38 replies to this topic

[Fome]

First I'd like to preface by saying that this writeup came at no small effort. Below is the evolution of arrows I've created and tested extensively both in accuracy and range. They may look only slightly different but the difference in performance is very notable.



Here are your materials:



You'll need:
-Craft foam (at most hobby/craft stores)
-1/2" Pipe insulation (I found mine at an Ace hardware, it should not have a slit)
-Hot glue (low temp)
-Liquid glue (Elmers might work, I used Mod Podge)
-A blue or purple pen
-an adjustable craft knife
-a template for canting your fins

This is your template, which is easily the most important and difficult thing to construct.



You'll need to find some sort of tube that fits your foam perfectly, I used the cardboard roll of some Scotch packing tape. You'll also need to cut three angled, lengthwise holes for marking where your fins should be. These holes should be spaced precisely evenly apart and all have the same angle. With a little math and a lot of measuring and diligence you'll produce something that looks like the above picture. If you make your template correctly, you'll be able to quickly make arrows that perform very well.

Next, measure and cut your foam pipe insulation. This particular brand came in 6 foot lengths, so I cut my arrows to 7.2 inches. Use the template and a sharp knife to make square cuts.



Now, get your craft foam and measure and cut out the pieces that will make your fins and caps.
My fins are 2.5 in by 1 in and the caps are the OD of a 1 inch PVC coupler. (you could greatly expedite this process by finding an appropriately sized cookie cutter or large hole punch) Also, if available, use thick craft foam for the caps. Some weight at the front is necessary for the arrows to perform well and more padding is always a plus.





Bevel your fins and make hot glue sandwiches with your circular caps.





Now, take your template and place it over one side of the foam. Use a pen to mark the cant of the fins.



Next, adjust your hobby knife so that it barely perforates the surface of the foam. It should cut into the foam but not through it. Cut into the marks you made, the length of your fins.



Smother one end of your fins with your glue and then place them securely into the slits you just cut.
(This will dry clear)





Hot glue the foam caps to the other end of your arrows. Stand them upright and let dry overnight.








Additional tips:
- Do not use hot glue to secure the fins. You'll add an unnecessary and unbalanced amount of weight to the back of the arrow.
- Make sure all of your fins are uniform
- If you decide to deviate from this writeup, keep in mind that longer arrows and larger fins yield better results than shorter arrows and smaller fins.
- These arrows work best with blasters that have a high volume of air.
- Making barrels is really easy. Take a length of CPVC, wrap E-tape until the arrow fits snugly, and then cover it with a clear coat/sealer to prevent the tape from snagging. I used Mod Podge.

Comments are more than appreciated.

[AgentMoe64]

I thought the yellow version was great, but this...this is awesome.

[Coal Ten]

Have you noticed a difference in range or accuracy with different fin angles?

[SonReeceSonJensen]

Very nice, I like the deviation from typical/conventional ammo a great deal.

Now just put some tacticool straps on a 5 gallon paint bucket to carry your extra shots around in.

[Lt Stefan]

When I made my own rockets a while ago, I found that fins didn't help. However I did use foam board, not thin craft foam sheet. Have you experimented with no fins?

Also do you think it would be too much work to have maybe four layers of foam on the tip, each getting smaller? It would make the tip rounded and might improve flight.

Edited by Lt. Stefan, 28 May 2010 - 02:45 PM.

[Fome]

@ AgentMoe: Thanks!

@ Coal Ten: I have not played with different fin angles. I chose an aggressive angle to get as much spin as I could to have more stability. I'm sure there's some range loss from the added drag, but the accuracy is well worth it. I have, however, played around with BBB arrows which have a much slighter angle. They're also wildly different in other ways (huge fins, thin body, the "barrel" is much much smaller). Having a really good spin seems to keep the arrows flying straight even under high pressure shots, which is where the loss in accuracy becomes apparent in the BBB arrows. (Also in my earlier designs, which simply didn't have big enough fins)

@ SonReeceSonJensen: Thanks. I made a couple bandoleers out of different sizes of cargo strap and buckles. You can see one of them in this picture:


But yeah, ya gotta get creative with how to carry these fuckers around.

@ JSB: That's a great idea. I'll definitely be doing that in my next batch. Thanks.

@ Lt. Stefan: I experimented with simply weighting the tips too.



I can say pretty confidently that arrows are superior in almost every way except ease of construction. The biggest advantage (to me), is that because they're so light, and therefore require less force to actually propel, they can be fired at relatively low pressures and still achieve awesome performance.

Some of my earlier designs did this exact thing. It doesn't seem to have much effect, the biggest factors are your fins and the lengths of your arrows. You also want to be careful about adding too much weight to any part of the arrow (the front is the best place for it however), you want these to be light.

Edited by Fome, 29 May 2010 - 07:22 PM.

