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Dart Component Weight Ratio

anyone know?

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#1 SonReeceSonJensen

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Posted 22 July 2009 - 01:43 PM

I do not have a precise scale to measure this, so I want to see if anyone knows the weight ratio of the head of a dart (hotglue and BB) and the body.

I know this will vary incredibly from dart to dart depending on length variances, foam type, Steel or Copper BB’s, but if someone has could give me even a rough ratio guess that would be awesome.

Why
I have acquired 4” diameter foam battens that would make killer super-sized Stephens, but I have no idea how much material to put in the tip and I wouldn’t mind a rough starting point before I go nuts with experiments.

Preemptives
• I searched each forum for “weight ratio” and found nothing useful
• This is in no way for war-worthy creations
• Yes, I searched Nerfhaven
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#2 bobbybilly60

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Posted 22 July 2009 - 02:16 PM

The size 7 fishing weights that seem to be the generally accepted standard weight by comparison are heavier than these washers. Size 7 split-shot tin fishing sinkers are 1.16g (See this chart), these washers are .8g dry, and 1.2g with the felt disc attached. The resulting dart weighs exactly the same, unless you accidentally purchased lead fishing weights, which weigh 0.6g more than the tin fishing weights.


I don't know about bb stefans, but according to CaptainSlug Washer stefans weigh 1.2g. All the weight is in the tip.

Edit: Oops I realized you asked for dart ratio not weight. Ignore my post.

Edited by bobbybilly60, 22 July 2009 - 02:29 PM.

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QUOTE
Hooah!

#3 TantumBull

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Posted 22 July 2009 - 03:35 PM

I'd say your first issue would be finding a weight that can be evenly distributed across the top if you're using foam with a 4" diameter. I've found for missiles that shuttlecock heads work well. Plus it's awesome when you hit a wall.
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#4 CA13

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Posted 22 July 2009 - 05:47 PM

I have acquired 4” diameter foam battens that would make killer super-sized Stephens, but I have no idea how much material to put in the tip and I wouldn’t mind a rough starting point before I go nuts with experiments.


Stephens. I like that.

For weight, you should probably just experiment. Forsaken Angel 24's "mongo" ammo type was just 1-2 inches of hollow foam with hot glue and weights he found to be about the right amount.

Four inch foam probably wouldn't be comparable to a mega or micro, due to differences aerodynamically. You should probably find a ball that you could cut in half and place on the tip of the "Stephen" to weight it and give it less drag. Then, of course, add weight with hot glue/bearings until you achieve a good range.
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#5 Doom

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Posted 22 July 2009 - 06:26 PM

Why do you want a weight ratio? The center of mass would be more useful if you're interested in dart stability.

Anyhow, I measured something for you. The one Slug-style dart I tested with 2 inches of foam weighs about 1.02 grams. The head weighs about 0.91 grams and the foam weighs about 0.11 grams.

Based on some rough calculations, this puts the center of mass about 0.17 inches away from the tip of the dart. This is fairly good--you want the center of mass to be close to the tip as this makes the darts more stable.

Aerodynamic forces act at the "center of pressure", which for most of us is impossible to locate, but it's most definitely not as far front as the center of gravity. The dart will rotate around its center of mass, so if the angle the dart is heading into the air (the "angle of attack") is not zero (i.e. if the dart is not parallel to the air flow), then a relatively large aerodynamic force will rotate the dart back down around its center of gravity. This is how Nerf darts gain stability.

You can scale this up if you want a starting point. The head is about 1/8" long and the foam is about 2" long. So the center of mass is about 8% of the way down the dart from the front.

Edited by Doom, 23 July 2009 - 10:34 AM.

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#6 Zorns Lemma

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Posted 22 July 2009 - 07:16 PM

Converting Doom's mass point to a weight ratio, and assuming that 2" slug darts are the pinnacle of foam perfection, and also that this can be easily scaled up, then you want the weight at the front of your dart to be 9x heavier than the foam blank to give you the magical hand-waving 8% This is if your superstefan is cut to 2"

Figuring out if it's the same ratio for a 4" or 6" superstefan is going to require more math, which I'll do after eating.
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#7 Blacksunshine

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Posted 22 July 2009 - 07:31 PM

All that math is really worthless. scaling up say from a 1/2" stefan to a 4" would be horribly inaccurate unless you are taking specifics of the usage into account. If you just scale up directly one of my standard darts weights 1.2gr. So if 4" is 8X that does that mean you will then need 9.6gr of weight for your giant dart? No. Chances are that it will not fly far if at all. What are you using for propulsion? how are you going to be launching them? That is going to be more important then anything else when you are trying to determine the amount of weight you will need to use. Honestly I think trying to launch 4" wide foam is not likely to work for you unless you are using highly compressed air.
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#8 wingd man

