Jump to content


Photo

Does a pier increase max load?

  • Please log in to reply
15 replies to this topic

#1 Don Marcotte

Don Marcotte

    Sputnik

  • *****
  • Posts: 34
  • Joined: 04 Jun 2007
  • Loc: BC Canada

Posted 16 June 2013 - 11:32 AM

Mounts have payloads numbers that are optimistic to say the least. I am considering a CG-5 which claims a max load of 35lbs but members here say is more like 20-22lbs for astro imaging. My brand new 190 Mak-Newt with camera and PowerMate will be over 25lbs. But I have a pier at my cottage and I wonder if the pier will add stability thereby increasing the effective max load to the 25-27lbs range. Strangely enough I once owned a CG-5 but sold it and used a Kenko Skymemo after experiencing severe Achilles tendonitis in both feet. I never tested the load limits.

#2 Wouter D'hoye

Wouter D'hoye

    Surveyor 1

  • *****
  • Posts: 1519
  • Joined: 27 Jun 2003
  • Loc: Belgium

Posted 16 June 2013 - 11:38 AM

Hi,

A pier hardly contributes to the load capacity of a setup. There might be a slight improvement in regards of dampening time if the tripod was of inferior quality.

Kind regards,

Wouter.

#3 Raginar

Raginar

    Fly Me to the Moon

  • *****
  • Posts: 6138
  • Joined: 19 Oct 2010
  • Loc: Rapid CIty, SD

Posted 16 June 2013 - 02:25 PM

Max load is max load. I imagine it's built into how they make the gears and the entire 'train'. However, a pier will significantly improve your ability to polar align (permanent) and improve dampening like Wouter said.

It's not a fix for your CG-5. The biggest problem you're going to have with that Mak-Newt is it's moment arm and it's focal length. If you're imaging planets... sure. But, you're not going to have the mechanicals in your CG-5 to guide a 35# payload on a mount that can carry that weight for visual only.

You'll find most people say you should buy the best mount you can afford and then worry about the scopes... A mount can be forever if you buy the right one.

#4 microstar

microstar

    Apollo

  • -----
  • Posts: 1223
  • Joined: 05 Jan 2008
  • Loc: Canada

Posted 16 June 2013 - 02:35 PM

I'll put in a dissenting voice here. I think a solid pier does increase the payload potential of your mount when it comes to imaging. I base that upon using a LXD75 mount first on a tripod and then on a solid steel pier bolted to a concrete foundation. Even though my imaging payload was higher than recommended for this mount, I was definitely able to get better images with the pier than I ever did with the tripod. I think a solid base does give better support for a modest mount and allows you to push your imaging payload to higher than the usual 50% of visual payload. Won't turn a modest mount into an AP or Paramount of course, but it helps.

...Keith

#5 Don Marcotte

Don Marcotte

    Sputnik

  • *****
  • Posts: 34
  • Joined: 04 Jun 2007
  • Loc: BC Canada

Posted 16 June 2013 - 04:20 PM

Thanks guys. I am unsure whether a mount claiming 35 lbs can really do that. As I understand it, it is a theoretical number. A MN definitely will create added stresses compared to my C8HD. I can afford a CG5 but not a CGEM right now. I will have to decide how much risk I am willing to take.

#6 EFT

EFT

    Vendor - Deep Space Products

  • *****
  • Vendors
  • Posts: 2544
  • Joined: 07 May 2007
  • Loc: Phoenix, AZ

Posted 16 June 2013 - 05:03 PM

A pier may increase stability which may increase the practical load of a mount, but it cannot increase the rated maximum load of a mount if you consider the maximum rated load to be anything other than a simple guess. The practical capacity of a mount (that is the load that the mount can reasonably handle for a particular purpose with particular equipment) may be increased for many mass-produced mounts, but you should consider the maximum rated load of a mount the maximum above which bad things may (or may not) happen. You have to assume that something went into the decision of what the maximum load should be.

#7 Stew57

Stew57

    Mercury-Atlas

  • *****
  • Posts: 2526
  • Joined: 03 May 2009
  • Loc: Silsbee Texas

Posted 16 June 2013 - 05:25 PM

Abetter tripod/pier must make some difference is certain situations. The motors/gears/bearings/castings are all the same between the CGEM and DX. The capacity is different. The only changes related to capacity would be the tripod and controller chip allows more current draw for imbalance situations with a heavy load.

#8 Cliff Hipsher

Cliff Hipsher

    Apollo

  • ***--
  • Posts: 1147
  • Joined: 31 Dec 2008
  • Loc: North Chesterfield, VA

Posted 16 June 2013 - 05:40 PM

The short answer is no. The long answer involves measuring things like motor stall currents, torque loads, maximum gear tooth loads, gear mesh tolerances, clutch friction coefficients, and so on. Then you get to do a whole bunch of math, and the answer is still no.

If you want to carry a bigger load you have 2 choices:

1. Buy a "bigger" mount.
2. Upgrade your current mount with "better" drive components.

#9 Cliff Hipsher

Cliff Hipsher

    Apollo

  • ***--
  • Posts: 1147
  • Joined: 31 Dec 2008
  • Loc: North Chesterfield, VA

Posted 16 June 2013 - 08:09 PM

Have you done a complete tear down and side-by-side comparison of both machines and personally verified your statements?

#10 Stew57

Stew57

    Mercury-Atlas

  • *****
  • Posts: 2526
  • Joined: 03 May 2009
  • Loc: Silsbee Texas

Posted 16 June 2013 - 09:05 PM

I did talk one of the celestron engineers. I have also talked to others that tear both down for a business. The internals are the same save for the controller chip in the motor control board. The External differences are obvious such as the tripod and counter weight shaft. Email Celestron. They will be very upfront and the service may pass you on to an engineer if they feel it is warranted. I had a CGEM that had problems and went through 3 to a serviceable mount. I did get passed to an engineer trying to diagnose problems.

#11 EFT

EFT

    Vendor - Deep Space Products

  • *****
  • Vendors
  • Posts: 2544
  • Joined: 07 May 2007
  • Loc: Phoenix, AZ

Posted 16 June 2013 - 11:20 PM

Abetter tripod/pier must make some difference is certain situations. The motors/gears/bearings/castings are all the same between the CGEM and DX. The capacity is different. The only changes related to capacity would be the tripod and controller chip allows more current draw for imbalance situations with a heavy load.


The CGEM DX only gains you 10 lbs in capacity, but there are some solid reasons for that gain. In addition, it does have a higher practical capacity out of the box than the standard CGEM. Both mounts very well balanced and tuned could reasonably handle about the same amount of weight. However, the heavier tripod of the DX will give it greater stability. More important, the heavier counterweight bar of the DX makes it possible to add more counterweight on the mount than the standard CGEM and this does matter. The electronics are different and the DX electronics do seem to run the mount smoother, but except for the initial start of a slew, supplying more power to the same motors in a well balanced and tuned system really should matter very little.

I like my C11 on my DX a lot more than on my standard CGEM, but I would not particularly like a C14 on either. It is a matter of practical payload vs. rated payload. I would say that in general the DX has a greater practical capacity (and thus a greater imaging load capacity) than the standard CGEM, but the maximum capacity of both mounts is still only 10 lbs different and that makes sense.

#12 TxStars

TxStars

    Apollo

  • *****
  • Posts: 1328
  • Joined: 01 Oct 2005
  • Loc: Lost In Space

Posted 17 June 2013 - 12:03 AM

No it will not increase the max load a mount can hold.
1) A well designed pier will provide a stable platform for your mount.
2) It will give you a large clear movement arc for your scope.

#13 Midnight Dan

Midnight Dan

    Voyager 1

  • *****
  • Posts: 11209
  • Joined: 23 Jan 2008
  • Loc: Hilton, NY, Yellow Zone (Bortle 4.5)

Posted 17 June 2013 - 06:36 AM

First let me say that I'm no expert on mounts. But I am an engineer and find it interesting to evaluate and compare these things. Seems to me that the mount's maximum capacity can be limited by 3 things:

1) Breaking capacity - the point at which too much weight will cause a structural failure
2) Dynamic capacity - the load that the bearings and moving parts were designed to handle without damage.
3) Stable capacity- how much load the mount can handle and still maintain a stable view for long exposure AP.

In most cases, I think you'll never get near the breaking capacity of the mount which is likely to be MUCH higher than the rated load. The dynamic capacity is probably of more concern, but still likely to be somewhat higher than the rated capacity to allow some margin of safety.

The stable capacity is the one we're most concerned with, and will often be considerably LESS than the rated capacity, depending on things like focal length and the length of the scope's moment arm. It will also be dependent on the individual astrophotographer and how fanatical he or she is about getting perfectly round stars.

In view of how many threads there are regarding people moving to heavier tripods or to piers, it's clear that the stable capacity of mounts increase by going to a more solid underpinning. Since the stable capacity is nearly always the limiting factor in AP, my opinion is that yes, a pier will increase the maximum load that you can use on a mount and still get acceptable photographs.

If you're talking about breaking or dynamic capacity, then no, a pier will not increase the maximum load capacity.

-Dan

#14 Raginar

Raginar

    Fly Me to the Moon

  • *****
  • Posts: 6138
  • Joined: 19 Oct 2010
  • Loc: Rapid CIty, SD

Posted 17 June 2013 - 09:54 AM

Misty,

One option is to design your setup around something that can fit on a CG5. They're cheap, but they're strong performers when you manage their weight and take low focal length exposures. Perhaps a smaller scope like an ED80 would be an excellent starting scope for AP? You add a mini-guider setup and you'd be in business!

But, I would say you'd be unhappy with a mak-newt on a CG-5.

#15 Madratter

Madratter

    Fly Me to the Moon

  • *****
  • Posts: 6206
  • Joined: 14 Jan 2013

Posted 17 June 2013 - 10:05 AM

I managed to image with a CG-5 and a C8 with an f/6.3 focal reducer. BUT the declination axis on the CG-5 is simply horrible at that focal length and amount of weight. The only way to get it to work was to get the polar alignment very good (within about 1' of perfect). I have since replaced it with an Atlas and am MUCH happier with the performance.

I am certain that a pier would have done nothing for the declination axis problems whatsoever. BUT it would do a considerable amount for getting a good polar alignment and keeping it there.

That said, do yourself a favor and avoid the CG-5 for this application. You will be in for considerable frustration. It just is not designed for that amount of weight/focal length doing AP.

#16 David Pavlich

David Pavlich

    Transmographied

  • *****
  • Administrators
  • Posts: 27311
  • Joined: 18 May 2005
  • Loc: Mandeville, LA USA

Posted 17 June 2013 - 12:36 PM

First let me say that I'm no expert on mounts. But I am an engineer and find it interesting to evaluate and compare these things. Seems to me that the mount's maximum capacity can be limited by 3 things:

1) Breaking capacity - the point at which too much weight will cause a structural failure
2) Dynamic capacity - the load that the bearings and moving parts were designed to handle without damage.
3) Stable capacity- how much load the mount can handle and still maintain a stable view for long exposure AP.

In most cases, I think you'll never get near the breaking capacity of the mount which is likely to be MUCH higher than the rated load. The dynamic capacity is probably of more concern, but still likely to be somewhat higher than the rated capacity to allow some margin of safety.

The stable capacity is the one we're most concerned with, and will often be considerably LESS than the rated capacity, depending on things like focal length and the length of the scope's moment arm. It will also be dependent on the individual astrophotographer and how fanatical he or she is about getting perfectly round stars.

In view of how many threads there are regarding people moving to heavier tripods or to piers, it's clear that the stable capacity of mounts increase by going to a more solid underpinning. Since the stable capacity is nearly always the limiting factor in AP, my opinion is that yes, a pier will increase the maximum load that you can use on a mount and still get acceptable photographs.

If you're talking about breaking or dynamic capacity, then no, a pier will not increase the maximum load capacity.

-Dan


Thanks, Dan! Load capacity is what it is. Components used by the manufacturer have specified "breaking/failure points". Sticking it on a pier doesn't change that part of the equation. HOWEVER, a properly constructed pier will be more stable than a tripod. With that, as one approaches the maximum imaging loading or visual loading, the chances of unwanted vibration is less allowing the higher weight to be handled without concern that your views will be shaky or your images will have bad stars.

Besides, a mount always looks terrific on a pier. :grin:

David






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics