allu's projects

Discussion in 'Slingshot Crossbows' started by allu, Dec 5, 2015.

  1. allu

    allu Junior Member

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    Hi all!

    Decided to start one universal thread for my projects as I don't feel like having several threads covering the same area: crossbows. So I'll post all my current and future projects here, easier to find and easier for me too.

    Earlier threads:

    Flipper style crossbow
    Flipper style crossbow version 2
    Cobra pistol crossbow modding

    Yesterday I challenged myself to turn my cobra pistol crossbow into some sort of flipper. Well that kind of failed before it even started, couldn't find any suitable materials. Plywood was too flexible at required dimensions and didn't have small enough steel square pipe. Could have worked with different design, but didn't feel like stopping there. The parts from my old version 2 flipper were still intact and available, so decided to build a simple survival crossbow flipper thing instead :D

    [​IMG]

    [​IMG]

    Made it as simple as possible, and while it looks ugly it functions just fine. Well, as fine as it can, the trigger is really primitive and the whole thing is kinda clumsy due to its sheer size. Draw length is around 70 cm (~27,5 inches). About the performance, well, it did fire once before the arrow bounced of the target and disappeared into the snow -facepalm- Man I never learn, sharpen the point and make them stick to the target instead of having them bounce off and zip into the snow. So the performance testing gets to wait for a new arrow :D

    -allu
     
  2. allu

    allu Junior Member

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    After a long time took my trusty cobra pistol crossbow and went out to shoot with it and had a blast! It's so much fun to shoot even if it doesn't pack that much of punch. But that's what I'm going to change next. Found a perfect sized piece of fiberglass pole (from an old kids' bow) and we'll see if that can be fitted behind the original prod. Probably won't do much but you never know! :D

    Just to make comparison possible arranged a quick test, shot from 10, 15 and 20 meters with the lighter bolts and then at 20 meters with my homemade bolt. Took a few tries to hit with the homemade one, it's so heavy that at 20 meters the bow really struggles to launch it that far. Aiming point moves like 1 meter upwards compared to the lighter bolts. Target was a piece of 7 mm ply and here's the results:

    [​IMG]

    Original bolts:
    -Lowest pierced and went through, shot from 10 meters.
    -Middle pierced but didn't go through, shot from 15 meters.
    -Highest, barely pierced, shot from 20 meters.
    Homemade one:
    -Straight through with ease, mass really helps with penetration. Would penetrate even better with a sharper tip.

    Hopefully the mod works and I can start shooting bigger bolts out of it, because who doesn't like extra power? ;) If the results are encouraging maybe I'll even make a stock for this to increase stability and accuracy. (Just turning my thread into a blog, oh well I like writing down my thoughts :rolleyes:)

    -allu
     

  3. bigdh2000

    bigdh2000 Administrator

    Watching this study closely. Enjoying the results.
     
  4. allu

    allu Junior Member

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    Glad to hear, always nice to get feedback! :)

    Well it turned out the fiberglass pole wasn't ideal after all. It was shaped more like a circle than a flat piece, so it didn't want to bent too well. It was possible to place it behind the original prod, but when I tried to string it it let out a loud cracking noise and I forgot the idea altogether.

    Next idea was to use pvc. Well I got it working:

    [​IMG]

    But there's some weird black magic happening. It loses most of its power after a handful of shots but next morning it was fine again for another few shots. I guess it rather changes shape than works as a spring, so I guess it's time for a third try. But I have to say the bolts were speeding out of it while it was working well, and crashed straight through that 7 mm ply. Well it was fun as long, or should I say short, as it lasted :D

    Although pvc didn't work out too well it still gave it a small but noticeable performance boost. This time I was testing at 10, 20, 25 and 30 meters. Using three different types of bolts: original full aluminium and aluminium with plastic fletching bolts and of course my homemade one. Again target was the same 7 mm ply but this time I also paid more attention to accuracy. Here's the results:

    10-20 meters the heavy homemade one dominates, the lighter bolts are no match.
    20-30 meters the second heaviest original bolts with plastic fletching are the best.
    +30 meters the lightest bolts win.

    This is pretty confusing :confused: My theory for this is that after 20 meters the heaviest bolt requires such a high launch angle that it loses most of its kinetic energy on the way up and on the way down gravitational pull isn't enough to make up for the lost speed. At 30 meters the same happens to the second heaviest bolts and that's why the lightest bolts carry most kinetic energy at range, but not up close. Just my idea, feel free to correct me if I'm completely wrong!