[Merzlin]

That's incredible, Fome. May I ask what pump you're using on your Mavcannon? I have a spare Titan tank and few shells....and an Ace that's a 5 minute walk away! Again, great job!

[Fome]

Merzlin, on May 28 2010, 03:31 PM, said:

That's incredible, Fome. May I ask what pump you're using on your Mavcannon? I have a spare Titan tank and few shells....and an Ace that's a 5 minute walk away! Again, great job!

Thanks.

It's the titan pump, The pump handle is simply a 3/4" CPVC coupler and 3/4" CPVC endcap glued together. The "grip" is made with lines of hot glue. The paint is rubbing off but it's very comfortable.

[Hippopotamus]

It seems that you have a hefty amount of them, do they go to wars?

[KaneTheMediocre]

If you're arrows are the same fit as Nerf arrows, steel EMT makes a great barrel material. It can be pressed into thinwall PVC to mate with PVC connectors, or around CPVC (with the aid of a hammer). Home depot sells it for less than 2 dollars for a 10 foot length of it, and the OD is close to 27/32" (.71875"). Also, the ID is the right size for shooting stock micros/taggers out of an airgun (with the WHOLE dart inside the barrel).

[balisticjoe]

Really glad you made a write-up for your new type of arrows fome. I have 9 feet of foam just waiting to be turned into these. Keep up the good work.

[Split]

A simple trick for making the template: Use a measuring tape to measure the outer circumference, and divide that by three. Mark three dots along the circumference at that interval for your top holes. You need at least two of the following factors: the length of the fin (as the hypotenuse) and the height of the template (as the long/adjacent leg) or the angle for your fins as the adjacent angle. A little trigonometry will find you the short leg. That length is the distance for the offset of the bottom set of dots from the top set. Measure your height down from the top dots and to the side by the distanced you measured. You only need one of the bottom row, and you can measure off for the other two.


I'm sure you already know that fome, just for the rest of 'em. Love the arrows, love the devotion. much props.

[ricochet]

Here is a simple equation you could possibly use to figure out the optimal fin angle on arrows. It is the same way gunsmiths find optimal twist rates of a bullet when rifling barrels. The equation can be written as T=150•(d/r), where d is the diameter of the arrow and r is the diameter of the arrow divided by the length of the arrow(the 150 is a constant). So, Twist=150•(diameter/ diameter divided by length). For example, if the equation gives you 50 cm, that means the arrow must twist 1 full rotation every 50 cm it travels. Once you know that, measure out, in this case, 50 cm, on a tube or pipe and draw a helical line from one end to the other so the line will end the same way it was facing at the the start. Then copy a portion of the line (preferably the length of yoir fins) into your template and whalla you have the optimal fin angles. Hopefully that makes sense, I havent tried this myself but it seems to be effective so maybe play around with it if you would like.

Edited by ricochet, 29 May 2010 - 11:57 AM.

[KaneTheMediocre]

ricochet, on May 29 2010, 08:53 AM, said:

Here is a simple equation you could possibly use to figure out the optimal fin angle on arrows. It is the same way gunsmiths find optimal twist rates of a bullet when rifling barrels. The equation can be written as T=150•(d/r), where d is the diameter of the arrow and r is the diameter of the arrow divided by the length of the arrow(the 150 is a constant). So, Twist=150•(diameter/ diameter divided by length). For example, if the equation gives you 50 cm, that means the arrow must twist 1 full rotation every 50 cm it travels. Once you know that, measure out, in this case, 50 cm, on a tube or pipe and draw a helical line from one end to the other so the line will end the same way it was facing at the the start. Then copy a portion of the line (preferably the length of yoir fins) into your template and whalla you have the optimal fin angles. Hopefully that makes sense, I havent tried this myself but it seems to be effective so maybe play around with it if you would like.

A formula similar to this is probably useful, but the arbitrary constant 150cm indicates that there are other factors in the equation, which are probably about the same between different guns, but may not be the same between guns and nerf blasters. Also, some arbitrary trade-off between drag and accuracy was probably made to stick with 150cm.

Also, if I understand correctly, diameter/(diameter/length)= length, so T= 150 * length. Which doesn't smell like an accurate formula.

[ricochet]

KaneTheMediocre, on May 29 2010, 09:43 AM, said:

ricochet, on May 29 2010, 08:53 AM, said:

Here is a simple equation you could possibly use to figure out the optimal fin angle on arrows. It is the same way gunsmiths find optimal twist rates of a bullet when rifling barrels. The equation can be written as T=150•(d/r), where d is the diameter of the arrow and r is the diameter of the arrow divided by the length of the arrow(the 150 is a constant). So, Twist=150•(diameter/ diameter divided by length). For example, if the equation gives you 50 cm, that means the arrow must twist 1 full rotation every 50 cm it travels. Once you know that, measure out, in this case, 50 cm, on a tube or pipe and draw a helical line from one end to the other so the line will end the same way it was facing at the the start. Then copy a portion of the line (preferably the length of yoir fins) into your template and whalla you have the optimal fin angles. Hopefully that makes sense, I havent tried this myself but it seems to be effective so maybe play around with it if you would like.

