800mm focal length - I have an eye on the Explore Scientific 102mm f7 which weighs only about 7lbs - is my main requirement. And yes, I confess that buying AP gear by weight and volume may be "a bit" unusual …

Clear skies
Wolfgang

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May 25, 2022

I don’t know why harmonic drives weren’t used earlier.

To give a few more comparisons to mounts I own(ed): Compared to the AZ-GTi, the RST is in quite another class (as it should be at 10x the price). I would also rate it easier to use and setup than the belt-modded Heq-5 and the Losmandy G11: Only rough balancing necessary, no backlash. It, however, does not fade quite as much into the background as my 10Micron.

Talking about the price, the guiding hassles seem to be resolved with the encoder in the RST-135E. Depending on budget, it‘s worth a consideration. It won‘t allow you to go unguided at 800mm FL, probably.

Before I bought the RST, I also looked at the Astrotrack 360, at the Vixen Advanced Polaris and the TTS Panther.

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Topic starter

May 25, 2022

Torben van Hees:
I don’t know why harmonic drives weren’t used earlier.

To give a few more comparisons to mounts I own(ed): Compared to the AZ-GTi, the RST is in quite another class (as it should be at 10x the price). I would also rate it easier to use and setup than the belt-modded Heq-5 and the Losmandy G11: Only rough balancing necessary, no backlash. It, however, does not fade quite as much into the background as my 10Micron.

Talking about the price, the guiding hassles seem to be resolved with the encoder in the RST-135E. Depending on budget, it‘s worth a consideration. It won‘t allow you to go unguided at 800mm FL, probably.

Before I bought the RST, I also looked at the Astrotrack 360, at the Vixen Advanced Polaris and the TTS Panther.

I actually have access to an Astrotrack 360 which is a very interesting mount. The possibility to use it in different configurations is ingenious. However I have some doubts about the maximum load of 10 kg, although I may not push the limits. Main issue for me is the lack of an ASCOM driver (so far). An INDI driver and a TheSkyX driver is available though. Unfortunately both of them are quite useless to me. Of course the price is quite steep too. Will have to perform more testing with it. Of course it's also a "version 1.0 product" and for sure a niche product, so some glitches have to be expected too. Currently it's still my favorite among the non-harmonic-drive options.

I considered the Vixen Advanced Polaris too, but it shares the limited capacity of the other trackers. Didn't know about the TTS Panther. However, with it's 16 kg it's a bit on the heavy side. Thank you for the suggestions.

Clear skies
Wolfgang

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May 25, 2022

Torben van Hees:
What AP capable mount that fits into carry-on luggage with a capacity for a 4“ refractor would you recommend instead?

I have no idea what constitutes a carry-on luggage in terms of volume but I doubt it would allow you to fit a proper tripod in it. Excluding that the cherished GP would probably fit the bill and would take your so prized 4" refractor in its stride no question asked. Like everything in this world mount fashions come and go, same as telescope type and so forth. I'd reckon that they only see the limelight because is the one design the western makers didn't bother to pursue (for good reasons or not) and that left the far-east manufacturer free to exploit the design. To me it is a solution in search of a problem. Where I'd put my money on is in direct drive mounts, once hi-res encoders become more mainstream. Still 4k buys you a heck of mount in any other way you'd like to consider.

Topic starter

May 26, 2022

andrea tasselli:
Torben van Hees:
What AP capable mount that fits into carry-on luggage with a capacity for a 4“ refractor would you recommend instead?

I have no idea what constitutes a carry-on luggage in terms of volume but I doubt it would allow you to fit a proper tripod in it. Excluding that the cherished GP would probably fit the bill and would take your so prized 4" refractor in its stride no question asked. Like everything in this world mount fashions come and go, same as telescope type and so forth. I'd reckon that they only see the limelight because is the one design the western makers didn't bother to pursue (for good reasons or not) and that left the far-east manufacturer free to exploit the design. To me it is a solution in search of a problem. Where I'd put my money on is in direct drive mounts, once hi-res encoders become more mainstream. Still 4k buys you a heck of mount in any other way you'd like to consider.

Thank you for sharing your opinion Andrea. I dare to oppose the "solution in search of a problem" part. Given the interest in harmonic mounts and in small tracker-like mounts and looking at all those people - including me - who try hard to get the AZ-GTI going, there is a real wish - and therefore a market - for small and lightweight mounts. This wish may very well be naive and maybe in a few years we look back at a number of failed harmonic drive mounts. At the moment we have to get along with the options in place. Unfortunately I don't see any direct drive mounts available which wouldn't break my back. I'll happily buy one in the 10kg weight range. No doubt direct drive mounts beat the heck out of any other mount in terms of accuracy but they are just not suitable for my purposes.

