Inswinger crossbow (Rubber powered)

First topic message reminder :

Here is my one version of the "in-swinging,springs (rubbers) propelled crossbow". It came from various inspirations like: oss William tell, French ww1 grenade launcher,manubalista etc...
The mock-up.



The test bench



The draw length: 18"



Next step is to put the rubbers and the winding-drum under the side
frame and the levers in the upper side of the frame. I actually use only
two packs of 15 rubbers but i can put lot more i will see that letter
on. I will probably use this trigger assembly:

Whit red dot lens. I plan to put a Picatiny rail.

You've noticed the "stirrup"( in fact one L each side to save some space) . It's actually crank by hand but I by a Barnet cranking device I haven't put it yet because I don't understand how to set it I'll post a picture tomorrow, if anybody know the system and can provide a picture of a Barnett crossbow whit it (dismantle) it will help a lot.
I try soothing whit only 1/4 of the power, everything work smooth I'll put more power soon ,it is very promising!!! I'll publish a video.

Oh YEH!!!!

Looking really cool, jeep!

I like the "T" stirrup, have been thinking about the exact same thing for my build - if made to fold up it can be the most compact stirrup ever.

You might want to add a set of string stoppers just before the front sight, so the string doesn't slap against it.

All in all - Cool Stuff!

And you said - "new trigger"...any chance you can include an example in your next post? Gotta love these little bits!

Good Luck! Can't wait for the video!!!

Ivo

Trigger is inspiration from the one of the forum

Those two last day I concentrate on the cranking device. This is the one it is a Batnett product.

It happen to be very difficult to do. The Barnett crossbow are pre moulded to receive this stuff so I had to produce my own version of this setting , it need a very,very acurate adjustment !! Here some pictures of my version:

The winder:

The ratchet and the handle ( it can be put right or lef)

In place ready to crank.... If it work I will suppress the "stirrup". But in the mean time I broke one of the two swinging arm trying to adjust it ... Then a bit more delay to fix it!!!
It is part of the fun of it......When I get time I will add a coverd to make it more sexy...

Here is the first descriptive video. I had a second one with shooting but the string break!!!! then i have to do a new one before proceeding. The most difficult part of the final adjusting is to balance the power stroke between the to pivoting lever. You can see i had to had pulley to give two anchors point for the string, that way it cant slide and you span straight. I inspired from warhamer , the survival rubber crossbow and the devil fork from hobimekey

preparing for stringing whit the new stringing jig, tank to the forum!!!

Jeep, you don't sieze to amaze me.

Moving on quick and steady.

I recognize the trigger. Pretty cool little guy indeed with that auto safety and all.

Wanted to answer your question about the spanning mechanism, but with the little time I had at the time, couldn't find the patent for it. Sorry on that bit, but it looks like you figured it out well on your own.

As for the string jig...here you really did it man.

It would, however, be better if you used actual string material to bundle up a string instead of using a nylon cord (that is if it's what I think it is and not a Dacron sailing cable.)

All in all, cool and high tech machine you there...can't even capture all the details I like in it without writing up an essay. Looking forward to seeing it shoot.

Ivo

Thank Ivo you are right whit the nylon cord, it is the reason way it break . The one you see on the jig is only here for adjusting the jig at the right lengt . The definitive string will be archery Dacron tread..I am not satisfy whit the crank device, complicate fragile slow. If I have time I'll try to put the similar system used by the" OSS William Tell" .The adjustment and balance of a "in swinger"string is very,very tricky: You meet all the usual problem of a normal string plus the fact you have 4 anchoring points , each time you change any think you change the draw lenght !!! You constantly have to play whit the trigger position,the arms length which influence the frame position and the arrow speed....It certainly can be computerised but I am not qualify .One of the solution to save some time and materiel is the "mock-up".Personaly I work step by step, some components are here since the beginning.But one think is sure: The basic ideas hare valid : In-swinger, bull-pup,rubber propellent (or gaz,spring etc..). Next step would be :composite materiel frame , work on a better ergonomic,work on the propellent position,form of pulley,crank system ...well a full field of study. I am certain we will see this concept in or archery shop soon....

