AM5 - Counterweights for heavy scope

spot37a

Question for ZWO folks:

AM5 spec says mount can handle a 20 kg load if counterweight is used.

From a mechanical engineering point of view, what is the maximum weight that can be added to the end of the 9 inch counterweight bar without running a risk of mechanical failure, like tearing the threads out where the bar attaches to the AM5 mount body?

I'm trying to figure out how heavy a counterweight I should use at the end of the little 9-inch counterweight bar, for a relatively heavy scope.

Here's my specific case:

Operating in alt-az mode for visual observing
6-inch refractor in 7-inch diameter tube in Parallax rings, one inch between saddle and tube
scope weight with rings, dovetail bar, diagonal, finder scope, and eyepiece: 40 lb

I'm slightly under the 44 lb specified limit, so I SHOULD be able to use the AM5 without damaging it.
I could add quite a bit of weight to the little counterweight bar, but I don't want to cause failure of the threads that hold the bar to the body of the mount.

I know I don't need perfect balance between the scope and the counterweight, but any imbalance puts a side force on the RA bearing. Also, coming close to balance reduces the risk that the tripod will fall over.

If I put two 11-pound weights out at the end of the 9-inch bar, would I be in danger of breaking the bar threads? Could I go heavier than that?

Thanks!
Jeremy
Glen Head NY

MrAstro

maybe this help..

spot37a

Thank you, MrAstro.

ZWO is saying 5 kg is the maximum weight that should be mounted on the 25cm counterweight bar. Am I understanding that correctly?

For my scope the distance from the center of the mount to the centerline of the scope (as shown at 20cm in drawing) is 23.5 cm.

So at 18 kg total scope weight there is a lot more weight on the scope side.

I assume that would not break the mount.

But in alt-az mode, I am left with a concern that the tripod would be prone to tipping over.

I can put weights in the sling on tripod legs, but I’m still thinking I probably should get a mount upgrade for this big scope, to be on the safe side.

Opinions on that appreciated.

Jeremy

Kevin_A

spot37a a more rigid and beefier tripod is always a good thing.
I use 2 stone bags and a lower counterweight for my tripod and sometimes I use a scope counterweight for the mount. In my upper bag I have transformers, lower bad gets a big round stone and my counterweight on a rod just moves the center of gravity lower.

My heaviest scope is 28 lbs and I dont find I need a counterweight but I have used it.

spot37a

Yes, thanks Kevin_A, adding weight to hold the tripod down may be the way to go, within the capacity of the tripod.

My heavy scope is about 45 inches long, so I need to get it up pretty high for comfortable visual observing high in the sky. The little ZWO carbon fiber tripod is great but not tall enough for this.

So I'm looking at a much taller, beefy tripod, maybe a Berlebach Planet, with a few inches of pier extension on it.

QUESTION TO ZWO -- do you have any clear recommendations for dealing with the big weight imbalance that comes with using AM5 near its payload capacity?

Jeremy
AM5 owner (and several ZWO cameras)