I actually find the friction drive approach of the AstroTrack 360 interesting too. Obviously friction drives put a natural limit to the payload.

Clear skies
Wolfgang

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May 26, 2022

andrea tasselli:
Torben van Hees:
What AP capable mount that fits into carry-on luggage with a capacity for a 4“ refractor would you recommend instead?

I have no idea what constitutes a carry-on luggage in terms of volume but I doubt it would allow you to fit a proper tripod in it. Excluding that the cherished GP would probably fit the bill and would take your so prized 4" refractor in its stride no question asked. Like everything in this world mount fashions come and go, same as telescope type and so forth. I'd reckon that they only see the limelight because is the one design the western makers didn't bother to pursue (for good reasons or not) and that left the far-east manufacturer free to exploit the design. To me it is a solution in search of a problem. Where I'd put my money on is in direct drive mounts, once hi-res encoders become more mainstream. Still 4k buys you a heck of mount in any other way you'd like to consider.

There is no need to put a tripod in carry-on, they are sturdy enough. I prefer to carry expensive and fragile equipment with me instead of offering them to the vagaries of checked-in luggage. I understand there is a point to be made to just pay overweight luggage, toss 3 Heq-5s in and hope they survive longer than one RST.

The (far eastern) Vixen GP is no longer manufactured. The western manufacturers decided to pursue and perfect the worm-and-wheel drive ands its variations (with a few boutique exceptions) and most of them left or never entered the „small-and-portable“ market. The only direct drive mounts coming readily to my mind are from Planewave and ASA - both don‘t really work well for a portable solution.

I just checked, briefly, and for 4-5k€ you can get these high-quality mounts:
- Avalon M-Zero, capacity 8kg, weight 5.5kg
- Astrotrac 360, capacity 10kg, weight 5kg (actually, only 3.2 k€)
- Losmandy G811G, capacity 22kg, weight 12kg
- Losmandy G11 (not available, and I believe the price is pre-inflation)
- Vixen SXP2 (quoted accuracy +/- 4“… with PPEC). Capacity 17kg, weight 12kg

As you are using a Gemini mount, also this:
- Gemini e.Fric (Very little information. Both links to FAQ and technical spec sheet lead to 404 pages, so I can‘t say anything about capacity, weight or bulk).

There may be more „boutique“ solutions available, but after my experience with the Mesu mount I‘m done with one-man-shops and friction drives. If I forgot anything important, please add to the list.

So, I think the RST pricing isn‘t so inflated. Worm-wheel-drives also have their quirks, but since they are more common, the workarounds feel more comfortable. From my experience, the Losmandys are far from hassle-free to own and use. So, depending on where your priorities are between price, capacity, overall quality and weight, the RST can be a compelling offer. Which is why I bought it. Price need not always be a main concern when considering a purchase. If it is, there is a plethora of Chinese mounts with higher capacity for less money. Many people get beautiful results with them.

I don‘t think high precision encoders are coming down in price. They have been very stable in pricing for a long time and current shipping and supply chain issues will drive their prices up, the same as for many other specialty components. Why do you believe their cost will decrease?

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Björn Arnold

May 26, 2022

Torben van Hees:
The fact that harmonic drives are known since 1955 but only recently get used in astro mounts is actually one of the facts which I find a bit suspicious. Did they only recently get into an affordable price range or did just nobody come up with the idea? (Or am I ignorant and just not aware that they were used earlier?).

My impression is indeed that it's the manufacturing costs. Considering how these drives are designed, they have some rather high requirements on material and precision, compared to classical gear designs.

Torben van Hees:
So, I think the RST pricing isn‘t so inflated. Worm-wheel-drives also have their quirks, but since they are more common, the workarounds feel more comfortable.

I agree with you that the price is reasonable for this technology. Most advantages that are usually mentioned for the harmonic drive are not necessarily an advantage for people without a high focus on portability. Every system has its quirks one just needs to know what they are and if one has the means to handle it.

andrea tasselli:
Where I'd put my money on is in direct drive mounts, once hi-res encoders become more mainstream. Still 4k buys you a heck of mount in any other way you'd like to consider.

