18 replies to this topic

[Langley]

So apparently Meaker IV just had a baby or something, so he PMed me about posting this and then never got around to it, and I figured it was cool enough to get it's own thread.

Explanation of the Venturi Effect, which is (probably) responsible for the inner workings of hoppers.

"The Venturi effect is the reduction in fluid pressure that results when a fluid flows through a constricted section of pipe."
Bernoulli's equation, together with conservation of energy shows that a stream of fluid moving through a constrained space at higher speed must be at a lower pressure. But that's kind of a boring and mathematical explanation. It also doesn't fully explain everything, in my opinion.

In this video, I'm demonstrating and explaining how compressed air can be used to create suction. Equations aside, that seems a little counterintuitive.

[BiwinningPanda]

Very interesting stuff. So if I am understanding this correctly, a greater amount of space/air in front of the wye could create a greater suction, helping darts feed in more consistently. Do you think this might work?

[Exo]

Very interesting stuff. So if I am understanding this correctly, a greater amount of space/air in front of the wye could create a greater suction, helping darts feed in more consistently. Do you think this might work?

Yes, but half of the effect would be due to the fact that the dart has more length to shift it's angle from the 135* from the hopper to more like 180*, or however you want to numerically describe that, but that could also lead to double feeding, etc.

[Phoenix66]

Wait, so hold on a second. Meaker IV made that video? Or he just found it.

[Langley]

Wait, so hold on a second. Meaker IV made that video? Or he just found it.

He found it, private messaged me to ask if it was okay to post, and they got busy with real life stuff.

[The Nerfaholic]

I'm surprised that you don't see this being used in dual-chamber Super Soakers or something. That aside this is really cool. Yay physics!

[KaneTheMediocre]

Cool story, bro. Try turning your wye upside down, and letting the Venturi effect suck the darts up into the barrel.

edit: Fondue makes a fair point. Try turning the barrel almost completely sideways, but slightly sloped down. If the venturi effect applies here in some significant way, there will be some amount of downward slope that it can overcome.

Edited by KaneTheMediocre, 15 September 2012 - 11:51 PM.

[Righteous Fondue]

Cool story, bro. Try turning your wye upside down, and letting the Venturi effect suck the darts up into the barrel.

It's still reliant on gravity, he never said it wasn't. The Venturi effect is just a contributing factor, so no need to act like a smartass.

[Jilliop]

I recall someone posting a cool mod/pj here of a Max-D X,000. I think it was a 2,000. Either way, they modded it so that it could be used to shoot darts, or his little sister could shoot glitter. Now, the glitter attachment was a bottle that hung off the barrel. He said that the vacuum created by the air moved the glitter up and out the barrel in a burst. I can't find the picture, but my point is that the glitter had a large distance to travel, but since the mass was so little, it was largely possible.

[Zorns Lemma]

Cool story, bro. Try turning your wye upside down, and letting the Venturi effect suck the darts up into the barrel.

edit: Fondue makes a fair point. Try turning the barrel almost completely sideways, but slightly sloped down. If the venturi effect applies here in some significant way, there will be some amount of downward slope that it can overcome.

Beaver has had hoppers that shoot sideways.

Where is your gravity now.

[makeitgo]

Although the Venturi effect may be responsible for chambering the dart (darts in the case of a double feed), it's still the explosive air pressure that 'pushes' the dart out. This is quite evident within the hopper as soon as the dart being fired is fully chambered into the barrel (due to the Venturi effect). As the dart is pushed out of the barrel, air also pushes the remaining darts back up into the hopper. Not sucked out through the barrel.

[atomatron]

Relevant; as you can see in the first shot the dart is already within the chamfered end of the barrel, I do not think that the Venturi effect is at work here. Though it is possible that it's acting upon the dart behind, as it appears to jump up a little (probably due to the pressure differences across the length of the clip) and then go back down as the first dart is leaving or has immediately left the barrel.

[Langley]

I'm not making any claims one way or the other about whether this is how hoppers work, I'm just passing on a cool video that another nerfer sent me. Whatever you take away from this, I think it's important to remember that air pressure can work in unintuitive ways. It's also notable that the Venturi effect can work in a hopper under the right circumstances.

Try this: Take a wye with a clear tube and remove the cap or open the ball valve or whatever. Do not connect a barrel to the outlet. Blow into the input (where you would typically connect a blaster) and darts will be pulled up the hopper and out the output, where you would normally connect a barrel. The constant air from my lungs was able to achieve this, but the brief puff of air from a big blast was only enough to slightly pull the darts up the hopper tube.

Even if the Venturi effect is not at work under normal circumstances, it's probably possible to use this effect in a hopper for a hamp or some other blaster that uses a continuous stream of air.

[Zorns Lemma]

It really doesn't matter either way as to what makes hoppers magically feed a dart around at least a 3π/4 bend. I'm not convinced that fluid mass really contributes that much, but it can't all just be fluid pressure either.

