Request for info on Renishaw encoders


#1

I have been thinking about upgrading my AP 1100GTO mount with AP’s Renishaw encoders. However, their cost makes me wonder about just how much better tracking and guiding acutally would be – that is, enough to justify the cost?

I was hoping someone running SGP and PHD2 Guiding with a Renishaw equipped mount would be able to post a screen shot of PHD2 Guiding’s graph to show the kind of guiding that can be achieved with PHD2 Guiding and Renishaw encoders.

TIA

Charlie


#2

Hi Charlie:

I “double dog dare you” to post this on CN!

I’ve decided to forego the luxury of adding AEs to my AP1600.


#3

Well, no one CN who posts actually owns any of that quality of equipment so you’ll just hear all the opinions. Most of which will tell you to downgrade to an Ioptron :smiley:


#4

Hello,
it depends on different variables (so to say).
Using those encoders the mount knows exactly where is looking, resulting in less work on autoguider especially if you can do a pointing model like those made by ASA and 10 Micron.
In your position I will also take into account a AO unit, that can also rise the image quality. I have no idea about your gear so I can only ques that you are working with long FL.
And about your question, I dont have a screen shot but the guiding corrections for 30 seconds exposure time (on guider) are in the ± 1 arc seconds (90/500 mm guider scope bin 2 Lodestar X2) depending on seeing (47 stars used in the pointing model).

Take care
Emil


#5

Actually, there are several people on CN using very high quality mounts equipped with AEs. It just turns out that all of them are 10 Micron mounts rather than APs.

And, at least one of them, would insist on two points specific to AP’s implementation of the Renishaws . . .

1/ The installation of AE’s is such a precise affair that an “add-on” kit for them, such as AP’s can just never be satisfactory!
2/ The way the AEs are “cobbled onto” the AP mounts results in their not being true absolute encoders at all. Meaning, the AP mounts can still become “lost in space” even when encoder-equipped.

Remember, I am playing devil’s advocate here. In his defense, I know of not one soul who has retrofitted an AP 1100 or AP1600 with the encoder DIY kit.

It is repeated over and over that the real advantage to AEs is to remote operators. Getting a mount “lost” can be a real nuisance to them and having a mount that can’t get “lost” is a real plus. But, that big advantage is totally lost with APs because, well, even with encoders, they can STILL get lost.

The other advantage to the encoders is that tracking is so precise that unguided imaging becomes more readily achievable. Now, it is pointed out that with additional software, the AP mounts can do unguided imaging. And they can do this WITH or WITHOUT encoders! That said, all the unguided images being shown are from encoder-equipped 10 Micron owners. Or, so it seems.

Spending $8,500US for the encoders on an AP mount is a very hard sell. The goal in doing so has to be more than a flatter guiding graph.

What I post here is the situation as I understand it. If you are seriously considering the AE kit from AP, you really need to have a talk with them about just what it is you expect the encoders to accomplish. Just trying to flatten the guiding graph is pretty pointless. The mounts are already more than capable of faultless imaging while being guided.


#6

Hi Terry,

Why don’t you post your request on the AP-GTO forum, or better, call Astro-Physics and ask for references to people with an AE-equipped mount?

Also, I think that the person posting that on CN is incorrect.

The 1100/1600 mounts were designed from the drawing board to take absolute encoders. They can be installed by the end user in 20 minutes. The encoders are pre-installed and aligned in an adapter ring. That said you should wait for the GTOCP4 to ship which will eliminate the need for the second control box. Here is a link to more information and some unguided images:

http://www.astro-physics.com/index.htm?products/mounts/1600gto/1600upgrades

BTW, I think you can make almost any mount lose it’s position as well simply by syncing to the wrong RA/Dec coordinates. If you lock down the axes the AP mount will never lose position (there are now safeguards in APCC to prevent errant syncs).

The encoders on that “other” mount are arguably not true absolute encoders in the typical sense but some sort of proprietary hybrid (i.e., I can’t find a part number anywhere!) The Renishaw encoders used by A-P have Renishaw part numbers and that proves they are absolute encoders. The 10 Micron encoders are said to be low resolution but 10 Micron supposedly fixes that in software at their manufacturing plant by using a high resolution master encoder to map out corrections to lower resolution encoder in each mount.

