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Old 19-09-2020, 03:39 PM
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The Mekon (John Briggs)
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Home built trebuchet.

Over the past few months I have been slowly building this scaled down medieval siege weapon. Today was the first test firing and it went rather well. My son is in a medieval recreation and fighting group and it is hoped to take it to one of their events once proper gatherings are allowed.

The arm is 2.8 meters, the counterweight can be varied from 42 to 85 kgs.
It has been built to fit in a box trailer for transport - otherwise it may have been a bit longer.

Some interesting physics is involved. Today I learnt why it is best not to "dry fire" the weapon. Doing so makes the whole machine buck. But firing with the correct weight projectile and achieving a good throw transfers most of the energy to the missile, and the machine hardly moves - all very much fun!
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Old 19-09-2020, 05:00 PM
Saturnine (Jeff)
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What a fun looking project, talk about big boys toys. All you need now is a castle to besiege, plenty of manor houses in your area but can't recall seeing any castles.
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Old 19-09-2020, 05:08 PM
Rainmaker (Matt)
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Originally Posted by The Mekon View Post
Over the past few months I have been slowly building this scaled down medieval siege weapon. Today was the first test firing and it went rather well. My son is in a medieval recreation and fighting group and it is hoped to take it to one of their events once proper gatherings are allowed.

The arm is 2.8 meters, the counterweight can be varied from 42 to 85 kgs.
It has been built to fit in a box trailer for transport - otherwise it may have been a bit longer.

Some interesting physics is involved. Today I learnt why it is best not to "dry fire" the weapon. Doing so makes the whole machine buck. But firing with the correct weight projectile and achieving a good throw transfers most of the energy to the missile, and the machine hardly moves - all very much fun!
You're a man of many talents John What a great project for posting
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Old 19-09-2020, 06:07 PM
17particles
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I've always been curious how the release works on these. Is it just a straight pin for the free end of the rope or do you need to bend it to an angle?

Looks good though...
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Old 19-09-2020, 06:18 PM
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The Mekon (John Briggs)
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[QUOTE=17particles;1492415]I've always been curious how the release works on these. Is it just a straight pin for the free end of the rope or do you need to bend it to an angle?

The angle of the release pin is one of the tuning aspects. The others are, counterweight mass and sling length. I had thought the release prong should be bent around 15 degrees up, but around 30- 40 degrees worked better. Such is the force that a stout 4.8mm nail well driven in was bent by the action of the machine. I was also using a single sling, ie, the rope was tied to the projectile (2litre or 4litre plastic container) and went with the projectile. On one firing the rope (rated 60-100kg) broke with a 3kg projectile, also showing how much force is imparted on the missile!
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Old 19-09-2020, 07:40 PM
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On one firing the rope (rated 60-100kg) broke with a 3kg projectile, also showing how much force is imparted on the missile!
They really were an upgrade from the catapult, weren't they?

So based on a tensile strength of 100kg with a 3kg projectile, gives an approximate 33N moment. What sort of range do you get? Back of the envelope maths with the ball being released at around 2m altitude puts it a bit over 55m.
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Old 19-09-2020, 10:04 PM
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That is really cool. Thanks for sharing and well done!
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Old 20-09-2020, 06:45 AM
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The Mekon (John Briggs)
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Originally Posted by 17particles View Post
They really were an upgrade from the catapult, weren't they?

So based on a tensile strength of 100kg with a 3kg projectile, gives an approximate 33N moment. What sort of range do you get? Back of the envelope maths with the ball being released at around 2m altitude puts it a bit over 55m.
Range with a 2 litre milk bottle was around 50 - 60m. But for the best range the bottle was releasing at a greater height than 2m - more like 4m - like a howitser, the best range is with the release at 45 degrees.

Being about 1/4 scale , this would indicate a full scale machine would throw a 120kg missile around 240m - about right according to historical records.
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Old 20-09-2020, 07:17 AM
Rainmaker (Matt)
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Range with a 2 litre milk bottle was around 50 - 60m. But for the best range the bottle was releasing at a greater height than 2m - more like 4m - like a howitser, the best range is with the release at 45 degrees.

Being about 1/4 scale , this would indicate a full scale machine would throw a 120kg missile around 240m - about right according to historical records.
I wonder what your neighbours are thinking about this ......
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Old 20-09-2020, 07:32 AM
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I wonder what your neighbours are thinking about this ......
They are being very polite and call him 'sir'.
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Old 20-09-2020, 07:51 AM
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I’d guess the immediate neighbours aren’t too worried, it’s the folks in the next street who have something to be concerned about!
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Old 20-09-2020, 12:56 PM
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This is great. I've always wanted one of these. Definitely on the to-do list before I kick the bucket. Well done
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Old 21-09-2020, 05:06 AM
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Great work! But we need a video!!
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