Just returned from a trip to t'frozen north, Tynemouth to be exact. Went to
Durham, Beamish (brilliant), Alnwick & Warkworth Castle. At the latter I
bought a working scale model of a trebuchet!

Haven't built it yet, but it will be around 200mm high when finished.
Always been fascinated by trebuchets and the plan is to scale up this model
so I can build one around 1.2m high.

So, is scaling parts up as simple as it seems? For example, one piece in
the kit is 240mm long, if I multiply x 10 it would be 2400mm long - about
right. The cross section is 20mm x 12mm, so that would end up as 200mm x
120mm - hefty timber.

Does it work like that?


--
Dave - The Medway Handyman
www.medwayhandyman.co.uk

On Thu, 31 Jul 2008 19:44:00 GMT, "The Medway Handyman"
wrote:

Just returned from a trip to t'frozen north, Tynemouth to be exact. Went to
Durham, Beamish (brilliant), Alnwick & Warkworth Castle. At the latter I
bought a working scale model of a trebuchet!

Haven't built it yet, but it will be around 200mm high when finished.
Always been fascinated by trebuchets and the plan is to scale up this model
so I can build one around 1.2m high.

So, is scaling parts up as simple as it seems? For example, one piece in
the kit is 240mm long, if I multiply x 10 it would be 2400mm long - about
right. The cross section is 20mm x 12mm, so that would end up as 200mm x
120mm - hefty timber.

Does it work like that?

No.

That's why Cathedrals arent like overgrown chapels and why it wasn't a
case of if the spire fell down but when (Think York).

Derek

"The Medway Handyman" wrote in message
om...
Just returned from a trip to t'frozen north, Tynemouth to be exact. Went
to
Durham, Beamish (brilliant), Alnwick & Warkworth Castle. At the latter I
bought a working scale model of a trebuchet!

Haven't built it yet, but it will be around 200mm high when finished.
Always been fascinated by trebuchets and the plan is to scale up this
model
so I can build one around 1.2m high.

So, is scaling parts up as simple as it seems? For example, one piece in
the kit is 240mm long, if I multiply x 10 it would be 2400mm long - about
right. The cross section is 20mm x 12mm, so that would end up as 200mm x
120mm - hefty timber.

Does it work like that?


--
Dave - The Medway Handyman
www.medwayhandyman.co.uk





rec.models.scale should be able to help

No because if you multiply each dimension by 10, you end up with the
volume (and hence the mass) going up by a factor of 1000


240 * 20 * 12 = 57600

2400 * 200 * 120 = 57600000

57600000 / 57600 = 1000

But that doesn't tell us if your original model uses that particular x-
section just because it was readily available, or possibly because it
"looks right" - rather than it be designed correctly for the stresses
on it.

I doubt the medieval designers of the real thing could calculate the
stresses either though (and it's a far from simple problem), so maybe
just go on experience and instinct.

Masses of online resources:

http://en.wikipedia.org/wiki/Trebuchet

However simply throwing bricks at non-paying customers would be a lot
less hassle.

wrote:
No because if you multiply each dimension by 10, you end up with the
volume (and hence the mass) going up by a factor of 1000


240 * 20 * 12 = 57600

2400 * 200 * 120 = 57600000

57600000 / 57600 = 1000

Thats what I wondered, I remember reading somewhere that if you doubled the
dimensions if a 1 pint milk bottle it would hold 8 pints or something.

But that doesn't tell us if your original model uses that particular
x- section just because it was readily available, or possibly because
it "looks right" - rather than it be designed correctly for the
stresses on it.

I doubt the medieval designers of the real thing could calculate the
stresses either though (and it's a far from simple problem), so maybe
just go on experience and instinct.


True enough. Start with 4 x 2 or 6 x 2 & see what breaks? Sounds
practical.

However simply throwing bricks at non-paying customers would be a lot
less hassle.

I don't do 'non-paying customers'. Never happens. Just want to build one
for fun!


--
Dave - The Medway Handyman
www.medwayhandyman.co.uk

The maths is really quite fun (this from the Wiki link)

http://www.algobeautytreb.com/trebmath35.pdf

as is the maths of the Roman cross-bow type catapult, which is also very
dependent on the properties of the sinew which they used for the springy
bits.

