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A BETTER MANGONEL (Read 4800 times)
jlasud
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A BETTER MANGONEL
Mar 10th, 2013 at 3:29pm
 
I had this idea,and did some research,without any findings to anything like this,or if it would be viable or not.
There are a few guys into siege engines,Hurling Thom comes into my mind,he's more a treb guy,but i hope i can find some advices,opinions,directions etc.
I would like to build a small man size one of this,but now i'm in the research,design phase.

So this would be a regular mangonel except it's arm swings like 160 degrees,instead of ~ 70 like the old ones.
I think this could add quite some speed to it.
Here's a quick  sketch of it done by me,not a 3 year old:

The front two,connected legs could be tied to the main frame,so it doesn't fell over or something.
Also,the legs would allow for elevation. I guess even a simple sight could be mounted this way on the main frame,after tuning in everything.
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Teg
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Re: A BETTER MANGONEL
Reply #1 - Mar 10th, 2013 at 5:09pm
 
This looks interesting and could be very versatile!

My thoughts:
- Rotation of the winch: I would put the rotation of the winch bar "towards" the frame. If you would put it in the "usual" direction there is the danger of tipping over the device at high elevations. Otherwise you could also charge it before erection.
- Method of charging: With a usual onager you can attach the winch cord at around a 45 degree at the lever. With this design you have lift the lever a bit by hand first. Otherwise the winch will not pull in the right direction. You also run into trouble that you will move the position of the lever in the torsion bundle longitudinally as well as laterally, as the winch will pull at a really bad angle during the first 90 degree.
- Make the stanchion / the legs so, that it can be fixed to prevent any movement. When you fire the device I think that the stanchion will first be lifted upwards and then pressed into the ground (conservation of angular momentum during the first period of the shot and in the second period absorbing the impact of the lever).

The stanchion has also to be quite stable as it has to absorb the whole impact energy of the lever.
Edited:
This statement is actually wrong. The stanchion does not have to absorb the impact energy of the lever but only some momentum gained during the throw. It's not that much.


- To allow for a near-to-180 degree rotation of the lever you have to make the stabiliser bar at the torsion bundle either quite flat or place it further away from the torsion bundle as it is desirable.
- Performance of the torsion bundle: A torsion bundle is not really linear in force. Therefore at low twist you will have not much force while at full twist the applied force will become way higher than expected from the first half turn. Well, at least that is what I experienced with my little onager Wink.

The biggest problem will be the charging/the attachment of the winch. If you operate it at low power (charging "by hand") you will certainly be able to shoot it. But if you go to higher powers you will run into massive problems to find an adequate charging/winching mechanism. One could think about something like deflection pulleys, but that would require a quite sturdy additional frame for them...

Good luck and let us know how the project goes!
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« Last Edit: Mar 10th, 2013 at 6:28pm by Teg »  
 
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squirrelslinger
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Re: A BETTER MANGONEL
Reply #2 - Mar 10th, 2013 at 7:07pm
 
I like it. I might build a permanant version from staves in my backyard- Nothing agianst catapults, just slings Wink
Tennis balls....
Anyway... Nice design, Here is my problem with it- when you shoot, the inertia of the moving arm might be enough to flip it over.
I had this problem with something I built. For every reaction, there is an equel and opposite reaction.
-Squirrel
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“Insanity is doing the same thing, over and over again, but expecting different results.”
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jlasud
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Re: A BETTER MANGONEL
Reply #3 - Mar 11th, 2013 at 1:20am
 
Thanks for the input guys!
As i wrote,the "legs" could be tied to the main frame,by a rope or connected with some thinner poles(adjustible method). That way it would form a big triangle,making it very sturdy,and not fell over when the throwing arm hits the padding.

