Do you want perfect tracking with no guiding?

[Bassnut (Fred)]

If you have smooth PE and a short FL, yes , external autoguiding at 2 secs can work perfectly, it will track PE, but if for instance you use internal guide with an SBIG guiding with 10 sec guide exposures or more with long FL, PEC and low PE become very important.

The point in spending money on low PE, is the reduced reliance on fast tight guiding. This product becomes very usefull with long FL long internal guide exposure times. Rather than a waste of money, it saves money on expensive mount upgrades

[rajiva]

Hi Fred,

Originally Posted by Bassnut

you quote ASA as a source of anything that actually works?

no, I do not have a ASA mount and i would never buy one!
But this mount DO NOT have a PE so it MUST be far better then the TDM

BTW, I did not say encoder driven PEC (EPEC) is a useless feature. In my opinion, beside the horrible price (the TDM Encoder is only 270 Euro ) and the fact you need additional guiding, the main disadvantage is that it is a external Box with no feedback of the controller! All the problems with guiding, GOTO and more could be solved if the TDM where able to know what the telescope controller is doing.

CS
Rajiva

[tlgerdes (Trevor)]

Originally Posted by rajiva

Without a polar scope

Hi Rajiva,

You seem to keep going back to alignment problems, bringing up the lack of Polar Scope and Autoguiding.

The TDM is not designed to solve the lack of ability in system setup and alignment, it is designed to give PE accuracy to your EQ6 or similar that is only found in $20k+ mounts.

If the problem is alignment, then this product not the answer.

BTW Down in the south where we are, most people dont worry about a polar scope as you cant generally see the SCP through it as it is so faint (5.5Mag or fainter) and the stars are more than 1deg off. People here learn to drift align, or use mount based electronic alignment procedures.

[AndrewJ]

Gday Freddy

Re

Hang on............ in reality, its an end shaft encoder, what pro observatories use, nothing magic about it at all. It elimates PE because its after the gearbox/worm gear etc..

Put aside the advertising and take it for what it is, an end shaft encoder, and its a very good price indeed for the reported res. Almost too good in fact, ive seen shaft encoders at this res for over $7K, just for the encoder.

This device is also being discussed on the LX200GPS Yahoo forum
Someone found the specs for the device as

"Heidenhain ERN-480" encoder with a 1/8th arcsecond resolution

The specs for the ERN-480 models show only up to 6000 lines
( which in quadrature mode gives about 54arcsec granularity )
As such, something else is going on, probably a precision geartrain between the RA axle and the encoder.
This may have PE in it, but that could be accounted for easily in the "black box" ( dunno if it is )
Also, unless the device takeoff is perfectly centred, you would still get slight tracking rate errors due to eccentricity
( assuming we are talking of 1/8 arcsec precision )
Soooo, it looks like a good device to remove the bulk of the geartrain errors, but guiding is probably still required.

Andrew

[rajiva]

Hi,

Originally Posted by tlgerdes

it is designed to give PE accuracy to your EQ6 or similar that is only found in $20k+ mounts.

6K mounts do not even have a PE. It's really funny that the comparison with real expensive mounts come up every time. A 20K mount is more then just a small PE and nothing can make a 20K mount out of a EQ-6.

Is the PE of your 2,5K G11 so bad that the autoguider can't manage it?
If no, why spend money for a TDM if you can get a G11, that will carry more weight, for the price of a EQ-6 + TDM?

I have a EQ-6 by my self and i know with a little bit adjustment nothing is so bad that a autoguider can't manage it. The TDM simply is not worth the money if you still need a autoguider that can do the FULL JOB without the TDM. I have a TDM like system in my stepper controller but with PEC the PE is so regular that I do not use it.

In fact all this PE size discussions are not worth talking about because if the PE is smooth it makes no difference for the autoguider if the PE is 5" or 50"
If a system can eliminate the need of autoguiding, yes then ask me again to spend this much money. But for sure the TDM isn't such device.

If the problem is alignment, then this product not the answer.

