UMi 17 Lite harmonic drive mount quick review

Living in NYC, I have always wanted a harmonic drive mount. It's easy to take to dark sites, easy to store in a small apartment, and easy to set up and tear down. This year, I finally made the purchase.

The most popular mounts in this category are the ZWO AM5 and AM3. Since they are based in China, I decided to do some research in Chinese. That's how I found the UMi mounts, which are said to provide better performance for less money. Intrigued, I decided to get one of their latest mounts, the UMi 17 Lite.

So here I want to offer some of my observations about this mount, and about harmonic drive mount in general, coming from someone who never used them before.

Who made this

The branding of this mount is a bit of a mess, which also makes information hard to find. To the best of my knowledge, the company that created the mount is called Meow Astro (喵星天文馆, lit. Cat Star Planetarium), and they have two mounts, the UMi 17 (小熊, lit. Little Bear), followed by UMi 17 Lite (小小熊, lit. Little Little Bear). It felt like one man operation. This year they rebranded to Proxisky (比邻星天文, lit. Proxima Centauri Astronomy) and launched a website for e-commerce, so now you can buy the mount from the manufacturer directly there. Previously, you have to either go through a dealer on eBay or Aliexpress, or contact them via Discord.

Price and Spec

As of today the mount costs $1250, which compares very favorably to ZWO's AM3. Further, it is advertised to use a Type-17 gear in RA axis, as opposed to Type-14 in AM3. However, even with all my Google-fu I cannot understand what those "types" mean. I suspect it correlates to the reduction ratio.

The mount body weights 2.8kg. I didn't buy their latitude base (more on that later) as I already have the William Optics one. With the WO base installed it weighs 3.9kg, which is the same as AM3.

However, contrary to some information online, the mount only has brake on RA axis, and there isn't a zero position sensor.

Packaging

The mount comes with a nice carrying case with foam cutout. However, there's no place for the latitude base. The small white box is a finder shoe.

Hardware and Design

Overall the mount is a long cylinder, like the Rainbow Astro mount. However, it is not a knockoff. One unique feature of the mount is the latitude base is not integrated. There's a 3/8 screw hole in the bottom of mount body, so if you plan to use it in alt-az mode you can leave the latitude base out.

This design has some drawbacks compared to the cube-like shape of ZWO / iOptron mounts though. Since the mount body is long, if you use a short but skinny scope, the accessories may not clear the back side of the mount, forcing you to move the entire setup towards the back, resulting in an unbalanced Dec axis. In theory since this is a harmonic drive mount, an unbalanced axis isn't a problem. However, in practice, this makes polar alignment difficult: since the system is back-heavy, adjusting the latitude up is going to be much easier than adjusting it down. The William Optics base does not have knobs, only knurled screw. This makes pushing the scope down quite painful. The official latitude base does have knobs though - I hope it would be easier to use. If your setup clears the mount (if you don't use a filter wheel for example), since the mount is long, it does mean if you balance the Dec axis, the mount as a whole will be front heavy.

Another problem is since the mount is skinny and short, even with the extension pier, you might not be able to slew to zenith without hitting anything. I did a test slew and had to cut the power to prevent that from happening. It also proved the RA brake works

Another interesting feature of this mount is the counterweight bar is mounted via a finder shoe, and you need to install the finder shoe yourself. Unfortunately the shoe provided is a little bit too short, so I had to add some felt to shim it. Also, once the finder shoe is installed the foam is no longer a perfect fit. I wouldn't trust a big counterweight on it. This is probably why counterweight is limited to 5kg in the official spec.

However the finder shoe does give you opportunity to mount something else there. I 3D printed a finder stalk adapter and mounted my mini PC.

On the side of the mount you can actually mount another finder shoe. Perhaps if you want to add a polar scope or something.

The saddle is Vixen only. They do sell a dual Vixen-Losmandy saddle for ~$100. It is spring loaded, so will not mar the dovetail bar.

The overall fit-and-finish is good, but not perfect, as my example had a small dent in the saddle.

Software

Software, unfortunately, isn't the strong suit. The control board is based on Onstep, so like most open source software, the experience is more utilitarian.

If you want to control the mount using ASCOM, you need to download the serial port driver and Onstep ASCOM driver from Proxisky’s website. Version does matter here - make sure you use the one on their website. Before you connect the mount in ASCOM, make sure to open the configuration window and turn off both Serial DTR Control and Use Error Correction Protocol. If you do not, you will have a runaway mount problem.