    When it comes to accuracy the original bolts can't compete with the homemade one. Those cheap bolts just can't fly straight, they're fine at short range but at 30 meters it takes like five bolts to hit the target. Not because of my bad aim but just the inconsistent flight pattern. On vertical axle they pretty good, but on horizontal axle they just fly left or right, maybe three of my 17 original bolts fly dead straight, made in china quality :rolleyes: But I'd still pick them over my homemade bolt simply because it's ridiculous to have the arrow flying like 3-4 meters high in the air on the peak point, and while it flies straight on both axes, it's still really hard to compensate for the drop :D

    Any suggestions for how to increase its performance? Feedback is always appreciated :)

    -allu
     
    Last edited: Dec 8, 2015
  5. RalphG

    RalphG New Member

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    Can you get a replacement prod for the cobra? Over here these are between 10-12€. Cut it short, about where the arms begin to make the outward curve and use this instead of pvc. Make sure to round off the ends of the short one properly, other wise the longer prod is prone to break at where the inner, shorter one ends. This should almost double the power at least rise it a considerable amount. Since the trigger is just pushing the string out of a groove AFAIK it can take the weight. If the spanning mechanism can take it, I don't know.
     
  6. allu

    allu Junior Member

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    Yeah I've seen someone add another prod on their Cobra with great results! He got like 235 fps out of it. But I'm so short on money right now that can't afford to buy anything, but hopefully I'll manage to land a job tomorrow (going to a job interview, eek) and one day I can afford it :D

    I have too many projects going on at the moment. It felt wrong to see my first flipper just lying there in the corner unused simply because the stock doesn't really stay together. The mechanism itself had nothing wrong with it, so I got this crazy idea to combine the swing arms and the failed cobra pistol crossbow stock. Though that sounds like awfully lot of work, so most likely I'll make a super sturdy survival crossbow out of it, mount it on a piece of 4 by 4 wood post. So a pretty similar concept to what was shown in the first post, but this time with a bit more sophisticated trigger. Either medieval or something a bit more modern. Something similar to what Joerg used in his Leach trench catapult could work too, since it would allow the arrow to be separated from the stock making any sorts of rails unnecessary. That'd be a big plus since I don't really have any tools that could carve such rail into a wood post easily.

    -allu
     
    Last edited: Dec 8, 2015
  7. allu

    allu Junior Member

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    Surprisingly the flipper was able to shoot the bolt I made for my Cobra pistol crossbow. Accuracy wasn't the greatest since the bolt had some play on horizontal axle (the bolt groove was too wide for it), but still accurate enough to hit the target at 30 meters. Man the bolt flew fast requiring minimal launch angle, definitely faster than my cobra :p These good results really encourage to built a new stock for it, some parts should be reusable too. But tonight I won't have time for that, job interview is more important and as Joerg said, in life you have to set your priorities :D

    -allu
     
  8. allu

    allu Junior Member

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    Having got a job now I'm able to spend a little bit on my projects as well. Cobra pistol crossbow was on sale for 20€ so I bought another one :D

    [​IMG]

    Obviously I had to try using the old prod behind the new one to boost performance. Everything went fine until I had to string it. Man it took me a frigging two hours to get it done and lots of frustration, such a pain in the ass, seriously. But finally I got it done and realized the edges of the old prod are cutting into the string slightly. No idea if it's enough to actually snap the string or does it just make it wear faster, no idea but time will show. Cocking it was a lot harder than before but still manageable, although the rail, in which the foregrip was attached, was torn off on the process. Chinese quality aluminium, oh well :rolleyes: Luckily I was able to attach the rail again.

    I got it working around 10.30 at night, so obviously wasn't going to do any outdoor shooting. But at point blank range the results were promising:

    [​IMG]

    [​IMG]

    7 mm ply was no match anymore so had to go up to 9 mm. Even that was pierced by both bolts! Can't wait to shoot it at distance tomorrow, just hoping it won't snap the string anytime soon. But if it does then I'll modify the second prod slighty, just by cutting of the tips all together so that they won't get on the way of the string. It should still give a nice boost. The reason why I'm not doing it now is simply I have no interests to fight with the string again, it's seriously a pain to take off and put on lol. That's all for now, more tomorrow!

    -allu
     
  9. allu

    allu Junior Member

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    Approximately 50 shots fired with the new configuration and everything is working fine! So far so good. Apart from my red dot sight that had its battery die at the very moment, so had to switch to original iron sights, they're quite terrible honestly.

    Man this thing is on steroids right now :D The speed difference is huge, original bolts fly with a super flat trajectory up to 30 meters and hit way harder than earlier. Not sure if that's a good or bad thing though, 7 bolts were killed in action today :( Most had their tip torn off while trying to remove them from the plywood, or my house's wall, whoops :rolleyes:

    Well some pics of destruction, first 7 mm ply from 15, 20, 25 and 30 meters:

    [​IMG]

    Then 9 mm ply. Was only able to hit it up to 20 meters due to it's small size (and the lack of red dot sight):

    [​IMG]

    Again same 9 mm but this time with the homemade bolt from 20 meters:

    [​IMG]

    Then a trick shot, managed to hit a rope (from clotheshorse) and the fletching stopped the bolt there :D

    [​IMG]

    Also the rail for foregrip didn't hold up so no foregrip anymore, hence even more inaccuracy. It shoots beautifully, but I have to say it's pretty inpractical at the moment. It's just painful to load, not bad for dozens of times but once you start reaching 50 shots in a row your hands and elbows are burning. A stock is a must now, maybe even some sort of fore grip if it's just possible to attach one to it. Hopefully I can find batteries for my red dot sight and do some more accuracy testing! :)

    -allu
     
  10. allu

    allu Junior Member

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    Got this done today:

    [​IMG]

    So much more comfortable to shoot and feels much more stable too. The iron sights are way too low though requiring quite an awkward position to actually see through them, but a red dot sight will solve the issue. Also figured out a new way to cock the crossbow without killing your arms: press the shoulder stock against your chest sideways, take a firm grip of the upper section of the stock, press the lever to release the cocking mechanism and pull from the "grip" (in front of the prod) with your left arm. Absolutely no effort at all and real quick :p Going to paint it black once I have time from work, most likely not until Wednesday. More about this then.

    -allu
     
  11. RalphG

    RalphG New Member

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    Nice results allu! I see the 2nd prod idea clearly worked. :cool: So now you have more power, the next you will want more accuracy, then a better stock and trigger mechanism.... and before you realize it you will have rebuilt he thing completely:D:D
    You seem to be hooked and cannot stop to tinker? Well,definitely a sign of a beginning addiction:D
    If you are worried the string may break, now that you can spend some money, get yourself a spool of dracon, sold in archery supply stores either as brownells b50 or BCYs B55. a 1/4lbs spool costs about 10-12€ and has 4300ft/lbs of thread - thats enough for many strings and will save you some money in the long term. String making is not overly difficult, there are many tuts on youtube and its also a valuable skill for other projects. Just dont forget to measure the intact string before it eventually breaks.


    As for shortening the 2nd prod, I already said it, make sure the ends are properly rounded off, maybe even tapering in thickness a bit. A fellow from another forum stacked 2 150lbs prods, it worked for a while but eventually broke exactly at where the shorter one ended. He deduced this was from the too sharp edge of the inner, shorter prod.

    [​IMG]
    [​IMG]
     
    Last edited: Dec 13, 2015
  12. Bone

    Bone Slingshot Shooters

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    That's a serious change. Nice pictures.
     
  13. allu

    allu Junior Member

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    Yeah the whole thing could be rebuild for something better. Especially the trigger is a bit primeval for 21st century and could do with an upgrade. But gotta live with it now, no way to change it. Thanks for the tip, I'll definitely start making my own strings if needed! :)

    That's what I was thinking as well, it can't be good for the main prod if half of it is way stiffer and the tips flex normally. This just results to uneven flex/bend and most likely breaks the prod in the long run. Shouldn't be a problem if the second prod is nearly as long as the main one and the draw weight is spread evenly. But on the other hand it eats strings more often, so it's kind of lose-win situation at the same time. Can't have it all, it's either extra power over durability or vice versa. As long as the cocking mechanism doesn't break I'm fine with shorter string life.

    Thanks! :)

    -allu
     
  14. allu

    allu Junior Member

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    Painted the stock today:

    [​IMG]

    Also made two new arrows and tried out new fletching method. Just simply glued on the vanes from those broken cheap aluminium bolts. Tried to make them slightly bend to make the arrow spin in flight, but we'll see how that worked out tomorrow :D

    Also there's a small problem with the string wanting to slip over the second prod on one end of the string. To describe it better here's a pic of how it's close to slipping off already:

    [​IMG]

    Fortunately I found a way to replace the string. Super easy and quick to do, but without the stock it's quite painful for your hands:

    [​IMG]

    If the slipping keeps happening I may try filing the tips of the second prod to V-shape so the string would automatically keep itself in place. But hopefully that won't be necessary, but we'll see tomorrow.

    -allu
     
  15. allu

    allu Junior Member

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    Pardon my inactivity, work and life issues haven't spared me a moment for my projects but it's getting better now.

    Still having issues with the string slipping off the second prod and there doesn't seem to be a simple way to fix it. Even with a groove on the second prod the string starts slowly sliding upwards after every shot until it slips off. Gotta figure out something else for that matter.