The Topic says: Do you want perfect tracking with no guiding?
And I say: This product is not the answer. Everybody has to deside by it's own if it is worth to spend 1,5K to have a "add on" for the still required autoguider and everybody has to deside if the autoguider really needs such expensive toy.

Enough for today?

CS
Rajiva

[rajiva]

Hi Andrew,

Originally Posted by AndrewJ

Heidenhain ERN-480" encoder

yes a Heidenhain Encoder is used. The price for TDM encoder is 270 Euro

CS
Rajiva

[Bassnut (Fred)]

Andrew. OK, if its not a true output encoder, then that changes every thing, Id be very wary.

Rajiva. Your right, PE, no matter how bad, as long as its smooth, can be guided out with 2sec or so guiding. Not so with 30 secs or longer guide exposures though, thats what Im talking about. Anyway, given that this product is not what I thought it was, it may be indeed a waste of money, and the TDM may well do the same thing for less money.

[AndrewJ]

Gday Fred

Andrew. OK, if its not a true output encoder, then that changes every thing, Id be very wary

Not necessarily wary, it does what it says, to a point.
If we assume it has a precision gearbox between the RA axle and the encoder, any PE in this is simply tested for and accounted for,
This could be done as a factory setup.
Thus, when in place and running, this gizmo would give a good "smooth and steady" tracking rate, thus removing a lot of the std problems seen with high freq PE and tooth spacing errors.
However, unless there is a true sky feedback mechanism, it cannot ever give a "perfect" tracking, "for taking piccies"
Also, look at how it gets fitted to a Meade Fork unit
No more swinging the OTA between the forks

Andrew

[rajiva]

Hi Fred,

Not so with 30 secs or longer guide exposures though, thats what Im talking about.

yes i totally agree to that point and for sure there are very rare situations where the TDM makes sense. But this is not what the company is telling.

The truth is simple: You still need a guider, the PE size is not the main argument, the TDM do not make a 20K mount out of a EQ6 and in most situations the TDM is simply wasting money for nothing.

CS
Rajiva

[AndyTheDoc (Andy)]

Originally Posted by AndrewJ

Gday Freddy

Re

This device is also being discussed on the LX200GPS Yahoo forum
Someone found the specs for the device as

The specs for the ERN-480 models show only up to 6000 lines
( which in quadrature mode gives about 54arcsec granularity )
As such, something else is going on, probably a precision geartrain between the RA axle and the encoder.
This may have PE in it, but that could be accounted for easily in the "black box" ( dunno if it is )
Also, unless the device takeoff is perfectly centred, you would still get slight tracking rate errors due to eccentricity
( assuming we are talking of 1/8 arcsec precision )
Soooo, it looks like a good device to remove the bulk of the geartrain errors, but guiding is probably still required.

Andrew

Hello!

I just read datasheets for Heidenhain encoders and I think they use model ERN 480 with sinewave incremental signal output.

Here is citation from datasheet:
HEIDENHAIN encoders with sinewave output interface provide voltage signals that can be highly interpolated.

At photo http://www.slas.us/gallery2/main.php?g2_itemId=1386 there are 2 IC's at the left side of the box, I think it's a OP amplifiers, but what IC is on SOIC adapter? Probably 2 channels ADC...
Simple use of hi-res encoder on RA shaft - it's too expensive! That is why company asks their customers to not publish labels on the encoder, but it is very simply to discover by form... and nevertheless on one photo is visible number 5000

Yep, price is too hi for this device!

Cheers!

[ASTROMONK (David)]

I think you are missing an esential point here guys....yes a Heidenheim ERN 480 5000 is expensive for us amateur astonomers, but its a delicate piece of equipment, a professional would not think twice at spending £800 for an encoder. If you use an autoguider with it, you can guide on MUCH fainter stars, because the update frequency can be MUCH less.
For it to work properly the polar shaft does need to be accurately aligned, and it is best used on fixed observatory mounts rather than field trips. Yes, I use one on an Alter D6 (made the adaptor myself) and the PEC was reduced from +/- 4 arc secs to +/-0.5 arc secs.

