That looks amazing. Could you do a DIY guide?
Both of my links are to guides.
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There have been 510 items by Doom (Search limited from 19-July 93)
shmmee, quite nice work. I bet the hair was heavy!
Back in the day I used to build homemade water guns. I've gotten back into this lately, though the new one I built this year hasn't worked so well and I intend to re-purpose it. I'm planning another one which would completely avoid the faults of my newest one.
One homemade water gun I built that I'm particularly proud of I called SuperCPS.
This one worked nicely, but I broke part of it by trying to upgrade it. I never bothered to fix it, though I might now.
My most powerful one I called Supercannon II. Not practical for actual water fighting in any way, but it's extremely powerful and gives a good buck when shot, especially when the nozzle is removed so you have a 1.5" diameter water jet.
Back in 2008 or so I bought some hefty constant force springs (probably 9293K14) for a water gun design. You usually want constant pressure, so this would do that. I don't remember all the details, but after getting two of the springs (to avoid the balance issue you have) I scrapped the project and returned the springs to McMaster-Carr. I think I decided the springs were way too unwieldy, and I was skeptical of the safety of the design. But this is making me reconsider given that it could be combined with another crazy idea I have for a water gun, which probably wouldn't require the largest springs.
Ultimately, I think Kane is right and increasing force is better for Nerf. You want to build up pressure as quickly as possible, so you'd want higher force initially to get higher acceleration and more compression initially.
The age of the tubing is less of a concern than how many stress cycles it has been through. Silicone (silicon tubing does not exist to my knowledge and seems to be a typo on Hobby King) rubber can be pretty good in this regard from what I've read, but I've never seen comparisons with latex rubber. No time to look right now, but I'll post again if I find anything along those lines in the future.
Langley, I did an image backup in 2014, and it appears to be on the root of the NH server in a file called "nh_images.zip". Probably is worth checking out for images lost in the interim. I don't have the time to look at it right now, unfortunately. I also don't recall saving the images in a particularly logical format. I imagine they were all just put in one directory, and if I wanted a broken image I'd match the filename. There could have been conflicts.
Compressibility is a bitch. Just like a sponge can be squished and change it's density, so can a fluid, and all these easy equations go out the window. For a fluid to reach the point of compressibility, the air flowing in the pipe must be greater than 0.3. If the barrel is plugged by a dart, logically, the air flow cannot exceed the speed of the dart. In something like a suped up 4B, the FPS can reach 300 if you plug the pump, it's more like 250 for high end springers. So with the speed of sound at sea level being 1125 FPS, the mach number of a springer's barrel would be 0.22 and for a 4B, more like 0.27, so we get pretty close to compressibility being an issue, but dodged that bullet for now, so that above equation is valid. Honestly in some of these looser fit 4Bs I wouldn't be surprised if, when hooked up to the right equipment, we actually got into the realm of compressibility.
BUT if that restriction is made too small you begin to run into the problem of compressibility in homemades. For Nerf brand shit you won't have to worry about that.
(This is somewhat technical and can be ignored by most people.)
The phrase "compressibility" is used in several different senses in thermal-fluid science, and they can be confusing. The Mach number does not need to go above 0.3 (or whatever cut-off is set) to have compressibility effects. Take a sealed piston, compress the gas, and hold it still. The Mach number is zero, yet there's a change in density.
The Mach number is about the speed of sound. You can have a flow where the velocities are well below the speed of sound, yet density changes are important. Buoyancy driven flows (e.g., from combustion) are one major example. I work in fire protection, and the variable density low-Mach Navier-Stokes equations are the starting point. Nerf is another example. The density changes are appreciable, but you generally don't need to worry about the speed of sound effects. So that equation is not applicable.
This is not to say that Mach number effects are not important in Nerf guns. The flow could easily choke in restrictions. In my old Nerf gun simulators, that was the only place I took into account Mach number effects.
To get back to the original question, I can't comment on the effect of this on performance. Seems situation dependent to me. It could act to reduce deadspace as Aeromech points out, or it could just restrict the flow. I'm skeptical of the "Venturi effect" explanation, as it doesn't matter if the velocity near the projectile is fast; the no-slip condition says the fluid will be going the speed of the projectile at its surface. So if the projectile is still, the gas will slow down, etc. It's often more correct to think in terms of pressure. Would this increase the pressure behind the projectile? Probably not, though this isn't the entire story. There's one way to know. Agles, if you think this has promise, test it out and let us know here.
Putting fishing line in your blasters barrel is common in Singapore its supposed to act like a "rifled" barrel
This might be old news, maybe not, but we have this thread on different stock darts from the HvZ forum. Might be useful to be using darts from the same production run.
Apologies, rechecking my link and doing some copy pasta research I have determined it is impossible to link to an advanced member search. Thus the 'guide' to navigation makes more sense.
I always thought this was one of the main reasons for using washers over bbs/bearings/fishing weights - the washers have more surface area and are less likely to punch through the padding on the dart.
