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Dart Spinning (rifling) Test Rig

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#1 Landru

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Posted 27 August 2009 - 04:54 PM

There is an ongoing debate on whether spinning darts as they leave the barrel will improve stability. I have devised and constructed (still being greatly improved) a rig which allows darts to be fired from a brass barrel rotating at various RPM's (from 180 up to about 600RPM). I intend to show the ACTUAL effects of rotating a variety of types of stock darts as well as Stefans of different weight distributions.

First, here is the basic setup: 17/32" brass barrel, 10" long. Powered by 60psi run through an air nozzle. An old sewing machine motor is belted to the barrel, which is nested in the next size up brass tube, which acts as a cheap bearing.

Results so far: (Keep in mind this is the beta tester, and real data will be obtained after all the bugs are worked out)

At low RPMs (600 or so), there didn't seem to be much effect on stock darts or stefans. At about triple that most stock darts catostrophically fail, the plastic tip bends over and flops around and occasionally rips off. Streamlines cartwheel right out of the barrel.

At max rpm, crappily made stefans appear to have MUCH better accuracy than their non-rotating counterparts. I will make up a batch of identical weight perfectly made stefans to test soon.


Eye Candy:

Posted Image


If you have any thoughts/suggestions let me know. Just remember, i will have actual numbers soon and more info about the actual firing rpm, muzzle velocity, weight distribution of the darts etc.
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#2 flashflint

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Posted 27 August 2009 - 05:13 PM

Nice. I tried something similar awhile ago. I never made as nice a rig as you so I never got conclusive evidence. But I believe when you say it helps.
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#3 Bishop

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Posted 27 August 2009 - 07:39 PM

Can we add to the rules, "Please don't sign up if you would like to talk about rifling nerf darts." Would save people a lot of trouble.

Of course I'm just kidding but threads like this only bring <_< to mind. I do give you credit for actually trying... at least I think I should. If you read all the "debate" threads that don't seem like much of a debate to me they would probably dissuade you from trying something like this. Its always fun to see people testing new things... but maybe put your time to something practical, I'd hate to see time go to waste
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#4 SonReeceSonJensen

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Posted 27 August 2009 - 08:27 PM

I canít not tell you Iím impressed with the both the effort and the quality of your effort.

Iím interested to see results, but It might be awkward to carry both a backpack tank AND a car battery while running with the flag
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The Difference:
-Guns shoot bullets that kill people
-Blasters shoot darts that tag people

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#5 Zack the Mack

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Posted 27 August 2009 - 09:02 PM

Iím interested to see results, but It might be awkward to carry both a backpack tank AND a car battery while running with the flag


He's not planning on making an actual spinning barrel (At least, I hope he isn't). He's just seeing if causing a dart to spin has any effect whatsoever. There's no point ripping your hair out trying to cut helices in CPVC if the spinning won't do anything.

Also, that's one serious rig, and it's also technically a blaster. You should paint it brown and make it look like a platypus.
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#6 TantumBull

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Posted 27 August 2009 - 09:51 PM

Nice, finally some evidence. Only thing that might make results not be all that great is that the airflow on that blowgun nozzle and tubing is probably pretty shitty. You may want to consider putting brass on the end of a titan tank or something so it works with your set-up.

Also...

You should paint it brown and make it look like a platypus.

jokefail
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#7 Landru

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Posted 27 August 2009 - 10:05 PM

I think it would be reasonable to make an actual gun with a modified setup. I have a bunch of smaller powerful motors to spin the barrel and already have a backpack with power and air. Also could replace the air with a spring/piston setup. Half cocking the trigger spins the barrel, full pull fires. This is a topic for a future thread. Back to testing.

I'm not real familiar with the high power long range guns. I primarily do indoor nerf. What s the typical 'accurate' range for the +bow or BBB? What distance are they usually used at? Right now I'm thinking big target at 70ft, with 'precision' measured by the standard deviation from the geometric center of the spread pattern.

I'm going to try and use a dishwasher valve so I can automate the firing to make the results more accurate and squeeze some more power out of the tester.
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#8 SonReeceSonJensen

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Posted 27 August 2009 - 10:57 PM

...and already have a backpack with power and air.


?!?!?!?

A pic please. Just one?

I was joking with my last comment but you have put some serious brainpower into this.
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The Difference:
-Guns shoot bullets that kill people
-Blasters shoot darts that tag people

I do not play with guns.

#9 Landru

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Posted 27 August 2009 - 11:04 PM

...and already have a backpack with power and air.


?!?!?!?

A pic please. Just one?

I was joking with my last comment but you have put some serious brainpower into this.


http://nerfhaven.com...=15747&hl=caedo
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#10 Doom

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Posted 28 August 2009 - 08:47 AM

I'm very interested in what you find out and I have a few suggestions...

Wind should be minimized. Wind forces are definitely the biggest effect on precision and rifling won't prevent their effect.

Consistency of muzzle velocity within a trial also is very important. Here's some discussion I had at Spudfiles on this subject. This may not be practically obtainable at this juncture but dart velocity does have a major effect on precision (slower darts will be more effected by any uneven forces, faster light darts might fishtail, etc.). Muzzle velocity's effect depends greatly on the weight of the dart.

Ideally you would look at the velocity which produces the best precision for a certain weight, but you might not have the time to find that. You'd want to not only keep muzzle velocity consistent within a trial but try a bunch of different muzzle velocities for each dart weight.

I'm reasonably certain that spinning darts won't be statistically significantly more precise than the most precise muzzle velocity for that weight of dart. But I don't truly know that for certain. What I do know is that rifling is hard to get in practice and having a good weight distribution seems to be very adequate.

Edited by Doom, 28 August 2009 - 08:51 AM.

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#11 Zorns Lemma

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Posted 28 August 2009 - 10:17 AM

That setup looks great! Lightweight and mobile, I think I will rig something similar up to all my guns to get that extra bit of accuracy out at 110'.
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#12 Homestarune

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Posted 28 August 2009 - 11:44 AM

Before I begin, Iíd like to complement you on your demo. Youíve obviously put some time and effort into this, unlike most other people who have posted a ďconceptualĒ topic. First off, Iíd like to say that thereís not any debate that a properly rifled barrel would improve performance. That this even needs to be stated is rather pitiful in and of itself. We do not have the ability to rifle brass, or any other barrel material to a level where this would become at all practical.

At the risk of being pedantic, what youíre doing is not rifling. For those who donít know, rifles have grooves on the inside of the barrel that causes the bullet to spiral. This spiraling motion causes the bullet to be far more accurate. The same concept applies to football, where the quarterback throws the ball in a spiral. What youíre doing is spinning the barrel to try to make the dart spin, thatís not rifling.

Second off, youíre talking about 600 RPM being a low setting. That combined with all your equipment seems like it could be a safety hazard, not to mention heavy. You also have the issue of mounting this to a gun so that it isnít front heavy, and more importantly sealing. If you came to a war that I hosted, Iíd make sure that you would not be allowed to use this rig.

The fixation that people have with trying to make their guns better is absurd, but can be rather amusing. It seems that nerf is getting to a level, (if it hasnít already) where people prioritize making their blasters better over interacting with other members others of the community. I think Iíd have much rather nerfed in the early part of this decade when (as far as I can tell) the emphasis wasnít on winning or losing, or who had the most awesome gun, or who had the gun that you had to lift weights in order to be able to prime, but was about hanging out with a bunch of other nerds and playing with brightly colored toys that had crayola barrels slapped on the night before the war. And to me, that seems to be far more enjoyable than the direction that nerf is headed.

Zorn is being his normal sarcastic self, and heís right, this setup will never evolve to a point that it becomes war practical. If God forbid, that somehow we manage to get foam darts and barrels to meet tolerances at the level of thousands of inches, then Iím going to have to find a new hobby. Give it up kids, itís not going to happen, and it never will. However, please feel free to make fools out of yourselves. For those of you who still think that you can pull this off, hereís a picture of a rifled barrel.

Rifled barrel

Edited by Homestarune, 28 August 2009 - 11:47 AM.

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#13 Zorns Lemma

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Posted 28 August 2009 - 12:09 PM

At the risk of being pedantic, what you’re doing is not rifling. For those who don’t know, rifles have grooves on the inside of the barrel that causes the bullet to spiral. This spiraling motion causes the bullet to be far more accurate. The same concept applies to football, where the quarterback throws the ball in a spiral. What you’re doing is spinning the barrel to try to make the dart spin, that’s not rifling.


At the risk of being pedantic, this experiment has nothing to do about rifling a barrel, but is instead about what effects a rifled barrel (spinning the dart) would actually have on dart accuracy if it were even possible to rifle the barrel in the first place. If you get holes in your brain from doing too much meth, or because Mr Lobotomist took an icEffeminatek to it, it's all the same isn't it?

And while having results is nice and fine, it also shows that the whole idea is stupid because you need absurd amounts of spin on the dart to have any effect at all, which is a night floodlight on the "not worth it" billboard.

Edited by Zorn's Lemma, 28 August 2009 - 12:09 PM.

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#14 PVC Arsenal 17

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Posted 28 August 2009 - 12:34 PM

Homestarune: No need to criticize Landru's effort here. He's only sharing his experiments with the community. He's contributing something, we should all be appreciative of that.

To anyone who says the rig is impractical, you're just not thinking outside the box I'm afraid. A spinning barrel could be implemented very easily on many guns, especially my TFS using its additional barrel socket and a simple, lightweight motor/lipo setup like the kind I use on my rc planes. If I can get the AUW on one of my planes to just a few ounces, I can easily do the same here.
Posted Image

Whether or not the increase in performance is great enough to consider doing so is what Landru plans to find out for the community. If he comes up with anything conclusive, I may give this idea a shot.
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#15 Zorns Lemma

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Posted 28 August 2009 - 12:42 PM

To anyone who says the rig is impractical, you're just not thinking outside the box I'm afraid. A spinning barrel could be implemented very easily on many guns, especially my TFS using its additional barrel socket and a simple, lightweight motor/lipo setup like the kind I use on my rc planes. If I can get the AUW on one of my planes to just a few ounces, I can easily do the same here.


If I read the OP right, 1800 RPM is still in the "not much effect" area.

So good lucking finding a small and lightweight motor that has the wattage to spin a 10" barrel beyond 1800 RPM, be able to get the barrel up to speed quickly (keeping the barrel continuously spinning is going to impede dart load no matter how fancy you get), and run for a few hours off of a cheap, portable, electrical supply. Walking around with an HPA tank and 200 cubic inches of cells all strapped to your back is not "portable and lightweight"
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"In short, the same knowledge that underlies the ability to produce correct judgement is also the knowledge that underlies the ability to recognize correct judgement. To lack the former is to be deficient in the latter."
Kruger and Dunning (1999)

#16 VelveetaAvenger

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Posted 28 August 2009 - 02:57 PM

There is an ongoing debate on whether spinning darts as they leave the barrel will improve stability. I have devised and constructed (still being greatly improved) a rig which allows darts to be fired from a brass barrel rotating at various RPM's (from 180 up to about 600RPM).

At low RPMs (600 or so)


Sorry to chop up your post so much, but I think you made a mistake that is throwing a lot of people off. You meant that the low rpms are around 180 right?

Regardless, I think this will be a pretty interesting experiment, and look forward to reading the results. If you could let us know more about the technical specifications about the motors you're using I would be interested. I went to my local Ax-man earlier this week to look at motors for this same purpose, but wasn't sure what size or voltage I would need.

Anyways, it sounds like you're off to a good start, just make sure you don't go for any barrel taps with it, haha.
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#17 Landru

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Posted 28 August 2009 - 09:04 PM

well, the solenoid valve is on. Now it has enough power to put 3/4" dents in foam insulation. at 15ft. If it wasn't dark and raining I'd find some actual ranges outside. At high pressure it fishtails most everything out of the barrel. I suppose I need to make some very heavily weighted stefans now too. First real data set to be taken tomorrow if the weather improves.
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#18 Landru

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Posted 29 August 2009 - 01:28 AM

After clamping the rig to an adjustable drill press table. I did some low pressure indoor tests.


Procedure:
Load a 1" stefan with molded hemispherical tip 7" into 17/32 brass barrel. Pressure set to 10psi on regulator, and not changed over the course of all tests. (actual pressure is questionable, but it is assumed to remain constant throughout experiment). Hold down firing switch until dart hits target 20ft away. Repeat ~20 times. Mark each impact on the Styrofoam target. Repeat for ~400rpm and ~2000rpm. (tachometer is not currently available, so just rough guesswork on actual rpm based on motor pitch) The same dart is used for every shot.

Averages and standard deviations for each 'X' and 'Y' set of values was obtained

No rotation
3.42, 4.53 (average)
1.45, 5.93 (standard deviation)

400RPM
3.53, 5.86 (average)
1.22, 4.14 (standard deviation)

2000RPM
3.54, 5.91 (average)
.99, 3.99 (standard deviation)

Improvement from 0 to 2000RPM
X Axis 31.7%
Y Axis 32%

The data shows that spinning darts at 2000 RPM improves precision by 32%.

If you have really really perfectly balanced and formed darts, you will see less improvement from a spinning dart, which most of us don't.

My professional opinion (Yes I can say that, I'm actually an engineer) is that the rotating of the dart corrects for aerodynamic imperfections. In a normal firing, if the dart has a defect causing aerodynamic forces on one side, as it travels the force will cause it to travel to that side more and more. If the dart is spinning, that force starts on one side. As it spins, the force is moved to the opposite side, counteracting the initial force. The dart will technically travel in a circle on the X Y plane as it travels as opposed to veering way off to one side. The faster the rotation, the tighter the circle and more precision.

In conclusion, spinning your darts will help you hit your opponents, assuming you are aiming at them.

Myth Confirmed.

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#19 Doom

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Posted 29 August 2009 - 08:21 AM

Landru, could you post the data so others can independently analyze it? I see there is improvement; what I'm interested in is whether or not the difference is statistically significant.

Edit: I just did an f-test for no spin vs. fastest spin y values assuming sample sizes of 20. The f-value is 1.49 and the critical f-values are 0.46 and 2.16 for alpha = 10%. As the f-value is between the two critical values, this means that the two are not statistically different. This does not support the conclusion that spinning darts are more precise.

I did post some analysis earlier here but I did it dreadfully wrong. It's gone now.

Edited by Doom, 30 August 2009 - 10:59 AM.

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#20 Landru

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Posted 29 August 2009 - 11:42 AM

Well I guess additional data is in order.

And what do you mean by the darts people actually use?

Edited by Landru, 29 August 2009 - 11:44 AM.

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#21 Doom

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Posted 29 August 2009 - 02:31 PM

I think Bob meant longer darts (1.5 to 2 inches) with more typical heads. Something like CaptainSlug's darts would be adequate.

If you could get similar results with 60 or more trials it'd be nearly statistically significant. So you basically need to get data that's more in favor of spinning.

Another suggestion would be to calculate the distance from the center of the spread so you have one variable instead of two. The distance is all we're looking at anyway.
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#22 Landru

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Posted 29 August 2009 - 06:46 PM

From the comments, two future tests are planned.

1) My 'molded' darts, 50' range, 80 firings. No and Med RPM as the two groups.

2) Standard stefans with bb in tip, 1.5" length, 50' range, 80 firings. No and Med RPM.


From just playing around with the gun, it is appears the difference between spinning and not is more pronounced at further distances, so I'm upping the range of the test to 50ft.

Also, I'll put my spreadsheet with the values in the next post. And I'll calculate R instead of X,Y for convenience. I just thought it was interesting the Y spread was so much greater than the X.

Edited by Landru, 29 August 2009 - 06:48 PM.

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#23 durka durka

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Posted 29 August 2009 - 07:13 PM

This very interesting. A test of this dynamic should not be brushed off lightly. Based on the theory and tests ran so far, it seems fair to say that crappy darts might be somewhat corrected.

However, even if the tests turn out to show good accuracy improvements on imperfect darts, wouldn't perfecting your dartsmithing be more effective?
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