Whilst the designers didn't have the modern tools, there was a Scientific
American article on the latter a while ago that suggested they had got quite
close to the optimum

The Medway Handyman wrote:
Just returned from a trip to t'frozen north, Tynemouth to be exact. Went to
Durham, Beamish (brilliant), Alnwick & Warkworth Castle. At the latter I
bought a working scale model of a trebuchet!

Haven't built it yet, but it will be around 200mm high when finished.
Always been fascinated by trebuchets and the plan is to scale up this model
so I can build one around 1.2m high.

This was done on one of C4's scrapheap challenges, flinging cars.

http://www.channel4.com/science/microsites/S/scrapheap2002/challenges/CarFlinger/

--
Adrian C

In message , The Medway
Handyman writes
Just returned from a trip to t'frozen north, Tynemouth to be exact. Went to
Durham, Beamish (brilliant), Alnwick & Warkworth Castle. At the latter I
bought a working scale model of a trebuchet!

Haven't built it yet, but it will be around 200mm high when finished.
Always been fascinated by trebuchets and the plan is to scale up this model
so I can build one around 1.2m high.

So, is scaling parts up as simple as it seems? For example, one piece in
the kit is 240mm long, if I multiply x 10 it would be 2400mm long - about
right. The cross section is 20mm x 12mm, so that would end up as 200mm x
120mm - hefty timber.

Does it work like that?

not really

just type "how to build a trebuchet" into google - plenty of hits

and go kill some medway scum ...

--
geoff

In message , newshound
writes
The maths is really quite fun (this from the Wiki link)

http://www.algobeautytreb.com/trebmath35.pdf

as is the maths of the Roman cross-bow type catapult, which is also very
dependent on the properties of the sinew which they used for the springy
bits.

That's just plain anal ...

--
geoff

On 2008-07-31 23:35:50 +0100, geoff said:

In message , newshound
writes
The maths is really quite fun (this from the Wiki link)

http://www.algobeautytreb.com/trebmath35.pdf

as is the maths of the Roman cross-bow type catapult, which is also very
dependent on the properties of the sinew which they used for the springy
bits.

That's just plain anal ...

Oh I don't know. Have you ever been to Bluewater?

In message 4892400e@qaanaaq, Andy Hall writes
On 2008-07-31 23:35:50 +0100, geoff said:

In message , newshound
writes
The maths is really quite fun (this from the Wiki link)
http://www.algobeautytreb.com/trebmath35.pdf
as is the maths of the Roman cross-bow type catapult, which is also
very
dependent on the properties of the sinew which they used for the springy
bits.

That's just plain anal ...

Oh I don't know. Have you ever been to Bluewater?

Some kind of shopping emporium, isn't it ?

No


--
geoff

"The Medway Handyman" wrote in message
om...
Just returned from a trip to t'frozen north, Tynemouth to be exact. Went
to Durham, Beamish (brilliant), Alnwick & Warkworth Castle. At the latter
I bought a working scale model of a trebuchet!

Haven't built it yet, but it will be around 200mm high when finished.
Always been fascinated by trebuchets and the plan is to scale up this
model so I can build one around 1.2m high.

So, is scaling parts up as simple as it seems? For example, one piece in
the kit is 240mm long, if I multiply x 10 it would be 2400mm long - about
right. The cross section is 20mm x 12mm, so that would end up as 200mm x
120mm - hefty timber.

Does it work like that?

Nope. Read up on the square cube law.

Basically if you double the size of something (ie, double all dimensions),
then the strength of the object is increased by fourfold (ie, 2 squared).
However, the volume and weight of stuff required to make it increased by
eightfold (ie, 2 cubed). The problem you then run into is the fact that your
structure may have trouble supporting its own weight. Triple the size and
strength increases by a factor of 9 but the weight of it increases by a
factor of 27.

OTOH it's not likely that you'll build a big one out of identical materials
to the little one...

On 2008-07-31 23:58:02 +0100, geoff said:

In message 4892400e@qaanaaq, Andy Hall writes
On 2008-07-31 23:35:50 +0100, geoff said:

In message , newshound
writes
The maths is really quite fun (this from the Wiki link)
http://www.algobeautytreb.com/trebmath35.pdf
as is the maths of the Roman cross-bow type catapult, which is also very
dependent on the properties of the sinew which they used for the springy
bits.

That's just plain anal ...

Oh I don't know. Have you ever been to Bluewater?

Some kind of shopping emporium, isn't it ?

No

A trebuchet could be useful there.

Andy Hall wrote:
On 2008-07-31 23:58:02 +0100, geoff said:

In message 4892400e@qaanaaq, Andy Hall writes
On 2008-07-31 23:35:50 +0100, geoff said:

In message , newshound
writes
The maths is really quite fun (this from the Wiki link)
http://www.algobeautytreb.com/trebmath35.pdf
as is the maths of the Roman cross-bow type catapult, which is
also very dependent on the properties of the sinew which they
used for the springy bits.

That's just plain anal ...

Oh I don't know. Have you ever been to Bluewater?

Some kind of shopping emporium, isn't it ?

No

A trebuchet could be useful there.

I could make this a commercial venture! The original 'Warwolf' could chuck
a 100kg ball 200m. It was 20m high, so transport might be a problem, but
how much a day could you charge for destroying places like Bluewater?


--
Dave - The Medway Handyman
www.medwayhandyman.co.uk

The Medway Handyman wrote:
Just returned from a trip to t'frozen north, Tynemouth to be exact. Went to
Durham, Beamish (brilliant), Alnwick & Warkworth Castle. At the latter I
bought a working scale model of a trebuchet!

Haven't built it yet, but it will be around 200mm high when finished.
Always been fascinated by trebuchets and the plan is to scale up this model
so I can build one around 1.2m high.

So, is scaling parts up as simple as it seems? For example, one piece in
the kit is 240mm long, if I multiply x 10 it would be 2400mm long - about
right. The cross section is 20mm x 12mm, so that would end up as 200mm x
120mm - hefty timber.

Does it work like that?


Actually it sort of does: however the material you use will go up - in
the model airplane world - from balsa, to spruce, to aluminium as you
progress towards that full size spitfire. ;-)

In message , The Natural
Philosopher writes
The Medway Handyman wrote:
Just returned from a trip to t'frozen north, Tynemouth to be exact.
Went to Durham, Beamish (brilliant), Alnwick & Warkworth Castle. At
the latter I bought a working scale model of a trebuchet!
Haven't built it yet, but it will be around 200mm high when
finished. Always been fascinated by trebuchets and the plan is to
scale up this model so I can build one around 1.2m high.
So, is scaling parts up as simple as it seems? For example, one
piece in the kit is 240mm long, if I multiply x 10 it would be 2400mm
long - about right. The cross section is 20mm x 12mm, so that would
end up as 200mm x 120mm - hefty timber.
Does it work like that?

Actually it sort of does: however the material you use will go up - in
the model airplane world - from balsa, to spruce, to aluminium as you
progress towards that full size spitfire. ;-)

so it really doesn't


--
geoff

On Thu, 31 Jul 2008 19:44:00 GMT, "The Medway Handyman"
wrote:

bought a working scale model of a trebuchet!

Haven't built it yet, but it will be around 200mm high when finished.
Always been fascinated by trebuchets and the plan is to scale up this model
so I can build one around 1.2m high.

Trebs are sized by their beam length when dismantled. Mine is exactly
one Citroen XM length 8-) (about 2m beam)
http://codesmiths.com/siege/build/

They're easy to make and good fun. A 20-bricker is a good starter, in
this size. You need a _large_ ratio of weights between projectile and
weightbox. IMHE, 20x is just enough and more is definitely more.

Smallest I've had was a beam of carbon fibre kite spar and lead cast
into a Coke can, for throwing boiled sweets around the office.