Yeah, I always thought that Kane and the like were just being ridicules with all of their "safe dart" concepts. He was making a non-proven dart to solve a non-existent problem.
In your opinion, what is more important when trying to hopper an airgun, volume or pressure?
The only data I could find was CaptainSlug's Pepe, where he used a 10 psi 7 ci tank with a hopper.
Split at NerfHaven told me he couldn't get a hopper to work with a "small" 4 in^3 firing chamber.
I'm a little out of my depth here, but it would seem to me that double shots (two darts chambering from a hopper per shot) could be caused by too much airflow after the dart leaves the barrel. This may be fixed by lengthening the barrel.
I'd make a small tank, and then a tank an order of magnitude larger, and another 2 orders larger. Maintain vent hole size with each. Test each at various pressures with the same hopper and barrel system, with a fake barrel that's only a few inches long, in order to demonstrate chambering. Sound about right?
I have no idea how many variables would need to be accounted for in order to solve for barrel length, but it seems logical to say that the best barrel length would be found where the acceleration of the dart equals zero. This would correlate with the maximum muzzle velocity of the dart. If there was a way to track the position of the dart inside of the barrel, it would be easy enough to make a function from that data, find the second derivative of that function and solve for y=0.
I'm not entirely sure if any of this is exactly practical, or if it is the best way to solve this problem. I would love to hear what you think about the subject, and hopefully the community will eventually find a use for the fruits of this labor.
I know you already have your plate pretty full, but could you possibly make an article(or two) detailing the pressure and/or air volume required to hopper an airgun?
I would say that coefficients of friction for various brands of FBR on various brands of CPVC would be a good idea, but there is probably far too much inconsistency for useable data to be accumulated. Perhaps some common match ups could be outlined if a universal barrel length formula is ever created.
Hmmm. I was writing a ballistics program to calculate ranges at different angles and such. If I had a decent value on the drag coefficient of various NERF darts I could make a few tables/graphs for reference.
Are you going to be taking attendance, do we need to print out a copy of the syllabus, and when is the first exam?
Looking forward to the Flywheel lecture.
I'd like to second the request for a flywheel post. There's little to no knowledge in the community as to how variables like wheel mass, moment of inertia, and motor torque affect performance. If we could get a Real Life Physicist to teach us the basics it could really help people who want to build their own.
I would recommend lecturing about shady ass generic Chinese valves. They are fairly difficult to come across any factual information about them.
If you haven't, calculate the approximate drag force of a micro dart in terms of velocity (in ft/s for use with chronographs) and mass (in grams).
This way, we can use the drag force and gravity to create another formula to get an approximate range from Chronograph readings. This would only work for accurate darts, though. So not for streamlines.
The email spam I started getting yesterday makes it a possibility that someone may have been able to steal the NH database of user email addresses.
Although the specific email I examined actually came from a compromised host in the Netherlands, it claims to have been sent by Noodleownz, and other vaguely familiar names appeared on "To" addresses. The spammers had to get it either from the site or from another member, because I created an email address just for NH. It's probably even slightly more likely that some member who has exchanged email with me in the past was hacked, there are so many 0-day hacks for windows browsers now.
I'm willing to share the list of addresses and associated names but only with a site admin, if anyone cares to bother checking the database. If the addresses were to all match NH members, then the probability the addresses were hacked from here would be higher. I wouldn't even suggest it should be any priority, though. Spammers eventually get everything.
Regardless, I recommend everyone change your NH password.
And if you were ever fool enough to use the same password anywhere else, change those too, and make each one unique this time.
Hey, Also a newbie to Nerfing, and in the Austin area (about 3 hours away)
I've got a small group here and would be willing to drive if you got something good organized.
Once testing on the precision of any given Nerf blaster is underway, I'm fairly certain it will become a problem of proper blaster construction, barrel to plunger volume configurations, and dart-smithing. Not a calculation of MOA at 30 ft.
Who are "a lot of people"? Why are you under the assumption that 30 feet is the magical average engagement range?
You could construct some kind of structure that would keep the blasters level and aimed in the exact same way for every test, but that would take effort and resources and you would need a new one for every blaster since every blaster is shaped differently.
I think a dart-type accuracy test would be much more beneficial than a blaster accuracy test.
You can arrange tests and use whatever philosophical rating you want to employ as your logic for such tests, but to what end? These are nerf blasters we're talking about. You can find some magical grouping or calculation of accuracy at 30 ft, but what is this going to accomplish?
Speculating (no tests have been done), I think that what causes a blaster to be less accurate is mainly "barrel wobble" and muzzle blast.
While I believe testing blaster precision is a worthy endeavor, the intent is to meant for both person and blaster. I understand that one could make a very precise blasters and be a terrible shot. But the blaster precision data does him (specifically) no good, if he were to use the blaster.
Happy holidays everyone! I hope everyone had a great one! I wish it was colder here in SoCal. A 75 degree Christmas is not too great, but it is better than freezing.
... And congrats to Doom on his 500th post!