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GordonP 474 posts |
Aug 24, 2003, 08:11
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Yes it's got me baffled, I was baffled then and I'm baffled now. One point Nigel as we rowed it up the slope the stone was at all times parrall to the slope, it was not moved in a series of horizontal lifts. Therefore we were able to make as much ground as on level. It seems that the key to moving uphill is to ensure that forward movement is inciated as soon as possible after the stone is lifted clear of the ground. On the 4 ton stone I tried the time lapse in which to do this was small, that's why I used a brakeman. On a stone of 40 tons this time lapse could be much greater. It seems that the bigger the stone the more reluctant it is to move, but once moving the more difficult it is to stop.
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nigelswift 8112 posts |
Aug 24, 2003, 09:32
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Yes, I quite understood the stone was always parallel to the slope, but it’s movement can still be seen as a combination of a vertical distance and a horizontal one. Like going up stairs, for instance. The angle of elevation of the staircase is dictated by the ratio between the risers and treaders. The steeper the stairs the longer the risers, relative to the treaders. So, if you progressed up your slope at the same rate as you did on the level you must have been increasing the “riser” element of your effort, presumably sub-consciously, by pressing your levers down further. It would be only 12.5% more, so you might not notice. The fact that you didn’t notice absolutely proves my point that your method is the only one that can allow a situation where the ancients could employ a team of the same number of people to shift a stone for the whole journey, and wouldn’t have to bring in reinforcements for the steep bits. Julian Richards postulated to the Royal Academy that the Stonehenge builders might have used a workforce that was variable in numbers. So far as the transporting of the stones is concerned I think his suggestion can be dismissed. You’ve already managed to put the greased trackway theory onto a slippery slope… About the brakes: I was wondering, if you had an arrangement whereby you lashed some brake levers to the back of the stone and dragged them behind, with one end scraping along the ground, then when you stopped, and the stone wanted to slide back, the levers would dig into the ground and stop it. The brakeman’s job seems a bit hazardous, unless he can do it from the side. Even if you still need to use a brakeman, this arrangement would at least give an extra layer of safety for him.
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GordonP 474 posts |
Aug 24, 2003, 10:28
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Your probably right Nigel. I'm not much good with pen and paper, I seem to work almost entirely by trial and error. As regards the job of brakeman being dangerous, I'm quite prepared to try 40 tons on a slope of 1 in 8 single handed. The time lapse between it gathering enough momentum to reach me and my being able to escape would be plenty long enough. Anyway within a split second of it being released if the levermen were well practised it would be moving in the other direction. I have already done it with 4 ton and I know more about it now than I did then. In retrospect I think I'll try it with 10 tons first. I was talking to a farmer a couple of years ago and he was most dismissive of the greased slipway idea. Being a farmer his first thought was "How many herds of cattle would they have had to render down to do it that way" It was an angle that had never occurred to me.
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Steve Gray 931 posts |
Aug 24, 2003, 12:31
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Nigel, I don't think that resolving the motion into horizontal and vertical components is really relevant to Gordon's method. He will measure progress along the line of the slope (just like a car's mileometer would). For a given stroke of the "oars" that movement will be the same regardless of the slope. The only problem that the rowers have to overcome is the additional reverse component of the stone's weight. Since they are already lifting its entire weight quite comfortably in a vertical direction the additional slope component is small by comparison at moderate slopes. At 1 in 8 it will be about 5 tons for a 40 ton stone, but this is dividied amongst 40 rowers, so the additional component is only 280lbs per rower. This is further divided by the mechanical advantage of the lever (say 20:1), so it ends up at around 14lbs. On the other hand the brake man has to be able to resist the full force of 5 tons acting down the slope (albeit for a short time). I suspect several brakemen would be needed for a stone of this size. I like your idea of having trailing logs lashed to the stone to act like pawls against the ground. Mr Otis would be proud of you.
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GordonP 474 posts |
Aug 24, 2003, 12:53
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Don't think this wreak of a body can resist 5 tons, but I reckon I could still stop a 40 tonner single handed. As the stone is lifted follow it up with the lever so that the lever remains in contact with the stone. Quickly jam a forkstick log up against the lever handle, job done.
