Having renewed my interest in airguns (i.e., bb guns) I realized how cool it would be to do away with the costly, static paper targets and have a cheap, dynamic digital target to shoot at. This is the idea I'm currently prototyping, it's a large bb/pellet trap which uses a pico projector to show targets displayed via computer. A large touch pad will register the strikes and be able to instantly provide visual feedback and, with a bit more coding, score keeping/etc. The large paper roll is an optional feature I'm trying out, thinking that rather than require the material deflecting the bb/pellet shot to remain pristine, showing no marks from all the hits, I can instead use disposable paper as the reflective surface for the pico projector, and merely pull up the paper when it's full of holes. The trick will be to have just the right balance of materials in front of the touch screen, to allow the bb/pellet impact to be reduced to a mere touch, instead of a touchpad shattering blow; I'm just waiting for the touch pad to be delivered for this phase of testing to begin.
If you have any thoughts/suggestions, let me know!
Today I spent an hour testing the strength and resiliency of the various materials I gathered by shooting BBs against them with both my Uramax Walther CP99 pistol and my Drozd Blackbird maching gun. The results were surprising, but not shocking.
The materials I had gathered included:
- Fiskers Self-Healing Cutting Board
- Duraplex Extra Strength Acrylic Sheet 0.08 inch ("50x stronger than glass")
- Lexan Polycarbonate 0.093 inch ("250x stronger than glass")
- Thick Rubber-ish Floor Mat
- Not-As-Thick Rubber-ish Floor Mat
- No-Name Kitchen Cutting Sheets
I did all my shooting from about 10 meters.
Impact Survival of Material Combinations
The first thing I discovered was how much faster my Blackbird fires BBs than my CP99. Every material withstood the CP99 shots with no significant damage. The worst anything showed was a slight dent or scratch. This led me to falsely imagine that I'd picked great materials and that I wasn't going to have any trouble. I redid the experiment with my Drozd only to find that it was able to punch a hole through every single material I used except the Lexan sheet, in which it simply left a minor dent. The next step was to try to combine materials, knowing that much of the damage being done was because the material being shot had nothing firm behind it to reduce the distortion of the material.
The goal of the material combinations I was playing with is to come up with something that can withstand single or sustained bb fire (from my pistol or bb gun) allowing the transfer of enough energy to trigger the touch screen without damaging the glass touch screen and without the protective materials sustaining damage themselves. With the touch screen costing almost $200, I can ill afford to include it in the tests until I am fairly certain it will be completely undamaged. I'd rather err on the side of caution initially and struggle to have a "touch" detected than have it register only one touch before it shatters into a thousand pieces.
Because the touch pad is glass I suspect there are three primary things I need to worry about. The most obvious is excess physical distortion, having a BB cause the pane of glass to be deflected beyond its breaking point. I assume there is also a shock force to worry about, that even without being hugely deflected the glass could be shattered by the sudden, brief introduction of a dislocating wave of mechanical energy. And finally I assume that the two previous items could combine in a sense by the latter element introducing small fractures that could grow as a result of the former.
The first step is to find material combinations which stop the bbs without being damaged or worn down. The next step would be to narrow those results down to a combination which appeared to impart just the right amount of "touch" to an object behind them.
The real puzzler is trying to figure out how to ultimately test my best guess material combinations without risking the touch pad. To this end I gathered some scrap window pane glass from a local window installation shop.
I made a mockup in cardboard to check the model in the real world. Most importantly I need to know if the ShowWX+ laser pico projector would be bright enough with the current design and its blocking of ambient light. Sadly the results were not encouraging. Even with a cloudy sky an hour or two away from sunset the projected image is extremely washed out and difficult to see. I added some additional cardboard to further reduce the ambient light, and while that did made a difference I don't think it was enough to justify the use of the ShowWX+. It's inadequate brightness, combined with its horrible green ghosting, made worse by its curious tech support mechanism (fill out a contact form which has no place to indicate the problem you are having and just says you'll hear something in a couple of days), and lack of user community forums, mean it'll be returned in favor of some other, better product; what that is, I'm not yet sure.
[more to come]