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Pushing the Limit

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#1 atnbirdie


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Posted 03 March 2016 - 12:42 PM

I have a question about mount payloads for your consideration.  Manufacturers (in my case Celestron as I have its AVX mount rated at 30 pounds payload) advertise payload capacities.  I've read some opine in forums that the payload 'limit' is not a limit that will lead to breakdown, but more of an operational stability limit.  In other words, if you load your mount over its marked payload limit, you won't have as stable a system, but you won't necessarily damage your mount either.  Of course if you way overload (e.g., say 2-3 times the limit) then you'll likely do some damage. 


However, let's say I will only be doing visual observing.  Could I load my AVX mount with a 35 pounds scope (assuming proper balancing) and not worry that I'm 5 pounds over the posted limit?  I understand it won't be as steady as if I were 5-10 ponds under the limit, but if I'm careful to always balance the load well, should I expect the mount to fail significantly sooner or not?


I've read in some forums (e.g., related to NexStar 8SE mounts) that although Celestron rates the mount at just 12 lbs payload, there are folks who have consistently loaded it to nearly 20 well-balanced pounds and run it that way for up to 10 years without a repair.  Thus, I wonder if for visual work I could run a roughly 35 pound load on my AVX (rated for 30) without worry of the mount failing any time soon?  Yes, I'll have longer settling down times after an adjustment, but will the mount fail significantly sooner?


I'll be interested to hear folks' thoughts, particularly those with some actual experience of overloading a mount (any mount).  I've no doubt I'll get a lot of theoretical answers too ;-)   Just keep in mind that this is about visual astronomy NOT astrophotography which I know brings in a whole other list of considerations.

#2 blueman


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Posted 03 March 2016 - 01:06 PM

If you have balanced the scope and counter weights, then 5 lbs for visual should be no real problem. When the mount is balanced it does not cause the motors to over work or heat up, but off balanced and they might. So balance it well and if you don't see a problem at the eyepiece you should be fine. ;)


#3 Stelios



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Posted 03 March 2016 - 01:26 PM

I assume you mean loading a compact telescope, such as a C11 or a Mak.


In this case, you should be just fine *as long as 35lbs includes total weight of scope and accessories*. People use fairly commonly C11's on AVX mounts for visual. A C11 with 2" diagonal and large EP is about 30-31lbs, so not far from what you want to do. As Blueman said, balance carefully. Also be prepared for long damping times.


If, however, you want to load a 35lb 1200mm refractor and up, you will hate your life. 

#4 junomike



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Posted 03 March 2016 - 02:28 PM

Also, be aware that you will need wither another counter-weight or a CW shaft extension as the OEM CW's won't be enough to properly balance an OTA larger than recommended.

I've done both (added another CW or extension) and have no preference for one over the other, although the extension is lighter to carry.



#5 Chuckwagon


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Posted 03 March 2016 - 03:11 PM

The AVX dec bearing might be a tad more problematic than it normally is in an over the "limit" load situation.  But since this is visual use, you probably won't notice.  Also, be sure to lower your max slew rate.  Being over the "limit" by 5 lbs isn't likely to cause appreciable additional wear, but moving all that mass, starting, stopping, etc., will be best if not at max speeds.



#6 atnbirdie


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Posted 03 March 2016 - 08:22 PM

I'll definitely be careful to balance properly.  The VX already has a longer counterweight shaft than its predecessor the CG-5 had.  I've also ordered a second counterweight - a 17 pounder - so I'll have no problem balancing it.  I'll also consider the advice about using a less than max slew rate.


Stelios: Actually, the beast OTA I am evaluating to buy is an 1800mm 6" refractor.  The twist is, it's a folded refractor.  Apparently a one-of-a-kind made by Astro-Physics in the late 80's .  It's only 24" long and 11" wide.  I've only looked through it a few times so far, but it seems very nice and sharp.  So I won't have to recline on the ground to observe at zenith.  LOL

#7 Hobby Astronomer

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Posted 04 March 2016 - 07:31 PM

The big variable is the current wind speed. The more the wind is blowing, the lower the capacity.



#8 atnbirdie


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Posted 04 March 2016 - 09:27 PM

I had posed my question to Celestron Tech Support and just got an answer that confirms the performance limit idea.  Here it is:


"The payload capacity is 30lb. This is a performance limit. You can add more weight, but the more weight you add on the more stress is being placed on the gears and they will wear out faster than they normally would under better conditions. The greater the payload capacity the more it is able to move comfortably. If you aren't going to be using it for astrophotography then you might be able to get away with it for a while. I just wouldn't use it too much in that configuration. I hope this helps."


As we've discussed, if I end up keeping this beast of an OTA, I'll be very mindful of the balance.

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