The winch could take place just above the ground,below the throwing arm in cocked position.
Yes,maybe the first ~20 degrees it should be assisted by my arm,but as it's not fully 180 degrees rotation,the throwing arm would be pulled at a very steep angle,again with some manual help,it should be a problem.
Very good idea to put the winch towards the frame Teg! for small versions,with relatively low weight,it would be a must.
Now a problem,i see would be the release mechanism getting in the way of the sling in cocked position. Maybe the release could fall,soon after the release,making way for the sling to pass above it,swinging fast.
There's gotta be a good solution for this also.
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jlasud
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Re: A BETTER MANGONEL
Reply #4 - Mar 11th, 2013 at 1:22am
 
What do you think,Teg,would it add considerable speed to the throwing arm?
I would be satisfied with ~ 30% more speed  to it. Tongue
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squirrelslinger
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Re: A BETTER MANGONEL
Reply #5 - Mar 11th, 2013 at 2:23am
 
Jlasud, I think I have an idea for your release. just put 2 hooks on the corners of frame, a piece of rope over the arm, and on the hooks... or use  2 mechs to the corners. that way it is away from the center of the thing, so sling has a clear path.
-Squirrel
I might even test this out...
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“Insanity is doing the same thing, over and over again, but expecting different results.”
"You don't think the electricity is off. You check it 3 times to make SURE its off"
"Remember, this is not a scalpel. It is a steel wedge that you will be slamming into knotty wood. Hone accordingly."
 
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jlasud
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Re: A BETTER MANGONEL
Reply #6 - Mar 11th, 2013 at 5:17am
 
I'm not sure if i got you right SS,but if i did,i was thinking something similar.
I would like to make the frame from round wood and just winding up the throwing arm,by hand,then building in a inforcing beam in the middle,then the absorber padding. This way,i wouldn't need to bore holes,use metal etc.,and i could build it more quickly,more simply and cheaper. I hope it's possible..
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Teg
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Re: A BETTER MANGONEL
Reply #7 - Mar 11th, 2013 at 8:30am
 
jlasud wrote on Mar 11th, 2013 at 1:22am:
What do you think,Teg,would it add considerable speed to the throwing arm?
I would be satisfied with ~ 30% more speed  to it. Tongue


It will be more but I can't really estimate how much.

If you want I can calculate /model it for you. You just have to give me some specifications of the goal you want to achieve:
- Length of the lever
- weight of the lever
- weight of the projectile
- Torsion strength (how much force exerts the lever in relaxed position (160 degree), how much force exerts the lever in charged position (0 degree) .)

Then I can tell you a crude estimate of the initial velocity of the projectile with a 160 degree rotation compared to a 90 degree rotation.




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Bill Skinner
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Re: A BETTER MANGONEL
Reply #8 - Mar 11th, 2013 at 11:08am
 
I don't know anything about these, so this is just a question.  Will the joints survive the recoil of the weapon firing?  With the movement and the stress from cocking the weapon, it seems there is going to be a lot of tension on the pivot point of the frame and on the corners?
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HurlinThom
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Re: A BETTER MANGONEL
Reply #9 - Mar 12th, 2013 at 2:28pm
 
Mangonels/onagers are capable of fantastic performance. The long-rotation idea has been tried but it has some issues. To start off, performance mostly comes from how tightly the rope bundle is wound, and if the tension is already high cranking the arm way around can increase tension to the point where the frame will crack. Then, there's the point that your initial cocking effort will be extremely high because of the angle you're pulling at.

Your idea could work, but you'd need a very strong frame (actually first-effort mangonel frames usually have to be beefed up because they won't even take normal tension). Second, for a long arm rotation a longer than normal rope bundle will be very useful. Third, some way of improving the angle your cocking line pulls on the arm help.

I'd suggest that you build a more normal frame that can later be converted to the long-rotation mode. Learn the basics from the normal one and apply to the new situation.

Information on this page might interest you. The guy built a very small machine that flung golf balls a couple of hundred yards.

http://thehurl.wikidot.com/torsiontypes:onager

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Mauro Fiorentini
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Re: A BETTER MANGONEL
Reply #10 - Mar 14th, 2013 at 12:12pm
 
Topic added to the PW's Index.
Greetings,
Mauro.
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