Engineering Challenge- Spring Loaded Kicker Edition

[Ether]

Originally Posted by bman

I find it funny that no one started using actual math until halfway down the second page of the thread......

It's all because of the x^2 value in 1/2Kx^2 which is the energy stored in a spring which in a lossless world translates into kinetic energy of the ball. x^2 will increase the energy much faster than the K will decrease it in any situation. Messing with the equation and substituting in the equation for force of a spring defined by Fs=Kx, we get Pe=1/2(Fs/x)x^2 which = 1/2Fs(x) or in other words, at a constant Fs (stalling a motor) the potential energy stored in a spring is directly proportional to how far you pull it back (x).

This is very easy to see graphically. See the first attached GIF. The area under the curve of force vs distance equals stored energy. The area under the curve of the Weak Spring (shown in red) is larger than the area under the curve of the Strong Spring (shown in blue). Both the Weak and Strong spring areas have the same height, but the base of the Weak spring area is longer, so the area is proportionally greater (area of a triangle is 1/2 the height times the base).

Your analysis completely ignores pre-loading of the spring though. Most teams using spring-assisted kickers pre-load them.

By using a greater pre-load on a weaker spring, you can get more usable kicker energy at the same stall force and same distance. See the second attached GIF.



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