39 replies to this topic

[mikehager]

As a potential interested buyer of a RST135e mount I'm proposing the following brief survey of current owners within the CN community.

 

https://docs.google....ZWu7BbtIfI/edit

 

Thank you in advance to all who are willing to take two minutes to share your impressions by selecting the above link.  This is the 3rd of 3 such planned surveys of harmonic mounts on my short list.  FYI, by selecting the above link you should be able to either answer the survey or view other responses via tabs at the top of the form.

 

After completing the brief survey feel free to post a brief reply in this thread to indicate that you contributed, please.

Edited by mikehager, 07 February 2025 - 09:36 AM.

[astrohamp]

Link wants a sign in.  What's with that?

[mikehager]

Link wants a sign in.  What's with that?

Hmmm, I've tried resaving my last edit and exiting the app.  Perhaps try again and let me know if still an issue?   Sorry, I'm a newbie to the Google survey forms so if anyone has a suggestion on troubleshooting this please let me know.  Thanks.  -Mike

[Blue_Orca]

Your doc still wanting Google sign in for access.  Might be easier just ask the questions here and get people to respond.

 

If you are thinking about purchasing a RST-135E, and you know well its spec vs. your needs, I would wholeheartedly say go for it.

 

I for one am very happy with mine.  I guide with a MGEN3 on a Nikon 200mm f4 AIS lens as guide scope.  Just earlier in the month at a Bortle 2 site on a calm night with average seeing, I saw RA at 0.18"-0.22" and DEC 0.2"-0.3" throughout the night.  Guide exposure on MGEN3 was 3s.  The mount just works and I get to keep all sub exposures.  It's pretty much set and forget.

 

Some complain mount sometimes "jumps" when at the end of a polar alignment routine and you tighten it up with the two side knobs.  I have not seen that on mine but some of us mitigate that by using a Univeral Polar Alignment System from Avalon Instruments.     

 

The other thing is to remember to "Home" right after power on, and "Home" again just before you turn it off.  If you are using the hand controller to home the mount, remember to hit ESC on the keypad every time the mount finishes homing.

 

Edit: Corrected typo on guide scope focal length.  Correct fl is 200mm, not 20mm.

Edited by Blue_Orca, 07 February 2025 - 01:15 PM.

[psandelle]

Your doc still wanting Google sign in for access.  Might be easier just ask the questions here and get people to respond.

 

If you are thinking about purchasing a RST-135E, and you know well its spec vs. your needs, I would wholeheartedly say go for it.

 

I for one am very happy with mine.  I guide with a MGEN3 on a Nikon 20mm f4 AIS lens as guide scope.  Just earlier in the month at a Bortle 2 site on a calm night with average seeing, I saw RA at 0.18"-0.22" and DEC 0.2"-0.3" throughout the night.  Guide exposure on MGEN3 was 3s.  The mount just works and I get to keep all sub exposures.  It's pretty much set and forget.

 

Some complain mount sometimes "jumps" when at the end of a polar alignment routine and you tighten it up with the two side knobs.  I have not seen that on mine but some of us mitigate that by using a Univeral Polar Alignment System from Avalon Instruments.     

 

The other thing is to remember to "Home" right after power on, and "Home" again just before you turn it off.  If you are using the hand controller to home the mount, remember to hit ESC on the keypad every time the mount finishes homing.

Ditto, including the Avalon UPAS.

Paul

[astrohamp]

On a good day...(night) like this one was, I'm satisfied.

[mikehager]

Link wants a sign in.  What's with that?

Okay I think I found the issue in settings that hopefully is corrected now.   Thanks.  

[Catchlight]

unable to save responses. An amazing mount, lightweight, good capacity and excellent guiding, typically below 0.5".

[Poochpa]

...and with an excellent hand controller, too.

[mdrileynyc]

Ditto to both form not working and very positive experience with the rst135e

[Blue_Orca]

Your survey finally works for me.

 

One thing to be clear, RST-135E guides and performs very differently from the Non-E.  It is the one to get if you want your mount to fade into the background.

 

OTOH, RST-135 Non-E has many alternatives in the market that can perform just as well but priced much lower.  A little hard to recommend over its competition, unless other factors such as country of origin is important to you.

