Medieval Style Crossbow, Rubber Operated

[M-Cameron]

Machine......


the net energy of the system is independent of the distance............but thats not the same as the energy imparted to the projectile.

take a slingshot with only one band on it............and pull that ban off to one side.....and let it go.....that is where the energy goes....and That is exactly the same as the F Cos( theta) component of the angled band......

like i said before, that energy is transmitted back into the slingshot and into your arm.......

the reason you dont notice it is because you have 2 of them acting in opposite directions.

when you have an angled band, not all of the energy is going into throwing the projectile.


now joerg, i just want you to know that none of this is a criticism of your work, you know what you are doing and you designed your crossbow the way you did for a reason.....this is all simply a response to Glistam's question.

 

[MachineCrossbow]

M-Cameron, you want me to get a stroke.

 

[MachineCrossbow]

Never mind, Joerg, do what you think is right,
given all the circumstances, you must be right
about fork width, but what M-Cameron says...
that's medieval.

P.S. - I'm glad to hear you have a physicist brother.
One physicist is enough, huh?

 

[JoergS]

Well, here is some more field footage.

http://www.youtube.com/watch?v=fLPjIhqI9Ww

 

[M-Cameron]

Joerg, with the new rubber....that thing is crazy!....
How are you aiming it, is i just kind of a sight down the "barrel" thing....or do you have a technique?

Never mind, Joerg, do what you think is right,
given all the circumstances, you must be right
about fork width, but what M-Cameron says...
that's medieval

so you are saying, what Joerg said is correct.......and what Richard Middleton said in his book was correct.......but somehow i am wrong for saying exactly the same thing?

all while failing to show how any of my math or reasoning is wrong......

am i missing something here?

 

[MachineCrossbow]

Maybe we should start another thread and leave poor
people in peace. Then we could discuss this disturbance
in the Force, Jedi.
Whoamzzz. Kshhhhhhhzzmm.


Seriously, I don't want to second-guess Joerg's experience,
he and others might get better efficiency accompanied
by a narrower fork. I say it's unclear if there's an another
factor* interfering with efficiency. I doubt your reasoning,
that exactly and only the width is the reason of the efficiency change.

*For example: Joerg said the same rubber, stretched between
wider forks is less efficient. It's obvious, because
the rubber is prestressed even before drawing. So
there is less additional, usable energy you can store in it by drawing
before it breaks, as compared with a loose one.
So simple. I meant my statement with loose rubber bands.
With re-arranged (folded) bands, width changes,
rubber's the same, but still loose.
OK?

 

[MachineCrossbow]

all while failing to show how any of my math or reasoning is wrong.....

All right. Your math is not exactly OK, because you fail
to show how exactly that force of yours does work
on (actually non-existing) displacements. No displacement
sideway: no work by sideway force. You just calculate
the side component of the band pull force.

:banghead:

 

[MachineCrossbow]

The good thing is, anybody can alter the fork width while
keeping energy unchanged.
X times less spacing, X times more folds of rubber
band, still no play, smaller draw length, bigger
draw force, same energy.

 

[M-Cameron]

All right. Your math is not exactly OK, because you fail
to show how exactly that force of yours does work
on (actually non-existing) displacements. No displacement
sideway: no work by sideway force. You just calculate
the side component of the band pull force.

......ummm.......what work do you want me to calculate?

theres no sideways displacement.....thus no sideways work done.......

theres nothing other than the side component of the force to calculate.......which end up canceling each other out....

and theres no need to calculate work done by the vertical component, because that is going to change depending on factors we dont have.....and will contribute nothing to the question at hand

 

[Deltaboy1984]

Well, here is some more field footage.

http://www.youtube.com/watch?v=fLPjIhqI9Ww

Shoot I need to set down and make one for slingshot hunting. That is one Bad ole school machine.

 

[MachineCrossbow]

M-Cameron, your every line is either gloomy, not true, or contains pseudo-science.
Please don't take it as an offense, because it disturbs much more people
who take science seriously.

 

[The-Reaver]

That things pretty sweet...I can dig it. +1

 

[M-Cameron]

M-Cameron, your every line is either gloomy, not true, or contains pseudo-science.
Please don't take it as an offense, because it disturbs much more people
who take science seriously.

Machine......you have me seriously questioning your level of engineering education...


i honestly feel you are either a Troll or are still in high school basing your argument of off what you learned in Physics 101.

you claim my work is full of "gloom....lies.....pseudo-science.....and deceit"
even though all my work is based in pretty simple and well founded engineering principals.

you claim my math and reasoning are wrong, even though my finding are backed by 2 industry experts......all while failing to prove that anything i said was wrong.....and failing to provide any proof of your own to counter my logic( and that scribble you posted, not only was it illegible, but from what i could tell, was not even on the subject at hand)

simply posting that "my work is full of lies, gloom, and deceit" doesnt cut it in the real world........if you want to make bold statements....you need bold facts.....which you have failed to bring to the table....

......unless you can manage to grow-up, stop with the childish name calling, and actually provide a logical response, then we can continue,.........otherwise, im not going to spend any more time arguing with a Troll.

 

[JoergS]

Added assault rifle scope

I wanted to add a sighting system to the medieval style crossbow, which right now is my favorite plinker.

Not so easy, the rubber swings forward and does not allow the medieval "fork" sights at the front of the weapon. Everything has to be behind the lock.

I bought a few Hensoldt scopes, made for the German Army standard isse H+K G36 assault rifle. Surplus, fine condition, 5 Euros a pop. These are made to be installed INSIDE of the plastic G36 stock, so there is no adjustment of any kind. But just the right factor (3x) and nice crosshairs.

See the crosshairs in a pic

I made a mount system from wood, nothing that a medieval weaponmaker couldn't have done (minus the mordern screws).

Here you can see the adjustmemts, both horizontal and vertical.

The naked scope in comparison.

A peek through the scope (hard to do with a camera, it is just perfect in reality)

Only the back side is telling... modern technology.

It is amazing how accurate this is, and how easy the cocking is. I am plinking with TB black, a preteen boy can draw this out with both hands and a foot in the stirrup.

These inexpensive scopes are ideal for slingshot crossbows. A lot of fun!

Jörg

 

[Deltaboy1984]

Too cool!