Mount with +-0.3 arc sec periodic error

[Zaps]

Direct drive: no gears, no PE.

[AndrewJ]

Gday Andrew

I guess you could call it 'real time error correction' instead of periodic. Maybe RTEC is a suitable acronym?

Its not really that either, its more like RPTEC ( Real "Part Time" )
All any of these systems do is try and make an encoder go at a certain rate. They dont address how the OTA flexes and how the sky tracking rates change. By having an encoder on the final axis, it eliminates the geartrain ( and hence any teeth errors ) from the feedback loops, but it cannot affect all the other downstream errors.
Its certainly a big step up from a system where a cheap encoder is on the motor, but there are still a lot of other errors that it cant deal with.

Direct drive: no gears, no PE

Also very high price and still doesnt address all the other errors mentioned above. Its horses for courses.
Be good to see how the technology evolves, and a reduction in moving parts that have to be aligned would be nice, but it will still need a good encoder feedback system.

Andrew

[Zaps]

Which errors? There will always be compromises.

For instance, the Chronos mounts eliminate meridian flips and the need for counterweights, but at the cost of some carrying capacity. And they use gears, therefore exhibit PE.

OTOH, the "small" direct drive mounts now being marketed, such as the ASA DDM60, DDM85 and DDM150, or the Astelco NTM-500, require meridian flips and counterweights, but punch above their weights, and the tracking precision and resolution is crazy high. Best of all, being gear-free, they are also PE-less.

Here's a fascinating new friction drive mount that eliminates the need for counterweights and meridian flips, has an enormous carrying capacity, but which exhibits some PE. (Though very little PE, around that of a Takahashi mount.)

When you get up to the DDM85, Mesu-mount level, there's surprisingly little difference in price between them and, say, the Takahashi EM-500, Paramount ME, or the Astro-Physics 1200GTO, while exceeding the capability of those quite a bit. (Professionals and top-ranking astrophotographers consider zero PE systems to be better than low PE ones, and worth every penny.)

Like all things, it comes down to your budget in the end.

[gregbradley]

Thanks Andrew, that's a good explanation.

Greg.

[AndrewJ]

Gday Zaps

Which errors?

The initial 2 i would suggest are refraction and flexure.

And they use gears, therefore exhibit PE.

Not necessarily true.
You need to look at the underlying mechanics involved.
If you have a geartrain, and the encoder is on the motor,
( as per most cheaper systems ) then your statement is correct.
However, if the encoder is of good enough resolution, and is on the output axle ( ie RA axis ), then what happens between the motor and final axis is utterly irrelevant, as the motor PID loop just accounts for it.
To all intents and purposes, the drive "system" has no PE.

Andrew

[AndrewJ]

Gday Zaps

Here's a fascinating new friction drive mount that eliminates the need for counterweights and meridian flips, has an enormous carrying capacity, but which exhibits some PE. (Though very little PE, around that of a Takahashi mount.)

Just had a look at their site, but until there is a bit more feedback,
i will take it with a grain of salt ( or two )
Ie in their blurb, they actually mention
"No measurable periodical error"
yet spend a great deal of time showing how they measured it
It may well be good, but theres lots of stuff out there these days saying its good before its tested. ( Just like politicians )
Until there are a few more reviews its just spin.
Also ,( with my mech engineers hat on ), it would be interesting to see some real world values as to how much flexure there is when under load,
as ( gut feel first impressions ) indicate the design looks like it would be suspect to considerable flexure if heavily loaded.


Andrew

[Mesu]

Hello astronomers,

I'm the designer/vendor of the Mesu-Mount.
Saw the very interesting discussion about telescope mounts.

I like to explain things about the periodic error graph on the Mesu-Optics website.

The graph is made with a 65kg Takahashi epsilon 300 on one site of the mount and another 65kg on the other side. (a picture of this setup is on the website)
Let it run on a star for 1/2 hour without autoguiding.
The graph is the mount's PE+seeing+flecture+wind+walk by's when operating the mount and maybe more things that I don't know.

