Here is a bit simpler design; http://www.inpharmix.com/jps/_images/SG_jig_final_2.jpg from http://www.inpharmix.com/jps/Jims_chrono.html It is just a cutup piece of the same pipe used for the barrel. Obviously this is much easier with plastic than metal. You really don't need emitters with this desi...

Finished model;

Often people just drill a hole in a cap and add a nipple with nuts (and washers) on each side of the cap. http://www.truetex.com/co2b.jpg A 3D print file at https://www.thingiverse.com/thing:878942 soda bottle to 1/4" NPT https://thingiverse-production-new.s3.amazonaws.com/renders/ff/3b/2c/a8/28/2_l...

I'm obviously not an expert but ... I kind of doubt anyone in the world knows much about DDT in a gas fueled gun that is this large. Everything I've ever read about DDT suggests it is difficult to predict and even difficult to reproducibly create. Still, as a WAG, multiple sparks might reduce the ch...

There is something wrong with the report at https://arxiv.org/abs/1305.0966 Studying the Internal Ballistics of a Combustion Driven Potato Cannon using High-speed Video E.D.S. COURTNEY AND M.W. COURTNEY The numbers in Table I don't make sense. The "amounts between stoichiometric and the upper flamma...

jackssmirkingrevenge wrote:Your friend (relative?) has done a very good job, I'm particularly impressed by the metal finish.

son

Obviously non-functional

But the cylinder pivots out and he is making rounds that fit the chambers.

Obviously non-functional, but damn pretty (and not even done yet, the wood grips haven't been added) ... https://scontent-sea1-1.cdninstagram.com/t51.2885-15/s750x750/sh0.08/e35/22709426_299173657156705_8961771626169368576_n.jpg?ig_cache_key=MTYzMTQ1NzE4Njk0NDYzMDM4MQ%3D%3D.2 video--- https://www.in...

To be fair, using a ballistic pendulum just steps you back a couple hundred years in technology.

jackssmirkingrevenge wrote:Here's a dangerous thought, what about a premixed chamber of propane and air? The big risk is the thought that the whole main chamber would ignite, but I'm sure some safety measures like a non-return valve would avoid such a possibility.

"Dangerous" is an understatement.

kevin-db wrote: I bought black material(포맥스) because it was annoying to paint.

포맥스 is PVC foam board? Also called Fomex or Foamex?

Why not use gasoline, it's a much more energy dense fuel than propane and this means you would not need any compressed fuel around the launcher at all. The only trick is injecting the right amount, but internal combustion engines have been doing this for more than a century. And it only took thousa...

One challenge with opening a ball or butterfly valve fast is how do you stop it? The stronger the spring, the faster it opens, the harder it is to stop, the more likely it is that something breaks.

http://www.womackmachine.com/engineerin ... g-air.aspx

http://www.assakkaf.com/courses/ence420 ... pter11.pdf in particular, slides 27 - 32

Photobucket sucks.

Butane, propane, methane, ... are all essentially identical: http://www.inpharmix.com/jps/Combustion_fuels.html https://www.spudfiles.com/spud_wiki/index.php?title=Common_Fuels_for_Combustion_Spudguns As Dave said early on, the ONLY thing that really matters in terms of fuel is getting the right amo...