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NigeB

Mesu Owners: Opinion - am I overloading?

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Hello All,

Due to a bit of luck and a very understanding wife, I've acquired a used Celestron Edge 14 OTA. It has currently deposed my TOA-150 from the mount.

I'm aware that the maximum payload for the Mesu 200 is 100 kg (visual use); apparently it's rated for 75 kg (imaging) according to this article - though that seems very optimistic:

http://www.modernastronomy.com/images/products/Sky_firstlightmesu.pdf

I'd really like to put the two 'scopes on the mount side by side (I've run the TOA-150 and a C11 together and imaged without any issues). I've weighed the various parts. Rounding up to the nearest kg, the numbers are:

-14" OTA + dovetail rail: 25kg
-TOA-150 with rear counterweight: 20 kg
-Casady tandem bar plus Tak rings: 10 kg.

Total 55 kg. With camera etc onboard, it's going to be nearer 60 - 65 kg.

If the payload capacity numbers above are to be believed, this is well within spec, even for imaging. However, I suffer from a fairly significant case of mechanical sympathy, and I'm really nervous about putting such a big lump of 'scope on the mount. By size alone, the C14 seems to dwarf it. 

What do people think - too much, or go for it?

Thanks

Nigel

Edited by NigeB

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I think it'll work. We once put more than that on our Mesu - a 14 inch Dall Kirkham and a 10 inch Russian photomak plus Cassady T-GAD alignment system and two CCDs/filterwheels. The idea was to try it as a dual rig. The idea didn't work but the mount did its job. (The 14 inch was working at 0.66"PP and carried an autoguider. The additional scope and hardware didn't affect the guide trace but the slave scope always trailed slightly due, no doubt, to mirror movement in one or both scopes.)

What will be the pixel scale when using the C14 for deep sky imaging? To make it effective you're going to need some big pixels, I suspect! You could bin, of course. A guy on the French forum used to get great results from a C14 with CCD, though I can't remember which one. He did everything in bin 2 including luminance.

I always think payload gets too much press and accuracy not enough. If the scope is well balanced the extra mass doesn't have a huge effect. If you're concerned about it you might try to establish all the points of balance of the assembled payload before loading the mount. You can do this on a flat floor using a metal bar as a pivot, or you could borrow a conventional clutched mount, load it with your rig and mark up the dynamic balance points before transferring to the Mesu.

Olly

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Can only echo the previous posts, get the balance spot on and it should be fine.

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Hi Olly, Kirkster, Tomato,

Many thanks for your replies - and my apologies for the delayed acknowledgement. I've not been visiting the forum much of late (other things competing for time!) and oddly, when I did check in to SGL over the past couple of weeks I didn't see the usual red notification spot to say someone had posted. Anyway, I appreciate your responses.

So: I managed to get the 14" and the 6" mounted together, with the help of my other half. The simple mechanical axis locks on the mount made that a little easier, and I loaded the counterweights step-wise to reduce any strain during the process.

The good news is that I managed to get everything nicely balanced. Powered down, the telescopes could be put in any position with little more than finger-tip pressure, and they would hold that position. Powered-up, the mount seemed to slew around the sky happily - no visible or audible signs of strain or slippage.

The bad news is that the setup just didn't seem to have the stiffness required for such an arrangement. I can co-mount the TOA150 and a C11 without any significant issues. But the Edge14 is another ~12 kg. There was a very noticeable wobble  when tapping an OTA, or adjusting focus - large enough amplitude to see without any difficulty (I mean just by looking at the tubes - not through them!) at a frequency of ~2-3 Hz (from memory). It's not in the dual mounting plate - that's a Cassady item and it's extremely stiff. Much of the movement seemed to originate around the RA axis assembly, in the plane containing the polar axis and the Dec / counterweight axis (i.e. perpendicular to the rotation plane). In fact I'm pretty sure I could see the circular metal plate of the RA axis moving with respect to the mount housing. I didn't even try imaging - it seemed pretty hopeless, so I de-mounted and went back to a single OTA - all fine again!

So right now I'm in a bit of a quandary - the Mesu is great for one or the other OTA, but it seems not both together, and I don't really want to be swapping out these 'scopes more than necessary because they're both hefty lumps. I'm considering whether to take the plunge and change to something like a Paramount ME-II or a 10Micron GM3000.:sad2:

Olly, the 14" was something of an impulse - I've always wanted to try one, and a good used one came up at a reasonable price - but I have a feeling that I may not be keeping it long term. I got it mainly for imaging planets and small deep sky targets. It's not a good match for my 460ex CCD - the plate scale at f/11 is approx 0.24"/pixel - so yes, binning is definitely needed! Had I told my long suffering wife that I'd need to buy another camera along with the 'scope, I suspect I'd have been told to get my coat. And here we are now, contemplating another mount...

Thanks


Nigel

 

 

Edited by NigeB

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7 minutes ago, NigeB said:

Hi Olly, Kirkster, Tomato,

Many thanks for your replies - and my apologies for the delayed acknowledgement. I've not been visiting the forum much of late (other things competing for time!) and oddly, when I did check in to SGL over the past couple of weeks I didn't see the usual red notification spot to say someone had posted. Anyway, I appreciate your responses.

So: I managed to get the 14" and the 6" mounted together, with the help of my other half. The simple mechanical axis locks on the mount made that a little easier, and I loaded the counterweights step-wise to reduce any strain during the process.

The good news is that I managed to get everything nicely balanced. Powered down, the telescopes could be put in any position with little more than finger-tip pressure, and they would hold that position. Powered-up, the mount seemed to slew around the sky happily - no visible or audible signs of strain or slippage.

The bad news is that the setup just didn't seem to have the stiffness required for such an arrangement. There was a very noticeable wobble  when tapping an OTA, or adjusting focus - large enough amplitude to see without any difficulty (I mean just by looking at the tubes - not through them!) at a frequency of ~2-3 Hz (from memory). Much of it seemed to originate around the RA axis assembly, in the plane containing the polar axis and the Dec / counterweight axis (i.e. perpendicular to the rotation plane). In fact I'm pretty sure I could see the circular metal plate of the RA axis moving with respect to the mount housing. I didn't even try imaging - it seemed pretty hopeless, so I de-mounted and went back to a single OTA - all fine again!

So right now I'm in a bit of a quandary - the Mesu is great for one or the other OTA, but it seems not both together, and I don't really want to be swapping out these 'scopes more than necessary because they're both hefty lumps. I'm considering whether to take the plunge and change to something like a Paramount ME-II or a 10Micron GM3000.:sad2:

Olly, the 14" was something of an impulse - I've always wanted to try one, and a good used one came up at a reasonable price - but I have a feeling that I may not be keeping it long term. I got it mainly for imaging planets and small deep sky targets. It's not a good match for my 460ex CCD - the plate scale at f/11 is approx 0.24"/pixel - so yes, binning is definitely needed! Had I told my long suffering wife that I'd need to buy another camera along with the 'scope, I suspect I'd have been told to get my coat. And here we are now, contemplating another mount...

Thanks


Nigel

 

 

I'll PM you but I think it might have been worth a try imaging, all the same.

Olly

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Interesting read. I’m looking into putting a larger scope on my Mesu, so following this topic closely. Currently my Mesu is comfortly holding my 10” Quattro tight, but I plan to upgrade to a Hubble Optics HNA 16” or preferably 18”.

The weight is 35 kg for the 16” and 45 kg for the 18” plus focuser and camera equipment, so could end around 50 kg fully loaded if aiming for the 18”.

Your observation of possible flex with a load of 60 kg worries me, as I wouldn’t expect the mount to show visible flex. Could possible flex originate from the RA bearings? When you describe the movement/flex visible at the circular RA plate I assume you refer to the round black plate on top of the RA axis...the one where the mechanical lock can grab the RA axis?

 

Edited by Wieben

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Hi Wieben,

Yes, that's the plate I mean.

The slew behaviour looked and sounded normal to me even with this heavy load. Given that this is a friction-driven mount, I'd have thought that significant flex in the bearing would change the loads transmitted to the motor, which should give itself away in the slew behaviour. So I don't think that's the issue. I don't want to jump to any conclusions: the flexure could be coming from somewhere else. 

Given Olly's last post, I'm tempted to give it another go, when I can persuade my other half to help me load everything up again - this time I'll try an imaging run and look more closely at the flexure issue (I have to admit that I unloaded pretty quickly when I saw this the first time round). I'll let you know what the outcome is.

Nigel

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I have about 35kg of imaging scopes, cameras, PC, guiders, etc with the required counterweights (so 70kg) in total, in a side by side arranagement like you want, and it works perfectly on my MESU. Brilliantly. Have you tried to get the balance in all possible orientations before night time?

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Also, I am going to add my C925 to this permanent setup as well. 

The MESU is the best piece of Astro gear I have ever bought.

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2 hours ago, kirkster501 said:

 

The MESU is the best piece of Astro gear I have ever bought.

I'm inclined to agree - but, like you, I have a rival claimant in the form of a TEC140!

Olly

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I'd love to see a picture of that setup with the 14 Edge OTA mounted ! I was looking on Celestrons site yesterday for their 14" SCTs' and they never showed up . I don't think Celestron makes them that big any more to public use do they ? 

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1 hour ago, celestron8g8 said:

I'd love to see a picture of that setup with the 14 Edge OTA mounted ! I was looking on Celestrons site yesterday for their 14" SCTs' and they never showed up . I don't think Celestron makes them that big any more to public use do they ? 

It's still listed on FLO's website. I think there would be an outcry if this classic scope disappeared.

Olly

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9 hours ago, kirkster501 said:

I have about 35kg of imaging scopes, cameras, PC, guiders, etc with the required counterweights (so 70kg) in total, in a side by side arranagement like you want, and it works perfectly on my MESU. Brilliantly. Have you tried to get the balance in all possible orientations before night time?

No, your setup is around half the weight of the configuration I'm describing above. In fact, what you're describing is similar to mine pre- 14": with my TOA150 (~20 kg) plus Losmandy plate, rings, and a Wave 80 piggybacked on top, the instrument weight was around ~32 kg - then the counterweights are added on top of that, giving a total weight (instrument + counterweight) of ~70 kg. In this configuration I also get a very stable setup.

BUT... with the 14", plus Casady plate, and the TOA150, my instrument weight alone is around 60 kg. That's before counterweights. So I've got approximately twice the weight of your setup, and twice the weight of my pre-14" arrangement. But mount payload capacities refer to the instrument weight, before counterweights are added, and in that case I'm still well within the 75 kg imaging payload limit which is quoted for the mount.

Yes, the balancing was pretty much spot-on. No matter which orientation I placed the telescopes in, with power off, there was no movement when I let go - tested across the full range of RA and Dec travel.

 

Edited by NigeB

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4 hours ago, celestron8g8 said:

I'd love to see a picture of that setup with the 14 Edge OTA mounted ! I was looking on Celestrons site yesterday for their 14" SCTs' and they never showed up . I don't think Celestron makes them that big any more to public use do they ? 

I'll try to oblige... Based on Olly's reply, I'm going to give it another go to see what the imaging performance is like. I'll take a few photos of the setup.

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Very exciting indeed.

Fingers crossed, and hope to se the usual great Mesu performance.

Br. Heine

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This sounds very interesting.

I'm looking forward to the results.

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Hello All,

Well, I've put my two OTA's back on the mount for another go. So by request: here are some photos of a Mesu-200 carrying a TOA150 and an Edge14, with a very substantial Casady tandem bar keeping them in place. There's at least 60 kg on the top, and a corresponding quantity of counterweights at the other end. I've taken off the 70 mm finderscope from the Tak, and also the 80 mm Wave which usually sits on top. I may remove the rear counterweights from the Tak to reduce some weight and put the Wave back for solar and very wide field imaging, but first I'm going to try imaging as-is and see how that works out. Of course after a clear day, the clouds have rolled in here. I'll post some imaging results when I manage to get some.

I've looked again at the flexure, and need to correct myself: its not flex within the RA assembly as I thought originally. One of the movies below shows what happens when I tap the 14" tube lightly but repeatedly - a pretty extreme example I know, but it shows the mode of oscillation I'm talking about, which is visible to a smaller extent with a single tap (but harder to see on camera). The whole RA assembly is moving. I've not figured out whether it's flexure within the mount, or movement of the whole mount, i.e. some rocking of the base plate.

Photos and movies below.

Cheers

Nigel

 

 

IMG_4727.thumb.JPG.319e9ccdbac08c3552a20ec7199787e8.JPGIMG_4734.thumb.JPG.6ed60f313053d315390d5b5e3c3701a5.JPG

IMG_4732.JPG

IMG_4735.JPG

IMG_4739.JPG

MVI_4742
MVI_4737s

 

 

Edited by NigeB
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The clouds parted briefly last night and I was able to test out the new arrangement, albeit briefly. Below are a couple of very quick and dirty single 10 minute subs of NGC4631 (very dirty actually - just as they came out of the camera, no flats/darks, just a histogram stretch). These were taken with the 6" at f/7, through the luminance filter.

