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Vincent Le Chevalier




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PostPosted: Sat 24 Jan, 2009 9:34 am    Post subject: Alternative visualisation         Reply with quote

Quote:
Yep that would be a possibility, and I thought of it earlier, but I wanted to keep a rectangular area for the whole mass of the sword (light+dark). I could take out the dark area entirely... Then the size of the vertical bar going out of the rectangle would represent the proportion of mass in the point mass, but you won't be able to actually see the total mass any longer. Maybe total mass is not such a big deal though...


Actually there is a way around all this; I forgot I could play with the grey level as well Happy

This new diagram might be easier to read:



(As before, click for a PDF)

So here the area of the rectangle is proportional to the total mass, the grey level indicates the proportion of mass that resides in the uniform stick (black=100% stick, white=0%), and the black bar shows where the point mass is. As before, the red line indicates the reference that allows to line up the swords, the cross in my case. Seems to work for me but I don't know if people are generally sensitive to shades of grey, or if the differences show as well on other screens... As an example, you can see here that the iaito is the closest to a stick, and so is darkest. The Milanese dagger on the other end, is very close to a point mass, and the rectangle is very bright. And everything in between... Generally, when a weapon shows brighter on the diagram, in handling it will seem lighter than you'd think from its mass.

Don't pay attention to the residual lines that appear in some of the rectangles, it's an artefact of my drawing method and I'll work on removing it Wink

Thoughts?

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Vincent Le Chevalier




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PostPosted: Sat 24 Jan, 2009 9:36 am    Post subject: Effects of tapers         Reply with quote

While I was at it I tried to illustrate the effect of tapers, and how it shows on the diagram.

I computed the uniform stick + point mass equivalent of several increasingly tapered objects. Starting with a plain uniform bar (0% taper), I added linear taper on one plane (i.e. I only did profile or distal, but not both) on all the length, until reaching a sharp tip (100% taper). Here is how it shows up:



At 0% taper, you have a big black rectangle, and obviously no point mass. As you add more and more taper, the total mass decreases (the rectangles get thinner), but the stick proportion also decreases (they get brighter). In the end, the total mass is half of what we started with, but the stick part is less than 30% of what it was at the beginning. In effect it's exactly as if we reduced mass and concentrated the remaining mass further. That's why tapers are so useful when making a sword, they have a drastic effect on mass distribution, with only a very smooth transformation of the object.

Hope this helps,

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Jared Smith




PostPosted: Sat 24 Jan, 2009 5:24 pm    Post subject:         Reply with quote

One more thing to the above illustration; an indication of relative center of CoG and neutral moment of inertial pivot s (overall.) This should highlight the extent of effects of tapers. (I am expecting around 3". Some will call this "drastic" for a roughly 10% change.)
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David E. Farrell




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PostPosted: Sun 25 Jan, 2009 6:16 am    Post subject:         Reply with quote

yeah, I think the color scheme version seems to work a bit better - you could also use a color gradient from say blue to green to red or some other scheme.

I am still not sure about the total area being proportional to the mass... because in considering 2 swords, like the brecia spadona and the napoleonic briquet, it is tough to see which weighs more on this diagram - it just seems the area is pretty big in both cases. But this is easily remedied by listing the weights numerically in a separate table.


I am working getting those measurements for my Black Prince - hopefully I'll actually be able to do it today.

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Vincent Le Chevalier




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PostPosted: Mon 26 Jan, 2009 2:12 am    Post subject:         Reply with quote

Hi Jared!

Jared Smith wrote:
One more thing to the above illustration; an indication of relative center of CoG and neutral moment of inertial pivot s (overall.) This should highlight the extent of effects of tapers. (I am expecting around 3". Some will call this "drastic" for a roughly 10% change.)


Not going to do a plot just for that but here are the numbers... Assuming the bar with no tapers is 1m long, and weighs 1kg:

- The bar with no taper has its CoG at 50cm from butt, radius of gyration is 28.9cm
- With 50% taper it weighs 750g, CoG at 44.4cm, RoG of 28.3cm
- With 100% taper it weighs 500g, CoG at 33.3cm, RoG of 23.6cm

Not too sure of what you call "neutral moment of inertial pivot" but I guess radius of gyration (square root of moment of inertia around CoG divided by mass) is a fair measure of how inertia changes.

Now, whether you call that drastic or not is up to you Happy

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Jared Smith




PostPosted: Mon 26 Jan, 2009 2:32 pm    Post subject:         Reply with quote

"Neutral moment of inertia pivot" was a poorly worded phrase. Sorry. Radius of gyration is a pretty useful statistic for conveying the actual effect (how much torque-moment arm is required to accelerate or slow rotations of the object.)

I've only measured a few swords (Albion Knight, Sempach, and Munich.) The tapers are subtle (a couple of transitions occur such that taper increases as we talk about locations closer to the point/ tip. Allowing for both profile, and thickness taper, I would guess your "50% taper" is close for similarly common, straight, double edged, Medieval category swords? (Moves CoG about 10% compared to plain straight bar, radius of gyration change on the order of 2%, pertinent to perceived rotating inertia, is not my idea of drastic! Possibly I am still looking at this wrong though.)

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Vincent Le Chevalier




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PostPosted: Tue 27 Jan, 2009 4:20 am    Post subject:         Reply with quote

Well drastic is perhaps not a wise choice of words from my part... Drastic relative to what?

One thing is for sure, tapers are absolutely necessary in order to get the kind of balance many good swords seem to have, and keep a relatively solid blade. I'm going to take the Brescia Spadona here as an example.

According to Thom R. measurements and my own calculations, it has exactly the same dynamic balance as a stick 115.8cm long, weighing 455g, with a 1079g point mass located precisely at the cross (5mm forward to be accurate). You cannot build such a thing with no taper over the blade. If you start out with a plain bar, and try to just add mass at the cross or pommel location, it will fail. The best you could do is end up with a big 1kg cross, twice as big as the body of your sword...

If you figure out it's not realistic to add just a cross, you will add a heavy pommel to try and bring the CoG back. In this case the point mass in the equivalent object will not end up at the cross, but somewhere between cross and pommel instead. You'll be able to keep a bigger core rod that way, but the final balance will be completely different, even if you manage to keep the same CoG. In effect you will have more mass in the stick, and the point mass will be located closer to the pommel.

Using tapers will allow you to appropriately concentrate the mass of the sword, without weakening the blade too much, and without bringing the mass too far back. You still need a pommel for the final adjustement, but at least it won't have to be heavier than the blade... And yet the final sword will still move exactly like a very light stick with a big mass very near your hand, which I figure is why its handling feels so nimble despite the mass.

I did the test with my Darkwood rapier as well. I computed the point mass + stick equivalent, and then I thought "hey, maybe the mass of the stick in there is close to the mass of the blade?". As a matter of fact, it is not so close. I weighed the blade separately, and it is heavier than the equivalent stick. There are already some elements of balance built into the blade, mostly through tapers.

And of course, if you taper along more than one dimension, the effect increases. The linear density of the sword will not vary linearly but quadratically, which will concentrate the mass yet more. I could do the computation but honestly these integrals start being boring after a while Happy

All of this is no big news. All the swordmakers that participate in the discussions in these forums have underlined the importance of tapers for years...

Regards,

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Jean Thibodeau




PostPosted: Tue 27 Jan, 2009 5:15 am    Post subject:         Reply with quote

Wonder if these statistic are enough for you to give your take on the handling of my RavenWolf sword by OlliN:
http://www.ollinsworddesign.com/osd-custom-RW.html

A sword that I'm sure you have heard of before. Wink Wink

Weight: 4 lb. 15 oz
OAL: 43 1/2 "
BL: 36 1/2 "
POB: 4 1/8 "
COP: 23 1/2"

Now as discussed in other Topic threads this sword feels much MUCH lighter and easy to move and control than the weight of almost 5 lb. would lead one to guess.

Distal taper: Lets just say that the blade is 3/8 " near the guard and distal tapers slightly for the first 8 " and then tapers sort of concavely to around 50 % thickness over the next foot or so and finally taper linearly to a bit under 1/8 " at the tip: So I guess one could call this a distal taper of 33 %.

100%---------------80%--------------------50%-----------------------------------------------------------33%

The blade is very stiff over the first 1/3 of length, mediumly so over the next 1/3 and very flexible on the last.

Just curious if your theoretical model and my handling agree with each other ? Oh, the pommel is quite heavy and so is the guard, so there is a good concentration of mass at the handle end including a full thickness tang.

( For those who haven't read the Topic about the conception and making of this sword or are new to the site here is a link to the very long multipage " Saga ": http://www.myArmoury.com/talk/viewtopic.php?t=8131&start=260 )

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Vincent Le Chevalier




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PostPosted: Tue 27 Jan, 2009 5:27 am    Post subject:         Reply with quote

Jean Thibodeau wrote:
Wonder if these statistic are enough for you to give your take on the handling of my RavenWolf sword by OlliN:
http://www.ollinsworddesign.com/osd-custom-RW.html

A sword that I'm sure you have heard of before. Wink Wink


Oh yeah Big Grin

Well the stats given are not exactly enough, I would need a pair of pivot points on the top of that (the true centers of percussion). The CoP given, which I guess is the blade node of vibration, is not used in my model. I need that to evaluate the moment of inertia, I cannot get it by any other means. I can send you a description of the exact method to measure these as accurately as possible if you're interested.

I can make a guess as to where the point mass would land (probably at the cross judging from the rest of the swords), and then compute the rest from that, but it would be more interesting to start from the real, measured stats you can get, and then build the mass+stick equivalent.

With that kind of taper I think that the overall balance could be surprising. Different from my type XI to be sure...

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Jean Thibodeau




PostPosted: Tue 27 Jan, 2009 5:53 am    Post subject:         Reply with quote

Vincent Le Chevalier wrote:
I can send you a description of the exact method to measure these as accurately as possible if you're interested.


Well if I can understand it I could try to give you more data: Can't guarantee how close to accurate the data might be ?

Something like a wiggle/waggle test and maybe some hitting on the side of the blade and trying to see where the blade vibrates the least or the most ?

Don't know if this relevant but if I hold the sword vertically with point up and move my hand forward and back the blade seems to want to rotate at a point 25" from the guard and 11" from the tip.

If I slap the pommel hard most of the vibration seems to happen in the last foot of blade.

Oh, if I hit my hand holding the sword instead of the pommel the amplitude of the vibration seems much less ??? What this means I don't know and since I haven't done any test cutting with it yet I'm not sure how the sword behaves in a cut and if this vibration would be excessive vibration making cutting less efficient ?

I suspect that this sword would behave differently if one uses the tip or last few inches of blade to cut or the much thicker mid part of the blade on harder targets like a shield rim ? Lots I don't know about sword behaviour and the subtleties of using the right part of the sword depending on the nature of the target: I can say this as specific to this sword and also for swords in general. ( Experience in cutting limited to melons or pumpkins, no mats or harder targets ).

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Vincent Le Chevalier




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PostPosted: Tue 27 Jan, 2009 6:12 am    Post subject:         Reply with quote

Well I might as well post publicly what measurements I need to build my representation. I'm not concerned at all by vibrations in that study...

Here is what I need:

- distance from the reference point (junction handle-cross) to the tip
- distance from the reference point to the CoG
- handle length (from the reference point to the pommel end), or equivalently overall length (since I have the length from reference to tip).
- at least a pair of pivot points measured as accurately as possible. Other pairs can be used to get a better estimate, or at least estimate the measurement error...
- and of course the total mass of the weapon

Most of these are very easy, the key difficulty is in getting the pivot points to show up. Most people find the waggle test a bit tricky at first... But with experience it gets easier.

First, you need to choose one point on the weapon. This will be the one you will move, so having it somewhere on the handle is probably a good idea... The weapon must be grabbed as accurately as possible at this point, applying as little pressure as possible. I usually grab the weapon between just index and thumb or major and thumb.

Let the weapon hang tip down. It is usually easier and safer that way. The test can be done tip up, but I do not recommend that, as it is less steady. Next, move your holding point back and forth as fast as possible. The motion must be quick but need not be ample, around one fifth of the length of the weapon is plenty enough.

If all goes well, you should see, down on the blade, a point that does not move. This is the pivot point (the real "center of percussion") associated to the one where you grabbed the weapon.

There are several mistakes that can disturb this measurement. First, if you apply a torque on your gripping point, it will unsettle the oscillation. That is why the grip must be as light as possible. Second, if the motion of your hand is not quick enough, there will be a motionless point on the weapon, but it will not be the pivot point, so you will not be able to link it to inertia. In fact, by varying the frequency of your hand's motion, you should be able to make the weapon pivot about anywhere you want. It is only when the frequency becomes high that the motionless point merges with the pivot point.

It is very important, when measuring pivot points, to be accurate on the location of both reference and pivot, i.e. for the waggle test, the spot where your fingers move the sword, and the fixed point on the blade. Both are needed to deduce the radius of gyration.

I think many people try the waggle test while holding the sword in the whole hand. This does not allow for a precise measurement, as your hand applies a bit of torque, and you don't have a very precise holding point...

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Jean Thibodeau




PostPosted: Tue 27 Jan, 2009 6:39 am    Post subject:         Reply with quote

Very interesting and useful information as I'm sure my method wasn't as precise but I think I was doing a quick back and forth motion but as you mention using the entire hand.

So the 2 paired pivot points are where the grip is pinched ( Probably just behind the guard ) and the point observed on the blade where it seems to rotate and not move.

Oh, other examples of where one should hold the sword to establish more pivot points pairs?

Oh, going to bed soon so I won't get back to this until late tonight or in a few days. ( Up all night and sleeping days. Laughing Out Loud ).

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Vincent Le Chevalier




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PostPosted: Tue 27 Jan, 2009 7:00 am    Post subject:         Reply with quote

Jean Thibodeau wrote:
So the 2 paired pivot points are where the grip is pinched ( Probably just behind the guard ) and the point observed on the blade where it seems to rotate and not move.

Yep, that's exactly it!

Quote:
Oh, other examples of where one should hold the sword to establish more pivot points pairs?

Junction pommel/handle is also interesting and easy enough to get. Of course the position of the junction should be noted accurately as well... Almost any point on the handle can be useful normally, if you have risers on the grip it is often easier to hold it here.

On some swords I try to iteratively find the holding point that produces a pivot right at the tip. Ordinarily it is on the blade, more or less close to the guard depending on the type. Depending on the guard configuration it may not be possible to find it, for example on rapiers it is hidden in the complex guard.

Overall, with several tries at the junctions cross/handle and pommel/handle, you can accumulate enough information. It does not have to be absolutely perfect... Mine are not either Happy

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Thom R.




PostPosted: Tue 27 Jan, 2009 8:01 am    Post subject:         Reply with quote

just FYI what I have been doing for PP's is i have a velcro strip that can loop over itself and on that i have a pin sticking out so that the pin is perpendicular to the blade...... the velcro loop can be moved up/down the blade and adjusted and the pin provides a better point of reference for visual observation than staring at the blade / blade edges. now the main error in the measurement (for me anyway) is what Vincent said about how you hold the sword at the cross. tr
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Vincent Le Chevalier




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PostPosted: Tue 27 Jan, 2009 8:37 am    Post subject:         Reply with quote

Thom R. wrote:
just FYI what I have been doing for PP's is i have a velcro strip that can loop over itself and on that i have a pin sticking out so that the pin is perpendicular to the blade...... the velcro loop can be moved up/down the blade and adjusted and the pin provides a better point of reference for visual observation than staring at the blade / blade edges. now the main error in the measurement (for me anyway) is what Vincent said about how you hold the sword at the cross. tr


Very ingenious Thom!

I'll be sure to try that one... On steel swords it is indeed a bit difficult not to loose the pivot when transitioning back to the ruler.

Thanks for that!

[Edit: fixed an embarrassing typo Happy]

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PostPosted: Wed 28 Jan, 2009 2:36 pm    Post subject: Swords and trainers         Reply with quote

Hello again!

With the new data sent by members here I've been able to draw a graphical representation of how real swords and training items differ in their mass distribution.

Here is the picture first:



From top to bottom I've plotted one-handed swords, one-handed trainers, two sorts of Japanese sword simulator, hand and a half swords, and hand-and-a-half trainers.

As you can see the wooden arming sword, and wooden swords in general, have their point mass a bit too far forward from the cross. My longsword (at the bottom), also from Purpleheart Armoury, is the most extreme in this sense. Their stick mass is also higher in proportion (the rectangles are darker). The Purpleheart Longsword belongs to Kyle H., who was unable to weight it. Therefore I've used the mass given on the website, 1.1kg. I doubt this is accurate, as I weighed mine and it is actually something like 700g. This changes only the area of the rectangle, not the point mass location nor the color.

The bokens are actually quite close to the iaito. I suspect this has to do with the way the japanese swords are balanced, shorter with not much taper. This balance seems to be easier to reproduce in wood. Boken 2 is a very heavy boken, very thick. As you can see it is almost purely a stick, and so the point mass location is not really relevant. Still, it lands very near the cross, as it does on the metal iaito.

The Hanwei has the opposite property, the point mass is too far towards the pommel. I think they were forced to do this by their blunt blade. The blunt blade has too much stick mass of its own, and they wanted a plausible CoG, so they added more mass at the pommel, but doing so they also pulled the point mass location further towards the pommel. It would be interesting to measure an Albion I33 to see how they settled that issue...

To sum things up, trainers are different from real swords in two aspects: they have a proportionally bigger stick (their mass is not as concentrated as that of the real thing), and the location of the point mass is off, either too far down the blade or too far up the handle. I think it sums up visually the complaints I've heard about these entry-level training items. Indeed they cannot really move as real swords do.

Measuring other training items, for example nylon wasters, Albion blunts, and the new line done by Mr Pearce and CAS/Hanwei, would be informative I think. I'm willing to bet the most sophisticated training gear manages to get really close to the swords on this kind of diagrams.


At the risk of repeating myself, note how the position of the point mass seems to be very tightly controlled on medieval swords. It is at the cross each time, within the accuracy of the measurements. Even for the Arms&Armour Black Prince, kindly measured by David E. Farell, you just see very little mass in the stick (a clear rectangle), but the point mass stays at the cross. Actually I didn't believe it would do that; with that big pommel I expected the point mass to be more inside the handle, and I was ready to adjust the theory... In the end no need to do that Happy

I wish to thank again Eric Spitler, Kyle H., Thom R. and David E. Farell, for feeding me some very valuable data Happy Keep it coming Big Grin !

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Vincent Le Chevalier




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PostPosted: Wed 18 Feb, 2009 8:51 am    Post subject: 'Big swords'         Reply with quote

Hello everybody!

Patrick Kelly and Jean Thibodeau have shared measurements of their 'big swords', respectively the 'Big Johnsson' and the 'RavenWolf' earlier and I think the results are similar in some ways. I'll try to comment them a bit...

I have tried several visual representations previously, here is a new one showing the big swords and some more ordinary specimens:



Here the area of each rectangle is proportional to the 'stick mass' of the sword. The vertical black bar materializes the location of the point mass. The length of the vertical bar is related to the magnitude of the point mass: if it is very small it barely stick out of the rectangle, if it is very big it gets very lengthy. The vertical red line is the reference that just allows to line the swords up; I choose the cross again.

Most quality medieval sword repros have their point mass nearly at the cross. As you can see both big swords are nearly in this configuration as well. They are a bit further forward than what I had seen before. This might help out in the cut, as the point mass will drive the stick into rotation. Yet, being still close to the cross, the point mass is easy to stop, because it is also close to the hand.

Interestingly the stick mass is not really that big in both swords. As you can see, the linear density of the equivalent stick is very comparable to other smaller swords. Actually, my Type XI by Angus Trim has more stick in it than the big swords. Even the Milanese Rapier from Arms&Armor has about the same stick. My understanding so far is that the stick mass is what lends solidity and blade presence to the sword. It makes sense that many cutting swords would have more or less the same.

Where the big swords really stand out is the magnitude of the point mass. This is the result of the aggressive non-linear taper that appears on both blades, I believe. The proportion of total mass in the point mass is actually more than 70% for both. That value I had only seen so far in rapiers and foils... But these do not have the stick mass to back it up.

Numerically:

- Big Johnsson: 395g in stick, 1011g in a point mass located 24mm from the cross

- RavenWolf: 534g in stick, 1706g in a point mass located 21mm from cross

My interpretation of the inner working of these swords, as of now, is this. The decent stick mass lends them impact and toughness. The very big point mass is used to accelerate the stick around the pommel end in cuts, but being close to the guard, it is also easy to recover it. That's why these swords seem nimbler than their overall weight would make us think. If the stick mass was bigger proportionally, moving the sword around in rotations would be far more difficult. If the point mass was located into the handle, it wouldn't be used as efficiently to transfer momentum to the stick. If it was located further down the blade, you'd be unable to recover as easily from cuts. So this would be sort of an ideal compromise for cutting swords Happy The drawback is that the overall weight is still big, meaning that you will tire yourself quicker moving these around.

All of this assumes that measurements of pivot points were correct of course, but seeing that it seems in agreement with users' experience I see little reasons to doubt it.

My renewed thanks to Jean and Patrick for sharing measurements!

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PostPosted: Wed 18 Feb, 2009 8:53 am    Post subject:         Reply with quote

now I think you need to see if you can get some leaf-blade numbers Big Grin

Very interesting results so far, good work Vincent!

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Jean Thibodeau




PostPosted: Thu 19 Feb, 2009 12:43 am    Post subject:         Reply with quote

Vincent: Like I said in our P.M. exchange I think this method of showing the " stick " and the size/scale of the " point mass " using the length of the crossing line works better for me than some of the other graphic ways of trying to show the same thing.

I agree with your conclusions, or rather your calculations seem to agree with my handling impressions, that my heavy sword handles quickly and is quick to recover from but the total mass means that one should get the fight over with quickly as it's total weight is still going to make one tire faster than a lighter sword.

Fairly sure that the RavenWolf or The Big Johnson would make any connecting blow particularly damaging but wouldn't be the best for fencing where speed and agility was the priority like 1:33 but with a kite shield or large heater shield or from horseback they could be effective. ( Or used two handed by holding onto the pommel with the off hand in spite of the short handle it reacts much more quickly and more importantly with two hands one doesn't get tired too soon ).

One does have to be able to hit and not be hit and a slower sword can be a disadvantage. but initially these two sword are fast enough until fatigue set in ? I will admit that my sword is a monster, a manageable monster, but still a monster. Wink Laughing Out Loud

Great praise should again go the Mark at OlliN for being able to make such an extreme design into a good sword: The fact that the numbers put it in the class of good period swords and is close to the Big Johnson made by Peter Johnsson in nature sort of tells me something right there. Big Grin Cool

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PostPosted: Thu 19 Feb, 2009 4:46 am    Post subject:         Reply with quote

Yes, measuring a leaf blade might be interesting too... I suspect authentic leaf blades might fulfill my hypothesis of having the point mass at the cross, through careful use of tapers. One could expect to see it further down the blade, but balance is not necessarily intuitive Wink

Actually there are plenty of things I'd like to see numbers about. In no particular order:

  • Rapiers. I think the point mass at the cross is a reasonable thing to do as long as you don't want to sacrifice cutting motions. Maybe specialized rapiers have it more into the handle, kind of like the Cavalier rapier but a bit less extreme
  • Messers. Would be nice to see how you can create a point mass where appropriate through the use of tapers only
  • Cavalry sabers. The one measured by George Turner seems peculiar among the rest of the real weapons. Maybe it's just this model, maybe it's all of them?
  • Katanas. I have only been able to measure training Japanese swords. It would make sense if katanas had a balance similar to that of quality iaitos, however this would have to be confirmed
  • And of course more medieval swords, one and two-handed Happy

Aside from that, I still have to put together some form of tool so that anyone can see the equivalent representation without having to do the math, check error propagation in this model, build very simple test objects with wooden dowels and washers to get a feel myself, and finally write the whole thing up in a consistent document...

Overall, enough to keep me busy for a while I think Big Grin

--
Vincent
Ensis Sub Caelo
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