Creating a siege engine.

[Haxxors]

Currently i'm creating a giant "Belly Bow" for fun, and just to see if I can do it.

I drew out some plans on art pad (Although they look terrible because I have no artistic ability) and everything looks simple enough, I just need to gather the materials and get to building.

I'm going to share the plans and the proposed dimensions of the piece, and hopefully you guys can give me some insight as to how it will work.

(This is all length)
The Arms - 3feet
The Body - 4-5 feet.
The Boxes - 6inches - 1ft
The Holding Block - 4 inches

Here are the overhead view of it, and the loading mechanism.

Overhead - http://www.imagedump.com/index.cgi?pick=get&tp=552109

Loading Mechanism - http://www.imagedump.com/index.cgi?pick=get&tp=552111

Once i'm finished i'll be sure to post some pics of it and some stats of how far it shoots. I'll even crunch some numbers to see if I can find out how much force it shoots with.

My only questions are, has anyone attempted something like this before? Anyone have any tips? And does anyone know what types of wood/rope would be best to use for this project?

Thanks.

 

[gameman]

If your going for realism then you need to know that there are two turning wheels connected to a turning block of wood were rope is secured and eventually tightened/stretched for the effect of a much stronger rubber band. You can add a big gear to each of the little gears to make the turning easier.

The gear's most important feature is that gears of unequal sizes (diameters) can be combined to produce a mechanical advantage, so that the rotational speed and torque of the second gear are different from those of the first.

What I mean by little gears is that you need a wheel with spokes to rotate the blocks with rope on them. You can replace the wheels with small gears and put the turning block ontop of a larger gear to add a mechanical advantage.

 

[Ninva]

You should really consult a lawyer or look at some law books yourself. I'm not certain if this kind of construction is allowed without a permit. This machine is a machine of war and destruction. You might get in trouble for building one.

 

[Wiseman_2]

It's funny you should ask this, as I just finished watching a TV show called Weapon Masters, and the subject was the Roman Scorpion, which is designed almost exactly as you've drawn up here.
I am assuming you know how this works judging from the designs here. The two arms are inserted into tightly twisted strands of rope in the tower, and then pulled back with the rope attached to the firing block. It is this which gives it the tension needed to fire. As such, the "support beams" have no purpose as the arms need to be able to move.

Unfotunately I can't find the episode on Youtube.
Anyhow, this image shows what I was trying to say:

Good luck... and don't shoot anyone with it

Also, the remake in Weapon Masters was made from steel with steel truck springs. I would personally just try to replicate the Roman version with materials because Steel would be very tricky to use. Use a strong wood and nylon rope. The Romans used Sinew but it breaks easier than nylon.

 

[Haxxors]

Haha thanks you for this. Actually the Scorpion is next on my list.

I'm trying out the "Belly Bow" first because mechanically I think it is the simplest. You are correct, the Scorpion uses the torsion power of the ropes to launch the object. The belly bow uses the power of the pulled rope. The Scorpion is a bit more complicated to put together and i'm going to do the "Belly Bow" first to get a bit of experience building machines such as these.

Thank you for your reply though I should be going to get the supplies this weekend.

I will be using Nylon for the rope

 

[Wiseman_2]

Oh, I misunderstood what you were saying. I actually made a miniature one myself out of Lego a few months ago