    I'm planning on building a simple survival crossbow flipper thing, something dead simple and quick to build but also effective. Planning on making it out of 10 x 20 mm metal square pipe, 4 mm flat steel and an aluminium u-rail as, well, the rail. We'll see how quickly I can get the supplies for it, though first gotta design it :D

    I was having hard time deciding between my flipper or an improved version of the cobra as my next project, but turned out the flipper is far more powerful. And it's completely home made, using a commercially made prod feels like cheating :D What helped me decide was simply shooting the same projectiles out of both weapons and comparing the damage done. Some pics:

    7 mm and 9 mm plywood completely penetrated, cobra could penetrate only the first one completely.

    [​IMG]

    2 cm thick wooden plank and 9 mm pierced. This was a real surprise for me since nothing I have shot with the flipper has ever come close to splittering to wood, but aluminium pole with dart head tip did it :D

    [​IMG]

    [​IMG]

    Hopefully more updates soon! :)

    -allu
     
  16. allu

    allu Junior Member

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    Finally three days off and got my some supplies, going to start building tomorrow. Hope my workshop heats up a little bit, it's been over -30°C here and it's lacking a proper heating equipment so I'm hoping not needing to work at +10°C. But if that's all I can have then I just gotta suck it up and craft :D

    Made a quick sketch with paint (of course, the best program for this kind of stuff!!! lol). Didn't bother marking different layers and parts with different colors nor naming them, because I remember them myself :p Here's the sketch anyway.

    -allu
     

    Attached Files:

  17. allu

    allu Junior Member

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    So after two days the stock looks like this:

    [​IMG]

    [​IMG]

    Made out of plywood and pine board mostly used for indoor applications. Not the best type of wood for the job but dirt cheap and easy to obtain. Hopefully the plywood and aluminum rails are enough to keep it from bending or twisting, but time will tell. Got it in a pretty good shape today, hopefully tomorrow I can finish the trigger and glue the parts together. More about that next time whenever I have time from work and personal life.

    -allu
     
  18. allu

    allu Junior Member

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    Still -30°C here but that doesn't slow me down anymore, so used to this crappy cold weather that can't even care anymore :D Got a lot done and it's pretty much in a shooting condition at the moment but still requires plenty of fine tuning.

    [​IMG]

    [​IMG]

    The trigger works very well, way better than I expected! Had to make three different trigger nuts because of my own stupidity, eyeballing the measurements never work :rolleyes: Rather heavy to pull (not much leverage due to its short length) but very consistent and secure, medieval engineers knew what they were doing :D

    The only thing preventing me from shooting it is the fact that while the frame holding the arms is at the right angle, somehow I managed to fail secure it in place and now it twists slightly and lifts the bow string off the rails. Gotta figure out a better way to attach it tomorrow, hopefully I can get the first shots off after! :)

    -allu
     
  19. allu

    allu Junior Member

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    First shots fired and results are quite disappointing to be honest :/ It hasn't got a great deal of power to begin with which would be alright if it was accurate. That's not the case, I guess the pulleys just multiply the problem of the arms not being 100% identical (I haven't got high tech enough tools for that). So each arrow got a small nudge on the left, enough to throw them off balance and make them fly anywhere but straight. The only arrow that could resist this was a new one that I made. Very front heavy and best fletching I've ever made and it flew relatively straight. Until it decided not to and missed the target and back stop and zipped into the snow never to be seen again :rolleyes: Waste of 30 minutes but at least I learned more about fletching.

    So I started looking for ways to get around the problem and turned out with a few modifications I can get rid of the pulleys and make this like a... erm, pulley-less flipper :D But more about that in the next update! :)

    -allu
     
  20. allu

    allu Junior Member

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    Yesterday while shopping for new gym shoes ended up visiting a local hardware store and couldn't resist buying some crossbow stuff. Found some dirt cheap wooden poles to use as arrow shafts, 1,90€ a pack of 5 (8 mm diameter) and 10 mm poles came in pack of 3. 50 cm long each, made out of beech and surprisingly sturdy! Magically also 2 commercially made 20" arrows and a rope cocking device found their way into my shopping cart, no idea how that happened :D That 5€ for a rope cocking device was just too affordable to miss out.

    Finally the crossbow saw some real improvement as well. Totally changed the arms from pulleys to non-pulley ones and also added an attachment point that allows two springs each side instead of just one. Some other minor changes were an improved arrow rest that totally removed the problem with misfires, and making the connection between the frame holding the arms and the stock more rigid, with a nail, so high tech :eek: Some pics:

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    Shoots fairly well already, 20 inch arrows nearly go through 9 and 7 mm plywood stacked together. The performance can definitely be improved by tightening the string and more significantly by adding another pair of springs :p However I may have to redo the stirrup, because I'm afraid it might snap under such heavy load. But we'll see if that's necessary.

    -allu
     
    Last edited: Jan 26, 2016