[w7ay]

Both RST-135 and RST-135e require autoguiding for astrophotography.  But if you use it for planetary, the RST-135e is far better, since the encoder can keep a planet inside a smaller ROI, and thus faster frame rates.  In any case, the good news is that the RST-135e can be autoguided even with the encoder turned on (not all encoded mounts can do this, with the encoder in the mount and the "encoder in the sky" fighting one another).

 

The worst case first derivative of the periodic error is not that much better on the 'e' than the "non-e".  But better, nonetheless.  By properly limiting the largest guide pulses to match the first derivatives, and using minimal "aggressiveness," I can get something in the region of 0.3"-0.35" total RMS (RA+declination) guide error on the "e" when there is no wind.  The "non-e" is in the region of 0.4" to 0.45" (again total RA + dec (sqrt(RA^2+dec^2) RMS).  Both optimal with 0.5 second guide cadence, which obviously require good multistar guiding to avoid chasing "seeing" with such short cadence.

 

The mount has so little backlash that you cannot use much loop gain ("aggressiveness"), otherwise you will be guiding to where the star was. (The guide frames are the average of the star position in the exposure from the past, and you don't want the mount to move there).

 

My first 135 was from the first manufacturing batch, with serial number 13 :-).  Had to go through the mount base update with that mount, otherwise polar alignment was unmöglich.  But even the newer RST-135e still have a problem when locking the altitude bolts.  You just have to lock it gradually, instead of waiting for the end of polar alignment to lock it all at once.

 

Not any real problems, otherwise.  Very pleasant mount to use.  Definitely cannot go back to use my EM-11.

 

Oh, no problem at all with third axis imbalance.  I use it with a 10mm thick dual saddle plate, with my guide camera on the side of the main OTA.

 

Chen

Edited by w7ay, 08 February 2025 - 06:28 PM.

[dan_hm]

I bought a new RST-135 (non-E) not long before the wave of strain wave mounts hit the market.  It's super light, well-built, and tracks accurately provided you use 15-16v to power it (very easy nowadays with USB-PD).  But I'll be honest, if I could go back I would have just spent the extra $ on the E.  The E can reliably carry even a long focal length scope.  And whichever one you get, neither will keep its value, so just get the more expensive one.  As soon as the cheap Chinese strain wave mounts came out the RST-135s plummeted in value.

[w7ay]

tracks accurately provided you use 15-16v to power it (very easy nowadays with USB-PD).  

I do use a 12V-to-15V buck/boost converter at the base of my tri-pier to power my RainbowAstro mounts.  It is powered through a homebrew DC uninterrupted power supply (UPS) to avoid any backdrive in case of power loss.  

 

(Nowadays, you can find power banks that will work as DC UPS, and not need to even built one yourself.)

 

Chen

[w7ay]

I just found this in my archives.  Unguided test of my first RST-135E when I first got it.  The width of the graph is 100 sec.

 

 

It is not completely unguided since this was taken on an ASIAIR which don't allow it.  I had turned the Declination pulses off, and the max guide pulse of the RA motor was set to 1 ms for every 0.5 second -- that pretty much causes no corrections.  Pretty much under 1" total RMS error.

 

With the non-encoded version, the periodic error would be more like 20", or perhaps a little worse even (20" RMS corresponds to about 60" peak-to-peak if the PE were sinusoidal).

 

Chen

Edited by w7ay, 13 February 2025 - 12:59 AM.

[Poochpa]

Interesting anecdotal story about my RST-135E:

I previously had the original 135 and sold it to buy the 135E when it came out. My first night out with the 135E was during a camping trip. I had an Askar ACL-200 lens and ZWO ASI2600 camera on the mount. Once everything was up and running well with the guiding looking great, I went in my trailer to take a nap. I came out about an hour later and noticed that PHD2 guiding had stopped, probably due to lost stars from a period of passing clouds lengthy enough to prevent guiding from resuming. Star FWHM looked the same whether guided or not with 4 min. subs, so I just left it running unguided. In processing I was able to use all subs with little difference between them. Yes, it was only unguided at a focal length of 200mm, but the encoder greatly reduces the PE and it is rare that I have to ever through out a sub, even when imaging at a focal length of 2100mm with an SCT.   It's an expensive mount, but the quality of manufacturing and its components are excellent. Additionally, I don't know of any other strain-wave mount that has such a high-quality hand controller.  I do wish it had an RA brake and a better alt-az base design for polar alignment, but I feel the mount will last a long time without the need for adjustment or repair.

