Author Topic: Siege engines  (Read 1662 times)

ElyDave

  • Royal and Ancient Polar Bear Society member 263583
Siege engines
« on: 17 December, 2019, 03:36:56 pm »
Having built the trebuchet a couple of years ago, last year I attempted a torsion powered ballista, but didn't get it to work. That one is now on the back-burner while I rethink it.

This year however, a torsion powered mangonel is the job. Found a good bit of 2x4 in the shed, and a couple of narrow bits of ex-shelf of the perfect length and thickness.

I will post pics eventually, but for now I have a substantial ladder frame base about 2ft by 1ft, will be adding uprights and spreader at the top, plus supports for the frame. I've got a 16mm spade bit for the cords to pass through with washers to reinforce. Haven't quite decided on the arm or bucket yet, but have plenty of options.  Will also add a simple trigger.  Daughter off school now, so will try and get her involved as a physics exercise.
“Procrastination is the thief of time, collar him.” –Charles Dickens

Cudzoziemiec

  • Eating all the pies and drinking all the tea.
Re: Siege engines
« Reply #1 on: 17 December, 2019, 03:55:44 pm »
We're going to have to see these machines in live action some time. Preferably before you get carted off by a black helicopter!
Riding a bike through a city is like navigating the collective neural pathways of a vast global mind.

ElyDave

  • Royal and Ancient Polar Bear Society member 263583
Re: Siege engines
« Reply #2 on: 17 December, 2019, 04:41:45 pm »
Somewhere on here there is a video of the trebuchet, I'll try and repost it here as well. My daughter's reaction is priceless.

Here it is
https://www.youtube.com/watch?v=hQRpuv0qAkk
“Procrastination is the thief of time, collar him.” –Charles Dickens

ElyDave

  • Royal and Ancient Polar Bear Society member 263583
Re: Siege engines
« Reply #3 on: 20 December, 2019, 02:20:02 pm »
photos of current build, since then I've added a block to the top of the frame to stop the arm earlier and give a better release trajectory


Basic ladder frame


Preparing the skein of string, I went for about 30 loops


Basic trigger, pivots across the launch arm


finished
“Procrastination is the thief of time, collar him.” –Charles Dickens

Re: Siege engines
« Reply #4 on: 29 December, 2019, 05:05:09 pm »
Tendon is what you want.  Massive energy storage.
And Darkness and Decay and the Coronavirus held illimitable dominion over all.

Re: Siege engines
« Reply #5 on: 29 December, 2019, 05:25:47 pm »
Having trouble with the neigbours Dave?
Get a bicycle. You will never regret it, if you live- Mark Twain

T42

  • *** fool in a hurry
Re: Siege engines
« Reply #6 on: 30 December, 2019, 10:16:39 am »
Have you got enough cordage on there?  I'd have thought about ten times that.
I've dusted all those old bottles and set them up straight.

ElyDave

  • Royal and Ancient Polar Bear Society member 263583
Re: Siege engines
« Reply #7 on: 30 December, 2019, 04:21:04 pm »
Its actually pretty reasonable. The string is wax coated and very strong, no idea where I got it from. The limiting factor actually seems to be the washers, one of which has deformed under the load. Tomorrow's task is to slacken off, add another washer each side and then see where I can get to. 

Release angle seems to be the major variable, too high - 90 degrees and its mostly a downward trajectory, I've worked around 60deg or so.
“Procrastination is the thief of time, collar him.” –Charles Dickens