I took a copy of the blurb off a “Technical brochure”
http://www.baader-planetarium.de/ava...near-Mount.pdf
This blurb is full of self contradictions, superlative laced claims and a few technical errors.
So on the one hand they make the claims :
“ . . . to completely fix any play or backlash issues, eliminating the excessive costs of the traditional mechanical devices”
and
“. . . eliminating any play and noise, at the same time assuring a very high precision.”
and
“. . . because no play or unpredictable behaviours are seen”
and
“so the motion is transmitted by the tooth belt in a very gradual and smooth way, without “peaks” and accelerations/decelerations”
All leading the unwary to believe that this is what they are getting when in fact what they are getting is a whole set of new tracking errors which are greater in overall magnitude, incapable of being tweaked out mechanically and unable to be described mathematically and removed with traditional PEC software.
Yet on the other hand they also state –
“ . . . the tracking error generated by the transmission devices inside the LineAR is large in absolute terms (typical, mean values are of +/- 5, +/- 7 arc-seconds)”
and
“The LineAR transmission, based on four stages of reduction, introduces tracking errors which can be larger than those shown by traditional mounts in the same price range,”
and
“ . . . it should be underlined how the PEC is useless with the LineAR, as well as the software commonly used to handle the periodic errors.”
and
“ . . . the LineAR mount requires an autoguider”
There is a lot more to comment on but this post is already extremely long !
I understand that the nature of the “periodic” error problems are different between their mount and say other mounts due to their multistage belt drive system, but in the similar price range mounts I think the comparisons and claims made simply don’t fly in the face of real world performance.
The fact that you can apply PEC to almost all of the other higher end mounts and virtually eliminate it whereas you cannot do so on the Avalon Linear is a huge issue.
But the sheer quantum of error that you will get in a Tak, Paramount, AP etc is not as high or as bad as they want you to accept either.
They appear to be conveying the notion that Periodic error only comes from gear teeth contact errors, which is of course erroneous – bearings can have concentricity and alignment problems, non concentric gears and pulleys caused by normal machining tolerance in the manufacturing processes or imperfect sizing or alignment of the shafts or bearings, eccentric loads caused by belt tensions, housing stresses, belt dimensional variations, dimensional errors in the machining process – eg incorrectly positioned bearing recesses and shaft support bores from one side of the case to the other etc etc
These exist in their system, and the more complex the gearing system, the more components are needed, the more errors and tolerance buildup you will get – ultimately resulting in more “periodic” error (-like) problems.
The fact that they can smooth these errors out a bit is not necessarily a solution – its just a difference ! It may mean that sharp changes – that are faster than a guider can guide out might disappear, but really we aren’t comparing their mount with cheap Chinese mounts are we !?
How many PE errors are so fast in other equivalent high end mounts that they cant be guided out ?
Can you guide it out using their mount – Yes !, and it would seem that is the only solution.
I wonder what a 20-40 minute unguided image would look like if it happened to coincide with one of the big 43 arc second peak to peak Lee found – I would think completely unuseable, yet there are plenty of mounts when accurately polar aligned that could yield superb unguided results.
I’d say it’s a case of marketing hyperbole.
A revolutionary technology: Tooth belt transmission
Designers at Avalon Instruments wanted to completely fix any play or backlash issues, eliminating the excessive costs of the traditional mechanical devices used on equatorial mounts (worms and gears) and making a new transmission system, based on pulleys and tooth belts. A four-stages reducer is used.
Those devices are used with great success for industrial mechanical applications, as they provide a perfect transmission of movements in a very linear way, eliminating any play and noise, at the same time assuring a very high precision.
Benefits of the tooth belt
A tooth belt, which has no play for itself, is better than other mechanical devices because of its working principle. In the gear-worm systems, there is just one, tangent contact point between the working parts.
Under these conditions, the lever arms and the efforts produced by the telescope-mount system introduce some small non-linearities in the transmission of the motion; they are visible as small shifts, evident in the images obtained with those traditional devices. Those small effects are proportional to the focal length, so they are particularly visible with telescopes having a long focal length. The tooth belt transmission does not introduce these troubles, as there is no contact among pulleys and motion is transmitted by the belt with no play at all. The belt has an extended contact with the pulley, so the motion is transmitted by the tooth belt in a very gradual and smooth way, without “peaks” and accelerations/decelerations, typical of traditional gear-worm systems and giving troubles while taking images, even with modern autoguiding devices. Autoguiders, indeed, often are not fast enough to compensate for those sudden anomalies coming from the gear-worm coupling.
As every experienced astroimager knows, well calibrated autoguiders are unable to provide perfectly tracked pictures with traditional mounts, even when they employ gear-worm systems with small tracking errors. These anomalies are not recorded by the guiding telescope, as they originate between the guiding device and the mechanics of the instrument.
Thermal variations, flexures and torsions, especially close to the meridian, transfer plays and mass to the gear (which is in equilibrium) and the resulting effects introduce several oscillations, creating unwanted shifts and sudden movements.
Images always perfectly tracked
Since the very first tests, the manufacturer noticed how easy it was to capture very well tracked, long exposure images, matching the primary goal of the project. While visual observing with high magnifications, the absence of any noise and a very fast damping time are clearly evident, as well as the lack of any play or backlash and the immediate, smooth response to the electronic commands:
We call it Fast Reverse because no play or unpredictable behaviours are seen, even with high payloads. The LineAR mount must be perfectly balanced –which is very easy to do, as the LineAR axes have no friction – because it has not the play troubles originating during the mass transfer while crossing the meridian.
The LineAR transmission, based on four stages of reduction, introduces tracking errors which can be larger than those shown by traditional mounts in the same price range, but the absence of peaks and sudden accelerations makes possible perfectly tracked – autoguided - long exposures, even with more than 20kg of payload, competing with more expensive, higher class mounts.
It must be stressed that the LineAR mount requires an autoguider (but it can be easily guided by hand, thanks to its smooth, gradual errors and the quick response of the commands, event at the lower - 0.125X –rates). Furthermore, it should be underlined how the PEC is useless with the LineAR, as well as the software commonly used to handle the periodic errors.
The LineAR mount redefines the Periodic Error concept
While the tracking error generated by the transmission devices inside the LineAR is large in absolute terms (typical, mean values are of +/- 5, +/- 7 arc-seconds), this is no reason of concern: the mount, which uses a four-stages reducer with tooth belts, has a very slow and smooth error, well spread over the time, so that it is very easy to handle with any autoguider, even while doing images with long focal length (2-3 meters) telescopes.
The LineAR must be used with an autoguider and a slow correction rate, as 0.125X, but it still makes possible to take unguided images with 500-600mm focal length telescopes. Furthermore, because of the technology used, having four different, very slow tracking curves, the PEC function is not useful (as well as the software generally used to optimize the PEC performances, which do not contemplate such a complex case).