A formula similar to this is probably useful, but the arbitrary constant 150cm indicates that there are other factors in the equation, which are probably about the same between different guns, but may not be the same between guns and nerf blasters. Also, some arbitrary trade-off between drag and accuracy was probably made to stick with 150cm.

Also, if I understand correctly, diameter/(diameter/length)= length, so T= 150 * length. Which doesn't smell like an accurate formula.

First off, 150 is not a measure of length, it is a number based on a specific range of velocities, the number can change for higher velocities. Also, I don't see where diameter/(diameter/length) equals length...

Either way, I have not attempted this myself, but after extensive research it seems quite feasible to me. I am just posting what I discovered as a suggestion to play around with, that way we will truly know if it is accurate or not. I plan to play around with it as well, but I won't be able to try untill I finish my volunteer work with service dogs.

Edit: If the pattern for the constant of 150 is continued, it can be changed to 120 to match nerf gun velocities much closer, I will try both and figure out which one is more accurate

Edited by ricochet, 29 May 2010 - 01:12 PM.

[Ice Nine]

ricochet, on May 29 2010, 12:58 PM, said:

Also, I don't see where diameter/(diameter/length) equals length...

d/(d/l)

d(l/d)

l(d/d)

l(1)

l

QED

P.S.

150*7.5 inches = 1 twist every 100 feet = virtually straight fins

50cm/150 = 3.3mm length arrows

P.P.S.

What you said is bad and you should feel bad.

Edited by Ice Nine, 29 May 2010 - 01:37 PM.

[ricochet]

Apparently I didn't explain with enough clarity. The formula used is the greenhill formula and since it seems to confuse everyone, I'll test it and then share the conclusion that I come to. There is no need to continue any debate on this thread.

[Warthawk]

Wow. I want to make a titan missle out of this.

Edited by Warhawk, 29 May 2010 - 02:18 PM.

[Ice Nine]

THIS POST NOW CERTIFIED WITH "THE DOOM SEAL OF APPROVAL."

ricochet, on May 29 2010, 02:16 PM, said:

Apparently I didn't explain with enough clarity. The formula used is the greenhill formula and since it seems to confuse everyone, I'll test it and then share the conclusion that I come to. There is no need to continue any debate on this thread.

Not only did you not explain with enough clarity, you didn't even have the formula listed correctly.

Twist = (CD^2)/(L) * (SG/10.9)^1/2, where L would be the length of the missile, and D is the diameter, both in inches, and SG is the specific gravity of the material (10.9 is the specific gravity of lead, meaning for lead bullets the second half of the equation is one).

The stuff you dropped out and also got wrong contribute to a SIGNIFICANT difference in the equation's meaning. The C constant is unitless to give twist a rate of inches per turn, which makes sense; the problem is the 150 value is used for bullets, which are without question going to have muzzle velocities significantly higher than Nerf missiles.

Fome did a very good job here and I don't think (although I've been wrong about optimization in the past) that using a formula like this is going to contribute noticeably better results.

P.S. You were still super wrong about the whole diameter/length issue.

P.P.S. Fome, have you thought about using cut-in-half foam practice golf balls for the tips of the arrows? The U3 picked up a few buckets of multicolored foam balls (at Wal-Mart, I think) that, if I recall correctly, are approximately the same diameter are the foam you're using to make the missile bodies.

ricochet, on May 29 2010, 02:40 PM, said:

Yes, I am aware of the imperfections of this method. I wont use the specific external balistics site for info anymore. Guess its back to the old guess and check method.

We're not talking about "imperfections of this method," I'm pointing out that the thing you posted was completely and utterly incorrect.

For the record, the radical expression on the right half of the equation that you dropped off for no reason yields a multiplicand of 0.096 when I approximated the density of foam to be 1/10 that of water. So, that's fairly significant.

Whoops! Turns out foam is about 0.015 g/cm^3. That multiplicand is now 0.037 and that reduces the result by a third as compared to the answer I previously approximated.

Edited by Ice Nine, 29 May 2010 - 02:52 PM.

[ricochet]

Yes, I am aware of the imperfections of this method. I wont use the specific external balistics site for info anymore. Guess its back to the old guess and check method.

Edited by ricochet, 29 May 2010 - 02:45 PM.

[Doom]

Fantastic work Fome. These look like a lot of fun. I'll be sure to try some.

Quote

I can say pretty confidently that arrows are superior in almost every way except ease of construction. The biggest advantage (to me), is that because they're so light, and therefore require less force to actually propel, they can be fired at relatively low pressures and still achieve awesome performance.

