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Equipment Discussions >> Mounts

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gdd
sage

Reged: 11/23/05

Re: Telescope Drive Master - The Truth of the Matter new

[Re: wolfman_4_ever]
#5259291 - 06/07/12 12:27 AM

I don't understand how the TDM can work in the wind other than to keep the object centered on average - it knows nothing about the wind. If you also had adaptive optics, that could correct for random variations from the wind for a complete solution. Right?

Gale

Post Extras:

alpal
Carpal Tunnel

Reged: 06/15/09

Loc: Melbourne Australia.

Re: Telescope Drive Master - The Truth of the Matter new

[Re: orlyandico]
#5259457 - 06/07/12 05:26 AM

Quote:

no, synscan won't work anymore. the SiTech controller is a complete GoTo retrofit, it basically replaces whatever GoTo controller is there. so it makes more sense for non-GoTo mounts.

as to why Skywatcher isn't using such technology - it costs too much. $800 for controller + $600 for the encoder is more than an entire Atlas costs.

That adds up to $1400.
I bet the Chinese could do it for $700 = half price
in the huge quantities they sell?

Repeating myself:

Quote:

Talking of Chinese mounts:
I notice this Ioptron mount:
The iEQ45-GT
GoTo German Equatorial Mount
With Renishaw Encoder

http://www.ioptron.com/index.cfm?select=productdetails&phid=cdde52d7-5d26-4d5b-84ee-cab88ed07bd2

for $4800 ready to go.

I think they're after the new innovation money.
Later on they'll bring out cheaper versions with all the goodies.
They are just going to milk this for a while to get the highest money.

Also

Quote:

synscan won't work anymore

That's a pity & puts me off the cheaper option.

Remember - we're not even talking about absolute encoders
which would used to point the mount to a target -
these are just incremental encoders which are only velocity sensing.

Post Extras:

orlyandico
Carpal Tunnel

Reged: 08/10/09

Loc: Singapore

Re: Telescope Drive Master - The Truth of the Matter new

[Re: alpal]
#5259464 - 06/07/12 05:37 AM

it's really hard to find high tic count encoders on the cheap.

that renishaw is probably in excess of $1000 (note that the encoder in the AP1600 is thousands of bucks). the $600 Gurley used in the SiTech is from Eastern Europe or Russia.

if the Chinese could make high-precision encoders cheaply, they would be using them and not the made-in-Britain Renishaw.

the iEQ45 is $1500. And with the Renishaw it's $4800. Granted some of that is milk money, but I bet (having scoured ebay for cheap encoders) that a big chunk - probably at least half - of that $3300 delta is the darn encoder.

Post Extras:

alpal
Carpal Tunnel

Reged: 06/15/09

Loc: Melbourne Australia.

Re: Telescope Drive Master - The Truth of the Matter new

[Re: wolfman_4_ever]
#5259474 - 06/07/12 05:55 AM

Quote:

• TDMv2.5 new version from 2012. This version has a built-in relay box so both TDM Out1 (TTL) and TDM Out2 can be used for both RA and declination control for guider support without any limitations. Extended control range limitation (+/-10”) can tolerate higher wind gusts without auto-reset and USART port provides tracking error codes by 10Hz frequency.

If your mount is shaking that much from the wind, I would think the stars in your pictures would be less than ideal...

I normally get < ±1 division on the PHD guiding dx,dy graph.
That's not bad at 1220mm fl.
At Mt Baw Baw -
I was quite often hitting ±3 divisions & sometimes off the scale when
a strong gust hit - in which case that sub frame had to be discarded.

The ±10” would be good.
My Lodestar has pixel size : 8.2 uM x 8.4 uM -
however I doubt that wind of high enough force to induce
a 10 pixel movement
( dx/dy scale of PHD is in pixels )
could be compensated for - so I'm agreeing with Gale.
This closed loop system should however respond in a dynamic way
to changes in velocity.

Post Extras:

Hilmi
Carpal Tunnel

Reged: 03/07/10

Loc: Muscat, Sultanate of Oman

Re: Telescope Drive Master - The Truth of the Matter new

[Re: wolfman_4_ever]
#5259475 - 06/07/12 05:59 AM

So will teleacope drive master work with a G11 with Gemini 2?

Post Extras:

alpal
Carpal Tunnel

Reged: 06/15/09

Loc: Melbourne Australia.

