New mount suggestions

[Freddie]

Unfortunately Altair are wrong!!!

I got the same info. from them but have just checked with the manufacturer who have confirmed that 27kg is the total payload so imaging would be about 2/3, which puts it slightly below the eq6R. To be honest, I would say that SW are over stating or Ioptron are understating payload as all reviews and feedback would indicate that the CEM60 is the better mount.

[vlaiv]

11 minutes ago, Freddie said:

Unfortunately Altair are wrong!!!

I got the same info. from them but have just checked with the manufacturer who have confirmed that 27kg is the total payload so imaging would be about 2/3, which puts it slightly below the eq6R. To be honest, I would say that SW are over stating or Ioptron are understating payload as all reviews and feedback would indicate that the CEM60 is the better mount.

There is more to the mount than weight capacity. CEM60 does have bunch of advantages over EQ6-R - like much less backlash due to "floating" worm gear - it is magnetically held against worm so any imperfection in worm won't result in change in engagement but rather just shift in worm gear axis position (held by magnets "in place"). Other important thing is stepper resolution. It is 0.06" per step (at 128 micro steps). EQ6-R is 0.140625" per step at 64 micro steps.

This means that CEM is probably featuring better stepper motor controller, and even if we observe them at 64 micro steps - has precision advantage (0.12 vs 0.14).

I guess overall finish and craftsmanship of CEM is also better (SW mounts are cast metal, not machined, not sure about CEM60 but it does look like some of it is machined). I would think that bearings system is also better in CEM60 - I know I had to change bearings on my HEQ5 to tune it for best performance, and saw a video once of CEM60 being balanced - thing moves extremely smoothly - like floating in space.

[Freddie]

I agree, as said, I think there is a bit of over or under stating of capacity going on and I don’t think Ioptron are doing themselves any favours with the figures they are stating for their CEM mounts.

[cotak]

People need to stop with the 1/2 and 2/3 rules. Those are for beginners.

The key to all this is moment arm. Which besides Astro-phyics now having some sort of a recommendation graph for the mach2, I don't know of any other manufacturers providing nearly as much information. Even the AP graph is only recommendations and you can't take the info and calculate expected performance from it. That's because they don't say what moment arm means in terms of tracking and guiding abilities. And that's the 2nd key: if the resulting imaging scale is beyond the mount's stability in tracking or guiding it's going to be useless.

Btw in Trump land they thinks the eq6 etc can only carry 1/2 and 2/3 of the stated paylod because over here in NA there's no 25kg payload listing. You have to wonder why you guys get a 18kg imaging payload number.  The manual say 20kg with for astrophotography in brackets. So what is the real number? 

I suspect you'll find the CEM60 actually can carry larger imaging payloads. I don't find anyone trying an RC10 or similar on the EQ6 but I know someone did managed to do 0.4 RMS with a CEM60 on RA with a Meade 12" SCT at 3000mm. It that likely a  typical experience? Maybe not because I suspect most people wouldn't even try. However, it show the rating isn't all BS.

I also think the obsession with payload a bit of a strange thing. I find it so because most people go spend a lot on their mounts only to never use their full capacity.

Edited April 29, 2019 by cotak

[pete_l]

13 hours ago, vlaiv said:

Other important thing is stepper resolution. It is 0.06" per step (at 128 micro steps). EQ6-R is 0.140625" per step at 64 micro steps.

This means that CEM is probably featuring better stepper motor controller, and even if we observe them at 64 micro steps - has precision advantage (0.12 vs 0.14).

There are many issues regarding microstepping that means we cannot rely on it to produce accurate guiding. A problem that increases as the load on the motor increases such as from imbalances or greater inertia from a heavier scope.

reference: Microstepping Myths and Realities [ PDF file ]

 

I think I might just have convinced myself that encoders do have a use after all Confused face ---> ?

Edited April 29, 2019 by pete_l

[vlaiv]

51 minutes ago, pete_l said:

There are many issues regarding microstepping that means we cannot rely on it to produce accurate guiding. A problem that increases as the load on the motor increases such as from imbalances or greater inertia from a heavier scope.

reference: Microstepping Myths and Realities [ PDF file ]

 

I think I might just have convinced myself that encoders do have a use after all Confused face ---> ?

I'm aware of issues with micro stepping - possible jumps / miss steps, and that it depends on step driver used. One of the reasons why I believe SW mounts can't do 0.5" RMS or less reliably.

Even with these taken into account, I think CEM60 can go 0.3" RMS - partly because x128 needs different driver, and I suppose it is better quality one than in SW mounts, and partly because increased step precision.

