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    WW2 Big Joe 5

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    WW2 Big Joe 5

    Post by jeep on Sun Aug 07, 2011 9:05 am

    First topic message reminder :

    Hello
    Member from this forum for some month (but experienced French crossbow builder) I decided to bring my contribution whit one of my work: The OSS BJ5 replica. For this, many thanks to Dr Brunner whit his constant help and encouragement . I bring some modifications due to the fact that I have not the wealth of the OSS research department and I had to build it whit the usual hand tool that you by in any tool general store...I am not sure to master the pictures uploading. First a picture from the original,then my version in detail.
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    Re: WW2 Big Joe 5

    Post by Ivo on Sat Aug 20, 2011 4:28 pm

    Hi...I'm back (computer all fixed and ready to roll )

    First of all...thank you for the hint on how to find your work on the forum *Owl*, I really enjoyed your research/build style. Some *very*very*very* interesting crossbows you bring to the table.Very Happy Very Happy Very Happy

    Now to catch up on the crossbow at hand.

    jeep wrote:it should be possible to use other mean of propulsion, I am sure
    engineers can tell us that new elastic tread can replace rubber whit
    better resilience and stability like carbon or else.

    I agree, but that would make it a bit more expensive to make.Smile Perhaps first we can maximize the performance of the original - using a few clever solutions. And only then move on to space age materials. However, the frame can benefit from a bit of composite work and still remain within a budget margin...an aluminum alloy or thin stainless steel tube encased in fiberglass should make it a somewhat lighter assembly...just throwing it out there. Smile

    Well, as I see it...there are a few things with the design that can be fixed...some easily without major modifications, others... not so easy and not without rebuilding major components, but I'll stick with the easier stuff since there are a few things I'm not sure of even there. Razz

    1. Positioning of the bands.

    This is the first variation that I came up with. While designing, I was aiming at reducing the amount of work required to replace the bands and also to improve the efficiency and accuracy of the crossbow.






    This way I've eliminated the dead weight of the metal link that reduces the efficiency. Also I believe this way of positioning the band will improve the energy transfer since it is no longer changing the angle during the draw...possibly giving a more direct access to the bands energy storing capabilities. The idler wheel in the center of the band is something in question, I can't quite picture whether it's going to work synchronizing both sides *which I think would be an essential function for any bow* Smile ...or if it will do the exact opposite and just throw things out of balance. scratch

    If you are wondering about the band used in this model, there are many different grades of it and it's commonly found on spear guns for fishing.
    Joerg Sprave wrote:


    It's all very roughly thought/drawn out, but let me know what you think guys. Smile

    Ivo




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    Re: WW2 Big Joe 5

    Post by jeep on Mon Aug 22, 2011 8:31 am

    Hi ivo what a good stuff can be done whit a computer program!!! I am not smart enough ,still whit a pen !! Very interesting designe indeed can certainly pull hight tension, but like this it will supress one of the advantage of this frame : to fold it.
    About the rubber: After testing different kind they find out that to realise a maximum of force in a minimum of time it wash better to use many smalls rubber rings then a massive one (don't know if they used the same material then yours:silicone or else?)There a test result paper of different type of rubber (OSS crossbow)I don't kno[w how to interpret but maybe someone know here..url=http://www.servimg.com/image_preview.php?i=37&u=16369594][/url].

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    Re: WW2 Big Joe 5

    Post by Guest on Mon Aug 22, 2011 10:36 pm

    THE LBJ5
    Velocity: 180fps
    Accurate lethal range: 60 yards/150 yards
    Extreme range: 260 yards
    dart: 44g (678 grain)
    rubber pull: 550#
    150 rubber ring x2 = 300 rubber ring
    Draw 10"
    You can find those stats and a lot more in the Bible of Dr BRUNNER.:
    THE OSS CROSSBOW,
    ISBN-0-932572-15-4

    WOAAAAAAAW!

    550 pounds of power in that thing?!?! Ivo probably had seizure when he read it. Laughing
    Looks very cool man. Careful - Ivo is an alien and everything he touches mutates.

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    Re: WW2 Big Joe 5

    Post by Ivo on Thu Aug 25, 2011 2:15 am

    Hi ivo what a good stuff can be done whit a computer program!!! I am not
    smart enough ,still whit a pen !!

    No biggie. Smile Sometimes a sketch on a napkin is more valuable than a computer model. In my opinion, it's easier to think simpler and keep ideas rational on a piece of paper than it is on the computer. On paper you just scratch it or scrap it...with a computer model you go back and redo it - adjusting everything. Thinking about it...both paper sketches and computer models have their advantages and disadvantages...I just like it because I don't have to photo/scan anything to post it...a little bit of MS Paint or Google Sketchup and we're in business. Smile

    Very interesting designe indeed can
    certainly pull hight tension, but like this it will supress one of the
    advantage of this frame : to fold it.

    Suppress - yes, but not to a noticeable degree. Smile

    I basically pictured it like this...

    First step - you pull the rubber back and over the roller on the top. This will remove the tension on the string and ultimately on the frame. Both the band and the string become easily accessible for maintenance/repair/replacement. This system will probably work with bands just fine...or even better. Can't wait to try it. Laughing



    Next is another thing I pictured would speed up the process is instead of nuts, simply use a pin to fix the end of the frame in place...so remove that and the frame is free to move. Perhaps a little quick release lock for the bottom of the pin to boost it's coolness factor. Very Happy



    I've noticed in your frame - the front is completely removable? Something I just noticed....interesting detail.Smile
    In my model the hinges are permanently linked, but are still free to move.


    About the rubber: After testing different kind they find out that to
    realise a maximum of force in a minimum of time it wash better to use
    many smalls rubber rings then a massive one (don't know if they used the
    same material then yours:silicone or else?)There a test result paper of
    different type of rubber (OSS crossbow)I don't know how to interpret
    but maybe someone know here.

    Interesting table. Some of the items are easy to understand abbreviations, while a few others are quite the puzzles. Smile

    Scale:
    Good
    Fair(OK)
    N.G.(Not Good)
    Are probably the abbreviations we see through out the table:

    G=Good

    F=Fair

    NG=Not Good

    Hyst. Loss
    Mod.
    Pers.
    Set.


    Tear
    Resist.
    Abras.
    Resist.
    30 to 50
    Cycles
    #70
    at
    360%

    Type
    Hitch
    Thickness
    Size
    Letter
    Date
    Life
    "Hyst. Loss" probably means "Hysteresis Loss"

    This is what I came up with after a bit of searching:

    Spoiler:
    http://en.wikipedia.org/wiki/Hysteresis

    Elastic hysteresis



    Fig. 3. Elastic hysteresis of an idealized rubber band. The area in the
    centre of the hysteresis loop is the energy dissipated due to material
    plasticity.[dubiousdiscuss]





    Elastic hysteresis was one of the first types of hysteresis to be examined.[5][6]

    A simple way to understand it is in terms of a rubber band with
    weights attached to it. If the top of a rubber band is hung on a hook
    and small weights are attached to the bottom of the band one at a time,
    it will get longer. As more weights are loaded onto it, the band
    will continue to extend because the force the weights are exerting on
    the band is increasing. When each weight is taken off, or unloaded,
    it will get shorter as the force is reduced. As the weights are taken
    off, each weight that produced a specific length as it was loaded onto
    the band now produces a slightly longer length as it is unloaded. This
    is because the band does not obey Hooke's law perfectly. The hysteresis loop of an idealized rubber band is shown in Fig. 3.

    In one sense the rubber band was harder to stretch when it was being
    loaded than when it was being unloaded. In another sense, as one unloads
    the band, the cause (the force of the weights) lags behind the effect
    (the length) because a smaller value of weight produces the same length.
    In another sense more energy was required during the loading than the
    unloading; that energy must have gone somewhere, it was dissipated or
    "lost" as heat.

    Elastic hysteresis is more pronounced when the loading and unloading is done quickly than when it is done slowly.[7]
    Some materials such as hard metals don't show elastic hysteresis under a
    moderate load, whereas other hard materials like granite and marble do.
    Materials such as rubber exhibit a high degree of elastic hysteresis.