Mike

Edited by Poochpa, 13 February 2025 - 10:12 AM.

[w7ay]

I do wish it had an RA brake and a better alt-az base design for polar alignment, but I feel the mount will last a long time without the need for adjustment or repair.

If I remember correctly from a post here on Cloudy Nights by Xuranus, RainbowAstro at some point (it was well before the E version came out, I think) had added a current sensing measurement to the servo motor.  When it sensed abnormally large currents, like when the instrumentation on the mount has hit the pier, it would back off.  There is a video showing it working too -- it showed that if you apply even a finger at the end of an OTA, you can stop the mount from slewing.

 

So, the RST-135 has the equivalent of "brakes" on not just the RA axis, but also the declination axis.  But, unlike electromechanical brakes, it does not work if you have a power loss.

 

By that time, I had already included my uninterruptible power supply since I wanted to drive the mount at 15V anyway, so I didn't bother checking it.

 

RainbowAstro was pretty innovative with mounts.  In their earlier German mounts (massive, traditional worm geared mounts), they had used current sensing to measure balance of the two axis (i.e., current into servos depends on the unbalanced load).  I had measured the current consumption of the entire mount, and indeed, the current depends on how much you imbalance the RST135.  Since I was measuring the total power, I did not have enough resolution to actually find where the mount was best balanced.  Plus, I have found that the RST-135 appears to guide better when it is slightly imbalanced -- I added a counterweight to my lightweight setup and the guiding got worse. ( I stay under 20 lbs payload because at my age and stature, I cannot handle heavy OTAs.)

 

WarpAstron WD20 has added this current limiting function to their firmware a couple of months ago (apparently the current sensing parts were already built in).  But it is likely that not many other strain wave geared mounts can copy this idea, since most of them are stepper motor based.  The WD20 and WD17 are servo based, albeit, the firmware upgrade did not include the WD17, perhaps it does not have the current sensor built in.

 

As to polar alignment, with the "new" base, I found that it was easy to align -- the problem is the locks, which do not apply only forces that are orthogonal to what they were locking.

 

Chen

Edited by w7ay, 13 February 2025 - 02:48 PM.

[dryfly]

I do use a 12V-to-15V buck/boost converter at the base of my tri-pier to power my RainbowAstro mounts.  It is powered through a homebrew DC uninterrupted power supply (UPS) to avoid any backdrive in case of power loss.  

 

(Nowadays, you can find power banks that will work as DC UPS, and not need to even built one yourself.)

 

Chen

What are the best commercial power supplies available (in your opinion) for the Rainbow Astro mounts?  I'm not a homebrew kind of guy....

 

Mike

[w7ay]

What are the best commercial power supplies available (in your opinion) for the Rainbow Astro mounts?  I'm not a homebrew kind of guy....

 

If you are not the homebrewing type, just use your 12V supply, but with very short cables, or very heavy (14 AWG like) cables.  Guiding will not be nearly as precise as a 15V to 16V supply, but should work well enough if you don't want to put in the extra effort.

 

(The recommendation for using a 15V-16V supply came from Xuranus on this forum some time back.  Xuranus [Byongyun Jeong] is an R&D manager at RainbowAstro and RainbowRobotics.)

 

If you are looking for a brick style switching power supply, in general I recommend using the "medical" type supplies, they have better noise specs than cheaper ones, and they have much better isolation from the mains, for safety (as required by the medical profession).  Like this 15V one,

 

https://www.amazon.c...l/dp/B08YZ214C2

 

Just look for a "medical" supply that is capable of more than 3A.  Mouser Electronics also sells the Mean Well medical power supplies, and have a more complete selection than Amazon.

 

https://www.mouser.c...an-well-medical

 

If you use separate power supply for the mount and the rest of your equipment, make sure that you connect the ground return of the 15V supply to the ground return of the of your regular 12V supply near to your mount, using a heavy ground strap, to prevent large currents through the fragile ground return of your USB ports.  Do this even if you are not a homebrewing type.