However, if a motor goes out the user may need to send the entire 10 Micron mount back for repair. I’m guessing that’s probably why the person on CN can’t understand how an encoder could be bolted on an AP1100 by the end user?

-Ray Gralak


#7

HUm…this is really going to bother me.
10 micron encoders a trully absolute for sure. What is said upward is
all wrong and intent misinformations.
No related experience till now on post self installed AE on an AP GTO.
The only AEs AP 1600 CN user known has given up and runs now a 10µm…

Anyway, encoders will not helps you to guide "better"
seeing will limit you whatever the technology you use.
Encoders are more a question of "comfort " and reliability.


#8

Fdx92190: I did not say it didn’t function as an absolute encoder would.

I wrote: “are arguably not true absolute encoders in the typical sense”. A typical absolute encoder consists of the encoder strip and a pickup with absolute “values” encoded on the strip. I think that the 10 Micron implementation is proprietary and is much more than just a strip and a pickup thus it is not typical. It is a combination hardware/firmware solution and, in the future, probably not the only one doing that.

As for the CN user (Dave Goodyear) you mention he is only one person. There are many people with A-P encoder equipped mounts that spend time imaging and not on the forums (not meaning to single Dave G. out).

-Ray


#9

Hi Ray:

Appreciate your post. Mine was to Charlie though, the OP.
I personally am not sufficiently interested in the AE kit to pony up the cost. I do not operate my 1600 remotely and, although intrigued by the going unguided phenomenon, do not consider it a grail to be pursued at high cost. Whatever improvement to my images I can muster will comes from bettering my processing skills, not adding AEs to my AP1600.
I think it a rare case where adding $8,500 in Renishaws will result in better images for an AP owner.

Charlie seems to be specifically asking if the AEs will result in a better PHD2 graph when acquiring data with SGP. My personal opinion is that his question is missing the point of AEs. Depending on his seeing, they may, or may not, result in a “better” graph. But will his images be noticeably better?
I suspect the difference will be crashingly minimal!

Do appreciate your opinion that the poster who continually decries APs AE implemenation is wrong. I’ve wondered about that and suspect you are correct. No evidence has ever been forthcoming to support his position.


#10

Hi Ray, not begining a eternal 10µ/Ap battle here, because this is nonsens.
To clarify : an absolute encoder do not own its name due to its technology (optical head and strip in renishaw case)
but the type of positioning information it provide: absolute/relative : That’is it.
Both renishaw and 10µm encoders are pure absolute positioning encoders.
The way the 10µm proprietary absolute encoder play its game is no special trick.
For those who are interested, the 10µm AE Patent is on the google patent search.
Easy to find , and easy to understand how 10µm was able to offers absolute encoders with a limited cost.
Very nice and innovative.

As for Dave goodyear, yoou are right and that was this guy i was talking about.
That would be nice that other AP users share their experience with Absolute encoders.


#11

OK – now you know why I didn’t post to CN :relaxed:

I appreciate the info from all. I was not considering installing the encoders myself but would send the mount back to AP for that work – and the new CP4 control box.

I am imaging with a 12" Meade LX850-ACF f/8 OTA (2440mm fl) and a QSI683wsg camera.

I was skeptical that a set of Renishaw encoders could work enough wonders to justify their cost. My personal speculation is that AP made them available to assist remote imaging operations and, to some extent, “keep up with the Jones.”

A couple of years ago, when I still had my AP900GTO and was having trouble getting good guiding traces in PHD Guiding, I contacted AP tech support and was basically told “if you are not using MaximDL we can’t help you.”

On a good night (seeing wise) at my observatory, I usually see the PHD2 Guiding graph staying withing the +/- 1 arcsecond brackets but the frame to frame points are pretty erratic. I suspect that is all seeing, however.

Primarily I was interested in hearing about the kind of performance people with Renishaw equipped mounts are seeing and to get a better understanding of their overall benefits.

I plan on using Ray Gralak’s PemPro to actually see what kind of periodic error I am seeing. I know AP ships their mounts with PEC installed but it never hurts to check.

