Where to position Lightbridge counterweights ?

[John]

In order to make my Lightbridge 12 inch a little less nose heavy, especially with a big 2" eyepiece in the drawtube, I've been looking at ways to add some counterweighting to the bottom end of the tube.

Not being great at DIY and not wishing to "bodge" something I've picked up a Meade Tube Weight system that is normally indended for use on their 10 inch SCT.

This is a low profile rail system with 3 slide & lock counter weights of 1, 2 and 3lbs in weight respectively. My cunning plan is to fit the rail to the lower tube assembly (LTA) and add / position the weights to achieve decent balance and to save the rather puny altitude brake that the LB comes fitted with from having to work so hard.

My initial thoughts would be to position the rail / weights on the outward facing side of the LTA in line with the finder position. I have been wondering though if the weights might be more effective if positioned elsewhere on the tube (eg: the underside / inward facing part or directly on the opposite side of the OTA that the focusser is on). I've seen some complex articles and diagrams showing how forces such as moment arm work in a dob mount but I've not been able to deduce from those whether or not it matters where on the LTA I mount the rail and weights, other than below the centre of gravity of course.

Has anyone any views on this before I start drilling holes ?.

Thanks,

John

[Doc]

John I'm looking at my LB now and I don't think there is enough room to fit it on the underside of the LTA.

As once it's put upright the weights will hit the cross board that joins the two two sides togethder.

[John]

John I'm looking at my LB now and I don't think there is enough room to fit it on the underside of the LTA.

As once it's put upright the weights will hit the cross board that joins the two two sides togethder.

Yes, I think if it went directly under the tube it would stop the scope pointing towards the zenith so that's out. Since posting my query I've been experimenting with some kitchen scale weights in a soft bag and it did not seem to make any difference if the weight was positioned on top of or underneath the tube.

I think what I'll do is to use some strong double sided sticky pads to fix the rail to start with so if it needs to be re-located I won't have drilled the tube unecessarily.

Thanks for having a think about it was well though

John

[John]

Well the weights and rail have arrived and I've fitted them to the lower tube assembly using double sided sticky pads in case I decide to move it. The photo attached shows the 1 lb and 3 lb weights in place but in practice I'll only need that much when I'm using the 31mm or 22mm Naglers. For normal use I reckon just the 1 lb weight will provide a nice balance.

I'm rather pleased with this arrangement

John

[Helen]

That looks good John! still looking for a solution for the 8 inch LB, preferably one which is easily attached so that it doesn't add to the carrying weight of the scope.

Helen

[John]

That looks good John! still looking for a solution for the 8 inch LB, preferably one which is easily attached so that it doesn't add to the carrying weight of the scope.

Helen

The rail on this weighs only a few grams and there are 3 weights supplied, 1, 2 and 3 lbs so it can weigh what you want it to within reason. They also slide on and off the rail very easily. The system costs around £100 new from Telescope House but I got lucky when one came up on E.Bay for half that.

I'm sure there are much lower cost DIY solutions though TBH.

John

[Doc]

Looks like a factory fitted item.

I like it a lot.

[acey]

When I needed to counterweight my 8" I used flexible training weights with velcro straps that I got from a sports shop - the pair of them together went right round the tube, if I remember rightly, and were effective for counterbalancing an 80mm scope that I was using as a finder.

Andrew

[hal2000]

I use a bungee cord hooked to each end of the eyepiece holder and slipped over the wheel. Works brilliantly.

[jarbi]

John,

I have two solutions for my LB 16":

1. I have ordered 2 of the LB counterweights from JMI:

http://www.jimsmobile.com/images/cw_lb1w.jpg

When this is not enough:

2. I have a 2,5 kg flat round counterweight from Skywatcher, with 4 small supermagnets on it. I have put black flexible tape around them to prevent from moving or scratching the tube. I can easily attach this at any point on the lower tube.

By the way, I received the silver shroud from Meade when I purchased my Dobson, and that is most probably much lighter than the Astrozap shroud - less problems with balancing.

cheers,

Janos

[John]

John,

I have two solutions for my LB 16":

1. I have ordered 2 of the LB counterweights from JMI:

http://www.jimsmobile.com/images/cw_lb1w.jpg

When this is not enough:

2. I have a 2,5 kg flat round counterweight from Skywatcher, with 4 small supermagnets on it. I have put black flexible tape around them to prevent from moving or scratching the tube. I can easily attach this at any point on the lower tube.

By the way, I received the silver shroud from Meade when I purchased my Dobson, and that is most probably much lighter than the Astrozap shroud - less problems with balancing.

cheers,

Janos

Thanks Janos,

I had a look at the JMI weights and sent them an e.mail asking about shipping to the UK - which they did not reply to

Having now fitted my counterweight and rail set (which is a Meade product) it's working very nicely - I only need the 3 lb weight, even with my 2.2 lb Nagler 31mm in the focusser - no need to use the altitude brake at all

The Astrozap shroud is pretty light and has 2 stiffened hoops built into it so the material does not sag into the light path.

Next mod: re-position the power supply socket for the cooling fan so that it does not interfere with a collimation knob when the supply is connected. These Lightbridges are a hobby in themselves - might get to look through it one day !.

John

[jarbi]

Thanks Janos,

These Lightbridges are a hobby in themselves - might get to look through it one day !.

John

Good one John . I have even rearranged my garden and built a path to be able to take my LB to the other side of the house. So - a LB is good for your condition and keeps you busy outside as well, not only in the evening !

Janos

[Doc]

Things we do for our Lightbridge

[The Warthog]

Here's a very simple solution. http://www.visualastronomy.com/2008/01/zhumell-mod-ota-counterweight.html

[acey]

Yep, that was pretty much my solution (though an all-in-one flexible training weight is neater). But in general the situation may not be a simple lever one - so doing weight times distance may not be enough to work out what's needed. When I mounted an 80mm refractor on my Orion 8" dob it was on a geared alt-az mount to allow fine adjustment. This put the finder quite high above the scope, making the whole assembly no longer effectively a "straight line" for the purposes of working out counterweights. Changing the altitude of the scope altered the balance of the whole thing. It was a case of just sliding the weight belt up or down the tube as needed - though the tension springs on my dob mount took up most of the extra force required to keep things balanced. I didn't stick with the arrangement for long - too much of a faff. I found the 30mm finder good enough once I'd invested in a decent star map.

Andrew

[The Warthog]

I have the same problem with my Newt, when I stick in an 8" long ep/Barlow combinaiton. It pulls the scope off balance on the side the ep is on, depending on the rotation of the tube. It's annoying, but I just live with it.

[joenap]

That looks pretty nifty. I've added the Farpoint weights and a modified ankle weight on a velcro strip to adjust (see photo) With the 20 Nagler T2 I still need a little more weight - I may have to go to the Farpoint additional weights, that should do it. I'm also considering the new Explore Scientific 100 degree 14mm eyepiece which weighs in at 2 lbs. For sure will need more.

Joe