Caerphilly Castle has a nice collection of siege engines, including treb
and perrier (aka traction trebuchet)

Get yourself a copy of Payne-Gallwey's splendiferous "The Book of the
Crossbow" which has an awful lot on trebs , ballistae etc. Then you
can build one of these:
http://www.jarkman.co.uk/catalog/random/onager.htm
That's a 12" hammer shaft as the throwing beam. I did a 9" for my son.


Scaling is tricky - it defeated Napoleon III when he tried to recreate a
medieval castle-smasher. One of the best science books I have _ever_
read is Pennycuick's "Newton Rules Biology". It's an analysis of
biological structures in terms of Newtonian scaling laws. Make
something twice as long and it will have 2^2 = 4× the area and 2^3 = 8×
the volume. This also implies a ratio of surface area / volume that
reduces with increasing size, thus making it hard to cool an elephant.
Elephant leg strength is also proportional to their leg bone
cross-section (i.e. area) which is why they can't jump.

So if you scale up your trebuchet to a 2m beam in 4"×4", it'll be fine.
But if you go to a 4m beam, things will start snapping, even if you
double the beam thickness. It's impossible to make a trebuchet of
military scale, without getting into the innovation of tapering the beam
along its length - even if you make it from carbon fibre.

Trebuchet design / simulation programs like WinTreb (probably others
too) will help to explain how important the sling and the sling release
hook are.

You'll also discover how the trajectory of a treb is a random factor of
the release point. They are _not_ controllable, not safe to fly in, and
easily capable of hurling bricks either backwards or vertically upwards.

--
Cats have nine lives, which is why they rarely post to Usenet.

On Fri, 01 Aug 2008 01:06:14 +0100, The Natural Philosopher
wrote:

Actually it sort of does: however the material you use will go up - in
the model airplane world - from balsa, to spruce, to aluminium as you
progress towards that full size spitfire. ;-)

The Spitfire was inspired by medieval trebuchet design, The wing spar is
a tapered beam, formed by laminating simple aluminium box sections of
varying length. Although broadly constant in cross-section, the wall
thickness tapers outwards.

The Medway Handyman wrote:
Andy Hall wrote:
On 2008-07-31 23:58:02 +0100, geoff said:

In message 4892400e@qaanaaq, Andy Hall writes
On 2008-07-31 23:35:50 +0100, geoff said:

In message , newshound
writes
The maths is really quite fun (this from the Wiki link)
http://www.algobeautytreb.com/trebmath35.pdf
as is the maths of the Roman cross-bow type catapult, which is
also very dependent on the properties of the sinew which they
used for the springy bits.

That's just plain anal ...
Oh I don't know. Have you ever been to Bluewater?

Some kind of shopping emporium, isn't it ?

No
A trebuchet could be useful there.

I could make this a commercial venture! The original 'Warwolf' could chuck
a 100kg ball 200m. It was 20m high, so transport might be a problem, but
how much a day could you charge for destroying places like Bluewater?


And where would "they" go without Bluewater? Got to think of the
consequences on other places.

--
Rod

Hypothyroidism is a seriously debilitating condition with an insidious
onset.
Although common it frequently goes undiagnosed.
www.thyromind.info www.thyroiduk.org www.altsupportthyroid.org

On 2008-08-01 08:07:29 +0100, Rod said:

The Medway Handyman wrote:
Andy Hall wrote:
On 2008-07-31 23:58:02 +0100, geoff said:

In message 4892400e@qaanaaq, Andy Hall writes
On 2008-07-31 23:35:50 +0100, geoff said:

In message , newshound
writes
The maths is really quite fun (this from the Wiki link)
http://www.algobeautytreb.com/trebmath35.pdf
as is the maths of the Roman cross-bow type catapult, which is
also very dependent on the properties of the sinew which they
used for the springy bits.

That's just plain anal ...
Oh I don't know. Have you ever been to Bluewater?

Some kind of shopping emporium, isn't it ?

No
A trebuchet could be useful there.

I could make this a commercial venture! The original 'Warwolf' could
chuck a 100kg ball 200m. It was 20m high, so transport might be a
problem, but how much a day could you charge for destroying places like
Bluewater?


And where would "they" go without Bluewater? Got to think of the
consequences on other places.

There is that, I suppose.