This Knife Throwing Machine Guarantees A Bullseye

Knife throwing is both an art and a skill that’s difficult to master. It takes both hand-eye coordination and just the right spin to embed the knife into a target, and the longer the distance, the more power and spin are needed. While movies make it look easy, in reality, it’s a difficult concept, but for Oregon-based manufacturing engineer Quint Crispin, it was a challenge. Taking inspiration from the movies, Crispin and his son set out to build a machine that could throw knives and stick them accurately in a target at any distance within the machine’s range. 

Crispin designed his knife throwing machine using a series of calculations concerning the force required to launch the knife, it’s mass and, of course, its spin. Everything about the design of the machine affected how it spun the knives. Every part needed to be weighed, for example, to make sure the momentum was applied to each knife correctly. Following the math, a pair of high-performance servo motors drive two parallel timing belts mounted to an aluminum frame. The belts then propel a carriage with repurposed carbon-motor brushes holding the knife along powered copper rails. One belt runs slightly faster than the other, which transfers to the carriage creating spin as the knife is launched. 

Crispin’s initial design made use of an electromagnet to secure the knives, however it wasn’t strong enough to hold the stainless-steel blades, so he replaced it with a solenoid-based mechanism that secures the blades that were modified with machined slots used for anchor points. The knives are fed automatically using a spring-loaded magazine housed in the back of the machine, similar to a bull-pup rifle, which is continuous when the trigger is depressed and held down. The spin rate and distance needed to match their rotation are accomplished by an onboard LiDAR, which also adjusts an aiming laser that paints the knives’ location on a target. 

Programming the Knife Throwing Machine was handled by Crispin’s son Shane, who coded the LiDAR sensor via I2C using the C programming language. As with any project, though, Crispin’s Knife Throwing Machine was fraught with bugs and needed to undergo revisions during the design and programming process. Unstable knife retention systems, explosive carriages and faulty electronics plagued the build; however the end result speaks for itself. While the Knife Throwing Machine has no practical applications other than being an accomplishment in itself, it’s a great example of what can be created in the mind of an engineer.