Honestly, I don't know if we'd need hi-res encoders. Through plate-solve (for pointing) and guiding one can achieve sufficient accuracy IMHO. From an engineering perspective, encoders aren't a full closed-loop control so you still may have external sources of error which your mount control cannot fix as it has a static model. Of course, dialling the control loop in is another difficulty of course.

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May 26, 2022

Torben van Hees:
andrea tasselli:
Torben van Hees:
What AP capable mount that fits into carry-on luggage with a capacity for a 4“ refractor would you recommend instead?

I have no idea what constitutes a carry-on luggage in terms of volume but I doubt it would allow you to fit a proper tripod in it. Excluding that the cherished GP would probably fit the bill and would take your so prized 4" refractor in its stride no question asked. Like everything in this world mount fashions come and go, same as telescope type and so forth. I'd reckon that they only see the limelight because is the one design the western makers didn't bother to pursue (for good reasons or not) and that left the far-east manufacturer free to exploit the design. To me it is a solution in search of a problem. Where I'd put my money on is in direct drive mounts, once hi-res encoders become more mainstream. Still 4k buys you a heck of mount in any other way you'd like to consider.

There is no need to put a tripod in carry-on, they are sturdy enough. I prefer to carry expensive and fragile equipment with me instead of offering them to the vagaries of checked-in luggage. I understand there is a point to be made to just pay overweight luggage, toss 3 Heq-5s in and hope they survive longer than one RST.

The (far eastern) Vixen GP is no longer manufactured. The western manufacturers decided to pursue and perfect the worm-and-wheel drive ands its variations (with a few boutique exceptions) and most of them left or never entered the „small-and-portable“ market. The only direct drive mounts coming readily to my mind are from Planewave and ASA - both don‘t really work well for a portable solution.

I just checked, briefly, and for 4-5k€ you can get these high-quality mounts:
- Avalon M-Zero, capacity 8kg, weight 5.5kg
- Astrotrac 360, capacity 10kg, weight 5kg (actually, only 3.2 k€)
- Losmandy G811G, capacity 22kg, weight 12kg
- Losmandy G11 (not available, and I believe the price is pre-inflation)
- Vixen SXP2 (quoted accuracy +/- 4“… with PPEC). Capacity 17kg, weight 12kg

As you are using a Gemini mount, also this:
- Gemini e.Fric (Very little information. Both links to FAQ and technical spec sheet lead to 404 pages, so I can‘t say anything about capacity, weight or bulk).

There may be more „boutique“ solutions available, but after my experience with the Mesu mount I‘m done with one-man-shops and friction drives. If I forgot anything important, please add to the list.

So, I think the RST pricing isn‘t so inflated. Worm-wheel-drives also have their quirks, but since they are more common, the workarounds feel more comfortable. From my experience, the Losmandys are far from hassle-free to own and use. So, depending on where your priorities are between price, capacity, overall quality and weight, the RST can be a compelling offer. Which is why I bought it. Price need not always be a main concern when considering a purchase. If it is, there is a plethora of Chinese mounts with higher capacity for less money. Many people get beautiful results with them.

I don‘t think high precision encoders are coming down in price. They have been very stable in pricing for a long time and current shipping and supply chain issues will drive their prices up, the same as for many other specialty components. Why do you believe their cost will decrease?

Vixens are still on sell AFAIK and the SX2 is a reputable little mount and at 7 kg is very portable. Even the AP would do with small refractors on top and it is even lighter. There are obviously far-east solutions from the usual ones and I find the iOptron GEM28 to be a very lightweight solution and eminently portable.

As for HR encoders they will become mainstream when they'll start appearing in cars, washing machines, tumble drivers and so forth. We're not quite there yet, agreed.

GTD page can be found here:
http://www.geminitelescope.com/efric-friction-drive-mount-german-equatorial/

Frequent contributor

May 26, 2022

Björn Arnold:
Honestly, I don't know if we'd need hi-res encoders. Through plate-solve (for pointing) and guiding one can achieve sufficient accuracy IMHO. From an engineering perspective, encoders aren't a full closed-loop control so you still may have external sources of error which your mount control cannot fix as it has a static model. Of course, dialling the control loop in is another difficulty of course.

For the DD designs that I know of yes they do. They control the motors turning by pulse-modulation of the 3-phase windages of those motors and they can only achieve that kind of resolution and accuracy in a closed-loop system with HR encoders.

Steven

May 26, 2022

Certainly find them interesting.

But, they're usually at a price point that I don't really want to spend on a single mount. And even if I was going to spend that money. That money would give me some amazing equatorial mounts.. Some go towards "skywatcher EQ8" money.

