T-Shirt Cannon Calculations Spreadsheet

After kicking it around for a couple years, our team has decided to make a T-Shirt Cannon robot this offseason. We’ve read all the posts on here and done a bunch of research and it’s been helpful (thanks!).

Wanting some more calculations I started a spreadsheet to help figure out some better estimates for flow rates, speed of travel, firing tank recharging rates and such:

However, some of the numbers don’t look correct to me. For instance, I’ve see people post about 30-40 ms valve open timings. But at that rate, it appears that not enough air would be discharged to even get the t-shirt out of the barrel. In fact, even at a 300 ms valve open timing, it’s still not quite enough to fill the volume of a 3" x 24" pipe. What am I missing?

Admittedly, I’m probably missing something here, so if you have some advice on this spreadsheet to improve it, please post and I’ll be happy to adjust it. And feel free to copy the spreadsheet and make it your own.

At a glance, it appears that you’re trying to fill the whole tube with 60 psi air. This would only happen if the shirt weighed several hundred pounds. While I haven’t done the detailed calculations, the work of launching a t-shirt seems to take place down around 1 or 2 psi gauge pressure; the 60psi supply is just needed to get the air through that 3/4" orifice quickly enough to really accelerate the load. Once the t-shirt clears the end of the barrel (and likely a few ms earlier), any additional valve time is just blowing air.

You might want to check this piece of software out! It’s what we are using to design our t-shirt cannon.

http://www.thehalls-in-bfe.com/GGDT/

That’s it. Totally missed that. I even had 1 pound of friction for the t-shirt and never used it!

Thank you so much! I’ll update and post a reply.

Thanks, that looks pretty interesting! I’m on a mac here, but maybe I can try to spin up a VM to try it out.

Thanks again Gus. I updated the spreadsheet with the compression factor and 37 ms valve timing seems just about right now. :smiley: