Search found 448 matches

by dongfang
Wed Nov 12, 2008 4:53 pm
Forum: Pneumatic Cannons
Topic: How can I make my piston seal against the barrel?
Replies: 7
Views: 759

Hi, If your valve is made serviceable, so you can take the piston out through the back, you can save it: Make a second piston with a flat front (maybe the original will work too), and glue (water soluble maybe) some good quality sand paper on the front of it. Attach a shaft of some kind that will st...
by dongfang
Sat Nov 01, 2008 5:13 pm
Forum: Pneumatic Cannons
Topic: Basic full-auto pneumatic
Replies: 13
Views: 2224

Hi, If you have a dremel, check the router table for it. You can stick a cutter tool in the dremel, set the height so it sticks up just a few mm, and then turn the part over the cutter. Cylinder side and end cuts are both possible. Side: Use a wheel cutter. End: Use a router cutter. I have used this...
by dongfang
Tue Aug 05, 2008 8:42 am
Forum: General How-To & Discussion
Topic: Burnt PVC
Replies: 10
Views: 715

Hi,

As far as I remember, the gases from burnt PVC produce hydrochloric acid when getting in contact with water. That's why even a moderate PVC fire can ruin large amounts of machinery, electrical installations etc.

But a single breath of that should'nt do much.

Regards
Soren
by dongfang
Sun Jun 29, 2008 5:58 pm
Forum: General How-To & Discussion
Topic: DIY Chronograph, am I doing it right?
Replies: 46
Views: 7914

Hi Jimmy, OK, good that you can get it to work ;) The CDS cells I have played with must have been much slower than yours. Those things took hundreds of milliseconds to detect anything at all. Semiconductor detectors, like phototransistors or -diodes are still 1000s times faster, I hope we can agree....
by dongfang
Sun Jun 22, 2008 12:01 pm
Forum: General How-To & Discussion
Topic: DIY Chronograph, am I doing it right?
Replies: 46
Views: 7914

Hi,

No, CDS won't work at all. They react very very slowly.

Regards
Soren
by dongfang
Fri Jun 20, 2008 5:44 am
Forum: General How-To & Discussion
Topic: Brand new pneumatic/explosion
Replies: 16
Views: 2357

Hi,

Yeah with all those stories about pumps kicking back (it happened to me too, but the piston and rod stayed connected to the pump), maybe an extra check valve would be a good safety feature.

Regards
Soren
by dongfang
Tue Jun 10, 2008 2:10 pm
Forum: Pneumatic Cannons
Topic: vacuum assisted pilot?
Replies: 13
Views: 685

Hi, I agree that sucking air out of the pilot probably will not make a difference. Besides, beyond a certain opening speed (which is not difficult to achieve), the returns for even better speeds start to diminish. BUT if you have some serious vacuum, I have an idea: Place a thin burst disk at the mu...
by dongfang
Tue Jun 10, 2008 6:14 am
Forum: Pneumatic Cannons
Topic: Presta valve = check valve?
Replies: 7
Views: 645

Hi,

I have used Prestas as check valves many times. Works fine.

If you need it to close at very small pressures, you can install it so that the poppet will drop shut by gravity, or you can use the spring from a ball pen.

Regards
Soren
by dongfang
Mon Jun 09, 2008 5:39 pm
Forum: Pneumatic Cannons
Topic: piston not sealing
Replies: 14
Views: 688

Hi, Glue a piece of paper (just with paper glue) on the front of the piston Fasten some carbon paper to the paper, carbon side towards piston, with a little dot of glue. Mark "up" side of piston. Insert piston and push it against the barrel. - Do you get a nice full circle on the paper? - If not: Do...
by dongfang
Thu May 29, 2008 5:46 pm
Forum: General How-To & Discussion
Topic: Remote Controlled missile?
Replies: 20
Views: 1368

Hi, rcman, I appreciate your information on the servos.. My first idea was just a misile with only tailfins, and a long enough body to have a little "lift" when the tailfins push the axis of the missile off the direction of the oncoming air... and with some sort of gyro spin stabilization, so I have...
by dongfang
Tue May 27, 2008 1:57 pm
Forum: Pneumatic Cannons
Topic: Bell reducers
Replies: 11
Views: 1658

Hi, Just a comment: In Europe (at least) there are pressure rated bell reducers, e.g. the babes on page 19 here: http://www.wacon.de/stock/service/cepex/PVC%20Pressure%20Fittings%20TC%20v2.pdf . The OP has no location in his profile (well OK he mentions shopping at Lowe´s...) - anyway the "bell redu...
by dongfang
Tue May 27, 2008 1:56 am
Forum: General How-To & Discussion
Topic: Remote Controlled missile?
Replies: 20
Views: 1368

Hi,

Thanks for the great ideas. To cut it short, I think I will try to build a water rocket now. First, uncontrolled and later controlled...

Fortunately, I can re-use many materials and tools from pneumatic spudding, not to mention experience.

Regards
Soren
by dongfang
Mon May 26, 2008 9:20 am
Forum: General How-To & Discussion
Topic: Remote Controlled missile?
Replies: 20
Views: 1368

Hi, OK thanks for the idea with rocket gliders. I didn't know about them. Hmm maybe a low-pressure, huge chamber and long barrel pneumatic is a solution. Spudfarm, about turns: I imagined to have an automatic thing that holds the thing fixed around the Z axis (the one going up from the barrel). Ther...
by dongfang
Mon May 26, 2008 6:30 am
Forum: General How-To & Discussion
Topic: Remote Controlled missile?
Replies: 20
Views: 1368

Remote Controlled missile?

Hi, Did any of you ever hear about anyone building a projectile with folding (or fixed) fins and an R/C receiver and launching it from a spud gun? Just like model aircraft, it wouldn't really have a purpose. Just satisfying a little curiosity. I could imagine the R/C doing some or all of: - Trajecto...
by dongfang
Mon May 26, 2008 6:06 am
Forum: Pneumatic Cannons
Topic: Leaky piston housing
Replies: 12
Views: 1100

Hi, I have used silicone successfully several times. It has almost no mechanical strength (but I suppose your bolts do that part - sorry I'm on business class here and there's a firewall against photobucket) but it will seal OK. Just apply some to the fitting and some to the cap, and push it on. Whe...