I detailed the project about five years ago and stored it here:
It is time to dust off the drawing boards, apply what I have learned, and get back on the lathe. I want to do it in a way that involves the community and is transparent but I also want to protect my work because it very well may have commercial value.
Tonight I will talk about one of the tools that I have been able to put under my belt thanks to George Mansfield, mentor and professor. George (and he'd have it no other way) has used Vissim for much of his consulting work and is the one that got me started on it. It is a software program, as per their website "A graphical language for simulation and model-based embedded development"
So what does it do? It solves equations that you setup, steps through 'time' and then re-solves those same equations with the updated values found from the previous iteration. The equations are setup in a graphical interface, connecting variables with operators and wires.
It is a very powerful program in that any situation can be analyzed as long as the governing equations are known. Let's look at how that can be applied to a paintball gun. I've included some screen shots of a model representing the plunger2 from several revisions back.
Geometry:
Kinematics:
Fluids:
Results:
In a nut shell, the forces on the bolt are summed, then divided by the mass of the bolt. That gives us an acceleration which can be integrated to find velocity and then integrated once more to find position. As the position of the bolt changes so does the volume of gas in front of or behind the bolt and also the pressure on either side. A new applied force on the bolt can then be calculated and we are back to square1, only this time it is square2. Step through time in an incy wincy bit, let the computer do all the busy work, and you end up with a nice plot.
The ability to change a parameter- operating pressure or a diameter on the bolt for instance- and then hit 'run' and see how the bolt and plunger position change with time is a very valuable tool. The whole gun can be virtually prototyped, without a single part machined.
It is important to note though, that the simulation is only as good as the equations used to model the behavior. In the model above, I have modeled friction as a result of a friction constant and velocity. Doing so is not accurate- I've ignored static friction completely. For now, it is okay but later I will go in and model friction in a more accurate way.
I will go into what is to be done with the plots in a later post, once that work has been carried out and I can give a better explanation with screen captures.
