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Discussion in 'Show off your homemades!' started by uberfreak9, Oct 17, 2013.
So no feedback? Is there something f'd up about the design or whatnot?
this is a cool concept!
is the slingshot firing golf balls at one point?
that looks really powerful but it doesnt seem to shoot that fast.
i think that the friction in the rollers is slowing the shot down but cool concept
Yes, the friction of the rollers does slow it down but only for a short instant of time where the friction coefficient between the 0.5inch brass sleeve and the underlying 0.375inch stainless steel sleeve is at its peak. Because that interface is lubricated with machine oil, it reduces the static friction coefficient significantly. It takes a tiny bit of the energy imparted with the draw to set those sleeves spinning, then the dynamic friction coefficient is a lot lower. I can't imagine I am losing more than 10% of the energy input by the friction, in fact, once those sleeves are spinning, I doubt the friction is significant. Pulley systems are inefficient but you have to consider the velocity of the system too which greatly reduces the dynamic friction coefficient. Of course I don't have the math calculations to back up my claims. If I do work out the math I'll post it here. I looked up some info on top-end 300lb pulleys used for climbing and they are 90% efficient (note that the efficiency is calculated at low velocity). My next test is to double up the bands on it with each band tapering from 4inches down to 2inches so effectively having 8inches down to 4inches over the 940mm length. I cannot tell you how powerful that will be but I THINK I will be able to draw on it and get some even heavier shots off.