Re: Telescope Drive Master - The Truth of the Matter new

[Re: orlyandico]
#5259476 - 06/07/12 06:00 AM

Quote:

it's really hard to find high tic count encoders on the cheap.

that renishaw is probably in excess of $1000 (note that the encoder in the AP1600 is thousands of bucks). the $600 Gurley used in the SiTech is from Eastern Europe or Russia.

if the Chinese could make high-precision encoders cheaply, they would be using them and not the made-in-Britain Renishaw.

the iEQ45 is $1500. And with the Renishaw it's $4800. Granted some of that is milk money, but I bet (having scoured ebay for cheap encoders) that a big chunk - probably at least half - of that $3300 delta is the darn encoder.

Yes - the Chinese won't get the price down until they
make their own encoders.
Whoever will be the first will sell lots of new mounts!

I think we're going to see some nice Chinese mounts
with encoders at quite cheap prices within 2 years.
I am however speculating.

Post Extras:

gdd
sage

Reged: 11/23/05

Re: Telescope Drive Master - The Truth of the Matter new

[Re: alpal]
#5260367 - 06/07/12 03:27 PM

Quote:

The ±10” would be good.
My Lodestar has pixel size : 8.2 uM x 8.4 uM -
however I doubt that wind of high enough force to induce
a 10 pixel movement
( dx/dy scale of PHD is in pixels )
could be compensated for - so I'm agreeing with Gale.
This closed loop system should however respond in a dynamic way
to changes in velocity.

You are saying if the wind gust changes the rotational velocity of the RA shaft, the TDM can detect and compensate? But TDM cannot detect or compensate for wind induced vibrations or flexure elsewhere in the mount, tripod or OTA?

So the TDM would help in a wind situation but would not be a total solution.

Gale

Post Extras:

alpal
Carpal Tunnel

Reged: 06/15/09

Loc: Melbourne Australia.

Re: Telescope Drive Master - The Truth of the Matter new

[Re: gdd]
#5261276 - 06/08/12 02:25 AM

Quote:

Quote:

The ±10” would be good.
My Lodestar has pixel size : 8.2 uM x 8.4 uM -
however I doubt that wind of high enough force to induce
a 10 pixel movement
( dx/dy scale of PHD is in pixels )
could be compensated for - so I'm agreeing with Gale.
This closed loop system should however respond in a dynamic way
to changes in velocity.

You are saying if the wind gust changes the rotational velocity of the RA shaft, the TDM can detect and compensate? But TDM cannot detect or compensate for wind induced vibrations or flexure elsewhere in the mount, tripod or OTA?

So the TDM would help in a wind situation but would not be a total solution.

Gale

Yes - it should compensate - but to what level - I don't know.

Post Extras:

Jerry Hubbell
member

Reged: 02/16/09

Loc: Locust Grove, VA, USA

Re: Telescope Drive Master - The Truth of the Matter new

[Re: alpal]
#5262705 - 06/09/12 12:18 AM

The TDM encoder measures the RA axis rate compared to the standard sidereal rate. Any impact from wind, or other factors on the RA axis rate will be corrected by the TDM at up to 5 times per second. It will handle periodic and non-periodic errors.

As I have stated before, I typically get +/- 0.7 arcsec TE or better 95% of the time.

Post Extras:

alpal
Carpal Tunnel

Reged: 06/15/09

Loc: Melbourne Australia.

Re: Telescope Drive Master - The Truth of the Matter new

[Re: Jerry Hubbell]
#5262755 - 06/09/12 01:11 AM

Thanks Jerry,
The TDM is certainly a worthwhile upgrade.
I hope the price can come down a little bit.

Post Extras:

Mert
Post Laureate

Reged: 08/31/05

Loc: Spain, Pamplona

Re: Telescope Drive Master - The Truth of the Matter new

[Re: alpal]
#5401138 - 09/03/12 01:57 PM

Hi Jerry,

This has been an interesting thread for me to read through,
with a lot of various point of view and considerations.
Do you know which encoder in particular is used in
your setup?
It is my believing it is Heidenhahn, but don't know
which model number it is.
Your equipment combination works like a clock for sure!

Post Extras:

petely
journeyman

Reged: 01/06/11

Loc: England

Re: Telescope Drive Master - The Truth of the Matter new

[Re: gdd]
#5402305 - 09/04/12 03:29 AM

Quote:

You are saying if the wind gust changes the rotational velocity of the RA shaft, the TDM can detect and compensate? But TDM cannot detect or compensate for wind induced vibrations or flexure elsewhere in the mount, tripod or OTA?

So the TDM would help in a wind situation but would not be a total solution.