The ASCOM configuration is also counterintuitive. In setting the location, latitude follows the convention (north is positive) but longitude is not (west is positive, as opposed to negative). Time zone is also the exact opposite, and does not use daylight saving (I.e. if you are in US Eastern, put down +5)

If you want to control the mount from your iPhone, the app is called MeowGoto, available in the App Store.

Using the mount

Harmonic drive mounts are indeed less hassle to use. Now I can move the mount together with the tripod out in one trip. Not needing to balance the mount is nice, although that just saves a minute or two.

None of the harmonic drive mounts have clutches. This is definitely annoying, as you must remember to park the mount before turning everything off. Furthermore, when parked the mount doesn't end up in the zero position occasionally, and you cannot just fix it quickly by hand.

The mount does not come with a hand controller, nor is one offered. 

Another quirk of the mount is you cannot move any of the axis until you turn on tracking. So do not turn off the "enable tracking on startup" option.

Guiding

As everyone knows, you never get clear weather when new gear arrives  However I did try to do some guiding test in the partly cloudy weather in my balcony.

Per standard advice, harmonic drive mounts require fast guiding. Together with the bad seeing in New York, it makes off-axis guiding difficult. So I used a SVBony mini guide scope (30mm f/4). I guided with 1s exposure on ASI290mini, using PPEC algorithm in PHD2.

I did order the carbon fiber tripod they have. However it is still on a boat from China, so I put everything on my AZ-GTe tripod, which is a little shaky for the mount. To increase stability I put 5kg weight in the tray.

I ran my tests near 10 degrees declination, and due to the balcony above I can only reach ~50 degrees altitude. Seeing is reported as below average to poor in cleardarksky. All in all, a pretty brutal environment for guiding test.

Test result is pretty encouraging. Overall RMS is around 1.12"; there are some large spikes though - it is unknown if they are due to ground shakes, wind, or defects in the mount. Excluding the spikes RMS is ~0.9" or so. I was only able to run test for ~15 min before clouds rolled in, so it was hard to discern periodic error. I will attach the guide log so folks more experienced than me can take a look!

Support

In China UMi mounts are renowned for their support, as the company is very responsive to DMs. I personally asked them a lot of questions and have got answers within minutes. In overseas market there is an official discord channel, and they are pretty responsive too. The real question, however, is how repairs will work should the need arise. Currently it seems that you can purchase replacement PCBs, but I do wonder how more complicated repairs will be handled - having to ship to China and back would be annoying.

What to look forward to

As I write this, Proxisky announced their next generation mount, UMi-17R. It uses direct drive servo and have integrated latitude base, and is priced very aggressively at ~$1500. I look forward to the review - it could be a worthy competitor to the WarpAstron mounts.

Guide log is here:

 

$1250, which compares very favorably to ZWO's AM3

But didn't you have to spend $300 on the WO wedge? And in the end it's way less secure and the whole solution definitely more clunky.  The lack of integrated wedge is a terrible design choice.

I understand that for people who drive their 50 or 70mm Redcats it's all the same and who cares but it actually is an issue for more serious gear that these mounts are arguably rated.  AM3 actually comes with an integrated wedge that's rather solid.

But didn't you have to spend $300 on the WO wedge? And in the end it's way less secure and the whole solution definitely more clunky.  The lack of integrated wedge is a terrible design choice.

 

I understand that for people who drive their 50 or 70mm Redcats it's all the same and who cares but it actually is an issue for more serious gear that these mounts are arguably rated.  AM3 actually comes with an integrated wedge that's rather solid.

No, the $1250 quote includes a wedge.

Interestingly the total weight of the mount body and WO latitude base is the same as AM3. It is definitely bigger though.

My experience has been better. I’ve had nothing but good results from the UM17-Lite. I’m running a RedCat with ASIAIR-plus.
Driver downloads and setup instructions, including OnStep are available on the Discord site and I had no difficulty on first light guiding at < 0.5” tot. At no stage did the guiding exceed 0.56 and often it’s in the 0.3’s
Cuiv has done a very informative video recently on these mounts and will shortly produce a followup on the UMi-Lite itself.
This mount has been a game changer for me and I’m looking forward to receiving the UMi17-R which has a DC servo drive on RA which promises even better performance.
I must also add that the mount is all but silent in operation 

Edited by Tphil, 24 May 2024 - 05:18 PM.

