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Zheng-ru
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Topic: On the trebuchet Posted: 26-Jun-2007 at 20:54 |
In addition to my plans to build a cho-ko-nu this summer, I plan to build a small-scale trebuchet. I have some questions and I was wondering if anyone here can help me.
This image has two circles. A shows one of two wooden blocks attached to the counter-weight. I believe they are meant to interrupt the movement of the counter-weight as it makes contact with the main frame. Perhaps this sudden stop provides the arm with more momentum. The frame is protected by the angled spar.
B shows a rope and a pulley. The rope seems to pass past the first winch and is wound around the second winch and upwards toward the arm and the pulleys.
So, my questions:
Did the engineers construct this type of trebuchet so that the counter-weight would hit the frame thus increasing its range (or affecting the arc of the projectile)?
And do the two ropes, from the forked branches on the end of the frame, pass under the first winch (the one farthest from the frame)?
Edited by Zheng-ru - 26-Jun-2007 at 20:55
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"The best victory is when the opponent surrenders of its own accord before there are any actual hostilities...It is best to win without fighting."
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hugoestr
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Posted: 26-Jun-2007 at 21:42 |
What a happy coincidence! I just built a model trebuchet with my daughter. She actually correctly identified the image in your post. I am one proud dad.
I would actually recommend building a simple model first so that you can see how it works. I watched some videos on youtube, but you really got to experiment with it yourself to get the true feel for it.
Okay, now to answer the question. You don't want the counter-weight hitting the frame, but to swing. If the counterweight hits the ground or the frame, it kills the impulse of the arm.
I believe that you only need the winch when the trebuchet gets big enough. My very small model didn't need it All what you need is to hold it with your hand.
Check this video:
http://www.youtube.com/watch?v=DYskeE0haik
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Zheng-ru
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Posted: 26-Jun-2007 at 22:20 |
Hello Hugoestr
I studied gravitational potential energy. I built a Roman ballista (posted on this forum). I modified it for greater range and historical accuracy (it is a much more complex design than any trebuchet). Therefore, I will not try a simpler model because it will not interest me. I have seen many of the videos as well (thank you for your link). I also spoke to someone who helped build a large-scale trebuchet. I realize that trebuchets are usually depicted and constructed so that the counter-weight falls in between the columns of the frame. However, if you examine the image closely, you will see that the image can be interpreted to show that the wooden blocks do hit the frame. Otherwise, do you have an explanation why they are there?
Also, I know that I do not need a winch (my ballista did not need a winch or a ratchet to function as a model, but rather for completeness as a replica).
I may seem ungrateful for your help, but I do appreciate it very much.
Truly,
Zheng-ru
Edited by Zheng-ru - 26-Jun-2007 at 22:22
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"The best victory is when the opponent surrenders of its own accord before there are any actual hostilities...It is best to win without fighting."
- Sun-tzu
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hugoestr
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Posted: 27-Jun-2007 at 11:44 |
Hi, Zheng-ru,
Well, old illustrations sometimes are tricky to interpret. I strongly doubt that they would hit the frame because of the reason that I gave in my previous post. Another reason why I doubt that they would hit the frame is that the force in which it would hit it would destroy eventually destroy the frame.
But, you can always build a quick model--he, he --and experiment with it hitting the frame and see what happens.
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Zheng-ru
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Posted: 27-Jun-2007 at 18:43 |
It seems entirely logical what you say, but then why would the engineers even construct those wooden blocks? Yes, the frame would be stressed, but perhaps not too stressed if the diagonal spars supporting the main columns are strong enough.
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hugoestr
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Posted: 27-Jun-2007 at 19:31 |
It is hard to tell how those blocks travel. They may hit the frame; they may not. Have you seen any models that have those blocks in? That should solve the problem. I will look for videos
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hugoestr
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Posted: 27-Jun-2007 at 19:43 |
Oh, darn you, Zheng-ru. Now I am going to obsess about those pieces of wood
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Zheng-ru
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Posted: 27-Jun-2007 at 20:37 |
Sorry Hugoestr!
I have not seen any models with the blocks included. I am still searching for medieval illustrations or descriptions which include the blocks.
This trebuchet in France also has the blocks:
http://en.wikipedia.org/wiki/Image:Trebuchet.jpg
This site may be very helpful for our investigation and contains some videos at the bottom:
http://www.cathares.org/mma-trebuchet.html
Edited by Zheng-ru - 27-Jun-2007 at 21:01
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hugoestr
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Posted: 28-Jun-2007 at 06:40 |
It was a joke. I find the whole thing enjoyable
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hugoestr
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Posted: 28-Jun-2007 at 06:47 |
The videos that you sent make it look like the blocks don't hit the frame, and it seems that they are used to give the counterweight some stability. Of course, the problem is that this is an animation.
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edgewaters
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Posted: 28-Jun-2007 at 08:27 |
Maybe the blocks are weights to adjust balance/alignment?
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Zheng-ru
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Posted: 28-Jun-2007 at 19:03 |
I know it was a joke Hugoestr!
I think you may be right Edgewaters, but how?
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edgewaters
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Posted: 29-Jun-2007 at 01:38 |
Originally posted by Zheng-ru
I know it was a joke Hugoestr!
I think you may be right Edgewaters, but how? |
Don't ask me ... you're the engineer.
I'm just looking at it and thinking that the arm would have to traverse well past the perpendicular before the blocks could hit the frame, so I don't think they did that - I would guess the projectile would have left the arm before then.
The only other thing that came to mind was that they could be used to hold weights, which might be useful to align the moving parts (the arm and the counterweight). Also I figure that whatever was being used to provide weight - in such a huge counterweight container, it would probably become poorly distributed after a few shots, so you might need some separate containers on left and right to adjust the balance every so often.
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Zheng-ru
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Posted: 29-Jun-2007 at 14:28 |
Yes, what you say makes a lot of sense, I think I will try the weights in my model and allow the smaller containers to swing past (suddenly we do not call them blocks anymore ). And what do you think about the two winches and the rope running underneath? I have seen pictures in which both winches are used, so maybe the rope at the end is only used as an anchor?
Edited by Zheng-ru - 29-Jun-2007 at 14:31
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