Heavier projectiles generally absorb more energy. Muzzle velocity (higher for low mass) and range aren't as well correlated as muzzle energy and range. You might want to reconsider your reasoning. Of course, if you've done tests, I might have to reconsider mine, but that's okay.

Spin stabilization is fine, but I'd also try arrows that are aerodynamically stable from their weight distribution. The Barrowman equations (fixed!) were developed in the 60s to determine the location of the center of pressure of rockets and they are most definitely applicable here. If the center of pressure is well behind the center of mass, the projectile is stable.

As for the Greenhill formula, I did a little research and I'm very confident that (even used correctly) it's not even approximately right here. Trial and error seems to have worked well for Fome.

Edited by Doom, 29 May 2010 - 07:29 PM.

[Fome]

Thanks for all the kind words guys.
Absolutely feel free to optimize this with all the fancy formulas and theories you want. I'm not going to, because I have something that works and works well and that's good enough for my purposes. I'm more than eager to see whatever conclusions you guys come up with. I think I've established enough general principals and construction methods for now at least.

Ice Nine, on May 29 2010, 12:26 PM, said:

P.P.S. Fome, have you thought about using cut-in-half foam practice golf balls for the tips of the arrows? The U3 picked up a few buckets of multicolored foam balls (at Wal-Mart, I think) that, if I recall correctly, are approximately the same diameter are the foam you're using to make the missile bodies.

I just stopped by Wal-Mart after reading this. Couldn't find any such practice balls. I'll keep my eyes out though. If they are the proper diameter and weight, yes, they could significantly reduce the construction time.

Doom, on May 29 2010, 03:50 PM, said:

Fantastic work Fome. These look like a lot of fun. I'll be sure to try some.

Quote

I can say pretty confidently that arrows are superior in almost every way except ease of construction. The biggest advantage (to me), is that because they're so light, and therefore require less force to actually propel, they can be fired at relatively low pressures and still achieve awesome performance.

Heavier projectiles generally absorb more energy. Muzzle velocity (higher for low mass) and range aren't as well correlated as muzzle energy and range. You might want to reconsider your reasoning. Of course, if you've done tests, I might have to reconsider mine, but that's okay.

Spin stabilization is fine, but I'd also try arrows that are aerodynamically stable from their weight distribution. The Bowerman equations were developed in the 60s to determine the location of the center of pressure of rockets and they are most definitely applicable here. If the center of pressure is well behind the center of mass, the projectile is stable.

You're probably* right, I didn't actually add the second layer of foam and hotglue to the tip of the arrow until later because they had "issues" with reliability. As soon as I have access to a proper measuring tape and some decent weather, I'll do some tests on greater weights vs lower weights. I predict more weight will yield higher ranges in more powerful guns and lower ranges in less powerful guns.

*I just tested my weighted rockets and my homemade arrows. At max pressure, the rockets went noticeably further. At only 5 pumps, however, the arrows went further. I'll need to amend my original statement.

Doom, on May 29 2010, 03:50 PM, said:

Trial and error seems to have worked well for Fome.

Exactly. I made several different types of arrows using a variety of construction methods and then spent several hours shooting them down a long hallway at a cardboard box using a titan pumped to various pressures. There's a shit load of variables here, but in the end I have something that allows me to use my titans indoors, I don't even have to pump them up very much to get decent ranges.

My main concern was accuracy and usability across a variety of pressures and different types of nerf guns. You may want to modify this writeup to fit your unique situation.

[Doom]

Fome said

*I just tested my weighted rockets and my homemade arrows. At max pressure, the rockets went noticeably further. At only 5 pumps, however, the arrows went further. I'll need to amend my original statement.

Interesting. I'm going to have to investigate this further. I've been looking for a project for the old 3/8" QEV I used in FANG.

[Merzlin]

While observing the pictures, one showed a foam rod with a slit cut in it. Does this slit yield worse results? I picked up 4 rods of black foam, only to realize that it had a slits cut in it when I got home. Is there a solution to this?

[Fome]

Merzlin, on May 29 2010, 05:38 PM, said:

While observing the pictures, one showed a foam rod with a slit cut in it. Does this slit yield worse results? I picked up 4 rods of black foam, only to realize that it had a slits cut in it when I got home. Is there a solution to this?

How deep is the slit? If it's superficial it's really not a problem.

My first arrows I made had a slit that went all the way through the foam. If you dont want to return the stuff, you can continue as normal but tape up along your fin angle. I did something similar in my first writeup. It's quite a bit more work but they performed well.

Edit: The foam I got from Ace looks like this.

Mine was $1.29 for a 6ft roll, this stuff seems even cheaper.

You can see it's advertised to have a "pre-slit", so even though there's a visible slit, it's only a few mm deep.

Edited by Fome, 30 May 2010 - 02:19 PM.