Gale

Depending on the angle of the OTA wrt. the ground, wind will also impart a force in the Dec direction, as well as the RA direction. Since the TDM is only acting on the RA axis, you stand the risk of still having elongated stars along the uncorrected direction.

Edited by petely (09/04/12 03:38 AM)

Post Extras:

Jerry Hubbell
member

Reged: 02/16/09

Loc: Locust Grove, VA, USA

Re: Telescope Drive Master - The Truth of the Matter new

[Re: Mert]
#5420162 - 09/13/12 10:54 PM

Hi Mert, sorry for the delayed response. The encoder is a Heidenhain ERN 480-5000-1 incremental sin/cos encoder.

Jerry

Post Extras:

orlyandico
Carpal Tunnel

Reged: 08/10/09

Loc: Singapore

Re: Telescope Drive Master - The Truth of the Matter new

[Re: Jerry Hubbell]
#5420233 - 09/13/12 11:39 PM

That's weird. That is only a 5000-slot encoder, however it is analog so an interpolation box can be used. Heidenhain does have 50:1 interpolators, but that would only give 250,000 counts per rev.

Post Extras:

Jerry Hubbell
member

Reged: 02/16/09

Loc: Locust Grove, VA, USA

Re: Telescope Drive Master - The Truth of the Matter new

[Re: orlyandico]
#5420280 - 09/14/12 12:21 AM

Nothing odd about it. The analog sine/cosine signal is converted with an equivalent 11 bit a/d giving an estimated 2^11 or 2048 counts per cycle or about 10 million counts per revolution of the Ra axis. Remember this is an incremental rate encoder, so the nominal sidereal rate provides 8 x 15 counts per second or 120 counts per second rate.

Jerry

Post Extras:

orlyandico
Carpal Tunnel

Reged: 08/10/09

Loc: Singapore

Re: Telescope Drive Master - The Truth of the Matter new

[Re: Jerry Hubbell]
#5420299 - 09/14/12 12:45 AM

Ah I see. So they are using their own A/D and not using the stock Heidenhain interpolation box.

It is not a true 10 million counts per revolution, but rather a 2048-point interpolation of a 5000-count per revolution encoder. Not a true metrology solution.

This is good info. Because I've been wanting to do my own TDM-a-like, and I could never find million-count encoders in small packages. This explains everything, it's aggressively interpolated.

There are true million-count encoders, but they are huge (physically). I believe the AP1600 / 3600 are using these types of encoders because Roland mentioned the 1600 had to be so large because of the encoder requirement.

Post Extras:

Luke Jones
journeyman

Reged: 03/27/09

Re: Telescope Drive Master - The Truth of the Matter new

[Re: orlyandico]
#5432324 - 09/21/12 09:24 AM

If you really want to build your own, you can find Renishaw read heads for around $200 on eBay.
I got lucky, and got one that came with the gold read strip. Couple that with a $40 arduino and a couple of opto isolators to read the quadrature encoder input, guide through an ST4, as well as send laptop feedback and accept long-term guides - and you're onto a winner.

You're welcome to any pictures, circuits or my Arduino code.

By the way, whatever you think of the TDM interpolation factor - I'm pretty sure it works as well as it needs to.

Post Extras:

rpineau
member

Reged: 05/30/12

Loc: CA, USA

Re: Telescope Drive Master - The Truth of the Matter new

[Re: Luke Jones]
#5432670 - 09/21/12 01:01 PM

@Luke : if you have any picture , schema and code, I think some people here would be interested .. starting with me.
Thanks.
Rodolphe

Post Extras:

Mert
Post Laureate

Reged: 08/31/05

Loc: Spain, Pamplona

Re: Telescope Drive Master - The Truth of the Matter new

[Re: rpineau]
#5432766 - 09/21/12 01:57 PM

Hi Luke, I fully agree!
I am also very much interested in pics/schematics and
code for the Arduino ( will do an Arduino TDM-alike
myself soon I hope )
Pm'd you my mail-address, thanks for sharing!!

Post Extras:

Mert
Post Laureate

Reged: 08/31/05

Loc: Spain, Pamplona

Re: Telescope Drive Master - The Truth of the Matter new

[Re: Jerry Hubbell]
#5432776 - 09/21/12 01:59 PM

Hi Jerry, thanks a lot, that explains a lot to me!!

I will have to go for a cheaper encoder but with
interpolation ( 1024x per half cycle *4 quadrature ) will
give me enough ticks to get the job done!

Post Extras:

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