I finally got good weather in New York, albeit on full moon. This time I am running a C6 Hyperstar with the 30mm f/4 guide scope. Seeing is reported as poor. I am using 0.5s exposure this time. Results are better this time - I got ~0.7 RMS, at Dec = 12 degrees. This is indeed very good - on par with my CEM70.

I'm sure once I get my tripod (it's clearing customs right now!) and try this in places with better seeing I would see better numbers.

Cuiv's video also answered the question I mentioned in the post. The "types" of the gears refers to the maximum torque, so Type 17 have higher torque rating, which probably explains why UMi 17 Lite have better weight capacity than AM3.

Edited by HeavenlyFox, 24 May 2024 - 10:37 PM.

I finally got good weather in New York, albeit on full moon. This time I am running a C6 Hyperstar with the 30mm f/4 guide scope. Seeing is reported as poor. I am using 0.5s exposure this time. Results are better this time - I got ~0.7 RMS, at Dec = 12 degrees. This is indeed very good - on par with my CEM70.

 

I'm sure once I get my tripod (it's clearing customs right now!) and try this in places with better seeing I would see better numbers.

 

Cuiv's video also answered the question I mentioned in the post. The "types" of the gears refers to the maximum torque, so Type 17 have higher torque rating, which probably explains why UMi 17 Lite have better weight capacity than AM3.

So if this UMi 17 Lite has a better weight capacity than AM3 then what about the UMi 17 standard which is having even more payload capacity than Lite version? Will this be also better than AM5 for example? 

I keep thinking about this mount or the standard non Lite version, or even another harmonic mount of another manufacturer but almost in same price of this Lite, ZWO harmonic mounts are all expensive according to their payload actually, i mean i can have a harmonic mount of AM5 capacity but with AM3 price, i don't follow ZWO products to be dedicated to them only, but i still think about a harmonic mount that can accept the weight of my RC10 Truss with accessories and guiding good enough and not so pricey.

So if this UMi 17 Lite has a better weight capacity than AM3 then what about the UMi 17 standard which is having even more payload capacity than Lite version? Will this be also better than AM5 for example? 

 

I keep thinking about this mount or the standard non Lite version, or even another harmonic mount of another manufacturer but almost in same price of this Lite, ZWO harmonic mounts are all expensive according to their payload actually, i mean i can have a harmonic mount of AM5 capacity but with AM3 price, i don't follow ZWO products to be dedicated to them only, but i still think about a harmonic mount that can accept the weight of my RC10 Truss with accessories and guiding good enough and not so pricey.

Without counterweight, the rated capacity of the Lite and non-Lite are similar - I suspect they have the same motor and gear in RA axis.

With counterweight the capacity of non-Lite is a few kg higher, likely due to its ability to accept heavier counterweight.

I heard good things about performance of the non-Lite version - better than AM5 from what I read. However, it is significantly heavier, which kinda defeats the purpose of harmonic drive mounts.

Without counterweight, the rated capacity of the Lite and non-Lite are similar - I suspect they have the same motor and gear in RA axis.

With counterweight the capacity of non-Lite is a few kg higher, likely due to its ability to accept heavier counterweight.

I heard good things about performance of the non-Lite version - better than AM5 from what I read. However, it is significantly heavier, which kinda defeats the purpose of harmonic drive mounts.

I hope if that "better" performance means i can use my RC10 truss with it just fine, i don't worry much about being heavier, it will be way much less weight than my AZ-EQ6 head alone.

I hope if that "better" performance means i can use my RC10 truss with it just fine, i don't worry much about being heavier, it will be way much less weight than my AZ-EQ6 head alone.

It's a bit difficult to work with RC10, but for the UMI 17 version, RC8 performs well

Perhaps you can take a look at their future UMI 20 releases

thank you for the detailed review. 

type 17 - nema 17 stepper motor

type 14 - nema 14 stepper motor

at least this is what I suspect. so it is not about the strain wave gear but the motor size. 

It's a bit difficult to work with RC10, but for the UMI 17 version, RC8 performs well

Perhaps you can take a look at their future UMI 20 releases

Yes, i am waiting their new model.