According to legend, King Edward III once said: “If you want to train a longbowman, start with his grandfather.” Consistently making accurate hits with any bow, especially on moving targets, takes many hours of practice. Or, if you’re [Shane Wighton], you can spend a comparable amount of time building, debugging, and rebuilding a robotically-enhanced bow to do it.
The goal was to shoot flying targets out of the air, so [Shane] had to create a system that could track the position of the bow and the target, and automatically adjust the position of the bow and loose the arrow at exactly the right moment to intercept the target. The position tracking was done with the same Optitrack cameras [Shane] used on his robotic basketball hoop, with reflective marking balls on the bow, target, and the release mechanism. The auto-aiming is done with a two-axis rack and pinion mechanism driven by a pair of stepper motors. [Shane] first used the cheapest recurve bow he could find online, which caused accuracy issues likely related to the Archer’s paradox. The setup also made him repeatedly hit himself in the face, because the servo-operated release mechanism would release unexpectedly without having a proper anchor with his draw hand.
[Shane] eventually upgraded to a compound bow, which reduced the tension he had to hold while lining up the shot, but also increased the weight of the system dramatically. This leads him to fully embrace the mech suit look, and use a Steadicam vest to hold the weight of the bow. This finally allowed him to reliably William Tell shots and hit the flying targets.
Compound bows (unlike recurve bows, their more mechanically-simple relatives) use a levering system with pulleys and spring tension to grant the user a mechanical advantage. We’re not exactly sure what to call [Zünder’s] bow design. He shared his unconventional take on a DIY bow that uses coiled springs as well as some other unique features.
What we really dig about [Zünder]’s design is how easy it is to grasp how it all works. As he demonstrates using the bow, the way the levers, pulleys, and spring tension all work together is very clear. The 3D-printed quiver and arrow rest are nice added touches, and we especially love the use of three toothbrush heads to provide contained support for a nocked arrow. The ring of bristles are sturdy enough to easily support the shaft, and don’t interfere with the arrow’s fletching.
[James], aka [Turbo Conquering Mega Eagle], is not your typical Hackaday poster boy. Most of his builds have a “Junkyard Wars” vibe, and he’d clearly be a good man to have around in a zombie apocalypse. Especially if the undead start driving tanks around, for which purpose his current anti-tank compound crossbow is apparently being developed.
At its present prototype phase, [James]’ weapon o’ doom looks more fearsome than it actually is. But that’s OK — we’re all about iterative development here. Using leaf springs from a Toyota Hi-Lux truck, this crossbow can store a lot of energy, which is amplified by ludicrously large aluminum cams. [James] put a lot of effort into designing a stock that can deal with these forces, ending up with a composite design of laminated wood and metal. He put a lot of care into the trigger mechanism too, and the receiver sports not only a custom pistol grip cast from aluminum from his fire extinguisher foundry, but a hand-made Picatinny rail for mounting optics. Test shots near the end of the video below give a hint at the power this fully armed and operational crossbow will eventually have. The goal is to disable a running car by penetrating the engine block, and we’re looking forward to that snuff film.
Have you ever wanted to make your own compound bow for fun or even fishing? [New creative DIY] shows us how in their YouTube video. Compound bows are very powerful in comparison to their longbow grandparents, relying on the lever principle or pulleys. meaning less power exertion for the same output.
Compound bows can be really sophisticated in design using pulleys and some exotic materials, but you can make your own with a few nuts and bolts, PVC pipe, string and a tyre inner tube. The PVC pipe can be melted into shape using a heat source such as a portable stove or even a blow torch, and once you have shaped your bow you will want to put a small piece of pipe at both ends with a nut and bolt. Then you can use rubber to give the flexibility your bow needs to shoot arrows, using the tyre inner tube cut to the right size. A piece of string for the ends of your arrows to rest on is then all you need, attach this to either end of your pipe and you should have a DIY PVC compound bow ready for shooting arrows. Alternatively you could always make a recurve bow out of skis.