[resending from different server, first attempt failed]
I want something small that will throw a golfball or tennis ball an
impressive distance. So I was thinking maybe a "King Arthur" style
trebuchet (with a fixed axle, not floating.)
Has anyone here built something like that? Maybe I'm at the wrong
group, but I don't think so.
How important is it to be able to adjust the amount of counterweight? I
was planning to use a sledgehammer for the hanger arm and counterweight.
Or maybe a beer can sized block of lead -- about 8 to 10 pounds.
I assume the throwing arm needs to be as light as possible, especially
towards the end.
No idea how one adjusts the sling.
Best regards,
Bob
In article <[email protected]>, zxcvbob <[email protected]> wrote:
>[resending from different server, first attempt failed]
>
>I want something small that will throw a golfball or tennis ball an
>impressive distance. So I was thinking maybe a "King Arthur" style
>trebuchet (with a fixed axle, not floating.)
>
>Has anyone here built something like that? Maybe I'm at the wrong
>group, but I don't think so.
Did that about 10-12 years ago with my son, for a science fair project. :-)
>
>How important is it to be able to adjust the amount of counterweight?
Very. For any given trebuchet, there's an optimal ratio between projectile
mass and counterweight mass, which results in the maximum throw distance. If
the counterweight is too light, the arm rotates too slowly, and imparts too
little velocity to the projectile. If the counterweight is too heavy, the arm
rotates too quickly, and launches the projectile at too shallow an angle to
achieve maximum distance -- and, as we discovered in our experiments, if the
counterweight is grossly too heavy, the arm rotates very fast, and launches
the projectile after it has already swung past vertical (i.e. launches on a
downward trajectory). This leads to a very short throw.
So at least until you discover the optimum ratio for your design, it's
critical to be able to adjust the counterweight mass. You also need to be able
to adjust the counterweight mass if you will be launching projectiles of
significantly different mass.
IIRC, we found the optimal ratios to be approximately 4:1 for length of
throwing arm to length of counterweight arm, and about 25:1 for counterweight
mass to projectile mass. Don't take that as gospel, but it's probably a good
starting point for experimenting.
>I was planning to use a sledgehammer for the hanger arm and counterweight.
> Or maybe a beer can sized block of lead -- about 8 to 10 pounds.
We used free-weights from a set of dumbbells. The set had two each 2-1/2 pound
and 5-pound discs, having a convenient 3/4" diameter hole in the middle. We
attached a 3/4" dowel to the counterweight end of the arm, and cross-drilled
each end for cotter pins to hold the weights on.
>
>I assume the throwing arm needs to be as light as possible, especially
>towards the end.
Correct.
>
>No idea how one adjusts the sling.
We didn't use a sling. The original medieval trebuchets used buckets or
baskets to hold the payload; the sling was a later enhancement. Ours emulated
the original design, with the role of the bucket played by a kitchen measuring
cup duct-taped to the throwing arm.
On Sun, 21 Dec 2008 22:06:49 -0600, zxcvbob <[email protected]>
wrote:
>[resending from different server, first attempt failed]
>
>I want something small that will throw a golfball or tennis ball an
>impressive distance. So I was thinking maybe a "King Arthur" style
>trebuchet (with a fixed axle, not floating.)
>
>Has anyone here built something like that? Maybe I'm at the wrong
>group, but I don't think so.
>
>How important is it to be able to adjust the amount of counterweight? I
>was planning to use a sledgehammer for the hanger arm and counterweight.
> Or maybe a beer can sized block of lead -- about 8 to 10 pounds.
>
>I assume the throwing arm needs to be as light as possible, especially
>towards the end.
>
>No idea how one adjusts the sling.
>
>Best regards,
>Bob
>
>
>
A Pretty good set of instructions at:
http://images.google.com/imgres?imgurl=http://medieval.mrugala.net/Armes%2520de%2520siege/Tennis%2520Ball%2520Trebuchet%2520Plans/tennistrebuchet.jpg&imgrefurl=http://medieval.mrugala.net/Armes%2520de%2520siege/Tennis%2520Ball%2520Trebuchet%2520Plans/Tennis%2520Ball%2520Trebuchet%2520Plans.htm&usg=__RLmREFByfzgWhidiYymTAcei3QA=&h=583&w=452&sz=26&hl=en&start=2&um=1&tbnid=T1kA1k2NUQxSDM:&tbnh=134&tbnw=104&prev=/images%3Fq%3Dtrebuchet%2Bplans%26um%3D1%26hl%3Den%26sa%3DX
(or):
http://preview.tinyurl.com/7jdwj6
A Google search will turn up many more.
Bill
On Dec 22, 8:33=A0am, zxcvbob <[email protected]> wrote:
> Bill wrote:
> > On Sun, 21 Dec 2008 22:06:49 -0600, zxcvbob <[email protected]>
> > wrote:
>
> >> [resending from different server, first attempt failed]
>
> >> I want something small that will throw a golfball or tennis ball an
> >> impressive distance. =A0So I was thinking maybe a "King Arthur" style
> >> trebuchet (with a fixed axle, not floating.)
>
> >> Has anyone here built something like that? =A0Maybe I'm at the wrong
> >> group, but I don't think so.
>
> >> How important is it to be able to adjust the amount of counterweight? =
=A0I
> >> was planning to use a sledgehammer for the hanger arm and counterweigh=
t.
> >> =A0Or maybe a beer can sized block of lead -- about 8 to 10 pounds.
>
> >> I assume the throwing arm needs to be as light as possible, especially
> >> towards the end.
>
> >> No idea how one adjusts the sling.
>
> >> Best regards,
> >> Bob
>
> > A Pretty good set of instructions at:
>
> >http://images.google.com/imgres?imgurl=3Dhttp://medieval.mrugala.net/Ar.=
..
>
> > (or):
>
> >http://preview.tinyurl.com/7jdwj6
>
> > A Google search will turn up many more.
>
> > Bill
>
> That's pretty close to what I had in mind, but where the hanger and count=
erweight start
> out pointing *up* instead of hanging down. =A0It falls along an arc first=
, while the
> throwing arm is still latched. =A0When the counterweight arm approaches t=
he bottom of its
> swing -- say, at a 90 degree angle to the throwing arm -- it releases the=
throwing arm via
> a secondary trigger. =A0So the throwing arm doesn't move until after the =
counterweight has
> built up considerable kenetic energy.
>
> (it's not my original idea, it was invented by Chris Gerow, who built the=
first one for a
> Punkin Chunkin' contest:http://www.supertrebs.com/History.html)
>
> Maybe I should build a tiny one first, using steel washers for weights an=
d a pingpong ball
> for a projectile.
> Bob
Bob-
check out
http://www.onesixsigma.com/crystalball/Implementing-Design-For-Six-Sigma-DF=
SS-With-Crystal-Ball-And-JMP-01102006
scroll down & you'll see the output of the US Army Wintreb
a simulator that will allow you to vary physical charatertiscs of the
machine & see the effect
you can download Wintreb at
http://sixsigmatrainingtools.com/WinTrebDownload.asp
fun to play & see the different trajectories you can generate......by
varying the geometry you can get "mortar behavior" or long range
artillery behavior.....at the extreme you can throw the projectile
nearly straight up
cheers
Bob
On Mon, 22 Dec 2008 13:13:30 GMT, [email protected] (Doug Miller) wrote:
>Very. For any given trebuchet, there's an optimal ratio between projectile
>mass and counterweight mass, which results in the maximum throw distance. If
>the counterweight is too light, the arm rotates too slowly, and imparts too
>little velocity to the projectile. If the counterweight is too heavy, the arm
>rotates too quickly, and launches the projectile at too shallow an angle to
>achieve maximum distance -- and, as we discovered in our experiments, if the
>counterweight is grossly too heavy, the arm rotates very fast, and launches
>the projectile after it has already swung past vertical (i.e. launches on a
>downward trajectory). This leads to a very short throw.
Thanks for the flashback, Doug..
For most trebs, the counter weight should be roughly 16 times the projectile
weight..
>
>IIRC, we found the optimal ratios to be approximately 4:1 for length of
>throwing arm to length of counterweight arm, and about 25:1 for counterweight
>mass to projectile mass. Don't take that as gospel, but it's probably a good
>starting point for experimenting.
>>I was planning to use a sledgehammer for the hanger arm and counterweight.
>> Or maybe a beer can sized block of lead -- about 8 to 10 pounds.
>
>We used free-weights from a set of dumbbells. The set had two each 2-1/2 pound
>and 5-pound discs, having a convenient 3/4" diameter hole in the middle. We
>attached a 3/4" dowel to the counterweight end of the arm, and cross-drilled
>each end for cotter pins to hold the weights on.
>>
>>I assume the throwing arm needs to be as light as possible, especially
>>towards the end.
>
>Correct.
>>
>>No idea how one adjusts the sling.
>
The sling is a real trial and error thing..
I used cloth slings and nylon shock cord, one end of the cord is attached to the
throwing und of the arm, the other end has a loop to go over the hook at the
same end..
I think I started with the entire sling (pouch folded in half and string ends
equal) about 3/4 of the arm length and adjusted from there..
It's right when the loop comes off the hook on the forward stroke without
tangling, and the projectile actually comes out of the sling..lol
When everything is tuned correctly, the projectile should be thrown at about a
45 degree angle..
mac
Please remove splinters before emailing
Bill wrote:
> On Sun, 21 Dec 2008 22:06:49 -0600, zxcvbob <[email protected]>
> wrote:
>
>> [resending from different server, first attempt failed]
>>
>> I want something small that will throw a golfball or tennis ball an
>> impressive distance. So I was thinking maybe a "King Arthur" style
>> trebuchet (with a fixed axle, not floating.)
>>
>> Has anyone here built something like that? Maybe I'm at the wrong
>> group, but I don't think so.
>>
>> How important is it to be able to adjust the amount of counterweight? I
>> was planning to use a sledgehammer for the hanger arm and counterweight.
>> Or maybe a beer can sized block of lead -- about 8 to 10 pounds.
>>
>> I assume the throwing arm needs to be as light as possible, especially
>> towards the end.
>>
>> No idea how one adjusts the sling.
>>
>> Best regards,
>> Bob
>>
>>
>>
>
> A Pretty good set of instructions at:
>
> http://images.google.com/imgres?imgurl=http://medieval.mrugala.net/Armes%2520de%2520siege/Tennis%2520Ball%2520Trebuchet%2520Plans/tennistrebuchet.jpg&imgrefurl=http://medieval.mrugala.net/Armes%2520de%2520siege/Tennis%2520Ball%2520Trebuchet%2520Plans/Tennis%2520Ball%2520Trebuchet%2520Plans.htm&usg=__RLmREFByfzgWhidiYymTAcei3QA=&h=583&w=452&sz=26&hl=en&start=2&um=1&tbnid=T1kA1k2NUQxSDM:&tbnh=134&tbnw=104&prev=/images%3Fq%3Dtrebuchet%2Bplans%26um%3D1%26hl%3Den%26sa%3DX
>
> (or):
>
> http://preview.tinyurl.com/7jdwj6
>
> A Google search will turn up many more.
>
> Bill
That's pretty close to what I had in mind, but where the hanger and counterweight start
out pointing *up* instead of hanging down. It falls along an arc first, while the
throwing arm is still latched. When the counterweight arm approaches the bottom of its
swing -- say, at a 90 degree angle to the throwing arm -- it releases the throwing arm via
a secondary trigger. So the throwing arm doesn't move until after the counterweight has
built up considerable kenetic energy.
(it's not my original idea, it was invented by Chris Gerow, who built the first one for a
Punkin Chunkin' contest: http://www.supertrebs.com/History.html )
Maybe I should build a tiny one first, using steel washers for weights and a pingpong ball
for a projectile.
Bob
On Mon, 22 Dec 2008 13:13:30 GMT, [email protected] (Doug Miller)
wrote:
>In article <[email protected]>, zxcvbob <[email protected]> wrote:
<snip>
>>
>>No idea how one adjusts the sling.
>
>We didn't use a sling. The original medieval trebuchets used buckets or
>baskets to hold the payload; the sling was a later enhancement. Ours emulated
>the original design, with the role of the bucket played by a kitchen measuring
>cup duct-taped to the throwing arm.
I built a small one for throwing golf balls. I used a curved hook at
the end of the arm and found that adjusting the angle of the hook
would adjust the release angle of the sling.
HTH
Bill
zxcvbob wrote:
> [resending from different server, first attempt failed]
>
> I want something small that will throw a golfball or tennis ball an
> impressive distance. So I was thinking maybe a "King Arthur" style
> trebuchet (with a fixed axle, not floating.)
>
> Has anyone here built something like that? Maybe I'm at the wrong
> group, but I don't think so.
>
> How important is it to be able to adjust the amount of
> counterweight?
> I was planning to use a sledgehammer for the hanger arm and
> counterweight. Or maybe a beer can sized block of lead -- about 8
> to 10 pounds.
>
> I assume the throwing arm needs to be as light as possible,
> especially
> towards the end.
>
> No idea how one adjusts the sling.
For a first go why not try
http://www.redstoneprojects.com/trebuchetstore/golf_ball_trebuchet_plan.html#?
After you've done one with plastic pipe you'll be in a better place to
do one in another material if you want to.
--
--
--John
to email, dial "usenet" and validate
(was jclarke at eye bee em dot net)
zxcvbob skreiv:
> [resending from different server, first attempt failed]
>
> I want something small that will throw a golfball or tennis ball an
> impressive distance. So I was thinking maybe a "King Arthur" style
> trebuchet (with a fixed axle, not floating.)
>
> Has anyone here built something like that? Maybe I'm at the wrong
> group, but I don't think so.
>
> How important is it to be able to adjust the amount of counterweight? I
> was planning to use a sledgehammer for the hanger arm and counterweight.
> Or maybe a beer can sized block of lead -- about 8 to 10 pounds.
>
> I assume the throwing arm needs to be as light as possible, especially
> towards the end.
>
> No idea how one adjusts the sling.
>
You might find some inspiration here:
http://www.catapultkits.com/