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Smokedaddy
03-08-2009, 12:55 PM
I am curious what those of you think, that have done precision machining, and understand encoders, why this telescope mount is so expensive. Is it a combination of precision machining and the Renishaw Encoders. I would love to "specifically" know why the cost is so outrageous? At least to me it is. (about $18,000 US).

http://www.astrosysteme.at/eng/mounts.html

and here is another with harmonic drives

http://www.chronosmount.com/

... prices on the Chronosmount start at $14,000 and go up to $50,000.

-SD:

lazlo
03-08-2009, 01:16 PM
It's Austrian :) I don't know anything about telescopes, but from looking at their product pages, I gather they're the Schaublin or Dixie of the telescope world...

nheng
03-08-2009, 01:27 PM
For one thing, they are talking 0.01, 0.02 arc seconds, though I think their decimal point is off unless they derive this mechanically. Renishaw shows up to about 1 arc seconds for their optical angular encoders.

I was talking to a shop a few days back about angular accuracy that they could hold for us and their Haas CNC tables have a spec of about 45 arc seconds.

Add bearings, precision fits, small quantity product runs (most likely), etc. It adds up quickly.

Like many things, you might be able to build it yourself and save thousands or like many of us, make a $50 CNC'ed door stop instead of stopping at HD for a $3 one :D

Den

Evan
03-08-2009, 01:39 PM
They are claiming 0.01 arc second angular position accuracy using Renishaw encoders. At the Renishaw site their Signum ultra high accuracy angular encoders only go down to 2.00 arc second. Since I don't think Astrosysteme is lying that means they paid Renishaw to custom make encoders 100 times more accurate than their best on offer to the general public.

That level of accuracy is nothing more than bragging rights. Any image taken through the atmosphere will be displaced by a refractive error that changes from around 0.5 degrees near the horizon to approximately zero at the zenith. Since during any particular observing session the telescope will be tracking either toward or away from the horizon and zenith the angle of refraction will vary moment by moment.

If you need to worry about that, and not many do, then you use an auto guider that locks on a target star and follows it.

In the astronomy business there are a large number of very well heeled amateurs that like to show off how much money they have without being over the top ostentatious. The equipment they bring to a star party is how they do that. Everyone knows that an Astrosysteme mount costs as much as a car and there will be a small crowd of admirers asking how nice it is to use. The owner will bask in the reflected glory of his ultra expensive toy and everybody will get their money's worth, especially Astrosysteme.

lazlo
03-08-2009, 01:45 PM
They are claiming 0.01 arc second angular position accuracy using Renishaw encoders. At the Renishaw site their Signum ultra high accuracy angular encoders only go down to 2.00 arc second.

Or possibly they're just interpolating the resolution? Hokey, yes, but that's pretty typical these days. Half the digital cameras people buy quote interpolated resolution, which is completely bogus.

lenord
03-08-2009, 03:35 PM
If you are looking into harmonic drives, I started making mounts using them now. http://www.gototelescopes.com/harmonic%20mount%201.html
You are correct in that their prices are obscene. I can get harmonic boxes for under $1k each. Cost of a mount if you are a machinist, with little skill I might add, is under $4k.

The first link states that you won't need to autoguide, which is bull. Anything can make even the best mount or OTA move enough to be seen on a CCD chip. AG is needed. When the mounts and cameras can compensate for wind, critters, thumps on the ground etc., then they can claim that. The AO part of the SBIG cameras may do most of that, but I have yet to test it out personally.

Torque motors...well...I'll be offering them very soon too. Nothing really new there.

Accuracies to .2 or .4 arc seconds using a good encoder is possible. I friction gear a little 10k tick cheap encoder and interpolate it with the one on the motor, seems to work ok. Gurley make an encoder with 1 arc second accuracy right out of the box for under $1k.

Cost is what the market will bear. Also has to do with the volume of mounts made, low volume, high cost. Of course, then why are AP/Losmandy mounts so expensive ? Number of vendors that can make a mount that can do what the best mounts can do.....
Then there are the scope snobs....they do exist. More money than brains.