Overall it's looking encouraging, but in both cases, mid-way through the integration the PHD2 trace showed a large jump, simultaneously in RA and Dec (~50 pixel displacements registered in each axis). In both images the effects can be seen as a pattern of 3 or 4 displaced points next to every bright star - at around the 2 o'clock and 3 o'clock positions. The pattern of displacements is very similar, but not identical, in each image. Unfortunately the clouds rolled in after these were taken so I wasn't able to do any more.

This isn't the same issue as the RA jumps people were reporting last year - they were rectified with a Sitech software/firmware update which has already been applied to the system. This also doesn't look like a flexure issue, which is the main thing I was concerned about when contemplating the dual telescope mounting. I've a few things to check - there are some dangling cables which might be getting caught, and I'm going to tweak the balance. I'll do a long run and see whether the jumps come at regular intervals.

There's also a big heavy floppy mirror on the mount now, and any movement in that assembly could be transmitted to the mount (the object had not long transited the meridian at this point). If I hit the same issue next time after making these changes, I'll de-mount the 14" and try again.

N.

 

NGC4631_L_600_1.jpg

NGC4631_L_600_2.jpg

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That’s a spectacular rig. Myself and Tomatobro are in the early stages of mounting an Esprit 150 and Altair 102 on a Mesu, so if you can make your set up work we should be in business. 

Tried for first light on the Esprit last night but the clouds (plus a host of initial set up issues) beat us.

262160F0-E950-41FF-A17B-CE5A79F73794.png

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8 hours ago, celestron8g8 said:

Wow your setup is awesome !! Thanks for sharing the pictures and videos ! 

Thank you Ron! Hopefully I'll solve this jump issue and then it will live up to that compliment.

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3 hours ago, tomato said:

That’s a spectacular rig. Myself and Tomatobro are in the early stages of mounting an Esprit 150 and Altair 102 on a Mesu, so if you can make your set up work we should be in business. 

Tried for first light on the Esprit last night but the clouds (plus a host of initial set up issues) beat us.

Hi Tomato,

Thanks! At the moment I think it looks better than it performs but I'm hopeful the jumping will be solved with a decent clear night to do some testing and adjusting. Unfortunately as you're also finding, the clouds have just rolled in again...

I'm absolutely certain you'll get your Esprit and Altair working nicely together on the Mesu. That 150 looks like a beast in your photo. Before the 14" arrived I had the TOA150 co-mounted with a C11. Looking at the specs, I think the TOA is perhaps 4-5 kg heavier than your Esprit once you include the Tak's cell counterweights (about the same without). And the C11 OTA is 12 kg, compared to something like 5 kg for your Altair, before you add rings etc. So the TOA+C11 assembly is a little heavier than the one you're putting together, and I had no problems at all with that combination on the mount.

I will say however, that it took me three attempts before I found a side-by-side mounting plate that I was happy with. Going from a single to a dual scope configuration inevitably changes the mechanical characteristics of the rig, and I noticed a significant increase in damping times for both OTA's when they were mounted together rather than individually, which I found difficult to tolerate. I traced the problem to the side-by-side mounting hardware rather than anything to do with the mount itself. After trying a dual mounting solution from TS and then Altair, neither of which I was happy with, I happened upon a used Casady plate (which contains about 50% of China's annual steel output). The damping times went down after that!

It's obvious but I'll mention it anyway: the dual mounting configuration pushes both 'scopes further out from the centreline of the mount, and that can lead to clashes with the tripod/pier before you reach the slew limits which are achievable with a single 'scope or a piggyback arrangement.  Just be aware when you first try it out, and get ready to stop the slew.

Good luck with the mounting work!

Nigel

 

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The mounting of the C11 without tube rings makes me a bit nervous. You're dependent on the integrity of its tube.

Unfortunately the shifts could be due to almost anything but drive slippage can't be ruled out. It's good to see your scopes close together because that reduces one of the moments. I think I'm right in saying, also, that heavier counterweights closer to the fulcrum have a lower moment of inertia than lighter ones further out when both give the same balance factor. Years ago one member posted the equations.

Gorgeous setup, as aready noted!

Olly

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