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Guys,
From 5 years of physics and 2 of engineering that thinking about forces simply isn't right. You have a few forces to think about:
1. Dead weight on the bearings = OTA + bar + mount head + counterweights
- a longer counterweight bar will dramatically lower your counterweight and so dramtically lower the weight your mount has to carry
2. Turning moment and inertia (think of a ice skater doing pirouttes, pull your arms in and you turn faster to conserve angular momentum, but you are also decreasing weight making in an inexact comparision).
- The turning moment will be zero if the scope and counter weights are balanced. When you wish to move the scope lengthening the bar will make it easier for althought your weight is further out - your weight is linearly smaller, so less energy will be required (its like picking up a bowling ball striaght up or picking up a shot put with your arm almost fully extended). Now try and throw both those balls over arm - bet the shotput goes alot further! Adversely - it will take more force to stop the turn you have started!
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More weight on the bearings that is moving will produce more wear and tear, put simply weight * coeffiecent of friction = work done. More weight = more work, thats why its harder to push a car than a bike with the same sized wheels - the car weights much more.
Yes a longer bar has more flex - but 15 kgs on a 30 cm bar versus 10 kgs on a 45 cm bar or 3 kg on a 1.5 metre bar will all be roughly equivalent - in fact the lighter weight at a greater distance may just flex less!
The bar in question is 2cm diameter - of probably 0.5% carbon steel - call it a mild peroeutectic steel with minimal heat treatment. Well anything under 100 kgs at lengths that are a less than half a metre are simply too small to flex a bar that short more than a few micrometres. So without a micrometer it would be hard to tell any flex in the bar with the human eye. You'd have more worry that the longer bar will expand more in the heat and so throw off your balance by a few tenths of a newton of force.
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