Bang (Patreon)

It's funny how the projects that I think will be easy always end up being really hard (and vice versa). This explosive bat has been really kicking my butt. One of the challenges for me is that I don’t have any experience doing engineering analysis on explosions. Being able to say if it is safe and actually works is tricky business. The big question on my mind is how close is the barrel to exploding? This is the main measure of safety that I really need to know. 

My strategy has been to sidestep tedious calculations (which I have high odds of getting wrong anyway) wherever I can. I took the worst case numbers, and then over built things to definitely be safe. This worked for most things but in a couple of cases the worst case numbers were obviously wrong. Using these numbers would result in a ridiculous design (think many pounds of steel on the end of the bat). Since safety is paramount and I don't really trust my numbers, I’ve been doing a lot of real world testing with my basement firing apparatus to validate the design.

This rig is great since I can stand behind a shield and quickly launch baseballs. I’m expecting the ball to eventually get flung off this, so I have thoughtfully aimed it at the least expensive stuff in my shop. This lets me see if it is mostly safe, but it still doesn't tell me how close the thing is to failure. I've ordered some strain gauges which I can attach to the barrel and measure how much the metal is stretching when fired. From this information I can calculate the pressure inside the bore and know how safe it really is.

It’s also good I did this testing before building the whole bat because my first design didn’t work at all. I really underestimated how sensitive this device would be to ANY pressure leaks. I machined the parts to have a very close fit but nature finds a way. You can see in the gif below  that the piston barely even actuates with pressure leaks from very tiny gaps in the base of the unit. The ball moves up maybe a foot which is totally useless. I rebuilt all the parts to be totally sealed with o-rings and now it works great. O-rings aren't the best choice but they are what I had on hand. Ultimately I need to use something like piston rings. 

Analyzing the video of the working unit, the power of a single cartridge moves the ball at about 50 mph immediately after being hit. A quick googling suggests that the average MLB ball velocity coming off the bat is ~100mph. Hopefully firing 3 cartridges at the same time will get me up to superhuman ball speeds. Theoretically I should be able to given the energy in the cartridges but the efficiency of the energy transfer is  ¯\_(ツ)_/¯. My remaining challenge is firing 3 shells at the same time. With my test rig I can't get enough force from the ball to fire any of the shells when I have three. It looks like there isn't enough force to adequately smash multiple shell rims simultaneously (which is what causes a rimfire shell to detonate). I've been reading up on firing pin design and it looks like I'm far from optimal. I'll be tweaking this and hopefully everything will just work™. 

I started work on fabricating the bat and hope to be acquiring pressure data and hitting balls in a day or so. As always I'll be posting more fine grained updates in the discord so join that if you're interested!