Charlie

BTW – here is a link to a picture of my setup, if interested:

http://www.astrobin.com/203823/


#12

Well, “a couple of years ago” is a long time in this game. SGP was in its infancy! Maxim was perhaps THE standard. Maybe it still is? Especially, if that “couple of years” is actually 3-5 years, as it so often is, the way time plays her cruel tricks with us all.

I am curious though. Why would you “send the mount” back for encoder installation? That seems to play into the critics’ game that it just isn’t possible that a user can add AEs to their mount on their own. Either AP’s “add on” AE kit works or it doesn’t. There’s not a shred of evidence it does not!
Just a single, non-AP user claiming so, over and over, on another forum. AP offer it. I expect it to work! It sure isn’t cheap!


#13

Gentlemen,

I am perfectly happy if you mention me by name :wink: I am indeed “the one non-AP user” who has doubts as to whether encoders of Renishaw caliber could really by fitted by a user. The reason is purely mathematical. Assuming a wheel diameter of 20 cm, a radial displacement of the encoder ring by 0.5 micrometers, or 0.00000002", will cause encoder read shift by one arc-second perpendicular to the displacement. In a factory, this problem is addressed by a) better tools for alignment and mounting, and b) optionally modeling the encoder so that any eccentricity is compensated for in software. This is why Bisque and 10Micron, and most likely Planewave, SkyVision and ASA, don’t let the users fiddle with encoders.

One arc-second of error gradually over the axis movement is ten times the encoder resolution, so a cheaper encoder could then be used instead, matching the potential radial displacement of the mounting tolerances.

Apart from being “the one”, I am also perfectly capable of changing my mind and admitting my mistakes openly. AP may well have some means of compensation for potential radial misalignment, but they have never surfaced in the discussions that have gone on.

AP mounts are fine pieces of equipment, and the doubts I have are solely about the encoder implementation. Change my mind, if you will, but let’s do it on other fora than SGP.

Now, given the original question, I think PEC along with APCC is the way to get the best results with your mount. If it is in good mechanical shape, encoders do not really add any great advantage that warrants the cost.

All the best,

Per


#14

Hi Per,

you are absolutely right in your analysis. It will take an unreasonably small amount of error in mounting the encoder to create an absolute error much larger than the resolution.

Fortunately, this kind of absolute precision is not necessary. What is necessary is a very high resolution, a very good repeatability and a smooth error variation. Once we have that, we would just build a good pointing model and this is it. This is anyway necessary – assuming unguided exposure - as no matter how good the absolute precision of the encoder might be, it will be killed by the nonlinearities of the system.

Best regards,
Horia


#15

Per, thanks for owning up!

I’m going to give you the same advice I gave earlier. If you really want a good explanation of the encoder mounting kit and A-P encoders in general, then post your questions on the ap-gto forum or call Astro-Physics. Roland or Howard (from A-P) will gladly educate you on how it is done. Forums like Cloudy Nights are meant for end-users and they often get the facts wrong. Plus, Cloudy Night’s vendor policy is over the top restrictive so vendors, who usually know much more than the users, cannot always correct the misinformation that sometimes abounds.

BTW, with your StickStation product I expect you should be asking for (or summarily granted) vendor status on Cloudy Nights? Have fun with that! :slight_smile:

-Ray


#16

Haha, vendor status… Yes, I have been asked if I wanted vendor status, but I declined on the grounds that the turnover of astro products in my company constitutes less than the stipulated 25 or 30% (or whatever they quoted). Actually less than 0.5%, so nowhere near the minimum requirement. Still, CN is a good forum in many respects, and a way for us on this side of the pond interact with you Yanks, including you.

'Nuf said. Back on topic.

/p


#17

Per, ok. lucky you!

So what non-astro products does Blue Astro Products sell?

http://blueastro.se/index.php?id=4

-Ray


#18

Blue Astro is a trade name for Blue Ice AB, which sells system solutions related to ice management in the Arctic, as well as consultant services around that.


#19

That seems like a nice loop hole. The work I do as a consultant and for PEMPro constitutes much less than 25% of my regular full-time job (income and time), yet I am deemed a vendor. I should revisit my vendor status with CN using you as an example. Thanks for the insight on this. :slight_smile:

-Ray


#20

No loop-hole - rules. We can move this discussion to CN so that the rest of the people are spared.


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