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quiet asian man

Member Since 01 Nov 2007
Offline Last Active Jul 07 2008 06:10 PM

Topics I've Started

Rotating Valve

07 July 2008 - 07:15 AM

Has anything like this ever been attempted?

I intend to build this in the near future but right now I'm very busy with summer school. I would like suggestions in helping me to improve this design or otherwise how to go about constructing it. Please don't refrain from saying "wow, this is a big failure waiting to happen."

Currently I'm going to find a large hunk of plastic for the internals and see if it's even within my price range. The outside will be made of pvc fittings and seals will be made with large rubber washers around the pressure chambers.

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Is there a specific name for this type of thing? Searching "rotating valve" on google gives me useless information and this topic appears on the first page of results.
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New Style Plunger

22 June 2008 - 04:36 PM

Pictures worth 100 words.
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My plunger slides over the guiderod, greatly reducing mass and removing that pesky rod sticking out the back of your snap 1. It's made out of a X -> 0.5" bushing with a drilled out endcap as a catch and an O ring sandwiched between sch80 0.5" pvc to seal against the guiderod.

The guiderod is sealed at the end with plumbers goop.

With this setup you can easily recreate something similiar to Carrtoons Tec 9. Just remove the cotter pin, unseal the brass, and glue on a combination of brass and pvc as an outer stop.

Photogates And Nerf

31 May 2008 - 02:50 PM

Hello all.

I did a physics project on nerf guns. I tested the effect of RSCBbarrels on dart velocity using normal barrels as a control.
big SNAP data

Dart velocity did not gradually decrease as I fired more darts. In fact, velocity seemed go randomly go up and down after the first shot. However the gun also had inconsistent results using normal barrels, so I can't draw a direct conclusion other than "the plunger is so big that the deadspace filled by darts means nothing." But it still got me thinking about energy conservation.

My theory is that when you prime and maneuver the gun, darts shuffle around randomly inside the ammo tube. When shot level to the ground, the gun wastes random amounts of energy moving these darts to the back of the ammo tube before firing the dart. The gun would waste more energy if the darts were clumped at the base of the barrel than if they were at the back of the ammo tube.

This explains the problem Carbon had with his ball SNAP with an endcap follower here:
The endcap is like a very heavy ball that the gun moves in addition to his first ball. The gun wasted more energy moving the endcap up than it did going through deadspace. In addition the last ball fires the hardest because the gun wastes more energy moving the extra balls in the ammo tube.

I unfortunately do not have time to take more data for my project, but I will test whether the gun really wastes energy moving loose darts by pointing the gun at a 45 degree angle up and down to clump the darts and compare the velocities.

Testing Conditions
-Big SNAP with CS-866 spring in addition to cut down SNAP spring (full spring is too long and warps when fully compressed)
-all barrels are 17/32 brass
-plunger volume ~17.7 cubic inches (2.125" ID and plunger travel 5")
-deadspace caused by 11 shot RSCB ~5 cubic inches
-darts are 2 inches long and weighted with 1/4" slingshot balls and a flat hotglue tip (pressed against a wet plate to harden)

Data was collected by mounting a photogate on the end of my barrel. The beam is about 1~ infront of the the barrel. The end of the gun was stabilized on a bar because the mass of the photogate causes the barrel to bend. The photogate had to be mounted on the barrel because recoil causes darts to go high and barely scrape or miss the beam entirely.

Can anyone confirm my findings? And would anyone else be willing to get solid velocity data using similar equipment? I'm especially curious how my snap compares to the +bow, which has less plunger volume but likely a much lighter plunger. I also suggest photogates as an alternative to range testing if your school has access to these tools.