After selecting the Smart Parts Ion as the basis of our paintball gun project, the next phase was to get the design details worked out. Designing on paper is a lot more efficient that trying to work out details in metal as we were doing when we started the project.
The main goal of this part of the project was to get detail drawings made of each component, with the analysis to back them up and ensure the gun will function as desired. Ideally, this work would be done in a solid modeling package with detail drawing support. At the time, I hadn’t found a good solution that was in my price range … I mean free. Fortunately, I stumbled upon Creo Elements/Direct Modeling Express, which fit the bill nicely. I’d highly recommend checking it out if you’re looking for a solid modeling CAD program for hobby work.
With the CAD question answered, we needed to get started on the design. Again, ZDSPB.com was a great resource. The cross-sections, animations, and functional descriptions were extremely helpful, and enabled us to reverse engineer the Ion without having access to one.
Instead of simply copying the design, we wanted to make a few changes along the way. Our design should operate on 90 psi and uses standard NPT fittings rather than microline. These changes facilitate hooking the marker up to an air compressor, and minimize the cost of hardware we have to purchase. Using an air compressor should allow us to do some initial testing of the firing assembly without having to make or buy a high pressure regulator like you’d find in a regular paintball gun. We also simplified a few areas of the gun to better suit the limited capabilities of my shop.
The drop in pressure required some math to determine the required dump chamber volume. Without going into too much detail, we put together a spreadsheet to calculate the velocity of the paintball as a function of chamber volume and operating pressure. It’s surely not exact, but it should be close enough to work. Here’s the predicted projectile velocity as a function of time for 80 psi in the dump chamber in our design:
(Read the rest of this post…)