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Forum Index > Off-topic Talk > Slo-mo video: Javelin & amentum, slings etc Reply to topic
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David Colter





Joined: 02 Apr 2010

Posts: 9

PostPosted: Fri 02 Apr, 2010 6:58 am    Post subject: Slo-mo video: Javelin & amentum, slings etc         Reply with quote

I think you might be interested to see these videos I have shot with a 300 frames/sec video camera:

Javelin with fixed amentum http://www.youtube.com/watch?v=HmPSKu6-TMM

Javelin with detaching amentum http://www.youtube.com/watch?v=YtCDobXr9Gg

Sling, showing axial-spun release of biconical bullet http://www.youtube.com/watch?v=lJjXXnDSB4s

Staff sling http://www.youtube.com/watch?v=reEaUOTU1KI

Atlatl and dart http://www.youtube.com/watch?v=Ik6_bRSmPJk

Archery http://www.youtube.com/watch?v=1TTI2DrfSLg

There is a lot more on slinging there as well.
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M. Livermore





Joined: 20 Aug 2008

Posts: 90

PostPosted: Fri 02 Apr, 2010 8:43 am    Post subject:         Reply with quote

I am glad to see the tangential deflection of the dart captured so well by the atlatl video. I have been trying to explain the concept to some friends, and this will be of great help. What is that dart made from?
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David Colter





Joined: 02 Apr 2010

Posts: 9

PostPosted: Fri 02 Apr, 2010 12:34 pm    Post subject:         Reply with quote

It is six feet of 12mm pine dowel. There is a 1/2" iron bodkin point and feather fletching. Flexibility is what determines the length of your dart. It should bend out sideways if you push lengthways on one end with about 7lbs of force. If it is too stiff it wont launch right, the tail will be pushed down by the final movement of the atlatl and the dart will porpoise badly, costing you accuracy and power.

Some people will try and tell you about 'stored spring energy' and other such stuff, basic arithmetic shows that there is no such thing going on.

Whats is really going on is that the natural frequency of oscillation of the dart needs to be such that the dart's ends are bending downwards as the tip of the atlatl goes 'over the top' and heads downwards. That way they match up and no downward force is imparted to the dart before they separate. If the dart is too stiff and oscillating too quickly then the flexing will have reversed already and the tail will be trying to move upwards as the atlatl spur moves downwards. They fight against each other and the dart loses, getting its tail pushed downwards.
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Steven H




Location: Boston
Joined: 10 May 2006

Posts: 545

PostPosted: Fri 02 Apr, 2010 12:44 pm    Post subject:         Reply with quote

Thanks for sharing.

Those Javelins look small too me. Are those a Medieval design or something else?

Cheers,
Steven

Kunstbruder - Boston area Historical Combat Study
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David Colter





Joined: 02 Apr 2010

Posts: 9

PostPosted: Fri 02 Apr, 2010 1:29 pm    Post subject:         Reply with quote

Javelins vary widely across history. This length of about 52" seems right for Greek/Roman skirmishers but the shaft diameter of 1" is probably too much. The spearhead is one I bought from a festival blacksmith in Germany, the shaft is a broom handle with the tail end tapered to move the balance point to one-third of the way back from the tip.

The javelin I used is the middle one of these three:



A closeup of the fixed amentum:



The detaching amentum I used was braided from jute cord, modeled on this:

http://www.nma.gov.au/cook/artefact.php?id=337

And used like this:

http://www.antiqueprints.com/proddetail.php?prod=f7238


Last edited by David Colter on Fri 02 Apr, 2010 2:05 pm; edited 1 time in total
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Steven H




Location: Boston
Joined: 10 May 2006

Posts: 545

PostPosted: Fri 02 Apr, 2010 1:36 pm    Post subject:         Reply with quote

Thanks for the additional info David.

Do you have info on what Medieval javelins were like as well. I'm gonna be building some soon.

Cheers,
Steven

Kunstbruder - Boston area Historical Combat Study
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David Colter





Joined: 02 Apr 2010

Posts: 9

PostPosted: Fri 02 Apr, 2010 2:04 pm    Post subject:         Reply with quote

I have no info on medieval javelins. I would be surprised if there was much standardization there, the javelin is a cheap and simple weapon for skirmishing. You carry several, chuck them at the enemy and dont expect to get them back again.
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