On a separate note (OP, please forgive yet another excursion in discussion), I was thinking what would be a good mount construction and came up with interesting configuration that might work extremely well, yet be quite of acceptable cost.

It would combine low precision absolute encoders, stepper motors (vs servos), friction transmission and belt transmission

"Schematic" would go like this:

Stepper is used via belt transmission to drive friction pin. Absolute encoder would be coupled with friction pin shaft to make sure rotation speed of friction pin is constant (removing all problems with stepper precision, belt transmission and gearing in between). Friction transmission in last stage as replacement to worm gear would ensure no periodic error - or very slow moving periodic error. All other errors would be "ironed" out prior to friction pin with use of low precision absolute encoder.

We can do quick calculation / estimation:

like said 22 bit gives 0.3" per encoder step when coupled with main shaft. If we make something like 200mm friction disk and 2mm friction pin, ratio would be x100.

This means that we have roughly 42000 steps for 0.3" resolution. With 18bit encoder on friction pin shaft we could have ~0.05" encoder resolution.

There is 1296000 arc seconds in a circle. With two step belt reduction - each being around x5 and main reduction of 100 we have total reduction of x2500. Steppers have 200 steps (1.8 degrees per step). So with this gear system we will have 2.592 arc seconds per step. We can then use 64 micro steps to get to 0.0405" per micro step. We can of course tweak two stage belt reduction to get match between encoder and stepper - both at around 0.05".

Makes sense?

 

[RolandKol]

1 hour ago, vlaiv said:

 

There is 1296000 arc seconds in a circle. With two step belt reduction - each being around x5 and main reduction of 100 we have total reduction of x2500. Steppers have 200 steps (1.8 degrees per step). So with this gear system we will have 2.592 arc seconds per step. We can then use 64 micro steps to get to 0.0405" per micro step. We can of course tweak two stage belt reduction to get match between encoder and stepper - both at around 0.05".

Makes sense?

 

From my personal experience,

then you reduce Stepper using Driver by 32 or 64, signal becomes not 100% reliable!  I would not go lower than 16

 

[cotak]

2 hours ago, vlaiv said:

I'm aware of issues with micro stepping - possible jumps / miss steps, and that it depends on step driver used. One of the reasons why I believe SW mounts can't do 0.5" RMS or less reliably.

Even with these taken into account, I think CEM60 can go 0.3" RMS - partly because x128 needs different driver, and I suppose it is better quality one than in SW mounts, and partly because increased step precision.

On a separate note (OP, please forgive yet another excursion in discussion), I was thinking what would be a good mount construction and came up with interesting configuration that might work extremely well, yet be quite of acceptable cost.

It would combine low precision absolute encoders, stepper motors (vs servos), friction transmission and belt transmission

"Schematic" would go like this:

Stepper is used via belt transmission to drive friction pin. Absolute encoder would be coupled with friction pin shaft to make sure rotation speed of friction pin is constant (removing all problems with stepper precision, belt transmission and gearing in between). Friction transmission in last stage as replacement to worm gear would ensure no periodic error - or very slow moving periodic error. All other errors would be "ironed" out prior to friction pin with use of low precision absolute encoder.

We can do quick calculation / estimation:

like said 22 bit gives 0.3" per encoder step when coupled with main shaft. If we make something like 200mm friction disk and 2mm friction pin, ratio would be x100.

This means that we have roughly 42000 steps for 0.3" resolution. With 18bit encoder on friction pin shaft we could have ~0.05" encoder resolution.

There is 1296000 arc seconds in a circle. With two step belt reduction - each being around x5 and main reduction of 100 we have total reduction of x2500. Steppers have 200 steps (1.8 degrees per step). So with this gear system we will have 2.592 arc seconds per step. We can then use 64 micro steps to get to 0.0405" per micro step. We can of course tweak two stage belt reduction to get match between encoder and stepper - both at around 0.05".

Makes sense?

 

On paper yes in reality you have too many variables between input and output it becomes unusable. These are mechanical systems so all the bits have to flex and give in order for them to move .

Otherwise it would be done by everyone already and we will all be very happy people.

Edited April 29, 2019 by cotak

[andrew s]

A mount is the sum of its parts mechanics, electromechanical, firmware, software and importantly support.

How these are integrated and optimised can make it a joy or a pain as several threads on SGL will confirm.

There are no technical magic bullets all have strengths and weaknesses. Given that we require them to point and track at such fine tolerances it is almost a miracle that such fine mounts are available. Even more so when you consider price.

