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Mounts, weights and limits!

astrophotography mount tripod
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#1 GalaxyPiper

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Posted 18 January 2020 - 02:49 AM

So tell me..

Are you one of those people that ignore the rated limit on your mount, and thinks that gives you a green light to put the limit of the rated weight on both sides of your mount and think it is ok, as long as it it balanced?

At what point does this have an adverse effect on your mount.

 

My rule of thumb is, scope and gear on one side and weights on the other do not exceed the rating of the mount. 

Some mounts may be robust enough to handle just about anything, except excess enthusiasm of those that think more is better.

Does anyone have an idea, or are some tempting fate?

 

Examples below. (not any of my scopes.)

 

c0243e0e8412cde6f5a5a20a427fecc0.jpg16rc1w.jpgDRI4GAAUIAA2CHk.jpg

 

Top left photo: Astrophotography by Kirk Rodgers: http://www.kiroastro...ent/ap1200.html

Top right photo: The 16" RC Telescope of Keith Quattrocchi, MD, PhD:  http://www.observatory.org/install.htm

Bottom Photo: Huntsman Telescope: https://twitter.com/...untsman?lang=ca


Edited by GalaxyPiper, 18 January 2020 - 11:32 PM.


#2 Ralph Paonessa

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Posted 18 January 2020 - 03:10 AM

My rule of thumb is, scope and gear on one side and weights on the other do not exceed the rating of the mount.

 

My Paramount MYT has a 50 lb. capacity, and Software Bisque says that's the weight of the gear not counting the counterweights. And they state that weight spec if good for imaging (while for my old Atlas the prevailing wisdom was take the 40 lb. capacity and divide it in half for imaging).

 

I haven't tried to exceed the MYT 50 lb. limit. I also don't have a really long refractor that would probably perform worse than a shorter scope of the same weight. (Different moment arms.) (But there is a Youtube video from SB showing it slew a much larger load back and forth repeatedly (but "don't try this at home") just to show how Mighty it is (150 lbs.).

 

I suspect that it would take an awful lot of excess weight to actually damage a mount, and you'd no doubt see it struggling to perform well at weights much below that.

 

P.S. I used to wonder why you couldn't really put a lot of extra load weight on a mount, as long as it's perfectly balanced. But then I realized that the torque it would take to get it to move would still be very high even though it's balanced. So there's no free lunch.

 

Just my thoughts.

 

Ralph


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#3 macdonjh

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Posted 18 January 2020 - 07:23 AM

 

I suspect that it would take an awful lot of excess weight to actually damage a mount, and you'd no doubt see it struggling to perform well at weights much below that.

 

P.S. I used to wonder why you couldn't really put a lot of extra load weight on a mount, as long as it's perfectly balanced. But then I realized that the torque it would take to get it to move would still be very high even though it's balanced. So there's no free lunch.

 

This.  It's not the weight alone that stresses a mount, it's the inertia which accompanies it.  As far as static limits are concerned, a telescope mount and the bearings inside could support hundreds of pounds without damage.  The rub comes when you want all that mass to move, and to move accurately to a new position.

 

For what it's worth, I used a G11 for several years with fifty-five pound scopes (some years portable with a tripod, some years in my observatory on a pier) and it performed well.  I had to be careful with balance as you said, and I lowered the maximum speed the mount was allowed to move to about 1/3 of maximum.  Note the Gemini controllers have a power "ramping" feature, so the servo motors accelerate and decelerate rather than just switching on and off.  I don't know which of the other controllers do that, I don't think SynScan does.


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#4 WadeH237

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Posted 18 January 2020 - 07:39 AM

As long as the loads are balanced, the Astro-Physics and Paramount mounts shown in the pictures are in no mechanical danger whatsoever, so there is no "tempting fate".  The weight rating stated by the manufacturer is the point at which the performance is considered "good enough".  The load bearing capacity of the mechanical parts exceeds that by orders of magnitude.

 

I would say the same thing for most other mounts, too.  Unless a mount has something silly, like plastic gears or way underrated motors, the capacity is stated in terms of "the mount performs to the manufacturer's standard", and not as "mount damage happens".  Note that different manufacturers may have radically different standards of acceptable performance.

 

And in all cases, the load needs to be balanced.  A properly balanced, large mount can carry hundreds of pounds and still be easily moved with one finger with the clutches released.  A significantly unbalanced mount will stress the motors, and in extreme cases could cause the entire thing to topple over.


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#5 TOMDEY

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Posted 18 January 2020 - 07:50 AM

I try to honor several rules, some of which may be logically contradictory >>>

 

>technically/theoretically/pragmatically/prudently... loading to half or less total rated max load would be the safe, prudent approach. True for me and reasonable to recommend to friends and enemies alike, but only if asked.

>if I abuse my mount, eyes open... that's my business, not yours; converse also true. Don't photograph my overloaded mount, and then tell people what a dope I am.

>some of us intentionally overload our mounts, just to get the school-marm types to cringe and self-righteously snicker. It's fun to see beads of sweat erupt on someone else's forehead, when we push the envelope on our own turf. It's a sociological my space / your space dynamic.

>Moment(s) Of Inertia are not problematic, provided you adjust accelerations to throttle torques to half of max recommended ratings on clutches and drive-trains. Some mounts let you get in and program those... some don't. It's up to you to realize and think that through.

>perform multi-axis balancing on all overt and virtual axes. Most avocationals and even professionals are blissfully-unaware of this best-practice. Once achieved (and maintained), you can point to any spot above the horizon, always and everywhere remaining in perfect balance.

>pre-load axes (especially RA) using springs, magnets or similars... so that the bias is not conditional/pointing-dependent. Sliding a counterweight violates that, providing only conditional balance... not good, invitation to premature mount failure. What you need is global balance.

>provide six layers of safety on each drive axis: software, firmware, proximity, slip-clutch, hard-stop, and manual kill-switch.

 

Here's my old Cave mount, bearing 650# without complaint. To my surprise... it handled that offensive burden with dignity and grace. Balanced on all axes and spring loaded/biased at just one foot-pound, each guide axis. Collected several thousand hours guided imagery back in the 1980s with small sub arc-sec finesse. Decent for the era.    Tom

 

~ click on ~ >>>

Attached Thumbnails

  • 06 Tom at Astrola annotated 90.jpg
  • 05 Astrola showing few of the surrgate balancing weights.jpg


#6 junomike

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Posted 18 January 2020 - 09:39 AM

I'm 100% visual so overloading is common and more acceptable. 

Never had an issue aside from an increase in vibrations at higher magnifications.



#7 bogg

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Posted 18 January 2020 - 12:55 PM

i know a lot of the time we concern ourselves with the maximum weight that can be put on a mount.  One question that I have not seen much is what is the minimum weight that a mount will handle without affecting the PE or anything else that could cause a problem.  For most of the mounts in the commercial amateur area under 18kg load I would assume this would not come into the equation.  The mounts I am thinking of are those in the 25kg and up load capacity.  I know it sounds unlikely but would a scope like a 80mm have problems tracking?  Would it be too light to keep the gears properly engaged?



#8 WadeH237

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Posted 18 January 2020 - 03:24 PM

i know a lot of the time we concern ourselves with the maximum weight that can be put on a mount.  One question that I have not seen much is what is the minimum weight that a mount will handle without affecting the PE or anything else that could cause a problem.

I have run my AP1600 with just an 80mm F/6 refractor for imaging.  That is a 100kg payload capacity mount, carrying 3 or 4kg.  I used one counterweight (my smallest), which was offsetting the weight of the mount's own declination assembly more than the actual imaging payload.

 

Performance was just as flawless with near zero load as it is loaded. The caveat that the heaviest payload I've used is probably between 30 and 40kg.  I bought the larger mount because there is a chance that I may run a much bigger scope in a permanent observatory when I retire.

 

On the cheaper end of the scale, I have run my PST on my Celestron AVX with no counterweight at all (and no attempt to balance).  It's a visual only setup, but it's rock solid and tracks all day long with no significant drift.



#9 GalaxyPiper

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Posted 18 January 2020 - 04:00 PM

I guess What I am asking is, how does the manufacture decide on what the rating of the mount means, and how does that relate to the customer.

Do they internally break a mount in testing, then rate it 20% lower to sell to customers?

 

Does it mean that the worm gear drivetrain can handle a max of the rated weight before it breaks?

Does it mean that is the weight total on one side of the arm when unbalance?

 

Yes my question sounded a bit snide, but I wanted someone to correct me with some criteria, because I think it is important info.

Yes, if you want to overload your mount that is your business, but I'm thinking of longevity here, as will as, resale ability when the time comes.

And of course, for Warranty purposes.

 

Nothing lasts forever, but I for one would like it to last as long as possible, and if I am overloading my mount, when to know it, and when I should buy a more robust one.

Just because some one can tell me that they have put a locomotive on one side, and several Lexus automobiles dangling on a bar on the other side, with their moments out about a mile, leaves me to have some introspection.


Edited by GalaxyPiper, 18 January 2020 - 04:29 PM.


#10 macdonjh

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Posted 18 January 2020 - 04:33 PM

I guess What I am asking is, how does the manufacture decide on what the rating of the mount means, and how does that relate to the customer.

Do they internally break a mount in testing, then rate it 20% lower to sell to customers?

 

Does it mean that the worm gear drive train can handle a max of the rated weight before it breaks?

Does it mean that is the weight total on one side of the arm when unbalance?

 

Yes my question sounded a bit snide, but I wanted someone to correct me with some criteria, because I think it is important info.

Yes, if you want to overload your mount that is your business, but I'm thinking of longevity here, as will as, resale ability when the time comes.

And of course, for Warranty purposes.

 

Nothing lasts forever, but I for one would like it to last as long as possible, and if I am overloading my mount, when to know it, and when I should buy a more robust one.

Just because some one can tell me that they have put a locomotive on one side, and several Lexus automobiles dangling on a bar on the other side, with their moments out about a mile, leaves me to have some introspection.

To the concerns at the end of your post: it would be tough to actually break a mount in use- I mean actually separate a part into more than one piece.  Unless you're going to get really ridiculous with the weight of your gear (like loading a C14 onto an EQ-2, perhaps buckling the tripod), it'll be imbalance which damages gearing or burns out a motor not the gross load on your mount.  Basically, if you use it properly, it shouldn't "break".

 

If I were designing a telescope mount I would look at two major criteria: how much torque does it require to move the scope/ gear load and can that be accomplished with a motor which runs smoothly enough not to have a negative effect on observing, and precise movement from one orientation to another.  

 

That torque criterion helps restrain the choices for worm wheel diameter.  An example: my Mountain Instrument MI-250 and G11 both use the same servo motors, but the MI-250 is rated to carry something like 100 lb (never did find a published rating) and Losmandy rates the G11 "classic" for 60 lb.  The worm wheels are much different: 8" (I think) vs. 5-5/8".  Just look at the 11" Beyers gear in TOMDEY's old mount for his Cave...

 

Precision pointing will set boundaries for the precision of the machining required (or sophistication of the controller firmware, or requirement to include encoders) to achieve the desired pointing accuracy.  Sure, tracking accuracy is also important, but I think one follows from the other.

 

Marketing hype also enters into the business.  Sure, a CG-5 type mount will carry an 8" f/6 Newtonian, but I doubt anyone reading this thread would be satisfied with the results.  At some point, you have to buy robust enough gear that using it goes beyond "possible" and becomes "enjoyable".  

 

Since you're asking the questions, I don't think you're the type of person to load-up an AV-X with seventy-five pounds of hardware and complain when the scope shakes while he focuses, or leave your CEM-25 five foot-pounds out of balance and wonder why the RA motor burned up during a slew.  I wouldn't worry about the mechanical durability of your gear too much.  Electronics are another matter...  Moisture and reverse polarity be gone!


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#11 SonnyE

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Posted 18 January 2020 - 05:57 PM

Since I'm an Astrophotographer, I've subscribed to the 50% rating of my mount.

Which has been fine since I do DSO Nebula imaging. My equipment, from the Vixen rail up is 13.2 pounds. (Payload)

On a 30 pound rated mount.

 

My understanding of mount ratings has always been clamp up. So a 30 pound rating means 30 pounds of telescope, rail and all. The balance weight is just that, balance.

And it doesn't take 30 pounds to balance a 30 pound payload. In fact, my past mount came with an 11 pound counterweight. Too heavy! It hit the ELV handle at times. One size does NOT fit all.

I made my own smaller counterweights (about 9 pounds) to balance my equipment.

The actual bearings in most mounts are rated far above the manufactures weight ratings.

 

The only time I've seen blatant ignorance of capacity was a guy in Wyoming who bragged he could get 2 tons of hay on his 3/4 ton pick up. The axles and bearings were rated for 1500 pounds of payload.

So going 2500 pounds over that was asking for breakage.

 

Just stick with the recommended capacity of your chosen mount.

My next one is going to have a 50 pound rating. 50 pounds of photographic equipment. I will never be close to it's rated capacity.

Simple economics, I can't afford enough stuff to overload it. smirk.gif


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#12 SonnyE

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Posted 18 January 2020 - 06:11 PM

DRI4GAAUIAA2CHk.jpg

 

When I see such a ridiculous mess as this, it makes me want to shake my head at the wiring mess of it.

Completely dumb.

Makes me want to grab my tie wraps and spiral wrap and fix it.


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#13 Calypte

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Posted 18 January 2020 - 06:24 PM

When I see such a ridiculous mess as this, it makes me want to shake my head at the wiring mess of it.

Completely dumb.

Makes me want to grab my tie wraps and spiral wrap and fix it.

In my own set-up, I'd be very concerned if the wiring looked like this.  I wonder: what happens when the scope swings to the south?  What happens on a pier flip?  But as long as it works for Mr. GalaxyPiper, who are we to criticize?



#14 WadeH237

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Posted 18 January 2020 - 06:59 PM

I guess What I am asking is, how does the manufacture decide on what the rating of the mount means, and how does that relate to the customer.

Do they internally break a mount in testing, then rate it 20% lower to sell to customers?

 

Does it mean that the worm gear drivetrain can handle a max of the rated weight before it breaks?

Does it mean that is the weight total on one side of the arm when unbalance?

I addressed this directly in my earlier post above.

 

To reiterate, the mount's capacity is based on what the manufacturer thinks will give "good enough" performance.  There is no standard whatsoever on what "good enough" means, so it's very difficult to compare two mounts from different manufacturers, based solely on their specs or marketing materials.  This is where the "50% rule" comes from for imaging (and for what it's worth, I don't buy the 50% rule at all; I think that mount performance involves lots more than just the payload weight).  The best assessment for the real world performance of a mount comes from the community of actual users, like the folks here.

 

Also, the manufacturer's weight rating is not in any way related to how much weight the mount can carry before it breaks.  Assuming proper balance, mounts can carry far more (like 5x or 10x or more) than their weight rating before mechanical failure.  There are two caveats to this.  First off, there are some mounts that have plastic gears.  I would not consider them to be imaging mounts, and I don't know of any current popular mounts that do this.  And second, they must be balanced.  Running a mount that is significantly out of balance can stress the motors, potentially to failure, even if you are running with less than the rated payload.

 

That said, I don't overload any of my mounts beyond the manufacturer claims.

