New product - 1 arc-second tracking ability without using conventional auto-guider

[gregbradley]

Hi David,

I see ASA is also making a mount with a similar approach.

There is also an advanced low friction coating that is quite cheap that is
claimed to reduce PE considerably on all mounts.

http://www.andysshotglass.com/astromo_mod_store.html

Perhaps a combination of both would setup the mount to be
able to have just a slow autoguiding like once a minute to correct
for flexure or slow polar alignment drift.

In my experience with a few mounts, exact polar alignment and
balance is one of the most important factors.

Self guiding is good but limited. Blue filters often stretch the
guide times out longer than ideal for the mount and the guide chip is tiny
and very low resolution which weakens the result. I get far better results
with an external guide scope.

I also find guide star selection can really make a big difference.
If I get higher than expected guide errors I pick another star. I often see
the right star giving 1/3rd the error of another star. Often the brighter stars
are a bit bloated and the centre of the star being computed by software may be
more prone to error than a tight small star. With self guiding your
choice of stars is very limited and none of them are what you would call
tight.This is why I like the ST402ME for the guide camera. It is similar to the
Starfish in FOV and is cooled and I can get quite good resolution for gudie stars
using a cheap AT66ED lightwieght scope that does not seem to flex (20mins seems fine
if not windy and polar alignment is OK) 30 mins is also fine. This is a Tak NJP mount and
its PE is around 2 arc seconds by itself.

If I read the site correctly it seems you can also use an AO device with this as well.

So wouldn't the best of both worlds be the gears coated with low friction coatings, the TDM,
the AO and then an autoguider set for 1 minute corrections to pick up flexures. Perhaps that would
be a super setup. SBIG are releasing their new standalone autoguider with an artificial star to correct
for flexure as well as normal corrections. That'd be a beauty.

Greg.

[Dennis]

Originally Posted by gregbradley

>snip
So wouldn't the best of both worlds be the gears coated with low friction coatings, the TDM,
the AO and then an autoguider set for 1 minute corrections to pick up flexures. Perhaps that would
be a super setup. SBIG are releasing their new standalone autoguider with an artificial star to correct
for flexure as well as normal corrections. That'd be a beauty.
Greg.

Hi Greg

From the TDM website, some of the scenarios listed for utilising the capabilities of the TDM unit are just what you have described above in your thoughtful and interesting analysis, vis-à-vis:

• TDM is firstly recommended for the observers who intend to take a lot number of shots per night about different parts of the night sky quickly and easily. (E.g. supernova patrols, comet and/or asteroid hunters, observers of cataclysmic variable stars, etc.)
• For amateurs or professionals who have backyard or institutional observatory for permanent telescope installations (with permanent and good polar alignment).
• TDM can be an extremely advantageous application for robotic telescope owners who needed to find bright enough guide stars within the field of view manually so far.
• For "tourist amateurs" who do not want to drag an extra tube and CCD just for autoguiding purposes up to the peak of the mount escaping from light-polluted regions.
• If you want to use a narrow band filter (e.g. H-alpha) but you have a dual chip CCD or just an AO-7/AO-8 adaptive optics as guiding equipment, your guiding chip will be in almost total darkness... But TDM will help.
• If you have just a tiny guiding chip at the bottom of a small aperture tube, you probably will not always be able to find an appropriate guide star... TDM will help you again.
• TDM together with AO-7/AO-8 adaptive optics is the best equipment that you can have!!! TDM will eliminate the periodic error of your mount (independently of the magnitude of its amplitude) and AO-X will eliminate the rest of the deviations like scintillation and/or refraction. This is the ideal, ultimate set of serious astrophotographers!
• Who is not satisfied with his/her mid-ranged telescope mount's tracking ability but does not want to spend another couple of thousands of euros/dollars for a top rated one (which has much more PE then TDM...), those will appreciate this cheaper solution.

Cheers

Dennis

[DGK (David)]

Thought I'd drop a line to let you know I managed to get the TDM encoder signals converted to TTL without messing up the TDM. It seems to work very well and gives me 20,000tic/rev for my Argo Navis as well as providing what the TDM needs. The encoder plugs into the converter and a new cable connects the converter to the TDM.

I put an ERN120 on the DEC axis to give me 20,000tic/rev on that axis and this plugs into the enclosure for the TDM encoder converter circuitry. A 9pin to RJ45 cable supplies the Argo Navis with the RA and DEC TTL quadrature signals. Both encoders are powered independently of the TDM and Argo Navis so I have the option of just using the Argo Navis when not imaging.

Now I need to wait for clear winter skies and then I can test out how good a quick 4 star polar alignment can be with these encoders and further test/use the TDM.

Cheers

David

[Dennis]

Nice work David, it looks like you’re really getting under the hood of the TDM to tailor it to your needs. If what you have done could be of use to others out there, with similar equipment and operational requirements, might it be worth while dropping the TDM designer an e-mail?

If your modification is easy to incorporate as a custom model, you might end up with the “TDM-David” variant!

Cheers

Dennis

[Bassnut (Fred)]

Ive been wondering about this design for a while now, putting aside the overall usefullness arguement, it appears the output encoder is used primarily as a speed feedback device (digital tacho) to achieve very low PE, rather than for absolute positional accurracy, which would require a much higher resolution encoder, as used in expensive pro rigs (hence my apprehension earlier on the cost of the encoder).

Great if thats the case and it appears to work, smart idea, but then it doesnt improve pointing accurracy, not that matters perhaps, dont know. I also wonder, since it doesnt rely on absolute position for calculating tracking accurracy, whether it might suffer long term drift?.

[AlexN]

Fred, I think it would still suffer long term drift... take for example if your polar alignment was less than optimal.... It also wouldn't correct for any dec drift (which there shouldn't be any if everything is aligned perfectly) however I know no matter how much time i spend polar aligning, my guider is still making dec adjustments...

[DGK (David)]

Hi Dennis,

Actually, I only needed to look at the input side of the TDM to see what it was doing. Given the encoder type I pretty much expected the approach taken, it was no surprise. I have no detailed understanding of how things are done further down the pipe, and don't really need to anyway. The change I've implemented does not modify the TDM in any way, it just sits between the encoder and the TDM. Much to my surprise it all worked the first time I've let the developer know what I've done, he was not really sure that I was going to be successful during my early enquiries so he suggested getting the straight through encoder configuration just in case. Anyway, one fun challenge out of the way, now I need to check it out under the stars.

Oner other cool thing is that with the encoders powered outside of the AN I can push that ota around really quickly and there's absolutely no errors. Not bad for 20,000tic positioning resolution.

Cheers

David

[DGK (David)]

I tested the TDM last night with the Argo Navis taking the position information from the encoder and it works well. The drift test using an Intes Micro M809 and webcam at f/24 is posted on the CN forum Dennis linked - similar to that seen earlier with the lower resolution scope, close to +/-1arcsec correction. With the AN being provided with 20ktic/rev the TPAS model is coming back at 35arcsec RMS which is very nice - +/-1arcmin pointing over the whole sky.

[Dennis]

Hi David

That's great news. It appears that the TDM system is ideally suited to your particular requirements and you also seem to have tailored the system to even better meet your needs – a double bonus.

I really do enjoy reading about these new products, brought to market my talented amateurs, especially when they work as intended and the end user is able to derive the benefits they were looking for.

You have posted some impressive looking data (updated) compared to the native GPDX before you fitted the TDM system.

Cheers

Dennis

[AlexN]

I posted in the thread on CN.. Definitely looks like a great improvement...

[DGK (David)]

Last word from me on this, just posted pdf's of three 600sec drift test on CN. My mount RA tracking has been taken from 35arcsec peak to peak down to +/-1.25arcesec 90 percent interval. Hope some found it interesting, if maybe not useful to most.

Cheers

David

[Dennis]

Thanks for the wrap up David, the CN graphs certainly reveal the effectiveness of the TDM.

