Question about AM5 with heavier refractor and tri-pier

ASIMount@ZWO

Dadek182 Hi，do you know how much weight your aluminum tripod can support? The greater the load capacity compared to the actual weight, the better.

Dadek182

ASIMount@ZWO Hi, sorry for the late reply! It can handle 50kg of payload.

AstroDude42

Dadek182 i do own the same tri-pier. Only difference is that it's not the TS brand but the WO (William Optics) brand (WO calls it "Mortar"). Other than that it's 100% the same.

This tri-pier can handle up to 50 kg of payload. I use it with my RainbowAstro RST-135 mount (max capacity with counter weight is 18 kg) and different scopes/gear combinations. The heaviest is my Celestron EdgeHD 8" SCT with OAG, filter wheel plus filters, camera, EAF, guide cam, dew shield, ASIAir and a PowerBox maxing out at about 16 kg. For this i need to attach the 3kg counter weight to the mount.

According to the specs, the AM5 with counter weight can lift up to 20 kg (2 kg more than the RST-135). So if your scope plus other gear doesn't exceed that weight you should be good to go. I have no clue about the guiding though, as i do not own a AM5. There are some threads on this forum discussing guiding using the AM5. For example, see this lengthy thread: https://bbs.zwoastro.com/d/15989-getting-the-best-performance-from-my-am5

Please be aware that it's always the best option to not max out the weight on the mount, as it might wear out some belts inside the mount.

Hope this helps somehow.

w7ay

AstroDude42 i do own the same tri-pier.

I actually have my Mortar legs bolted now to 2040 and 4040 extruded aluminum, with lots of concrete step stones and bricks to weight everything down, so I don't use any counterweights.

The thing is stable enough that I do polar alignment only perhaps once a year (after the snows have finished), or when I do something major to the dual saddle plate and move things around. Everything is left outdoors, with a large dry bag over the mount and electronics (in that gray ABS box).

I also bought the TS one as a standby after WO stopped manufacturing the Mortars. The disadvantage with TS is they are only available in 1000mm heights. My Mortar is the 800mm version, which fits my body height better (I am 5' 2").

The photo shows the other extreme, an RST-135 that is on a small Takahashi metal tripod, with a short Vixen and full frame ASI6200, which does not demand as much stability.

I am getting 0.35" RMS type guiding with this setup (sometimes 0.25", and sometimes glitching up to 0.45") with the RST-135e shown, using an FMA180p as the guide scope, with the ASI678MM (2µm pixels) as the guide camera.

Aloha, Olli.

Chen

Dadek182

AstroDude42 Thanks a lot for the detailed reply!
My setup is Askar130PHQ, EAF, OAG, Filterwheel, ASI120mm, ASI294 Mono, so it should total on around 14,5kg.

Since the new AM5N came out with a max payload of 15kg without couterweight I thought to get that N version.
Do you think it should still be fine without the counterweight? It's quite close to the max payload without counterweight...
Other option is to go for WD-20 mount with 20kg payloud without couterweight.

Thanks again for the time you took to reply!

Cheers

AstroDude42

w7ay aloha Chen,

nice customization of the Mortar :-) mine needs to be taken outside for each session. I initially ordered the 800 but only the 1000 was available after months of waiting. I had to take what i get.

Back to the topic: i just noticed that ZWO released the AM5N. According to some online shop the improvements are:

New USB-C & DC 12v output ports on the mount saddle for improved cable management
New Bluetooth compatibility for improved connectivity
New base design eliminates azimuth locking knobs
Improved tracking with higher load angles & heavier payloads
Periodic error reduced from ±20 down to ±10 arcseconds

Let’s wait for some reviews.

Olli

w7ay

AstroDude42 i just noticed that ZWO released the AM5N.

I would not touch a mount from ZWO with a ten foot pole.

Chen

Dadek182

w7ay Why is that?

I am also looking into WarpAstron WD-20 due to higher payload option but the price definitely goes in favour of the new version of AM5.

I would love to hear your opinion on why you don't like the ZWO mounts.

Cheers!

AstroDude42

Dadek182 to be honest, i would not risk going against maximum weight without a counterweight. It‘s all about balance and your gear will physically fall over much easier and get some heavy damage. If you use a counterweight, the risk is minimized. Just my 2 cents.

Olli

w7ay

Dadek182 Why is that?

IMHO, it is a poor copycat of the RainbowAstro RST-135. It is a superficial (in appearance) copy, but don't match the mechanical precision of the RST-135.