 

That being said, any power supply needs to be close to the mount, otherwise there is too much voltage drop on the 15V cable unless you use heavy cables.  Even a pair of 18 AWG copper cable that is just 10 meter long (thus 20 meter feet total when you include the ground return) has 0.4 ohms, and will cause over 1V drop at the peak 3A when the mount is slewing.  This is why good larger supplies have 4 wires, two of which are sense wires, to make sure the far end of the cable is at the target voltage.  An example for a 15V supply is this:

 

https://www.amazon.c...l/dp/B08XQT35PF

 

A single 18 AWG copper cable has a resistance of 21 milliohms per meter.  A 16 AWG cable has 13 mΩ/m, and even a 14 AWG cable has 8 mΩ/m.

 

This is why it is better to simply install a 12V to 15V boost (or buck/boost) switching converter near to the mount, with a short cable from it to the mount.  And don't forget a ground strap between its ground return and your 12V ground return.  You can find many boost converters at Amazon, like this one:

 

https://www.amazon.c...r/dp/B08JG4FJ7N

 

Chen

Edited by w7ay, 14 February 2025 - 03:19 PM.

[Poochpa]

What are the best commercial power supplies available (in your opinion) for the Rainbow Astro mounts?  I'm not a homebrew kind of guy....

 

Mike

I use a Losmandy 12 to 15v PS:

https://store-losman...stores.com/acdc

[Blue_Orca]

What are the best commercial power supplies available (in your opinion) for the Rainbow Astro mounts?  I'm not a homebrew kind of guy....

 

Mike

Any power bank supporting USB PD and a 15V decoy trigger cable with a 5.5 x 2.5mm DC connector would do.  I use an earlier version of the Goal Zero Sherpa 100AC power bank, it gets charged from the mains, and when the AC fails, the battery will keep the mount powered.

 

See original instructions on Rainbow Astro blog.

Edited by Blue_Orca, 14 February 2025 - 06:31 PM.

[astrohamp]

Some folks have been advocating a Powerwerx unit like this.  Spec says it will crank up to 16v although I have no experience with it.

 

My Pegasus Pocket PowerBox Advance (PPBADV) wont allow voltages above 14.5v to go through their internal protection circuit.  Shuts down the outputs as I found out while operating my astro tech and charging the LiFePO4 battery it was powered from.  Because of this I have not operated by RST-135e much higher then the 13.8v any LiFePO4s I use first put out.

[psandelle]

Some folks have been advocating a Powerwerx unit like this.  Spec says it will crank up to 16v although I have no experience with it.

 

My Pegasus Pocket PowerBox Advance (PPBADV) wont allow voltages above 14.5v to go through their internal protection circuit.  Shuts down the outputs as I found out while operating my astro tech and charging the LiFePO4 battery it was powered from.  Because of this I have not operated by RST-135e much higher then the 13.8v any LiFePO4s I use first put out.

The UPBv3 can cook up to 24v.

 

Paul

Edited by psandelle, 14 February 2025 - 08:31 PM.

[w7ay]

Some folks have been advocating a Powerwerx unit like this.  Spec says it will crank up to 16v although I have no experience with it.

 

I power my astro gear with two of the fixed voltage version of that same PowerWerx supples, which I had tweaked with internal pots to put out 13.5 volts.   One goes to the mount through a homebrew UPS and a 15V boost, and the other supply goes to the rest of the electronics at the scope.  The two power feeds are ground strapped at the base of the tri-pier.

 

The power distribution is done through a PowerPole DC hub from the same company.

 

I try to use the dinky 5.5x2.1mm power barrels as little as possible.

 

Chen

Edited by w7ay, 14 February 2025 - 09:58 PM.

[w7ay]

Spec says it will crank up to 16v although I have no experience with it.

 

I just pulled out the variable voltage model that you mentioned, and the max unloaded voltage it can put out is this:

 

 

I don't use variable voltage anything for astronomy gear, however.  This is one of my "bench" supplies.

 

Chen

Edited by w7ay, 14 February 2025 - 10:15 PM.