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nigelswift 8112 posts |
Aug 24, 2003, 14:27
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Steve, I think we may be talking at cross purposes, as I think what I said was right but I also agree with what you say. Not that the mechanics of the process matter, the point is we're all convinced Gordon can take a stone up a hill like a rat up a drainpipe and no-one else can! Pardon my ignorance but who's Mr Otis? Gordon, I can see your point about being the brakeman, and I suppose you'd be better at it than a mechanical brake, as that wouldn't kick in until the stone started slipping back, it's just the thought of you stumbling or coming over all funny at the crucial moment...
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Steve Gray 931 posts |
Aug 24, 2003, 23:39
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Elisha Otis invented an automatic braking system for lifts in 1854. It's basically a ratchet system with the pawls held off the ratchet by the tension in the cable. When (if) the cable breaks the pawls are released and engage with the ratchet, thus preventing the lift from plumeting. Quite similar to your idea I thought.
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nigelswift 8112 posts |
Aug 25, 2003, 08:59
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Sunday afternoon. Rocks, logs, holes in the lawn…. Gordon, hope you don’t mind all the questions. This time it’s about putting the uprights into the holes. Small scale, I had a problem with the stone not pivoting cleanly into the hole but sometimes sliding down on the pivot point, so the arc it goes through is elongated. I could design for that OK but it’s an intermittent effect, depending on how rough or uneven the stone is. As such, I was getting an unpredictable degree of inaccuracy. Any thoughts? Steve, do you have a lawn? The only way I found to cure it on the small-scale model was to have the stone tilted upwards instead of horizontal. That way, it seems to build up a bit more rotational speed when it drops –it’s already built up a bit of speed when it reaches horizontal, and after that it seems to pivot round more cleanly and not to start sliding down the pivot point. So that might be something worth thinking about. I suppose, if you did find tilting the stone was good, you could change your means of elevating it by building a sloping track and rowing it up until the end was supported on the A frame. At that point you could remove much of the track and end up with the stone supported in much the same way as you’re proposing, but tilted instead of level. (If it did turn out to work that way it would have a lot of advantages apart from the pivoting aspect: you could set the whole thing up before the stone was brought to it, it would involve less mechanical effort and time, and you wouldn’t be needing the stone to be raised so high. Also, it would be sweet if your Big Idea, stone rowing, was not only the key to transporting the stones but also to erecting them.) I tried this and it seemed to work, but I’m acutely aware that small-scale experiments may be quite different to what you’re proposing.
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GordonP 474 posts |
Aug 25, 2003, 10:15
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Mind? No I live to talk about it, ******* obsessed. What we are doing on this forum is known in the business world as "Brainstorming" and it can be very useful. For instance, you have identified something I was doing, either accidentally, or subconsciously. (I prefer to think it was the latter) I now realise the importantance of this one small detail. The stone must be tilted. I too was getting erratic results with the test model (I was using a capping stone from the garden wall) at the time I was only concerned with getting the stone to drop in the hole, I varied the height of the towers in relation to the bottom of the hole, with some success. However on the 4 ton stone (which is much more predictable in its movements) I used a piece of 4 by 3 across the balance piont which in effect tilted the stone, this tilt was increased as I placed the "A" frame under the stone. I now reckon both these facts are vital. The height from which the stone is dropped, in relation to its length and the depth of the hole, and the amount of tilt on the stone. On the plus side a stone of 10 ton should be even more predictable and so on. I've only given it a quick thought be feel instinctively that raising the stone on a tower will be much quicker and more stable than building a ramp perhaps I'm just anti ramp. I will think on and am open persuasion.
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GordonP 474 posts |
Aug 25, 2003, 11:09
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Another thought. Time spend building a stable ramp, and that would be considerable, must be added to the time it takes to erect the stone. The BBC built a massive ramp out of modern scaffolding to place the lintel stone which if made of earth and stone would have added weeks to the complete operation. If it is possible I want to prove that the trilithon could have been constructed from start to finish in one day. digging excluded.
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