[Loch-ruadh] Trebuchet project (long)

[Sluggy]

Let me first preface by saying that I am having trouble getting into the Yahoo
group intended for this discussion, but I will win that battle soon! In the mean
time....

r baker wrote:

> Wet Sand is aprox 118lbs per cubic foot.

Cool, glad to see an actual figure! Where did you get that figure, by the way?
The fiigures I quoted for various elements came from http://www.matweb.com , one
of my new favorites!

> Never-mind :)

Hey, the engineers' quest to fit the most function into the smallest footprint
has driven the specification of lead as a counterweight. That does not mean sand
absolutly will not be used nor does it mean that the counterweight can't be a
combination of available materials. For example, that we manage to scrape
together only 100 pounds of lead and use sand for the balance, the counterweight
would be almost a full cubic foot smaller and it would still be 500 lbs. Real
world limitations may well necesitate such decisions in the future. Lead provides
the best performance and is thus the favorite. While we have some lead ready to
use and some sources for scrap, we have not gathered it all yet.

HRAFNASDOT at aol.com wrote:

> If you're casting your own weights  - You could make them where you do away
> with the bucket by placing them directly onto an axle - think stringing
> washers onto a bar.

As is often the case, simplicity and efficiency are mutually exclusive. One of
the trebuchets on the Nova used that sort of design, and it worked very well, but
there is plenty of evidence that the swinging weight design is more efficient.
Essentially, the closer to vertical the falling weight can travel, the more
energy is transferred to the sling end of the throwing arm. This means that with
all other design elements identical, a trebuchet with a 500 lb swinging weight
should be able to throw the same projectile farther than one with 500 lb fixed
weight.

>  Might work better because think of the reinforcement for
> the bottom of the bucket and the sides to withstand the weight.

Such reinforcement could actually help us reach the desired counterweight size
with less lead.

>  The axle will have to withstand it anyway.  You maximize the volume of
> material by
> doing away with the bucket.

We would maximize the volume but at a demonstrable loss in efficiency that is
greater than the gain.

> Its not period but unless you have period weights, period windlass, pulleys,
> etc - what does it matter?

Actually, sand (or any fill dirt) _would_ be a better choice of weight for
staying in period. A large amount of lead, iron or whatever would have been
expensive to maintain and transport. Dirt and rock would be available at the site
of the seige.

As for what does it matter, the answer is purely philosophical. We strive to be
as period as we can. We compromise ideal period designs when we decide that
something required to stay in period is more expensive than we are willing to
spend. Sometimes that cost is in dollars, sometimes in hours, sometimes in less
tangible parameters such as safety, appearance and appeal.

I, for one, consider growing a field of flax or some such in order to make period
ropes to be too expensive in time and effort. I will do everything I can to avoid
flourescent braided nylon ski rope because that is just too expensive in terms of
period appearance. Now, that brown nylon twist rope? That looks period enough for
me and it won't stretch when it get's rained on or break down when trampled in
the mud, so I'm willing to accept that. Likewise, I don't have to fell a tree and
hew a timber throwing arm if I can drawknife a beam of composited kiln dried
lumber to look 90% like a timber one would.

Our goal is to build a trebuchet that strikes a balance between the most
efficient seige weapon we can produce within the rules and the costs.

> How do you plan to transport 800 to ton of weight?  And load it?

These are valid concerns for any seige weapon we would build. I predict that a
solution will be found, much like solutions to every problem we've faced have
been found. That we don't have an answer at hand this moment should not stop the
project.

> And how ARE you going to buy all that lead?  And WHERE?

There are a number of sources. Not all are free, but some are. I have a couple of
bags of shot that I acquired for another project, plus a few pounds of unused
bullets, plus a few bars used for interconnecting batteries for backup power, all
tolled about 50 pounds. I alone can thus provide about 10% of the total designed
weight without even going shopping.

A probable source for free lead is tire shops. They discard removed wheel weights
used for balancing. A bit of repeated footwork could likely produce a lot of
lead-antimony alloy from them.

> Home Depot or Loewes or Walmart, right now, has sand.  For under $5 everyone
> could donate one bag and leave it at the sight if we had to -

Again, nothing says that it absolutely must be 100% lead. The more lead we gather
for free, the less of anything we have to buy.

> sand, last time I looked, wasn't toxic.
> And casting lead is very easy, but dangerous.

The entire endeavor is dangerous. Things that could go wrong range from spinters
to death by crushing and everything between.

The particular danger of casting this lead will not fall on anybody who is not
willing to take such a risk. It will not likely be done on site, it will not
likely be done by more than two or three people (although I have my theories who
those people will likely be!)

Sluggy!