A PE graph that shows a fraction of an arc.sec PE can only be made by measuring pulses on an hi resolution encoder on the RA axis. That's what ASA does with his mounts. I talked about that issue when I met at a fair to promote our products. It's another way of measuring a PE and it can be don inside a building without telescopes.

Andrew has right when he writes.
"No measurable periodical error"
yet spend a great deal of time showing how they measured it
But I hope it's clear now why it's on the site in this way.
I measured the PE+all other things.

I think as other members mentioned that When the PE is on arcsec level and you still want to guide better because of the telescope resolution. Then you need feedback from the sky by autoguiding.

The MesuMount/ServoCAT autoguider can autoguide within a fraction of an arc.sec.

Best regards,

Lucas Mesu
www.mesu-optics.nl

[AndrewJ]

Gday Mesu

Thanks for the informative reply.
But this bit nails it ( for what i was trying to convey earlier in the thread )

I think as other members mentioned that When the PE is on arcsec level and you still want to guide better because of the telescope resolution. Then you need feedback from the sky by autoguiding.

Or use a lower class of drive and adaptive optics???
( There are multiple ways to skin a cat for a price )
Ie at the end of the day, you always need a way to keep the "camera" synchronised to the sky, not just a drive going at a set rate with no PE.

Just for info, i also noted that the design "looked" like it would be subject to flexure ( esp between the base and the DEC drive assy ) when under load.
Do you have any measurements for this ( at the arcsec level ) when loaded with 130kg of scopes???? ( or better still a very offset load )

Andrew

PS I do like the design principle, just interested in how good the real world numbers are.

[Mesu]

Hello Andrew,

Yes you can use adaptive optics as alternative for autoguiding.
But I'm not sure your gone save money.
The autoguider I use now for 2 years is a 50 euro webcam a 100 euro Newton and a 60 euro shoestring cable.

You can use a lower class telescope drive. But lower class don't mean that it cost less money.
When you read this.
http://www.dfmengineering.com/news_t...e_gearing.html
you can see a friction drive is a hi class drive for a low price.
That's why the Mesu-Mount in this very complete overview comes out very good.
http://lambermont.dyndns.org/astro/pe.html
If you want to save money on the telescope mount the next good candidate under the 7500 has a load capasity that's much lower than the Mesu-Mount. It has a meridian flip and all other disadvantages a worm gear has in it.

The Mesu-Mount is a very stiff mount with a good dynamic behavior.
Much stiffer than a German mount with tripod. The 130kg is no problem as you can see in the PE graph. That are the real world measurements on arc.sec level with 130kg telescopes. I didn't try it not jet but I wouldn't make a problem of it to mount 200kg telescopes on this mount.

Best regards,

Lucas Mesu

www.mesu-optics.nl

[rat156]

Hi Lucas,

Thanks for participating in the discussion. I like the Mesu mount, as I'm a fan of the ASA mount as well. Both mount look like they would eliminate the NEED for autoguiding, but as you have discussed, autoguiding is still necessary because of other factors, no matter how accurate your mount.

On the cost of mount + AO vs high accuracy mount, the high accuracy mounts are still a bit behind on the price equation. Your mount lists for Euro 7495 (about A$11k + tax and shipping), the ASA at Euro 5750 (A$8300 + T&S).

A Losmandy G11 is A$5200, + $1000 for the Ovision worm, which gets you to similar numbers for corrected PE. Add to this the (most expensive) SBIG AO gear (AOL $2k, MOAG $1k, RGH $800) and it comes to A$10k. But the key here is that all of this is new prices G11s come up often as used gear, as your stuff is so new (and the ASA as well), you can't buy secondhand. If you factor in secondhand prices (G11 $4k, Ovision $1k, MOAG $1k, RGH $400, AOL $1k), then it comes to $7400, which is approaching half the price of your mount. That said, if anyone wants to buy all my gear (as listed) for $10k I'll try out one of the ASA mounts and tell you what they're like!

I also realise that your mount can do extraordinary weights, which the G11 cannot, but not many of us have 65kg scopes.

Cheers
Stuart

[Mesu]

Hi Stuart,

Thanks for your post.

Yes you right the ASA DDM60 is a very good telescope mount. It tracks very smooth When you never need more than 25 kg load capacity and the meridian flip is no problem it could be my choice to. The G11 has about the same load capacity and a worm gear.

When comparing the Mesu-Mount with the ASA I like to mention the first points that come in my mind.
The ASA mount without meridian flip is the DDM160 and costs 28800,- ex. VAT euro. has a 40 ampere current consumption.

The Mesu-Mount is a mobile high-end telescope mount without meridian flip and a 130kg tested load capacity for 7495,- inc. VAT euro. On location I use a 12V motorcycle battery for a complete weekend operation.

Best regards,

Lucas Mesu
www.mesu-optics.nl

[Zaps]

Hi Lucas.

First let me say that I think your mount is incredibly innovative and truly stellar, and I hope it (and you) are very successful, because more choices and competition is great for us all.

Now, re the DDM160 from ASA, if I understand things correctly the 40A figure is the absolute maximum draw during very high speed slews only (15-25 degrees per second) and normal tracking consumption is 1-3A with a 300Kg load.

It really seems to be a professional class mount and not the kind of thing you'd find at a star party or in most backyard observatories.

Good luck with the Mesu-mount, it is a classy and exciting piece of hardware that deserves to do well.

[DavidU (Dave)]

Lucas, I must commend you on the Mesu-mount.Coming from an engineering background I enjoyed seeing the way you have solved many problems with imaginative thought.

[netwolf]

Has the price for the Ovision gone up? It was around 500USD when I got it without shipping etc. That coupled with a used G11 is still a good viable option.
However I like the Mesu mount for its outside the box thining and design. In the price bracket it seems to be the cheapest from a Load carying capacity perspective. Also the most awesome thing about it is uses are very own Aussie Argonavis.

Mesu, have you gusy considered using the Sitech Controller on your mount, would there be a option to get the mount wihthout the controller and use the Sitech/Argo instead? I assume you are using servo motors so the switch to an alternate controller should not be so difficult right?
There are some features of the Sitech I like very much especially now that the new one will also support Direct Drives.

Also is the price given with or without the VAT?

Regards
Fahim

[terrynz (Terence)]

This reminds me of the old-school asatrograph mounts that were a byres drive, 2 really big bearings, a 2-3in shaft and a rail for mounting your scope - they tracked very very well.

However its really nice to see such a simple design re-invented with 21st century technology.

Originally Posted by Mesu

Hi Stuart,

Thanks for your post.

Yes you right the ASA DDM60 is a very good telescope mount. It tracks very smooth When you never need more than 25 kg load capacity and the meridian flip is no problem it could be my choice to. The G11 has about the same load capacity and a worm gear.

When comparing the Mesu-Mount with the ASA I like to mention the first points that come in my mind.
The ASA mount without meridian flip is the DDM160 and costs 28800,- ex. VAT euro. has a 40 ampere current consumption.

The Mesu-Mount is a mobile high-end telescope mount without meridian flip and a 130kg tested load capacity for 7495,- inc. VAT euro. On location I use a 12V motorcycle battery for a complete weekend operation.

Best regards,

Lucas Mesu
www.mesu-optics.nl

[Mesu]

Thank you David!

Fahim, the sitech controller is no problem. Mesu-Optics can build that inside the box. The Mesu-Mount prices are given with VAT. We can make an offer for you. In that case please mail to info@mesu-optics.nl.
The Aussie Argonavis is a very good piece of equipment indeed.

Terry, that's interesting. do you have a picture of the mount?

Best regards,

Lucas Mesu
www.mesu-optics.nl