Regards Andrew 

Edited April 29, 2019 by andrew s

[david_taurus83]

On 26/04/2019 at 23:17, vlaiv said:

Bottom line, if heq5 can be guided down to 0.4-0.5" RMS in right conditions, then I would expect CEM60 standard version to be able to be guided down to 0.3" RMS in right conditions, and certainly 0.5" RMS most of the time. That is as good as can be expected in that price range.

I'm going to fly the Skywatcher flag here! My AZEQ6 recent guiding averages over a session have been in the 0.5" mark with peaks around 1.35". That's with a tripod setup and Sharpcap polar align each time. During the session I have seen guiding go into the high 0.3" bracket.

 

No doubt the iOptron is the better more consistent mount but it's quite the price difference for that extra 0.2"/0.3" benefit. If your using long focal lengths then maybe..

 

@souls33k3r Could you not belt mod your current mount if it's already a good one?

[souls33k3r]

17 minutes ago, david_taurus83 said:

 

@souls33k3r Could you not belt mod your current mount if it's already a good one?

Well i've sold my NEQ6 mount hence the reason why the post

I'm listening in and soaking in all the information which is being provided within this thread to make a decision. I'm in no rush so will take my time

[cotak]

When you guys are talking RMS are you taking total or RA only?

[souls33k3r]

24 minutes ago, cotak said:

When you guys are talking RMS are you taking total or RA only?

Good question, i was thinking total. I could be wrong.

[vlaiv]

28 minutes ago, cotak said:

When you guys are talking RMS are you taking total or RA only?

My personal "goal" would be 0.2" total. I'm also talking total in my posts - like having HEQ5 going down to 0.5" total RMS (my personal best was 0.38" total RMS on particularly good night).

With mechanically stiff and smooth mount - DEC should be already very small so it's contribution is going to be small - no significant movement in DEC axis in single guide exposure even in presence of poor PA (well not ridiculously poor PA, but "reasonably" poor PA).

When I talk about RMS error, I also take into account guide resolution and ability of centroid algorithm to provide measurement with enough accuracy. For such low RMS errors, accuracy needs to be 0.1" or less - which would imply ~1.5"/px or less guide resolution (I personally guide at about 1"/px when doing high res imaging).

2 hours ago, RolandKol said:

From my personal experience,

then you reduce Stepper using Driver by 32 or 64, signal becomes not 100% reliable!  I would not go lower than 16

 

Yes, I was hoping that absolute encoder would handle all errors prior to main transfer mechanism - in this case friction drive.

But you have a very good point there - I did not think about that at first - assembly that I propose would suffer much elasticity due to fact that friction gearing is "reversible" and any load on OTA/mount - like wind or whatever would transfer back down to step motor and it would be up to holding torque to resist it - not a good idea.

Advantage of worm / worm gear assembly is in the fact that it is unidirectional motion transfer - rotating worm just tends to shift worm gear left-right and not rotate it.

[FLO]

On 28/04/2019 at 17:51, Anne S said:

I checked with Altair Astro who are the distributor. 

They are not. 

FLO sources iOptron direct from iOptron. It leaves the iOptron factory, is put on a ship (or plane if we are in a hurry) and is sent direct to our warehouse here in the UK. No distributor. 

FLO is entirely responsible for her iOptron stock, sales and support. There is no connection between FLO and Altair Astro. 

Sorry if I sound pedantic but details like this matter, at least to us. 

HTH, 

Steve 

[cotak]

Getting down to 0.2 would be difficult, not because it's not possible just I think very few people have such stable skies. And if they did they might go into planetary in a big way. 

I do wonder about the guide result a bit sometimes because even if you look at a good mount like the Mesu the result are all over the place from very low 0.2 to almost 1".

[FLO]

Regarding the iOptron CEM60 & CEM60EC payload capacity. Since reading this discussion and speaking with @Freddie (I assume it's you) via email we have updated our product description to include: 

"iOptron's quoted max' payload is a guide only. If you will be using the mount for astrophotography (or your telescope is unusually long or large) we recommend the quoted max' payload be reduced by 1/3rd."

We understand that is a little simplistic but I think it reasonable and there is only so much info we can include on a product description page ? 

HTH, 

Steve 

[Rainer]

6 minutes ago, FLO said:

payload

Hi,

I think we should be careful with the word " Payload " ... as it is used to easily and always creates a big Tohuwabohu

 

https://dictionary.cambridge.org/dictionary/english/payload

 

Our mount is a transport device for our equipment ¿ agree ? and it moves our equipment plus counterweights in a slow way from East to West in the Northern Hemisphere and from West to East in the Southern Hemisphere ( If I understand this correctly) as I ahve never been Down Under ...