[DavidTrap (David)]

What's wrong with guiding?

I heard David Malin say in a lecture that the Siding Springs scope had an autoguider with a 10fps correction rate - faster than most of us use and I'd hope that mount is well polar aligned!

DT

[Barrykgerdes]

Originally Posted by DavidTrap

What's wrong with guiding?

I heard David Malin say in a lecture that the Siding Springs scope had an autoguider with a 10fps correction rate - faster than most of us use and I'd hope that mount is well polar aligned!

DT

I don't think it is polar aligned.

Barry

[g__day (Matthew)]

I must say I agree with Fred's comments - it sounds like a high precision RA encoder, and I'd guess a black box to apply King rates of elevation (and possibly altitude) calculated refraction adjustment to a bodies apparent motion. I smiled at Peter's comments - becuase that was exactly what I was thinking at the time. So basically a very expensive RA gearbox, marketed as the whole enclidea!

[AndrewJ]

Gday Matthew

So basically a very expensive RA gearbox,

Nup ( or at least "i" no longer think so )
In the original thread, i think "AndyTheDoc" got it right
with this bit

HEIDENHAIN encoders with sinewave output interface provide voltage signals that can be highly interpolated.

I read up on that a bit.
By not using quadrature encoding, they can effectively get much better resolution from the encoder, hence no gearbox etc reqd.
I still wonder how they control temp compensation and eccentricity in mounting to the accuracy specified, but im sure its going to be pretty close to what they specify.
Where it all gets interesting now is how the feedback loop into the scope
itself works.

Andrew

[bojan]

Originally Posted by rajiva

Even autoguiding without the need of a PC (stand alone) is much cheaper then this system that requires additional guiding equipment. In my opinion the TDM is simply waste of money.

CS
Rajiva

I second to that.
We had almost exactly the same discussion couple of years ago (V1?) and no-one managed to answer the question "what is the benefit of TDM +autoguiding (needed to sort out the rest of issues like flexures, poor alignment, refraction..) , when you have autoguiding?"

[cventer]

Another option if you believe the hype is the ASA DDM85

Direct drive. No PE. Supposed accuracy of 0.25" rms for 5 min exposures. And 0.4" for 10 to 15 min.

Sounds impressive. Massive payload and massive price.anyone know if these claims are true?

[alistairsam]

Hi,

Do these mounts automatically change the tracking rate depending on where it is pointing to in the sky as the tracking rate would vary slightly at different positions. so the high precision encoders I'm guessing are to ensure tracking rate at that position is within tolerance?
guiding is definitely far cheaper, but is dec guiding really necessary?

[Barrykgerdes]

Originally Posted by alistairsam

Hi,

Do these mounts automatically change the tracking rate depending on where it is pointing to in the sky as the tracking rate would vary slightly at different positions. so the high precision encoders I'm guessing are to ensure tracking rate at that position is within tolerance?
guiding is definitely far cheaper, but is dec guiding really necessary?

It is with an alt/azm mount which is what many of the large observatory telescopes are these days.

Barry

[gregbradley]

I haven't followed them recently but the ASA DDM85 mounts were in fact delivering impressive results in images I have seen regularly.

There are a few mounts out now that use these precision encoders on the final shafts. The Earths speed of rotation is a constant and known amount. So the spin rate on the shaft can be monitored to maintain that exact rate. I believe that is how they work. Like an internal autoguider.

Its someone's attempt to implement that approach on an existing mount.

Not sure why it is so contentious. It may work once your polar alignment is nice and accurate. You've got drift alignment and T-Point to get your polar alignment accurate. I guess the upset about no polar scope is more for Northern Hemisphere users who orient off their Pole star (which is not totally accurate anyway).

I think its good someone is developing mounts and improving guiding performance as an alternative to autoguiding which as well all know has its own set of problems and frustrations attached to it.

So I nominate Rajiva as the guinea pig to test it out!!

Greg.