38 replies to this topic

[Draconis]

Just a note about the foam balls. The yellow dimpled balls from Target and formerly Walmart have a mass of 12g, while the variety colored balls from K-Mart and Kroger/Fred Meyer are 4g. Various incarnations of OE Nerf/Buzzbee/ERTL balls are 5g. I've been using half of the dimpled balls on my big rockets, and they seem to work nicely. I was rather hopeful that we could use that equation to determine fin angle, so now I'm sad again.

[Roy]

Well done.

It's hard to improve on something cheep, that works well and looks good doing it.

Have you considered using hip wader repair (tough and chewy when dry) or 5200 sealant (3M makes it i think) to attach your fins?

Used sparingly with your weight concerns in mind, an adhesive like these may increase durability.

[Hipponater]

Very awesome. Along the lines of what Roy said, how is the durability of the arrows?

Also, what's an estimated cost per arrow, do you happen to know? Finally, where did you get your foam rod? I've only seen the stuff with the slit, like Merz found.

These seem like they could be pretty fun for an indoor war, if they're durable enough and not too expensive to make

[jakejagan]

I agree with Fome, so screw the formulas. Guess and check is the simplest method. I am glad that a good substitute has been created.

Fome, how many wraps of E-tape did you use for the foam? Did you do it in more than one area?

Edited by jakejagan, 05 June 2010 - 08:29 PM.

[Fome]

Just Some Bob, on May 30 2010, 12:23 AM, said:

More pictures of foamy stuff!
Got any of 'em in flight?

And anyway, fin-imparted spin really starts too late to add much accuracy. The fins can't contribute any significant force until the projectile has left the spigot. Whatever deviations have already happened at that point can't possibly be corrected. It will probably still improve consistency, but (in my opinion) it's more important that spinning missiles LOOK COOL! So do it, but don't overdo it.

I'll get a video up pretty soon. You're probably right about the spin being too aggressive, my arrow fins actually blur in flight. I'm not going to remake my template though, someone else can try that out.

Roy, on May 30 2010, 08:56 AM, said:

Have you considered using hip wader repair (tough and chewy when dry) or 5200 sealant (3M makes it i think) to attach your fins?

Used sparingly with your weight concerns in mind, an adhesive like these may increase durability.

I haven't had any issues with durability so far. The fins are actually held on really strong because not only is the foam expanding against the fins (thus mechanically sandwiching it in the slits) but the glue has a lot more contact area than simply adhering it to the surface.

Hipponater, on May 30 2010, 11:15 AM, said:

Also, what's an estimated cost per arrow, do you happen to know? Finally, where did you get your foam rod? I've only seen the stuff with the slit, like Merz found.

These seem like they could be pretty fun for an indoor war, if they're durable enough and not too expensive to make

This looks like the foam I found at an Ace Hardware. You can see that it's advertised to have a "pre-slit", which means it's only a few mm deep.

Foam pipe insulation (6ft) = $1.29
Craft foam (1 sheet, enough for 20 arrows) = $.99

Approx $.22 an arrow. More or less depending on how much glue/foam you use and how cheap you get your materials.

jakejagan, on May 30 2010, 11:36 AM, said:

I agree with Fome, so screw the formulas. Guess and check is the simplest method because IMO there are too many factors such as humidity, atmospheric pressure, gravity, wind, height of where it is fired, fluid friction, etc. I'm just glad that a good substitute has been created.

Fome, how many wraps of E-tape did you use for the foam? Did you do it in more than one area?

I'm actually curious to see the math. I have a suspicion that heavier tips and a less aggressive fin angle might produce better ranges in more powerful guns.

I'm not sure what you're talking about. I used E-tape to close the slit on my original writeup, but that was a lot more work than simply finding the right pipe insulator.

[jakejagan]

I'm referring to ONLY using math to get your answer. Now a combination of the two would would provide good results in my opinion.

Fome: Never mind about the E-tape thing.

[KaneTheMediocre]

Just Some Bob, on May 29 2010, 11:23 PM, said:

Equations suck. Even when they're right, and those were not.

More pictures of foamy stuff!
Got any of 'em in flight?

And anyway, fin-imparted spin really starts too late to add much accuracy. The fins can't contribute any significant force until the projectile has left the spigot. Whatever deviations have already happened at that point can't possibly be corrected. It will probably still improve consistency, but (in my opinion) it's more important that spinning missiles LOOK COOL! So do it, but don't overdo it.

I can't believe I'm even bothering to argue physics with someone who thinks "equations suck". Fin imparted spin starts in time to add plenty of accuracy--Believe it or not, the air that this rocket is flying through at high speed actually exerts significant forces on it after it has left the spigot. For arrows, most of the inaccuracy occurs as the arrow flys off course, rather than being shot crooked in the first place. So fins are absolutely crucial for arrows, which don't have the front-weight stability of darts. Sure, you can add weight to the front to stabilize it instead of fins, but then you don't really have an arrow--just an oversize dart that requires unsafe power to get any useful range.

[durka durka]

Fome these things are awesome. I have some of the pipe insulator, so its off to the craft store for some foam and then I can start building these things.

While equations could prove useful, hasn't this discussion taken the fun out of it? Why even bother if it isn't any fun?

These are made out of foam[u]. They aren't million dollar cruise missiles.They are very cheap to make, so there's lots of room to experiment with the design.

[ricochet]

Alright the equation stuff does suck. I did my math wrong(looked through the work I attempted when this idea ran across my mind), leading to a waste of time. As durka put it, it takes out the fun of dart/arrow making.

[nerf22]

I am definetly doing this.

[Fome]

2 things:

I experimented with adding straight fins to my homemade rockets. No noticeable effect, looks better though.
The rockets fly significantly differently from the arrows. I can shoot an arrow with my lanard shotgun about 30 feet, yet the rockets don't even leave the spigot. They will, however, fly farther fired from a fully pumped titan.






You can "correct" shitty arrows by adding more foam to the tip of the arrow. (more weight)




There are disadvantages and advantages to using weights versus fins to stabilize your projectiles. Some weight is necessary to correct the inevitable human error in making homemade arrows by hand. Luckily, it doesn't seem to be more than a few layers of craft foam and a generous helping of hot glue.

Edited by Fome, 12 June 2010 - 04:07 PM.

[taerKitty]

Good work. The ones in the first pic could almost pass for factory-made if you just showed them to me out of context.

[b1g13en]

Fome, on Jun 12 2010, 09:03 AM, said:

What are you using for the tip of the rocket and where can i find it?

Edited by b1g13en, 12 June 2010 - 09:11 PM.

[jaybo1996]

A nerf foam ball is used for the tip, available at Toys R' Us.