Some of the ZWO mounts appear to be mechanically unsound, by the looks of the autoguiding errors from what some users have posted. It is a lottery if you will receive one of the especially poor specimen.

Even with the ASIAIR with my also strainwave geared RST-135e mount (using Harmonic Drive LLC gears instead of Chinese strain wave gears) , I have been able to consistently get lower than 0.45" total RMS, averaging around 0.35" RMS, and half the time, hovering below 0.3". I have not seen a ZWO strainwave geared mount get anywhere near, and the RST-135e is even lighter in weight. Granted, RainbowAstro is a subsidiary of RainbowRobotics, and they have been using strain wave gears for their robotic arms for decades now, and know a thing or two about the strain wave gears. The RST-135 did not come out until 2019, and that was when I bought the first of my RSTs.

Notice that ZWO keeps harping on the amplitude of the periodic error, but that is of zero importance to autoguiding. It is only important to keep an object within the eyepiece for visual observations.

What is important for autoguiding (and thus astrophotography) is the first derivative of the periodic error curve, and the curves that I have seen show large and random spikes in the first derivatives -- that makes it very hard to guide even when using 0.5 second frame updates (2FPS guiding). And if you are not careful with limiting the guide pulses, leads also to undershoots right after the first derivative spike has passed.

Until ZWO starts fixing the first derivatives of their mounts' periodic error (and therefore show that they at least understand the principles of autoguiding), I am staying far, far away from their mounts.

As long as they harp on the amplitude of the periodic error, it shows they do not understand.

Chen

Dadek182

w7ay Wow, thank you so much for your very insightful reply!
That is a gold nugget of information that people on the forums and websites don't really describe.

I was checking out the Rainbow 135 but it also has a 13kg payload without cw. From what I found online the best candidate (so far) would be the WarpAstron WD-20 with 20kg payload without cw. I will now go and check it's specifications based on your input and see if it's worth to get it or simply wait for a new mount with the specs that would be good for my "fat" rig.

Cheers and than you once again!

w7ay

AstroDude42 If you use a counterweight, the risk is minimized. Just my 2 cents.

Olli,

The problem with counterweights is that they also add to the stress of the altitude bearings. The altitude bearings have to take the combined weight of the astronomical payload and the counterweight. You can tell that after adding a counterweight, the altitude adjustment bolts are harder to turn.

I have found (anecdotally; never actually measured) that a small amount of imbalance actually is not only not harmful to the RST-135, but appears to reduce autoguiding errors when the OTA is pointed towards Zenith. It might not apply to other stain wave geared mounts.

Some of my decent autoguiding results may even have been due to my use of a side-by-side saddle to mount the guide scope and its EAF. This introduces lots of third axis imbalance. But it may actually also have improved the meshing of the stain wave gears. So far, this imbalance has not been detrimental. My first RST-135 from 2019 is still working fine.

Chen

Dadek182

AstroDude42 Thanks, then I think I won't risk the AM5N as it would be at it's max payload almost.
Cheers!

AstroDude42

w7ay The problem with counterweights is that they also add to the stress of the altitude bearings

That’s a valid point, Chen. On the other hand, if manufacturers officially declare different specs for the same mount with and without counterweight, then i would expect that the mount has been tested thoroughly and an increased maximum weight when using a counterweight is not a fairy tale. Otherwise all manufacturers would be lying to their consumers.

What would be better? a) put 15 kg on one side of the mount which puts all pressure on the altitude bearings in one direction or b) put 15 kg plus 3 kg counterweight on two sides and balance the weight more evenly so the altitude bearings aren’t that much under pressure.
Unfortunately i‘m not good at physics so just my guts tell me it’s option b). I might be wrong though :-)

Aloha,
Olli

w7ay

AstroDude42 b) put 15 kg plus 3 kg counterweight on two sides and balance the weight more evenly so the altitude bearings aren’t that much under pressure.

Even better; put a main OTA on one side of the bearings, and a guide OTA on the other side by punching the declination bearing all the way through. Like the Avalon M-series mounts. No wasted weight on the tripod.

Recently, a strainwave mount has adopted this technique, too. I don't remember which now. I don't know why not more people do it. I don't believe Avalon has a patent on it. Perhaps they have.

Aloha, Olli. (You know, Thais use Sawasdee for both Hello and Goodbye, too. :-)
Chen

Johnico

Glad I found this chat. I too was going to purchase a 130phq and mount it to my an5n but now reconsidering it as it might damage the Am5n mount over time. The altitude bearings wearing out would concern me as over time the guiding might stray and not be consistent.