I’ll be keeping an eye on this product for my GPDX, although I am in two minds as I really don’t want to loose the Vixen Polar Alignment ‘Scope - I have come to rely on its ease of use, speedy set up and accuracy.

Cheers

Dennis

[Attila (Attila)]

Hi Everybody on this forum-topic,

It is very nice, even more, delightful for me to read these skeptical and sometimes hostile opinions regarding TDM.

I am one of the two developers of TDM from Hungary and I can only say that if you do not like milk, please, do not drink milk. But, in spite of it, milk is a very good drink for others...

At the same time, I need to refuse Wavytone's claim: "The website also shows the author has a very naiive understanding of the causes of tracking errors."
Hey guys, there is intelligent life outside of Sydney as well...

TDM is a working standalone application in practice but not just on "drawing board". MEADE Europe will sale it worldwide soon.

And let me have just one more sentence, please: TDM is NOT a competitor of autoguider technology but an alternative solution for a similar problem.

It is a bit more expensive compared to the cheapest autoguider system but much more cheaper than e.g. a Paramount ME. My EQ6 has less than +/-0.5" tracking error (with TDMv2) for a bit more than one tenths of the total investment of a Paramount which has +/-2 or 3" PE (or higher).

Each of the photographs of my website is true, there were exposed as I declared. Please do not insinuate me that I provide autoguided shots on my website.


Thank you,

Attila Madai
MDA-TelesCoop Llc.
Hungary

[Dennis]

Originally Posted by Attila

Hi Everybody on this forum-topic,
It is very nice, even more, delightful for me to read these skeptical and sometimes hostile opinions regarding TDM.
I am one of the two developers of TDM from Hungary and I can only say that if you do not like milk, please, do not drink milk. But, in spite of it, milk is a very good drink for others...
>snip
Thank you,
Attila Madai
MDA-TelesCoop Llc.
Hungary

Hello, Attila

Welcome to Ice In Space.

It’s always nice to have the developers of new gear drop by, to provide their unique insight, knowledge and experience of their products.

When a new product comes along that offers a new or different method of managing RA errors, I guess it will challenge the established views? So, in many ways, the fact that the pot was stirred in such a heated manner is actually good news, as a less capable product might have passed by unnoticed.

So, I would take the skeptical comments as a sign that you are hitting the right target for the scenarios you have designed the TDM System for, and described so well on your website.

Cheers

Dennis

[Attila (Attila)]

Originally Posted by Dennis

It’s always nice to have the developers of new gear drop by, to provide their unique insight, knowledge and experience of their products.

Dennis

Dear Dennis,

Thanks for your realistic words and for your welcome message above.
In spite of my limited time, I am willing to reply to your questions (if you have) sooner or later.

David has one of the TDM boxes but there are more than two dozens of TDM from the very first series in the world. EVERYBODY was satidfied with it and now we have the second version with higher accuracy and autoguiding capability. (And we have not finished the development yet...)

At least 90% of the questions arrived to this forum from skeptical or supporting people is explained on my website in details. Please read this at first.

TDM is not a "cure-all" product and I DID NOT CLAIME ANY FALSE OR DELUSIVE INFO ABOUT OUR TELESCOPE DRIVE MASTER!!!

We can definitely guarantee that your RA shaft will run on exactly sidereal or average King-rate (depending on jumper-settings) within +-1" (or better) accuracy in 95% of your exposure time within the explained limitations.
(By the way, just answering to one of the previous questions here, this TDM version provides AVERAGE King-rate but not position sensitive real King-rate. This is also explained in my website.)

But, if you have a "baggy" or "flaccid" mount and/or OTA, TDM will obviously not be able to change it to a professional instrument...

Astronomical measurement and photography needs very high quality hardware products and very precise human activity. TDM can help you to improve your existing mid-level mount's "mechanical quality" without changing it without spending ten thousands of bucks. (Nowadays it can be important point of view I think...)

But you need to do the rest of the job like polar alignment, fixing you flipping mirror, etc.

Attila