FWIW
Lenord

Smokedaddy
03-08-2009, 05:05 PM
Damn,

I have one of those expensive mounts, not the ones I mentioned above but another brand. Looks like that makes me one of those snobs. <red-faced> I have never been to a star party but guess I should start going to show off my equipment. <grin> I bought my Parallax HD200C at an incredible price so I figured I made out really good. I also have a couple of huge scopes (huge to me anyway) that I use with the mount, an 8 inch D&G achromat air-spaced doublet at F/15 and a old 1960's 16 inch F/5.1 Cave Newt.

I wanted to try and make my own mount for personal gradification but didn't know how percise it needed to be. Heck, I don't even know if I have the necessary machining skill level in the first place. If gear driven I would buy Byers gears but try to make everything else. Wish I knew a local machinist that shared my interest in Astronomy that wouldn't mind holding my hand now and then. O'well.

Lenord, thanks for the link and information, it is appreciated. I think I ran across your site once upon a time when I was searching the Internet for mounts. Very interesting.

I always looked at this sort of equipment differently. I figured (but wasn't sure) if I had the mechanical knowledge and the necessary machining skills that projects like this for personal use would cost considerably less than buying the real thing.

Regards,
-SD:

lenord
03-08-2009, 05:35 PM
SD,

No, snobs pay full price and buy new. You are just smart. Some are happy to tell you what they paid for it too.

You can make the gears, better than Byers too. Cost is a LOT less.
Fellow named Chris Heapy (sp) had a site that showed you how to do it. Mic 6 is available for cheap, drops from a shop.

Making the mounts need not be an ultra precise endeavor now. The controllers I use, and even the T-point software, will take out mount errors when tracking and doing GoTo's. Close tolerances are good, but they need not be to Evan's level of precision.

It is cheaper to DIY mounts, no doubt there. Should you ever have a question about it, I might be able to help, FWIW.

Lenord

Smokedaddy
03-08-2009, 05:49 PM
Lenord,

Believe it or not I found Chris's site, just way over my head at this point in time. Guess everything seems to be. <grin> At least the information is out there if you have the means to understand it. I also corresponded with Charley Wicks about the mount he made with inexpensive equipment I might add.

http://home.comcast.net/~charles.wicks/GEM2.html

Thanks again,
-SD:

mayfieldtm
03-08-2009, 06:06 PM
I too would like to build a mount.
Evan is 100% correct about the accuracy thing.
I want heavy duty that can handle a heavy scope with all the cool stuff I can hang on it.
I want it to have minimal vibration if there is a breeze.
And when I using the scope in manual mode, I want to be able to fine tune the balance so I can steer it with my nose while looking through the eyepiece.

Tom M.

Paul Alciatore
03-08-2009, 07:11 PM
Actually Evan didn't go far enough on the accuracy thing. Yes, you do want good bearings and a solid mount, but as for tracking accuracy down even to the minute level, well it is just not all that necessary. No, still too little: it is a TOTAL WASTE.

Tracking is needed for astrophotography, not for simple viewing with the eyeballs. Such photos are almost always time exposures and I mean many minutes or even hours long, not just seconds. It is not unheard of to expose an image all night or even for several successive nights. Any number of factors like athmospheric refraction will cause bluring of the image and as Evan said, the errors can be as much as a half degree. So manual or automatic guidance using a nearby star is an absolute necessity.

Many amateures have made mounts with really crude "worm wheel" drives. One such technique I saw described used a piece of threaded rod (Vee threads, not even Acme) that was bent around a wooden disc with a matching groove in the OD. The bent rod was embedded in epoxy to hold it in place t form a "worm wheel". A matching worm was made by using another piece of threaded rod and the two were "meshed". With some care, the author claimed he was able to get very good exposures over long time periods. BUT, he also used manual guidance techniques: he observed a star in the field of view and constantly made manual corrections. The worm drive just kept him in the ballpark. Heaven only knows what the accuracy of this "worm gear" was. Probably no better than 10 minutes (1/6 degree) and the error probably changed constantly in unpredictable ways.

Mounts and drives with the advertised level of "accuracy" are a total waste of money. I would put it in a better, bigger scope first. There's real bragging rights. Especially if you grind the mirror yourself.

Smokedaddy
03-08-2009, 10:32 PM
Thanks for the feed back, it is appreiated,

I am restoring a huge old Cave GEM mount. I need to find a 12 Volt DC motor to replace a DEC motor (the original is AC). I sent a message to Hurst tech support but they never replied. The DC motor is required to work with the JMI MotoTrac system I have.

Any ideas,
-SD: