The world speed record is broken

First topic message reminder :

Used audacity and the film 
"MANTIS Elite with uprated ENERGYWAVE technology gas spring."
to get 689 fps in Phil Abrahms Talisman Mantis crossbow.
That´s a remarcable word record ladies and gentlemen.


Congratulations Phil!

Hello,
I have never built a true crossbow before but have always been interested in ballista-type designs because it has potential for high efficiency with light high speed arrows. I am curious about the claims of speed with this mantis launcher.  I see claims of very high speeds, but haven't found any information about chronograph tests.

For the bow used in the video, what is the draw weight of the Mantis launcher?  What is the draw length and weight of the arrow?  What kind of string is used?

Thanks!

Alan

Rolnyd,
Is there some way you could share a copy of the article about Ruediger Koltze?  I hadn't heard of this before and am very interested to read about it. 

I started playing with the twin-bow, three-string design for flight shooting (shooting for distance). My best results were with two asymmetrical bows, oriented about thirty degrees toward each other. Unlike the Koltze design, I found it best that the limbs were not allowed to rotate about their axis. I shaped the limbs with a twist so that they acted much stiffer in the first several inches of draw. The design is very fast, but awkward. I have since gone back to seeing how far I can push more conventional recurve designs, but will probably return to work on the double bow again sometime in the future. 

Bulletin femmes,
It isn't easy to come up with bows that can reliably shoot projectiles at extreme speeds.  USA Archery used to hold an annual "Worlds Fastest Bow" contest in the 1990's. The results of the contest had some credibility because it used a standard test setup and impartial officials to oversee the process. It also led to a great deal of disappointment when most participants found that they couldn't come close to reproducing their claimed arrow speeds under controlled and monitored test conditions.

Harry Drake mentioned in his own notes about a 250+ pound compound with very long draw length that he was able to chrono light arrows in the high 600 fps range (drawn back with a winch). He never chrono tested any of his record breaking recurve foot bows or crossbows, but I am pretty certain they shot in the low 600s.  One weakness for Harry Drake was the bow string. He would break a string on every shot!

I would also like to know more about the golf ball throwing machine. Is there any information that you can point me to on that?

Phil,
If you are ever interested, there is an annual Flight Archery (shooting bows for distance) event held at the Bonneville Salt Flats hosted by USA Archery.  It is scheduled this year to take place Friday, September 4th, through Sunday, September 6th.  A mech-bow may fall outside the standard bow definitions, but that wouldn't stop you from shooting it and having it officially measured. 

Thanks for sharing!

Alan

Alan Case wrote:
I would also like to know more about the golf ball throwing machine. Is there any information that you can point me to on that?

It was in The Hurl forum, but their whole website seems to be down.
http://www.thehurl.com/index.html


IIRC it was a da Vinci clockwork type catapult.

But anyway, if we had a catapult arm out of carbon arrowshaft and just a normal crossbow prod swinging it , lightweight bullets might be going with intersting speeds.

A separate swinging arm takes energy out of the bow and makes it safer to dry-fire.

Here is the data http://www.talismancrossbows.net

It works and has almost the double energy compared to a 60 pound compoundbow. Take a look on all the youtube videos and you will see proof. The world speed record is broken -no doubt about it.

Oppenheimer,
I must be missing something somewhere?  I don't see any test data or actual chronograph measurements on YouTube, or anywhere else.  I see a claim of up to 480 fps with a very light 300 grain arrow, 300-lb draw weight, and 19.8 inch draw. This claim seems plausible, but the arrow used in the video that started this thread is heavier than 300 grains. So the physics don't add up. 

The equivalent energy of two 60 or 70-lb compounds at 30 inch draw is not nearly enough energy to drive speeds of almost 700 fps with a 400+ grain arrow. Per the rules of physics, it requires four times the energy to double the speed of a projectile.  In addition, all bows/projectile launchers lose efficiency with higher arrow speeds, so it may easily require six+ times the energy of a high performance compound to obtain these speeds.  The draw weight of the bow would have to be over 850 pounds to do this!  In addition, you would need an arrow an string capable of handling the enormous forces involved. 

Regardless, the Mantis is a neat idea, and it obviously works well enough for sporting purposes. 

Alan

Completely agree with Alan above.

Chrony results or it didn't happen.

Here is a second test
https://www.youtube.com/watch?v=5DNGXFDKseA
a "half power" shot
to get that kind of penetration terminal energy should be in couple hundred Joule ballpark.
So the required 500J ( 1/2 x ,028kg x (190m/s)²) for full power sounds possible.
Plus with half meter power stroke and efficient F/D curve it only takes bit over kiloNewton(~300lbs) force to do 500J work.

But what it is worth, as far as I have been playing with microphone tests, there seems to be delays from mechanical shock to resonated sound. So I would not take the speed measurements mentioned here as granted.
The sound speed test should allways be shot through two - preferably three- identical sheets of paper.

Well for sure ,that is why they make tools for this job. A chrony is what is needed, even a radar gun would be more respected. I have seen a lot of this phone stuff around rc airplanes and, it just AINT cutting it. I mostly can't say that that the phone is even close to the radar gun for planes . That's why you need a chrony,even so they are fussy, but mostly accurate .You can fire the bolt over a chrony , not so handy to fly over one,hence the radar gun.

Well yes i never chrono video'd it as of yet as i have been making some other development's on this bow,i have a way to increase the efficiency of the system by around say 5 -10 % maybe even more will see as i have been very busy to say the least so leave it with me guy's and i will when ready should be around several week's from now depending.Have to admit i am finding it very difficult to believe the speed that was unviel'ed on here i must say but there are certain factor's involve'd that doe's make me think otherwise will see,please bear in mind i am doing all this un aided so please be patient,many thank's and just enjoy doing what you do with xbow's as that is really what it is all about ,well to me anyway.

Ya  Phil, It's hard when you have to finance all the goings on out of your own pocket. You might be made out of money but, I seriously doubt it. I know with my own crap that sometimes other things are more important. Just stick with it and, it'll work out in do time.

One of the reasons this crossbow is faster than anything else built, is that it doesn´t have the big internal friction losses as other bows using the Shear Modulus https://en.wikipedia.org/wiki/Shear_modulus in the limb material. It makes them slower compared to the Mantis. 

It´s all called DEVELOPEMENT and is the reason why we don´t travel by steam locomotives these days. So stop blaiming Phil for having done anything else than some realy god crossbow developement we all can enjoy in the future.

As I wrote from the beginning a crony test is needed to do the exact speed measurement, but I have used this method a lot before and it seems to work well (especially when using one paper after the bow and one before the target and most exactly when placing the microphone exactly halfway to the target. Almost certain the Mantis is over 600 fps and no doubt it´s over 500 fps.

Don´t bend limbs anymore!

The more I read,the more I am inclined to think that the title of this thread should have been"THe world speed record may have been broken"...................
                                                                Hermit.
 '

Phil,
I like what you are doing with your mech-bow approach. It is creative and this keeps it fun and interesting. I believe the design should naturally lend itself well to flinging light arrows at high speeds and high efficiency.  Have you played with an out-swinging version as well?

I feel it would be well worthwhile investing in some test apparatus, especially since you market and sell your creations.  I am only an amateur bow builder that enjoys seeing how far I can fling an arrow, and I find a good calibrated weight scale and chronograph are extremely valuable.  I am curious, what kind of force-draw curve you get?  I am also curious about the behavior of the gas spring. Is the spring force created by a piston compressing a gas in a cylinder?

Alan

Oppenheimer,
A gas spring with mechanical components does lose a significant amount of energy to hysteresis. The piston and seals must overcome internal sliding friction when released. 20-30% seems pretty typical. 

A bending limb recurve design can be extremely efficient. The hysteresis in a well designed composite limb shouldn't exceed a few percent.  The majority of the energy lost with a recurve is due to the string mass, string elasticity, and limb vibration. The limb vibration issue can be minimized by the design and minimizing limb mass.

Alan

Alan Case wrote:Oppenheimer, The majority of the energy lost with a recurve is due to the string mass, string elasticity, and limb vibration. The limb vibration issue can be minimized by the design and minimizing limb mass.

The majority of the energy lost with a recurve is due to the limb mass. There are normally no vibrations that would be relevant to bow limb acceleration. Inertia can be easily calculated beforehand and it usually very precisely matches with measured speed.

hullutiedemies wrote:


The majority of the energy lost with a recurve is due to the limb mass.  There are normally  no vibrations that would be relevant to bow limb acceleration. Inertia can be easily calculated beforehand and it usually very precisely matches with measured speed.

Yes, the problem seems normaly to be having exaclty the right weight of the limb in relation to the arrow´s weight. It´s not hard for a bow to shoot heavy arrows with close to 100% efficiency, but for the same limbs to shoot a light arrow with high efficience is an art. It takes new design ideas to being realised. I dont say the Mantis is a close to 100% efficient solution. Acording to my calculations the speed theoretically could be 10% higher. Even higher speeds than that could be reached by another type of design.

-Yes I agree the threads headline should be "might had been broken" untill a chrony test is done.

-Friction in the internal cylinder slidings must be far less than 20-30% in this construction I guess. 

To all who still thinks the Mantis isn´t true I can only recomend watching the youtube films showing penetration capabillities. That´s how I got interested in how it works. I haven´t seen any better penetration in any crossbow yet.

Of course I´m waiting for the nailbiting chrony-tests as everyone here. I´m just shure to 95% yet.

Bow limb design for high arrow speed is a pretty big subject by itself. Here is something to think about.  If the string is perfectly inelastic (doesn't stretch when loaded) and had zero mass, and the bending area of the limbs acts across a small area so that it behaves almost hinge-like when drawn and shot, then the bow would be 100% efficient, regardless of how heavy the limbs are.

The reason a recurve isn't 100% efficient is because energy is lost to the following:

1) energy is lost to what I call "limb vibration", because it is directly related to the natural frequencies of the bow limb. But another way to look at it is as follows, any limb deformation that occurs in the limb during the shot which deviates from how the limb bends when drawn results in lost energy. This is why a bow design with a small hinge-like bending area will shoot light arrows much more efficient than a noodle-like long-limb design where the amount of bending is evenly distributed over the entire limb.  Ideally, the limb should come to a dead stop with no post-shot vibration. The trick is coming up with a design that doesn't over stress the materials.  The Mantis doesn't have this issue because of the pivoting ridgid ballista-like arms. 

2) All energy required to propel the string is lost. Lighter string with lighter serving means more energy is going to go into the arrow instead of propelling the string.

3) The string should be as inelastic as possible. The forces in the string rapidly increase in the last third of the shot. If the string stretches, then energy is lost stretching the string instead of transferring one last push to the arrow. This is where the limb mass plays a role in a real bow. Heavier limbs drive higher forces in the string, resulting in more stretch on the shot and requiring the string to be thicker & heavier in order to handle the higher forces. So, yes, I always try to minimize the limb mass. 

4) To a far lesser extent, some energy is lost to air resistance and hysteresis (structural damping) of the limb material. 

That's about all there is to it.

Alan

Thank´s for a realy good explanation Alan.

Please not this Kooi - Baker flat earth rubbish.

Alan Case wrote:If the string is perfectly inelastic (doesn't stretch when loaded) and had zero mass, and the bending area of the limbs acts across a small area so that it behaves almost hinge-like when drawn and shot, then the bow would be 100% efficient, regardless of how heavy the limbs are.

No it will not.
All it takes is Pythagoras and uniquity of zero to show this:
A "hickman bow" with infinite leverage must have measurable power stroke x while the limb is static .
Thus the string at brace and string at x will form a right angled triangle
where hypotenusa and one side are equal length while the other side is greater than zero.
QED
¹⁾


I remember the Kooi paper (IIRC chapter 2.6.) having a stupid sophmore level error that it assumed continuous accelerating force function.
Now obviously the accelerating force behind arrow being vector sum of string tension will rapidly approach zero when string approaches straight position at brace height. - So if there is infinite string tension in the end , the final force behind arrow will not be infinite but infinite times zero. A discontinuity point. Wich is where Koois whole card house came down.




To Further illustrate the point why "100% efficient limb vibration" theory is garbage there is the trivial case of single hinged ideal bow braced to zero height:
Now obviously limb and string half will form a symmetrical triangle where the bow tip exactly in the middle between arrow and the hinge throughout the acceleration. The speed difference of arrow and limb tip is approaching maximum ratio of 2:1. So limb tip mass must have measurable kinetic energy at any point during acceleration.




Sorry if this comes a bit grumpy, but during last decade this Kooi nonsense has done horrible damage to the global bowyer community. Saddest thing was to see Tim Baker soil his good name.


^{1) the proof above is freshman level university mathematics. If reader fails to comprehend it he/she is not qualified to take part in this conversation}

I don't know about grumpy,but to me it suggests a degree of intellectual arrogance.Your  footnote seems to disqualify people who lack certain qualifications from taking part in the conversation.Since when has lack of qualification disqualified people from expressing an opinion?.Politicians do it all the time,it's called freedom of speech
                                                      Hermit.

YE Hermit, I'll stand with you. This would be a very dull place if everyone was as smart as could be. I think it's the questions and the compelling explanations that make this place so cool. We are not all rocket scientists, nor do we want to be. I would be the first to admit that there are a few here  that are awful close though.    Hail the Hermit.

alan,
I don`t have the Visier magazine anymore but I have asked Mr Eichstädt,  The owner of the magazine, if its still possible to get it somehow. Maybe he`ll find the time to provide some additional Info on the Koltze Design. Informations about this are hard to find-  its been a while since then...

Its an awkward design for sure but , nothing that will see something commercially made ,but as you found on your experiments it imparts  some MA and thus enhances speed, plus the central  string is not exposed to excessive stresses.

I personally like the Inswinger type Ballista Mechanism (like in Watt`s "Firefly") which is also capable of great speed & long draw but a design like this is more difficult to implement than something with just two vertical bows.

So : The article on the  Koltze crossbow is still avaliable at the VISIER download archive, it can be individually downloaded at a cost of a meagre 1,-€.  Since its still under copyright please understand I cant just upload it here for free...

Here: http://www.vsmedien-shop.de/?sViewport=detail&sArticle=2009

The whole rationalization is in this U.S. patent.
 
 http://www.google.com/patents/US5720268