The only way we could take advantage of this knowledge is to build a hopper with a bulbous part around the chamber/wye/barrel. If this effect contributes a large amount, then darts would feed more consistently. But building such a device would be cumbersome, and that's assuming empirical testing shows this works at all.

[Meaker VI]

Now that I've caught up with Real Life^tm, I can respond to this.

I found the video and explanation over on the Woodgears site. The guy that runs that site is an engineer, and always does an excellent job explaining processes and doing tests. He also builds some cool shop equipment, and I'm sure careful study of some of his stuff could prove useful for building homemades.

This particular video showed him doing some things that are nearly exactly what hoppers seem to do - and I figured that it'd apply at least for us to study.

By bringing it up, I was not trying to say that gravity doesn't play a significant part in dart loading, or that the air pressure behind the dart doesn't actually fire it, but that I think the dart may be being chambered by the Venturi effect. And I figured that knowing that would allow many of you, the most innovative of nerfers, to use it effectively rather than accidentally or blindly; if in fact it is what is at work here.

I also think that we might benefit from purposely trying to use the Venturi effect -even if it isn't in use now - maybe we can make hoppers without end caps, for example. Another thought I had was that we might actually benefit from strategically restricting the airflow - in the video that tiny nozzle can blow around all sorts of other stuff (Obviously, he has an air compressor hooked up to it while we don't. He was mostly launching low-mass particles, we aren't. That isn't the point here); maybe the increase in air velocity would be helpful for getting darts fired.

[Buffdaddy]

Now that I've caught up with Real Life^tm, I can respond to this.

I found the video and explanation over on the Woodgears site. The guy that runs that site is an engineer, and always does an excellent job explaining processes and doing tests. He also builds some cool shop equipment, and I'm sure careful study of some of his stuff could prove useful for building homemades.

This particular video showed him doing some things that are nearly exactly what hoppers seem to do - and I figured that it'd apply at least for us to study.

By bringing it up, I was not trying to say that gravity doesn't play a significant part in dart loading, or that the air pressure behind the dart doesn't actually fire it, but that I think the dart may be being chambered by the Venturi effect. And I figured that knowing that would allow many of you, the most innovative of nerfers, to use it effectively rather than accidentally or blindly; if in fact it is what is at work here.

I also think that we might benefit from purposely trying to use the Venturi effect -even if it isn't in use now - maybe we can make hoppers without end caps, for example. Another thought I had was that we might actually benefit from strategically restricting the airflow - in the video that tiny nozzle can blow around all sorts of other stuff (Obviously, he has an air compressor hooked up to it while we don't. He was mostly launching low-mass particles, we aren't. That isn't the point here); maybe the increase in air velocity would be helpful for getting darts fired.

Well, the air pressure behind the dart DOES fire it. It then goes the path of least resistance - without that end cap, guess where that hopper of darts if going to fly...

So, in summary, gravity sets the dart just behind the barrel, and given enough air pressure to make this effect strong enough to "chamber" the round, you've got a working hopper. I think we've summed this up.

Again, you have to have a large enough pressure drop for hoppers to work - thus why you usually only see them on high-powered springers or airguns. smaller than that, you can sometimes get away with a BritHop - I'm taking a SWAG here and saying the extra ramp helps orient the dart closer to the barrel, thus making it easier for the small pressure difference to work?

[ferball]

I did some experimenting with the venturi effect for some other crap I was working on a few years back. I don't think it has much of a bearing on hoppers at all, and would not be a useful design element in foam blasters. The energy to move the dart has to come from some where, if you are going to use some of your "air pressure" to chamber the dart, it won't be available to propel the dart. One of the first mods you do to a blaster is drill out the air restrictor and/or open up the "nozzle" for better airflow. To get a decent venturi effect you would have to essentially put an air restrictor back into the blaster to create a decent pressure deference. We are better off letting gravity feed the darts so we can get the most out of our air pressure.

[Atlantis Risen]

I've got a quick question. I'm pretty new to Nerf, and very new to the idea of hoppers, and after watching the slow motion video showing a dart being chambered and firing through a clear hopper, it seems to me that since some of the energy of the spring, piston and air flow is going to the sucking of the dart into the barrel, that this would lessen the power and range, as opposed to a dart that is already chambered in the barrel. Is this what you guys have found when using hoppers?

[hamoidar]

I've got a quick question. I'm pretty new to Nerf, and very new to the idea of hoppers, and after watching the slow motion video showing a dart being chambered and firing through a clear hopper, it seems to me that since some of the energy of the spring, piston and air flow is going to the sucking of the dart into the barrel, that this would lessen the power and range, as opposed to a dart that is already chambered in the barrel. Is this what you guys have found when using hoppers?

Yes, you are correct. Plus, the added dead-space from the hopper tube also decreases range. But, the sacrifice in range is usually worth the rate/amount of fire.

Edited by hamoidar, 15 October 2012 - 09:32 AM.