OK, now coming back to PAYLOAD and Payload is normally the Load a Car, a Truck a Plane a ship can carry as the TOTAL additional weight it can carry ¿ right ?

Now iOptron specifies in all their mount carrying capacity and SPEAK from equipment and lways put there " Excludes counterweight " and in that moment the specified carrying capacity is NOT PAYLOAD ...

If we assume, again ASSUME and this is a guess the other missing part in Weight of the carrying capacity are the counterweights ¿ agree ?

OK, OFF TOPIC the CEM 120XXX is specified with a carrying capacity of 115 lbs ¿ OK ? Now I ahve 119 lbs of Counterweights  and if I calculated it correctly I have about  103 lbs of telescope equipment on it and so my Load on the CEM 120EC2 is 222 lbs  ...

Where is the specified Payload for the CEM 120EC2 ¿ I do not know ? The only thing I know is that both of my CEM 120EC2 have not broken down and are happily slweing at max 4° per second and happily trackin in any rate I put it to track ...

The only thing I know if that with 115 lbs of carrying capacity and I having 103 on it I still can add 12 lbs additionally. ¿ Would I do it ?  YES with out any doubt and perhaps even more.

¿ why ? because I had for 15 years two Losmandy G11 with a reated carrying capacity of 60 lbs and they were both working with more thern 75 lbs equipment and 70 pounds of counterweights and also were happily slerweing and tracking.

¿ Is it now clear what Payload means ?

 

https://dictionary.cambridge.org/dictionary/english/payload

 

[FLO]

4 minutes ago, Rainer said:

Hi,

I think we should be careful with the word " Payload " ... as it is used to easily and always creates a big Tohuwabohu

https://dictionary.cambridge.org/dictionary/english/payload

No problem. Would 'carrying capacity' be better? It would be an easy change to make. 

I have no idea what a 'Tohuwabohu' is ?

Steve 

[Rainer]

2 minutes ago, FLO said:

No problem. Would 'carrying capacity' be better? It would be an easy change to make. 

I have no idea what a 'Tohuwabohu' is ?

Steve 

Hi,

I was just trying to explain the implication with the word Payload as this seems to be creating also a lot of discussions ...

OH ☺️ and I just saw that iOptron uses the word Payload but in the next field they add, " ... exclude counterweight* "

Sorry and now even the mount producers creates confusion ?

Rainer

" Tohuwabohu " is a German expression meaning " making a big confusion " out of something

Uncle Google is out Sensei ?

https://www.wordhippo.com/what-is/the-meaning-of/german-word-9baf180df78e2208828aaa8640d6d167672fe79a.html

[souls33k3r]

2 minutes ago, Rainer said:

Hi,

I was just trying to explain the implication with the word Payload as this seems to be creating also a lot of discussions ...

OH ☺️ and I just saw that iOptron uses the word Payload but in the next field they add, " ... exclude counterweight* "

Sorry and now even the mount producers creates confusion ?

Rainer

" Tohuwabohu " is a German expression meaning " making a big confusion " out of something

Uncle Google is out Sensei ?

https://www.wordhippo.com/what-is/the-meaning-of/german-word-9baf180df78e2208828aaa8640d6d167672fe79a.html

No confusion here for sure. I think everyone wanted to know how much (recommendation) can you put on this mount for imaging

[Jkulin]

11 hours ago, cotak said:

I suspect you'll find the CEM60 actually can carry larger imaging payloads. I don't find anyone trying an RC10 or similar on the EQ6 but I know someone did managed to do 0.4 RMS with a CEM60 on RA with a Meade 12" SCT at 3000mm. It that likely a  typical experience? Maybe not because I suspect most people wouldn't even try. However, it show the rating isn't all BS.

Here you go ?

[Rainer]

Hi,

So far as I remember there is only one mount producer who specifies it very clearly and that is Paramount ...

regards Rainer

 

Edited April 29, 2019 by Rainer

[vlaiv]

49 minutes ago, cotak said:

Getting down to 0.2 would be difficult, not because it's not possible just I think very few people have such stable skies. And if they did they might go into planetary in a big way. 

I do wonder about the guide result a bit sometimes because even if you look at a good mount like the Mesu the result are all over the place from very low 0.2 to almost 1".

That should not be the case. Local thermals excluded (these are nasty things and there is no help with those that I'm aware), longish guide exposure is going to smooth out things, and even in 1-1.5" seeing, you can still guide with great precision. Star FWHM will not be that great, but it will not be due to guiding - it will be due to seeing.

[cotak]

2 hours ago, Jkulin said:

Here you go ?

What sort of guiding  values did you get with that beast?