    A word of caution: rubber behaves like a gas. When the rubber band is
    stretched it heats up. If it is suddenly released, the rubber cools
    down, very easy to perceive just by touching. So, there is a large
    hysteresis from the thermal exchange with the environment and a smaller
    hysteresis due to internal friction within the rubber. This proper,
    intrinsic hysteresis could be measured only if adiabatic isolation of
    the rubber band is imposed.


    Basically saying that the rubber "lags" upon return once the load is removed. This guy did a little video on it.



    First 100g load registered at 75cm on the ruler, weights were added until it reached 48cm...and as the weights were removed - rubber returned to it's previous position, BUT the lag in the rubber only allowed it to return partially (instead of going back to 75cm it only reaches 71cm) as some energy was lost in the process, but will return to it as time passes. Pretty much what you said earlier about rubbers limitations, and that would be the reading on the table you have...some types of rubbers having better return properties than others in this test. But don't take my word for it...Rubber is a bit of a new topic for me, so I'm also just doing research.

    Mod. - No idea what that is....hopefully some one will stop by to enlighten us. Smile

    Pers. Set. - Probably the amount of "permanent" stretch(set) the rubber takes during use.

    Abras. Resist. - Abrasion Resistance

    Tear Resist. - Tear Resistance

    30 to 50 Cycles #70
    at 360%
    - I would bet that this is the description of testing conditions -30 to 50 Cycles...load 70 pounds...stretching to 360%. Just my guess.

    Type Hitch - I'll get back to it *

    Thickness Size - Dimensions of the rubber being tested.

    Letter date - Probably the date when report was received.

    Life - Life is good. Smile Too bad we will never know how long subjects 1 through 26 (& #32) lived.

    So that's my take on it...and now the puzzle. drunken

    Type Hitch

    I first though it was a type of knot, but then put the names in the search. Here's what came up for Mentzer:
    Spoiler:

    http://www.patents.com/us-5816339.html

    Implement swivel hitch for use with a quick-coupler


    Abstract
    An implement hitch is mounted to the forward end of an implement tongue for
    swivelling about an upright axis. The hitch includes right- and left-hand
    arm assemblies which each include separate inner and outer arms mounted
    for swinging about a horizontal transverse axis defined by a connection
    pin located in respective rear ends of the arms. A first embodiment of the
    inner and outer arms includes apertured balls universally mounted in
    forward ends of the arms, with the balls of each adjacent pair of inner
    and outer arms having a hitch pin extending therethrough which is adapted
    for being received in the receptacle of the hook of the corresponding side
    of a quick-coupler carried by the three-point hitch of a tractor. In a
    second embodiment, radiused apertures are provided in the forward ends of
    the inner and outer arms in lieu of the apertured balls. In the first,
    embodiment, the arms pivot vertically relative to each other and the balls
    swivel within the arms when the quick-coupler tilts relative to the
    implement swivel hitch whereby the hitch pins also tilt without generating
    undue loads on the arms. The operation of the second embodiment is similar
    to that of the first embodiment, however, in this case the radiused
    apertures in the arms together with the separate movement of the arms
    permit the pins to tilt without generating undue loads.




    Inventors: Parsons; Stephen Kenneth (Ottumwa, IA), Mentzer; Matthew Jay (Zweibrucken, DE)
    Assignee:
    Deere & Company
    (Moline,
    IL)


    Appl. No.:

    08/885,461
    Filed:

    June 27, 1997

    Remind you of something?



    http://www.doublehh.com/hitch_linkage_diagram.cfm?catID=2
    Hitch & Linkage Diagram



    Three point hitch and linkage parts are used in
    the attachment of three-point hitch implements to the rear of
    agricultural wheeled tractors. COmponents are available for most
    Category 0, 1, 2, and 3 hitches. Tractor hitches are classified by the
    drawbar horsepower of the the tractor as shown in the table below.


    Hitch
    Category
    Maximum Drawbar
    Horsepower
    Top Link Pin
    Diameter
    Lift Arm Pin
    Diameter
    Category 0 Up to 20 Horsepower 5/8" 5/8"
    Category 1 20 Horsepower to 45 Horsepower 3/4" 7/8"
    Category 2 40 Horsepower to 100 Horsepower 1" 1-1/8"
    Category 3 80 Horsepower to 225 Horsepower 1-1/4" 1-7/16"

    As I understood it, Hitch described in the table is a "hitch" to or by which the bands where attached. Guessing...Like a trailer attaches to a truck. scratch

    Not much info on the PIN and Clover Leaf...just too many random things came up in the search...so that's another thing I'm wondering about and hope some one can come in with a fresh mind and try to clear this up.


    I guess I'm going to start building and see what happens in the process...think this triangular frame platform will work very well with the lever(ballista)crossbow concept. Everything should balance pretty well and it can be rubber powered...hmmm...I think I just got a glimpse at what I'll be doing after I finish the recurve I'm building. Smile


    Good Day,

    Ivo

    PS:
    Looks very cool man. Careful - Ivo is an alien and everything he touches mutates.

    Yep...that was once a banana. Laughing


    Last edited by Ivo on Thu Aug 25, 2011 11:36 am; edited 1 time in total




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    Re: WW2 Big Joe 5

    Post by Basilisk120 on Thu Aug 25, 2011 10:30 am

    IVO - TL;DR -- Razz Laughing Actually I did read the post it was good.



    Ivo wrote: Basically saying that the rubber "lags" upon return once the load is removed. This guy did a little video on it.
    I Liked your comment on Hysteresis I'll have to try to rememeber that as a way to quickly explain it. I have a bad habit of forgeting that the 4 years of Engineering classes added random things like that to my vocabulary and so I'll throw them into conversations thinking that everyone should know what Hysteresis is then draw a blank trying to think of a simple way to explain it. Well Hysteresis wouldn't be too bad trying to explain Moment of Inertia on the spot was bad, I fumbled initial explination so got derailed.



    And ctrl V (paste function) rocks. Didn't have to try to muddle through spelling Hysteresis a bunch of times. Given my usuall attempts at spelling each time would have been different.



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    Re: WW2 Big Joe 5

    Post by jeep on Sat Aug 27, 2011 3:59 am

    Thank you Ivo today I learn a lot more about rubber, now the checking paper should be more clear for all. I want to do my own test about small rubber rings because i plan to use them for a lever crossbow. The Bj5 spanning system is very efficient (like a crannequin) but heavy and complicate. There is another OSS crossbow that a would like to duplicate it is the final one produced ,taking all the best feature already studied by North west University this is the" Willam Tell" model (Dr brunne, OSS crossbow)

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    Re: WW2 Big Joe 5

    Post by jeep on Sat Aug 27, 2011 4:02 am

    william tell

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    Re: WW2 Big Joe 5

    Post by jeep on Sat Aug 27, 2011 4:18 am

    As you can see they use the stock for loading and instead of a ratchet bar there is a winch whit a cable :Lighter,simple,compact It also can shoot stock folded like a pistol crossbow.
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    Re: WW2 Big Joe 5

    Post by Ivo on Sat Sep 03, 2011 4:21 pm

    Interesting. Smile

    So they decided to step away from the triangular frame concept and simply did two posts linked by a cable that has a sight bead on it.

    I hope they got rid of the steel "H" connector, because in my opinion that was the biggest issue with the other crossbow.

    I like the folding stock that doubles as a ratchet arm - simple, but to the point. Smile You can probably re-purpose an ordinary automotive two way ratchet to simplify the build a little. Still however, I'm wondering about the system they used, because a ratchet is pretty damn loud.



    Crossbow in the video - АК-77Б (Custom made by one of Saint-Peterburg)

    Ivo

    PS: I'm also wondering about the trigger mechanism. I've seen it on the
    French forum and overall the chain-link/dog-leg triggers are known for their ease of release if made properly, but I didn't notice any information on your triggers performance. It
    obviously holds the weight, but what is the trigger pull weight?




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    Re: WW2 Big Joe 5

    Post by jeep on Mon Sep 12, 2011 9:52 am

    It is not a ratchet bar but it is spanned whit a cable and a winch drum,it was better,lighter simpler less cumbersome. They did use a little steel connector but very simple and lighter

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    Re: WW2 Big Joe 5

    Post by User8192 on Tue Nov 01, 2011 9:54 pm

    Ivo wrote:

    About the rubber: After testing different kind they find out that to
    realise a maximum of force in a minimum of time it wash better to use
    many smalls rubber rings then a massive one (don't know if they used the
    same material then yours:silicone or else?)There a test result paper of
    different type of rubber (OSS crossbow)I don't know how to interpret
    but maybe someone know here.

    Interesting table. Some of the items are easy to understand abbreviations, while a few others are quite the puzzles. Smile

    Scale:
    Good
    Fair(OK)
    N.G.(Not Good)
    Are probably the abbreviations we see through out the table:

    G=Good

    F=Fair

    NG=Not Good

    Hyst. Loss
    Mod.
    Perm
    Set.


    Tear
    Resist.
    Abras.
    Resist.
    30 to 50
    Cycles
    #70
    at
    360%

    Type
    Hitch
    Thickness
    Size
    Letter
    Date
    Life
    "Hyst. Loss" probably means "Hysteresis Loss"

    -- SNIP --

    Mod. - Modulus (a measure of the resilience or stiffness of a substance)

    Perm Set - The amount of "permanent" stretch (set) the rubber takes during use.

    Abras. Resist. - Abrasion Resistance

    Tear Resist. - Tear Resistance

    30 to 50 Cycles #70
    at 360%
    - I would bet that this is the description of testing conditions -30 to 50 Cycles...load 70 pounds...stretching to 360%. Just my guess.

    Type Hitch - I'll get back to it *

    Thickness Size - Dimensions of the rubber being tested.

    Letter date - Probably the date when report was received.

    Life - Number of stretch/relax cycles that the sample can withstand until it breaks (or until the test is terminated)

    Here's an enhanced version of the table image. Sorry about the residual distortion, but that's due to the camera angle and lay of the pages when the picture was taken; trying to straighten it out would cause further degradation of legibility.

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    Big Joe

    Post by arbalest on Mon Apr 02, 2012 12:28 pm

    I am very fortunate to have known a man (Gil Frey) who actually owned one of the few examples of this weapon known to exist. He lived in Gaithersburg, MD and worked for the N.I.H. or some other federal agency. He was a crossbow guru, right up there with Pop Bailey and George Stevens. He was instrumental in the design of the Jennings Devastator crossbow. Before he died, he donated his Big Joe to the C.I.A.'s Covert Ops Museum. I don't know if that museum is even open to the public. Thanks for bringing up some fond memories of a truly unique gentleman.

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    Re: WW2 Big Joe 5

    Post by JoergS on Thu Apr 12, 2012 12:51 pm

    jeep wrote:This is the main problem whit rubber: when you stretch it quickly it produce some heat and lost lot of power and if you wait before realising the power drop even more!!

    I researched very much in this regard, both by studying scientific publications and by doing a great deal of experimentation.

    I can now say that - as long as you don't exceed a stretch of factor 5 (eg. 10 inches relaxed band length, 50 inches stretched length) - the hysteresis effect SOLELY comes from the temperature effects.

    If you stretch rubber, it warms up. If you relax it, it very quickly cools down again. The energy is stored thermally, unlike any other known propellant media for crossbows.

    So if you keep a rubber crossbow cocked, the initial draw force is very high. However, the temperature drops, and the draw force drops as well. So your 550 lb will only be, like, 300 lb after a few minutes.

    It is not so bad, because this means that once the temp of the environment has been reached, the draw force won't go down any further.

    I have created a crossbow with integrated heating system, it works fine.

    So the main disadvantage of rubber is that it will only shoot accurately if you either always wait a few minutes after cocking, or by keeping the breaks between cocking and shooting about similar.

    Rubber based weapons really only work well between 5 and 38 degrees Celsius. Dr. Brunner has included documents into his book that support my observation in this regard.

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    Re: WW2 Big Joe 5

    Post by jeep on Thu Apr 12, 2012 1:27 pm

    You are absolutely right Jorg,It is probably wy the OSS crossbow have an incredible draw pull: BJ5=550# for a killing distance 20 to30 yd or even lot less at night time (it is an elimination weapon) at this distance the trajectory is flat and what ever is the hysteresis your a dead duck.....But it was certainly a problem to use it in European winter or in the moisture of the New Guinea jungle. I watch your work with a lot of interest about heating rubbers , I may try to use thermal film in a polar fur bag to wrap the in swinger rubbers units.

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    Re: WW2 Big Joe 5

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