I do like the new ZWO one, and it's a lot more affordable. I'm waiting to see how it performs, and then I might go for it "one day".
But, I already have 3 rigs with a skywatcher EQ6-R, Celestron VX and a skywatcher NEQ3-2, and those rigs are designed to fit the capacity of the mounts.. so.. it's not like I really need more mounts with my current setup. - And right now I have other elements of my rigs that I want to upgrade first.

Topic starter

May 26, 2022

andrea tasselli:
Torben van Hees:
andrea tasselli:
Torben van Hees:
What AP capable mount that fits into carry-on luggage with a capacity for a 4“ refractor would you recommend instead?

I have no idea what constitutes a carry-on luggage in terms of volume but I doubt it would allow you to fit a proper tripod in it. Excluding that the cherished GP would probably fit the bill and would take your so prized 4" refractor in its stride no question asked. Like everything in this world mount fashions come and go, same as telescope type and so forth. I'd reckon that they only see the limelight because is the one design the western makers didn't bother to pursue (for good reasons or not) and that left the far-east manufacturer free to exploit the design. To me it is a solution in search of a problem. Where I'd put my money on is in direct drive mounts, once hi-res encoders become more mainstream. Still 4k buys you a heck of mount in any other way you'd like to consider.

There is no need to put a tripod in carry-on, they are sturdy enough. I prefer to carry expensive and fragile equipment with me instead of offering them to the vagaries of checked-in luggage. I understand there is a point to be made to just pay overweight luggage, toss 3 Heq-5s in and hope they survive longer than one RST.

The (far eastern) Vixen GP is no longer manufactured. The western manufacturers decided to pursue and perfect the worm-and-wheel drive ands its variations (with a few boutique exceptions) and most of them left or never entered the „small-and-portable“ market. The only direct drive mounts coming readily to my mind are from Planewave and ASA - both don‘t really work well for a portable solution.

I just checked, briefly, and for 4-5k€ you can get these high-quality mounts:
- Avalon M-Zero, capacity 8kg, weight 5.5kg
- Astrotrac 360, capacity 10kg, weight 5kg (actually, only 3.2 k€)
- Losmandy G811G, capacity 22kg, weight 12kg
- Losmandy G11 (not available, and I believe the price is pre-inflation)
- Vixen SXP2 (quoted accuracy +/- 4“… with PPEC). Capacity 17kg, weight 12kg

As you are using a Gemini mount, also this:
- Gemini e.Fric (Very little information. Both links to FAQ and technical spec sheet lead to 404 pages, so I can‘t say anything about capacity, weight or bulk).

There may be more „boutique“ solutions available, but after my experience with the Mesu mount I‘m done with one-man-shops and friction drives. If I forgot anything important, please add to the list.

So, I think the RST pricing isn‘t so inflated. Worm-wheel-drives also have their quirks, but since they are more common, the workarounds feel more comfortable. From my experience, the Losmandys are far from hassle-free to own and use. So, depending on where your priorities are between price, capacity, overall quality and weight, the RST can be a compelling offer. Which is why I bought it. Price need not always be a main concern when considering a purchase. If it is, there is a plethora of Chinese mounts with higher capacity for less money. Many people get beautiful results with them.

I don‘t think high precision encoders are coming down in price. They have been very stable in pricing for a long time and current shipping and supply chain issues will drive their prices up, the same as for many other specialty components. Why do you believe their cost will decrease?

Vixens are still on sell AFAIK and the SX2 is a reputable little mount and at 7 kg is very portable. Even the AP would do with small refractors on top and it is even lighter. There are obviously far-east solutions from the usual ones and I find the iOptron GEM28 to be a very lightweight solution and eminently portable.

As for HR encoders they will become mainstream when they'll start appearing in cars, washing machines, tumble drivers and so forth. We're not quite there yet, agreed.

GTD page can be found here:
http://www.geminitelescope.com/efric-friction-drive-mount-german-equatorial/

Thank you for pointing me to the additional options. The Vixen mounts - except for the Polaris mentioned earlier - somehow escaped my attention. The capacity to weight ratio still seems to remain a unique selling point for the harmonic drive mounts and makes them tempting. Admittedly the "no counterweight" topic may be overrated. For small rigs 2 kg counterweight may be sufficient anyway, larger and heavier rigs may get in danger to tumble over if they are not on a concrete pier or on a heavy tripod.

Clear skies
Wolfgang

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