Any Engineers in the house?

[Dreadmaker]

So... this goes out to the more mathematically minded among us (or physically minded, or smashing watermelons off of buildings minded):

I'm building a trebuchet for a school project.

This is what I'm talking about. I don't intend for this to be an exact model of the above, but it will give those who don't know an idea.


So far, the plans I have set are these :

The arm will be roughly 20 feet in length.
the uprights will be roughly 11 feet in length.
The sling will be roughly 14 feet in length.
the counterweight will be roughly 600-800 pounds.

My arm will be made out of a telephone pole (hopefully) and the uprights are easy enough to procure (12 foot beams are easy to find). the sling is just rope, so that's fine, and we were thinking about casting cement right on the end of the arm for the counterweight.


My question is this : has anyone done anything remotely similar? I'm wondering if I can draw on anyone's experience. I have built one before, but the arm was a mere 6 feet, and it could only throw a softball about 50 feet. It wasn't particularly impressive. I found a simulator online that predicted I would get in the neighborhood of 500 feet with this set up, using a 10 pound projectile.


So does anyone have advice? are there any 'real life engies' out there who might be able to offer some insight? something I would be interested in is a substitute for cement on the end. as far as I can tell, cement is probably the most dense material for it's cost, and I would think it's probably the best I could do. if anyone has an alternative that is heavier than concrete per unit area, I would be interested to hear about it.


Thanks in advance all

 

[.7g]

I did that for AP physics :] it was fun but we lost :[

 

[Dreadmaker]

yeah, I'm doing it for a physics class also... but it's an ISU, so I'm not competing with anyone.

 

[Dreadmaker]

well, after 7 hours the thread has been kicked to almost the second page. things move fast in off-topic.

Anyhow... so nothing, huh? (little bump)

 

[Cpt. Hopi]

Well just to keep thread alive that looks awesome!!! Shame I'm only 13 years old so I have no clue how to build it but good luck.

 

[BioHazardd]

I asked my friend, who has a masters in mechanical engineering.

He said not to rely too heavily on the simulator, if its the one he thinks it is, its terribly inaccurate.
To check out this site (if you haven't already) http://www.trebuchet.com/

.. and he's a really slow responder, so if I get anything more out of him, I shall update the thread.

 

[pillar]

well dreadmaker, good luck to ya if you find the solution. it looks awesome in the pic. would love 2 create 1 myself, but i live in the city & theres nowhere w/ nuff space to have 1 of those built.

 

[featherfoot07]

One of the most important things to keep in mind is the length of the rope and the size of the sling. (these are connecting ideas, making them one). This is crucial to the process.

 

[Bas.B]

Looks cool. Even though I can't help you myself I remember seeing a documentary on Discovery Channel a few years ago where they built trebuchets of roughly the same size... Good luck and post a vid of the result, really interested

 

[Dreadmaker]

One of the most important things to keep in mind is the length of the rope and the size of the sling. (these are connecting ideas, making them one). This is crucial to the process.

Yea... this is something I was looking into pretty heavily. I think that in order to be optimum, the sling should be roughly 7/10ths the arm length. Of course, you need that sling to be taut, meaning that the counterweight needs to be huge