[Loch-ruadh] Trebuchet project(long)

[Adam Harrison]

--- HRAFNASDOT at aol.com wrote:
> --
> [ Picked text/plain from multipart/alternative ]
> Here is my to grommets worth:
>
> If you got a look at my model,

Yes I looked it over...

I used 15lbs. of
> rocks, threw a missle 30+
> yards consistantly and the whole thing was on
> wheels.

saw the competition... it performed well.

  It was ALL pegged and
> glued, and shows no stress.

Great for a model, bad for the real thing.  holding
together a structure with wooden pegs alone will not
take the stresses involved with a large engine.  In
period they did use Mortise and Tenon joints, which we
certainly can try to do, but using modern bolts will
be quite a bit safer and more structurally sound.

  I was going to
> reinforce the joins with twine
> rap (rope binding) which would further the period
> look and increase joint
> strength.

Again, looks good and would work for a model, but
wouldn't really work for the large engine.

  Weights that were considered were: sand
> bags (dampened to increase
> weight), water barrels, or more rocks.

We're looking for the largest weight per volume as to
have the smallest size counterweight that's still
extremely heavy.  The material that wins this contest
is lead.

>
> The model is valid as period (my only change was on
> the metal bar axles,
> which can easily be changed to wood dowel) and is
> very accurate.

I would venture to say that there were never any
trebuchets with an axle as wide/long as yours was(due
to your extremely wide counterweight) but the rest of
it looked pretty good.  Trebuchets are somewhat
accurate, but definately not VERY accurate, especially
in SCA combat.


  I simply
> did not install a trigger device because it was not
> required (but I designed
> it with one in mind).

ok

>
> The wheels are important in releiving stress to the
> frame, increases thrust
> and makes it a simple matter to adjust for aim
> (simply move it) AND is
> period.  Check out the Discover seige engine
> special.

Nope, sorry I'm going to have to call you on this one.
 The wheels are period and were used on trebuchets
with a fixed counterweight.  Your trebuchet(and the
treb we are going to build) has a hanging
counterweight.  Wheels were not used on a hanging
counterweight because they were not needed.  The idea
is the machine is more efficient if the counterweight
is allowed to drop in a straight line longer.  This is
accomplished in the hanging counterweight version by
having the counterweight swing.  The wheels on the
fixed counterweight machine allow the entire machine
to move forward and backward, allowing the
counterweight to drop in a straighter line.  The
position of the machine moves, but the counterweight
stays in relatively the same place.  Check out the
Nova episode again, this is explained in detail with
some nifty slo motion video.

One other thing worth mentioning is one the actual
trebuchet is put together it will be at least 800lbs
in weight.  I'd like to see us reposition it
effectively on soft ground(like gulf wars) using
wheels.  It's not going to happen easily.  If we want
to adjust trajectory, we should have a movable launch
trough(also demostrated on the nova show).

Also I have several historical paintings/drawings of
hanging counterweight trebs.  Not one of them has
wheels.  Some have Treadmills(human sized hamster
wheels) but those are used for cocking the arm, not
moving the machine.

  If you build a single
> frame instead of an assemblage, you prevent the wear
> and tear of take down
> and set up and get a stronger frame.  Think
> wagon/trailer.

Umm, I would LOVE to do that, however, I don't know of
any trailers that are at least 15' wide(the width of
the base), much less any roads that are.  Unless we
want to drive all the way to Mississippi and back with
a "wide load" I don't think we can entertain this
option.  That being said, some parts can be built as
one piece, but on the whole, it must be collapsible.

>
> Just my two cents from the modeling point of view.

Good modeling suggestions, unfortunately they don't
apply as well to a full size(or in our case half size)
machine.

-Bjorn

PS:  this discussion really should be taken over to
the LR-Treb-Project at yahoogroups.com list...

>
> Asa
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