 

Part of this is because my own personal standards are higher than the standards of most manufacturers.  I ran a Celestron CGE with a C14 for visual use for about 15 years.  Celestron thought that the CGE could carry 65lb, but I thought that my 50lb C14 was the very limit that I would accept for visual.  Heck, Celestron sold the C14 paired with a CGEM-DX.  Yikes.  Again, none of these mounts were in any risk of mechanical failure.  It's just that they were less than pleasant to use, because they just weren't solid enough for me.

 

And to make the point about no common standard, I also have a couple of Astro-Physics mounts.  Unlike Celestron, Astro-Physics has standards that exceed my own.  Astro-Physics originally rated the Mach1 for 40lb, but I'd seen them run beautifully with far more (seriously, a Mach1 can handle far more than a CGE, even though the CGE is rated for 25lb more).  And they rated the AP900 at 70lb, which again, according to my standards is really conservative.

 

TL;DR

 

The mount's performance is going to suffer long before it's in mechanical danger.  Use the manufacturer's rating as a guideline, but you are probably going to give up trying to add more weight to the mount due to poor performance long before you break it with too much weight (again, balance, balance, balance).



#15 DiscoDuck

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Posted 18 January 2020 - 07:14 PM

Don't forget that the size of the gear is important as well as its weight.

 

AP have a great chart (under the Specifications tab here  https://astro-physics.com/mach2gto) for the Mach2 capacity showing this dependency.

 

Note: For wider or longer scopes, the actual capacity may be much less than the headline limit.


Edited by DiscoDuck, 19 January 2020 - 12:20 AM.


#16 GalaxyPiper

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Posted 18 January 2020 - 11:36 PM

In my own set-up, I'd be very concerned if the wiring looked like this.  I wonder: what happens when the scope swings to the south?  What happens on a pier flip?  But as long as it works for Mr. GalaxyPiper, who are we to criticize?

Those are not my scopes, I wish they were. I updated my post and it shows now who they belong to. I put them up there to illustrate a point, of which I think with everyone's help I know have a better idea.

Thank you to all that have commented, and will comment on the future about this idea.

 

Bryan.


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#17 MalVeauX

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Posted 19 January 2020 - 07:15 AM

Heya,

 

There's more to the load than just the weight. If you take an inexpensive entry mount and load it up to its maximum capacity, or even a few pounds over, but you're using a stubby SCT, as long as it's balanced, it will handle it pretty much fine even for imaging (solar system imaging; not DSO imaging though) and is commonly used this way, lots of planetary imagers have full capacity loads using SCT's on their entry mounts and are producing the best planets out there. I find the folk with the premium mounts concerned with load vs capacity and imaging really are people focused on DSO as it's significantly different due to the nature of seeing the error in a long exposure, versus high speed short exposure video.

 

A really long, physically long scope will give a mount fits compared to a short fat stubby scope. The moment arm being generated just begs to vibrate, bounce and oscillate and punish the mount's gears, even when balanced. Long refractors and long newtonians for example, especially since to balance, the primary lens/mirror will be significantly heavier than scope so they're off-center but balanced, require more mount quality and rigidity and better guts to do long exposure photographs, than a heavy SCT that's short.

 

A setup with wires hanging everywhere and big OTA tubes also are great at proving that there's wind, even if you don't really think there is.

I do not subscribe to the "50%" conventional wisdom. That's a band-aid for not understanding all the different things going into play other than the actual weight of the instrument load. It again matters what you're imaging, or if you're visual and the distribution of weight and moment arms made by the load, even when balanced, that matters a lot. You can use your mount up to its rated capacity for various things, but not everything. For example, you can get an AstroPhysics mount rated at whatever weight for imaging, and let's put a 6" F20 long focus achromat (non-folded) on there, it won't weigh enough to exceed capacity. But it will be a nightmare to mount and a nightmare to attempt to image DSO with long exposure with.

 

Very best,




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