Nice!

To simplify things in tuning you might want to consider having the two levers share one poweresource, so that pull is always equalized through out the pull. The easiest way with your setup to upgrade (and cheapest) is to upgrade to speargun tubing. I have some 1/8 wall speargun with 1/4" inside diameter that is pretty heavy duty and puts up with a lot of punishment.

An easy way to help equalize them is to install a single pulley through the barrel and thread thread the tubing around that.

Remember the axle in the pulley should be in line with the lever axle to gain max. performance. From a 12 oclock position, your bow will produce 50% of its entire drawlength within the first 35-40 degrees of rotation depending on length of arms or levers. When you take away a portion of this movement, you are removing higher performance potential.

Great work!

You are absolutely right Warhammer ,but I can't use this Principe with this stock and frame. I really like the littles rubber rings because you can manage the power indefinitely adding or removing some.It ise also very easy to put theme or remove one by one.I am actually changing the axes of the pulley.

After lot of last minute adjustments and months of work!!!Here is the video of IN SWINGER shooting. It work pretty well. Infortunately I don't have any Chrony but I will do test with target at difference distances , immediat release and delayed release to test hysteresis . I am sure this kind of crossbow can reach 300/400 fps. easily.With modern components like composite,aluminium for the cam it can be one of the lightest of its class . But whit the very crude material I use I have to be very prudent increasing power!!!

I'm brand new at crossbows and am totally fascinated ! Drawn in by the simple medieval mechanics to now the modern day ..... seems it has become limited only to one's imagination ! I'm totally blown away! I just thought I was interested, now my mind is exploding ! And am totally emberassed that at this time I only have rescent knowledge of some old '50's magazine plans and have not yet built anything! I have nothing to bring to the table but fascination and questions! What an awesome web-site ! As someone noted and may I express I may grow old,but will never grow up ! At 63 yrs. it seems a new gift was just opened. Jeep what an inspiration !

I'll shut up and for sometime just enjoy the web site.

NICE. Thanx for the youtube posting. I also posted the youtube link on crossbownation.

Jeeptag: heres the address for crossbownation. Your youtube vid is under "Quest for Speed", last page.

http://www.crossbownation.com/forum2/forum/21-all-other-brands/

Congratulations jeep, very nice build and definitely proof of concept! And I really loved your Big Joe too!


One question I have with rubber as a powersource is that the rubber looses power the longer it is held under tension.
Meaning directly after cocking you have for example 100lbs after 60 sec only 92,5lbs after 5min cocked 80,23 lbs etc (these are no real figures just for example)
So if you do not time the shots exactly or wait after cocking until the rubber has settled to its final drawweight you are always shooting with a different power, are you not?
That means the accuracy is affected. Or am I wrong here? Do you have any experience concerning accuracy yet? Maybe its not noticeable at all?

This fundamental question have been often discussed here. Read again all of the post of this crossbow and the members answer. And for definitive reply look all of Jorgs post and particularly the following one

https://thearbalistguild.forumotion.com/t542-the-entropy-slayer-2000-revolutionary-sling-x-bow

For my in swinger I use the original rubber witch were selected for there good hysteresis result . I haven't tested this yet but I will publish result then.

Looks like it drives nails Jeeps, really cool stuff!

I've been twirling in my head a folding riser for these lever bows...I feel like a kid at the amusement park.

Thank you for sharing the progress. Hope it's as inspiring to everyone as it is to me.

Ivo

Jeep, thanks for sharing this amazing project. I dont have the expertise to address this, but will say that a project idea that has been bouncing around in my head for a few years is a minature Hatra inswinger machine, kind of a varient of a gastrophetes but small and handy. A full sized Hatra would be awesome, but will have to wait.

Dane