I am thinking of using coil spring/s as a power source for a crossbow. More like a kind of Arrow projector than a conventional crossbow. As I have not seen anyone using this kind of type I wonder if there are any disadvantages with using coil springs. As such a spring could be integrated into the stock of the crossbow it would lead to a much slimmer package.
The force would be transferred via a set of pulleys to lengthen the draw. Before I start a build I wanted to research as much as possible to lessen the chance of faliure, maybe someone here can give me some input on this topic? In his "crossbow perversions" Ivo had a drawing of a spring powered crossbow, I am thinking along those lines but not an exact similar type.
Is it mandatory that you have moving arms on the crossbow to get some kind of "snap" or can a more simpler fixed "T" shaped Stock with rollers at the end of the T´s small arms be used? In some modern crossbows (like armcross leopro, RDT) there is almost no forward movement of the prods, the power is more working to the left and right so this seems possible?.If you use a T shaped stock with fixed rollers how could the performance be improved by using some sort of cams instead of regular symmetrical rollers? Can someone enlighten me on the physics/mechanics and design of cams?
Is the distance between the rollers/cams crucial? What are the disadvantages when you move the cams further together?Any disadvantages from a more acute string angle at full draw?
In the book "Die Armbrust, Egon Harmuth, p195" he mentiones a Swiss crossbowmaker Marcel Burri who designed a crossbow with coil springs but I was not able to find a picture of this thing anywhere. Anyone seen this?
I know that because of the mass of the steelspring it will have a high inertia, making it slower than fiberglass/carbon prods. A coil spring is better than a conventional steel prod because it has a lower neutral Zone. can that be counteracted by movable arms giving the bolt more "snap"?
I think that if you are using more than one spring it is necessary to synchronize these somehow, easier way would be to combine the springs into one power source, right?
Robert van House designed a crossbow http://www.freepatentsonline.com/4169456.pdf and before switching to a air spring used steel coil springs. With this crossbow he was able to get arrow velocities in the 300fps range!When looking at this patent I wonder if one could not use a regular air spring which are used nowadays in mountain bikes as power source? In most of these rebound and overall force could be regulated so you could have a crossbow with variable power!