Gomtuu Posted April 2, 2013 Share Posted April 2, 2013 Quick question about counterweights.Just setting up my new NEQ6 in my living room and was wondering which is better, to use the extension bar or to add extra weights on a short bar? Or does it make no difference to stability? Link to comment Share on other sites More sharing options...
Baz Pearce Posted April 2, 2013 Share Posted April 2, 2013 I would say go for the shorter bar. The longer option will more prone to vibration i reckon.Baz. Link to comment Share on other sites More sharing options...
Baz Pearce Posted April 2, 2013 Share Posted April 2, 2013 Dang!! I just had another think about that, and i may have gotten it upside down. Either way you're probably right, it won't really matter too much as long as the system is balanced.Baz. Link to comment Share on other sites More sharing options...
Carbon Brush Posted April 2, 2013 Share Posted April 2, 2013 For static balance, a small weight on a long bar is the same as a heavy weight on a short bar.However, I think if there is a knock, or vibration, or the wind blows, things are different.The shorter bar should recover stability sooner.My physics & applied maths are very rusty from lack of use since the days of flared trousers (first time around). But from what I remember, once you get a weight moving, the stored energy is proportional to the speed squared. Also a long bar will flex more and so store more energy compared to a short bar. Link to comment Share on other sites More sharing options...
Oblong Posted April 2, 2013 Share Posted April 2, 2013 Having twice as much weight, but at half the distance from the axis of rotation, won't make any difference to the balance (which depends on mass*distance), but it will reduce the moment of inertia (which depends on mass*distance^2). It's a bit like when spinning ice skaters pull in their arms to speed up. This would make it easier to accelerate the RA axis, although the whole setup then weighs that bit more. Extra mass could be beneficial in terms of resisting breezes and other external sources of vibration. On a lighter mount, the choice might be more critical, but on an NEQ6, which is pretty beefy and already weighs a fair bit itself, then it's probably more important to make the choice based on ease of transport and setup. Link to comment Share on other sites More sharing options...
Jessun Posted April 2, 2013 Share Posted April 2, 2013 It's a bit like when spinning ice skaters pull in their arms to speed up.I don't think that's a fair comparison since the scater is still at the same weight. Inertia is the same for a balanced system - regardless of how you play with weighs and distances. Total weight - wear - on bearings, and flex of the bar, plus wind considerations might play a part. As would price perhaps - what's cheaper, a weight or a bar? I like compact setups, but there's no maths to back that it's better in any way. Just less to bump in to. It does mean more to carry around though.../Jesper Link to comment Share on other sites More sharing options...
brantuk Posted April 4, 2013 Share Posted April 4, 2013 From a practical point of view there's less chance of bumping into a short bar in the pitch dark and doing yourself an injury than there is a long bar. I have the bruises to prove it lol. Along with the shorter damping qualities of a none extended bar it's a no brainer really. (Of course there may be situations when an extension is required) Link to comment Share on other sites More sharing options...
Galilean Posted April 5, 2013 Share Posted April 5, 2013 I vote for the short bar extra weights option. And if you are worried about costs any sports shop will sell you weights far, far cheaper than an astro shop - may not be a good match cosmetically but who cares in the dark? Link to comment Share on other sites More sharing options...
michael.h.f.wilkinson Posted April 5, 2013 Share Posted April 5, 2013 The short bar will be better for all of the reasons above, plus an extra one: A long bar will vibrate at a lower frequency (much like a long pendulum), and these vibrations tend to be damped out more slowly (further compounded by the high moment of inertia). Link to comment Share on other sites More sharing options...
Gomtuu Posted April 6, 2013 Author Share Posted April 6, 2013 Thanks all, sounds like the short bar is the way to go. Fortunately, as I'm keeping my EQ5 for when I go out to do obs only, I have enough weights! Link to comment Share on other sites More sharing options...
laser_jock99 Posted April 8, 2013 Share Posted April 8, 2013 Another vote here for shorter + more weights. I tried the longer bar but it's only 18mm and starts to flex if you are 'really' loading it. BTW my system has six counterweights with a seventh on it's way!!! Link to comment Share on other sites More sharing options...
Gomtuu Posted April 9, 2013 Author Share Posted April 9, 2013 Blimey, what have you got on the other end?!!! Link to comment Share on other sites More sharing options...
x6gas Posted April 9, 2013 Share Posted April 9, 2013 I don't think that's a fair comparison since the scater is still at the same weight. Inertia is the same for a balanced system - regardless of how you play with weighs and distances. Total weight - wear - on bearings, and flex of the bar, plus wind considerations might play a part. As would price perhaps - what's cheaper, a weight or a bar? I like compact setups, but there's no maths to back that it's better in any way. Just less to bump in to. It does mean more to carry around though.../JesperSorry to disagree but I think it is a fair comparision as I believe Oblong was talking about conservation of angular momentum in a moving system - i.e. in real life when the mount has been nudged accidentally or by wind... Link to comment Share on other sites More sharing options...
Jessun Posted April 9, 2013 Share Posted April 9, 2013 What would be the point if we all agreed on everything .Let's have a tight rope walker out on the line. He carries a long pole to balance. All is well and good. We take a saw and cut the pole between his hands, and replace one end with a short stubby lump. Due to being so much shorter this new piece is much, much heavier than the original piece in order to balance perfectly in his hands.Would the new pole would have a tendency to act differently than the original one? How so then? Would it rather rotate in one direction than the other, would it take longer to stop rotating in one direction, compared to the other? I personally don't think so.Replace both ends of the pole with the stumps, and you'll have something just as functional but way too heavy for the tightrope man to handle.I see the point of the preservation for angular momentum depending on moment arm length. But I think the effects of an energy input at one end (OTA end) will have the same effect, and still fit in with any formula thrown at it. One way out could be to make the CW's as big as the OTA so the wind effect cancels out.The scater doesn't gain weight as he pulls his arms in - but our system does as we change the weights.But, I am no expert in physics - far, far from it. I'll happily listen and learn./Jesper Link to comment Share on other sites More sharing options...
laser_jock99 Posted April 9, 2013 Share Posted April 9, 2013 Blimey, what have you got on the other end?!!!A big scope! Link to comment Share on other sites More sharing options...
E621Keith Posted April 9, 2013 Share Posted April 9, 2013 Short bar + loads of weight near the centre = greater overall system weight = greater likelihood of bending the EQ6's altitude bolt.Long bar = greater flexure and vibrationTough choice. Link to comment Share on other sites More sharing options...
laser_jock99 Posted April 10, 2013 Share Posted April 10, 2013 I'm going to replace the southern altitude bolt with high strength bolt as soon as. I did some minor ajustment on the pier and quite frankly I thought it was going to bend under the static load...... Link to comment Share on other sites More sharing options...
faulksy Posted April 10, 2013 Share Posted April 10, 2013 A big scope!is the ota realy that big or are you very small lol. lovely set up mate Link to comment Share on other sites More sharing options...
Wobbly Bob Posted April 10, 2013 Share Posted April 10, 2013 Short bar with more weight, the longer the bar the easier it is to bump into. Link to comment Share on other sites More sharing options...
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