Search found 9 matches

by nik282000
Mon Aug 28, 2017 4:26 am
Forum: Pneumatic Cannons
Topic: Yet Another Vacuum Cannon and materials selection
Replies: 14
Views: 5129

Re: Yet Another Vacuum Cannon and materials selection

I had suspected that there is a limit for "deforming speed" (is there a real name for this?), polycarbonate is usually super tough and will distort heavily but at such high speeds it just shattered. I'm not sure about going up much in pressure until I lengthen the barrel, like I mentioned before I t...
by nik282000
Sat Aug 19, 2017 4:19 pm
Forum: Pneumatic Cannons
Topic: Yet Another Vacuum Cannon and materials selection
Replies: 14
Views: 5129

Re: Yet Another Vacuum Cannon and materials selection

Do not aim at eyes or face. I have always been curious about how strong those full face shields really are, after today I have decided that they should be re-labeled as splash guards. The face shield was made of polycarbonate and was about 1/8" in thickness, I has -27in/Hg of vacuum in the barrel an...
by nik282000
Thu Jul 13, 2017 12:22 pm
Forum: Pneumatic Cannons
Topic: Yet Another Vacuum Cannon and materials selection
Replies: 14
Views: 5129

Re: Yet Another Vacuum Cannon and materials selection

Compared to most of the pneumatic cannons here I am using no pressure at all, to get a repeatable 450m/s I am only using 80psi in my pressure chamber, any more than that and I have found that the balls shatter before making it out of the barrel. Given the barrel is only 11" long the ball is feeling ...
by nik282000
Tue Jul 11, 2017 2:43 am
Forum: Pneumatic Cannons
Topic: Yet Another Vacuum Cannon and materials selection
Replies: 14
Views: 5129

Re: Yet Another Vacuum Cannon and materials selection

I was thinking a better ball to barrel fit rather than more vacuum, not sure what that involves though. Four months later and I have an answer for you! There was a lot of blow-by and I'm not sure if it can be eliminated but I found out that it's effects can be almost completely canceled out. My fir...
by nik282000
Sun Mar 05, 2017 1:19 pm
Forum: Pneumatic Cannons
Topic: Yet Another Vacuum Cannon and materials selection
Replies: 14
Views: 5129

Re: Yet Another Vacuum Cannon and materials selection

I'm using 38mm balls and 1-1/2 pipe is a pretty close fit. I could try some wadding but I don't know if the added friction would counteract the better seal. Once my bag of 50 balls and mylar sheet shows up from ebay firing cost will drop off significantly, at the moment it's ~70cents a shot with con...
by nik282000
Sat Mar 04, 2017 9:36 pm
Forum: Pneumatic Cannons
Topic: Yet Another Vacuum Cannon and materials selection
Replies: 14
Views: 5129

Re: Yet Another Vacuum Cannon and materials selection

Good eye, that is from blow-by, I didn't get a hard enough vacuum. I have been working on repeatability but a couple cold days have mean that I can't get much faster than 400m/s. I did see something wild this week though, the energy dissipated during impact is enough to make either ball or contamina...
by nik282000
Tue Feb 28, 2017 1:35 am
Forum: Pneumatic Cannons
Topic: Yet Another Vacuum Cannon and materials selection
Replies: 14
Views: 5129

Re: Yet Another Vacuum Cannon and materials selection

I finally got my hands on pressure rated pvc pipe and fittings. Apparently it's a hard to find item in Canada, the 4 inch pipe was $10 a foot and had to be special ordered. I went with a 3:1 chamber to barrel volume ratio and nearly 1:1 pressure chamber to vacuum reservoir. Unfortunately the centeri...
by nik282000
Sat Feb 11, 2017 10:14 pm
Forum: Pneumatic Cannons
Topic: 750 fps marble launcher
Replies: 11
Views: 4901

Re: marble launcher

Awesome, it takes a lot of force to poke a hole in a hard hat.
by nik282000
Thu Feb 02, 2017 4:53 pm
Forum: Pneumatic Cannons
Topic: Yet Another Vacuum Cannon and materials selection
Replies: 14
Views: 5129

Yet Another Vacuum Cannon and materials selection

Hi guys, I am on the quest to put a Ping Pong ball past mach 2 and this forum has a lot of great info. To start, I am already getting speeds right around 500m/s which is satisfying/terrifying from little celluloid ball. The first GIF below was filmed at 1200fps with a 1/2000s shutter speed and only ...