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View Full Version here: : ASA 16" newtonian and DDM85XL setup in Perth.


alocky
05-08-2017, 05:17 PM
Hi all,
Just thought I'd put down some thoughts on this gear, since I've had the mount long enough to learn about its strengths and weaknesses, and finaly been able to try the OTA out.

Mount ASA DDM85 XL
This runs on 24V and can carry 200kg. Don't be fooled by the apparent size of the Dec shaft in the picture - that is 80mm in diameter, made from solid stainless, 600mm long, weighs a lot and is a ******* to thread into the Dec axis.
The other feature is the pier that lets the mount track through the meridian without ever needing a flip. The pier weighs nearly 100kg and had to be lifted up on to the roof with a crane. Polar adjustment is done by fine tuning the a ring of bolts at the base, and a tangent drive on the pier base. I also had to spend a fair chunk of cash to get a local engineering shop to change the angle and shorten it from its previous installation.

The mount is a direct drive mount, so no worm and wheel. Although this means no periodic error, it also means that the only thing stopping the mount from moving is the magnetic field in the motor. So when the power goes off, the mount is free to move and there is very little friction. So if you have unbalanced the system by removing a camera, or even by putting the end cap on and lose power, unless you've tightened the two hex-head bolts to lock the axes don't expect it to stay put. In normal use, while balanced this is a non problem and if I have a week of bad weather coming I just power it down without any worries.
The flip side to this is watching how the mount responds to gusts of winds. You can monitor the current being applied in the mount, and it is interesting to see this changing instantly in response to the wind gusts - but since the mount is using it's internal absolute encoders to maintain position, there is no detectable movement at the image plane.

Once you've tuned the mount for the payload, it's reasonably straightforward to drive, although one of the main negatives of this setup is that it cannot be driven unless you have a computer attached. There is no handset option, and the autoslew software written by ASA is the only way to control it. I used this for a year with no problems with my little 10" meade starfinder mounted on it, and was able to use Sequence Generator Pro via Ascom to acquire images with no trouble. Well, no trouble except that any slew at any reasonable speed caused the mount's 3 internal USB2.0 ports to drop out. And sometimes there would be a violent whine and the mount would make some very erratic movements.

I ordered the 16" OTA nearly three years ago, and after a number of problems, including a 12 month delay while they replaced a chipped primary and had to rebuild the mirror cell around it, the scope turned up, and the minor niggles in the mount turned out to be very serious.
This particular mount was originally installed in an observatory in Nth QLD, with a very large cassegrain on it, and I have no knowledge of the exact sequence of events regarding the Australian dealer, customer and ASA, the technical support team in Austria were unable to fix the fault while logging into the mount remotely, and the final diagnosis was the telescope was too heavy for the mount. So it found it's way to me and after another unsuccessful attempt by the Austrian team to get it working with the relatively light 16" OTA they requested I ship it back. Once there it was found to have defective bearings, and a few other components including the internal usb hub were replaced.

To be fair, the ASA guys were professional, generously gave me a 50% discount and got the mount back to me in about 3 months, but it wasn't free and I found myself a further couple of K out of pocket! Anyway now it slews at 12 degrees/sec (in almost complete silence) without a usb dropout and the pointing accuracy is absolutely astonishing once you build a pointing model, which is a relatively painless automated process best left for a moonlit night. Best guided performance to date is 0.11" rms over a 4 hour exposure, but there's another trick up its sleeve. One of the features of this mount is that for a long set of exposures it will first take a sequence of images along the track and plate-solve them, then build an extremely refined model just for that imaging run. This, in principal requires no guiding, and my first attempt at this process resulted in only slightly eggy stars that wouldn't have bothered me a couple of years ago. It is apparently possible to get this process perfect for 10 minute unguided subs, but since I'm using a QSI wsg with a lodestar hanging out of it, it's easy enough to stick to the autoguider for now.

OTA - 400N
This is a 16" f3.7 newt, with a CF tube. I'm not 100% clear on whether the optics are from Orion Optics UK or if ASA figured them using their new machine, but they at least tested it before shipping. They assemble, collimate and take a few test images before sending it, although they do not offer an interferometer report. Of course it had horrendous astigmatism which was caused by the secondary, but once this was fixed and they were able to send me a good star test image I paid up and it only took a couple of weeks to get here.
The OTA comes with a few goodies. There are 3 fans on the back, and 2 fans on the sides to blow across the mirror. Collimating the secondary is easy, with an extremely strong spider and simple three screw adjustment. Collimating the primary is a bit of a pain, as each of the three collimation screws has a single push, and two pull screws either side. You need to ensure that you end up with these all tight. Once you do there is no discernible shift in collimation from about 30 degrees above the horizon with the tube 'underslung' to about the same altitude with the tube above the mount. If they are loose, this range of movements causes a bit of a shift.
Other goodies are the focuser - this thing annoys the crap out of me and I regularly take a drink up into the dome and glare at it, since this is about all I can do with it and intimidation is the only thing not excluded by the warranty. There are two correctors for the scope, one 3" Wynne 0.96x that gives you a large, well corrected field bigger than a medium format film camera needs. The other is a barlowed 1.8x coma corrector. Each of these comes with a custom machined set of adapters to fit into the 3" focuser, I also have an OAG with a Nikon bayonet in case I want to stick the D810A on there some time. ASA make their own t-adapters, bayonets etc, which attach to the different correctors using 6 small screws. Although it makes switching gear out a bit of a pain, you can be sure it's held securely and there is absolutely no flexure. It also makes Takahashi's line of adapters look like a bargain, which is great since I also own a Tak FSQ 106...
So back to the focuser. Very cool thing with an absolute position encoder, temperature sensors, a wireless transmitter. Except the wireless isn't supported yet so the cool little aerial doesn't actually do anything yet. Also, it needs 12 v and a USB connection, but ASA wont supply you with cables that will let you use the 12V or USB available through the mount, so you have to have a cable hanging off the scope. Stern German Injunctions are also supplied regarding the modification of altering of these cables in any way. Having said that, it works. My problems with it come from the position encoder, which supplies an integer value via the ASCOM system in microns. Since it is constantly refining the position using a feedback loop and the encoder, the last digit in the position string is constantly flickering back and forward by 1 micron. The critical focus zone for this scope is 30 micron, so it doesn't really matter, but it means that the ASCOM focus position signal is not acceptable to Sequence Generator Pro, which expects a focuser to go exactly where it's told and then stay put. Fortunately the focus position doesn't seem to shift much, but I'm still trying to work out the best way around this, because SGPro stops the sequence if the autofocus routine times out because of this.
SO I can't use SGPro - which is a pity, because it's the only thing I trust to park the scope and shut the dome before the sun comes up. ASA supply their own software called Sequence, which uses Maxim DL to drive the camera, and has an autofocus routine and is also the only way to use the MLPT function (that's the local guiding model thing) of the mount.

Sequence is better software than I would write. But it is unstable, and highlights the weakest part of the ASA experience. They have only one software developer, who is actually a very busy physicist, and although the software mostly works, it is effectively written by an extremely talented amateur with absolutely no user support or ongoing maintenance. Driver upgrades supplied through Win10 frequently cause the hardware to stop working - because the software can no longer communicate with it this includes the GPS stick, the mount itself - including a very dangerous bug that could cause the mount to slew uncontrollably in the wrong direction during the 'homefind' sequence. This may not seem like a big deal but I had to physically put myself between the camera and the pier and power off the mount as it tried to point directly downwards once...
It's also worth bearing in mind that these guys build large observatories for research institutions, and us amateurs are only 'noise' in their sales portfolio.
Bottom line, the hardware is absolutely uncompromising quality, up there with the best. The quality of finish is excellent. The sales and technical (hardware) support team are also quite responsive and very helpful. There is no software support, you're pretty much on your own here - but there is a very helpful group of fellow victims who have largely been through it already and can generally help out.

glend
05-08-2017, 06:16 PM
Andrew that is a great write up of what is obviously wonderful gear, congratulations. One question i have, from the photos, is given it is all up in the air so to speak, how is pier supported? I assume its not just sitting on that timber deck. Is there something substantial underneath it?

Atmos
05-08-2017, 06:39 PM
Really nice write up Andrew.

I know that there is a lot of chatter on the internet in regards to the lack of friction when it isn't powered, I've never personally considered it an issue. Although lack of power may have it continue moving, it also doesn't add to making it continue to move.

I have had occasionally had the issue of a fast and wild movement when doing the Homefind. I personally find it usually done it after a balance or something that may cause it to have a potential position error. As long as I manually homefind after the balance routine I don't have an issue :) Being a manual setup there may be other issues that cause it on a permanent setup that I don't come across.

Totally agree in regards to the software side of things, I found Sequence to be really buddy at times, not a software package that I'd trust long term with imaging.
Build quality of the ASA amounts though is certainly top notch. Blows my EQ6 out of the water!

alocky
05-08-2017, 06:55 PM
Hi Glen,
There's a couple of cubic metres of concrete at the base of the pier under the decking, and the pier passes up through both levels of decking with 1cm clearance. It was hard work getting the chippies to accept that they couldn't bolt the decking supports to the pier but I won that one! I built this just as my wife won her battle to get me to build a new house for her, so I was able to incorporate all this into the design. I just wish it was 100 km away from the CBD instead of 10!

RickS
05-08-2017, 07:03 PM
Thanks for the warts and all review, Andrew. Very interesting reading.



Dang! I was hoping it would just be turtles all the way down :lol:

alocky
05-08-2017, 07:09 PM
Cheers Colin,
http://forum.astrosysteme.com/index.php?/topic/785-homefind-jump-problem/?hl=homefind
This seems to be part of my problem, although there was a fairly serious issue caused by the USB drivers that were causing issues with the mount. ASA even sent out a bulletin about it!
Totally agree on the quality - just for laughs, although I've always felt the Losmandy G11 that has served me so well is a nicely engineered piece of gear - compared to the ASA it's a Mustang next to a BMW M3.

RickS
05-08-2017, 07:12 PM
That's quite a counterweight shaft :eyepop:

Atmos
05-08-2017, 07:14 PM
Haha your counter weight shaft probably weighs more than the whole G11 looking at it!
I do have to agree, screwing the CW shaft is is a bit of a pain. The thread is reasonably large making it kinda fiddly at times getting it aligned correctly. CW shaft certainly doesn't suffer from any kind of flexure like the EQ6 does however :P

Slawomir
05-08-2017, 07:41 PM
A great write up Andrew - thank you for sharing with us your journey with the mount and the scope. QSI looks quite tiny in comparison with the focuser! BTW, that counterweight shaft is huge, not to mention pier, probably being the tallest in the country!

alocky
05-08-2017, 07:50 PM
As the actress said to the Bishop ...

alocky
05-08-2017, 07:54 PM
You should see the one that goes up into the Lowell Dome at the Perth Observatory at Bickley! It goes up 5 stories and supports a Boller & Chivens 25".
Cheers
Andrew.