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Posted 22 July 2009 - 07:40 PM

All that math is really worthless. scaling up say from a 1/2" stefan to a 4" would be horribly inaccurate unless you are taking specifics of the usage into account. If you just scale up directly one of my standard darts weights 1.2gr. So if 4" is 8X that does that mean you will then need 9.6gr of weight for your giant dart? No. Chances are that it will not fly far if at all. What are you using for propulsion? how are you going to be launching them? That is going to be more important then anything else when you are trying to determine the amount of weight you will need to use. Honestly I think trying to launch 4" wide foam is not likely to work for you unless you are using highly compressed air.

Maybe 4 titan tanks taped together? Or something along the lines of "Bike pump+3"PVC+ball valve"?
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#9 PC III

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Posted 22 July 2009 - 07:46 PM

If a titan can launch a mega missile it could launch this.
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QUOTE(ultra920 @ May 19 2008, 06:18 PM) View Post

Don't want to shove balls in tight spaces. Trust me, bad idea.

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#10 Blacksunshine

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Posted 22 July 2009 - 07:55 PM

If a titan can launch a mega missile it could launch this.


Titan missiles are also not weighted. That is another reason comparing this idea to a standard issue stefan is folly. And again not knowing the idea behind how this will be propelled is going to factor in because it will determine the optimal way these should be made.
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#11 PC III

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Posted 22 July 2009 - 08:01 PM

If a titan can launch a mega missile it could launch this.


Titan missiles are also not weighted. That is another reason comparing this idea to a standard issue stefan is folly. And again not knowing the idea behind how this will be propelled is going to factor in because it will determine the optimal way these should be made.


Yes, but at low speed would that much wait be needed? The missile isn't exactly the lightest nerf projectile...

Also, with a 2-4 inch barrel? the titan could do it. Have faith. lol

Edited by P.C. III, 22 July 2009 - 08:03 PM.

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QUOTE(ultra920 @ May 19 2008, 06:18 PM) View Post

Don't want to shove balls in tight spaces. Trust me, bad idea.

For sale: Vintage WWII French rifles. Dropped once, never fired.

#12 Zorns Lemma

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Posted 22 July 2009 - 09:20 PM

All that math is really worthless. scaling up say from a 1/2" stefan to a 4" would be horribly inaccurate unless you are taking specifics of the usage into account. If you just scale up directly one of my standard darts weights 1.2gr. So if 4" is 8X that does that mean you will then need 9.6gr of weight for your giant dart? No.


We're not scaling a stefan into a megastefan. We're transposing the proportions of the stefan into the megastefan so that the megastefan has the same aerodynamic principles so it flies best.

Assume CS-style darts are the best dart, you want the weight to be 9x the mass of the dart. This further assumes that Reece is going to be launching these from a 4" barrel, and not trying to make some sort of missile.

But to be honest, you're probably best off getting weights from 5x to 10x the mass of the rest of the megastefan and shooting each one. Empirical testing > theory.
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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)

#13 SonReeceSonJensen

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Posted 23 July 2009 - 08:34 AM

This has been the most productive thread ever in the history of Nerfhaven. Seriously, you guys have give hella thought to this and that is awesome.

For this specific idea I have a done some efforts so that might help in this discussion.

Propulsion
http://nerfhaven.com...=0

Prototype ammo
http://nerfhaven.com...=0
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The Difference:
-Guns shoot bullets that kill people
-Blasters shoot darts that tag people

I do not play with guns.

#14 Fome

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Posted 23 July 2009 - 12:37 PM

Alright, this is a far easier process than we're giving it credit for.

1. Take your blank projectile.

2. Tape pennies on to the end until it flies straight.

3. Keep adding pennies until the nose dives prematurely.

4. Take a few pennies off.

5. Count and weigh the pennies you used.

6. Success!

#15 SonReeceSonJensen

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Posted 23 July 2009 - 12:48 PM

Alright, this is a far easier process than we're giving it credit for.

1. Take your blank projectile.

2. Tape pennies on to the end until it flies straight.

3. Keep adding pennies until the nose dives prematurely.

4. Take a few pennies off.

5. Count and weigh the pennies you used.

6. Success!


I feel like a tool for not thinking of that. Pennies and tape are two things I have no shortage of.
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The Difference:
-Guns shoot bullets that kill people
-Blasters shoot darts that tag people

I do not play with guns.


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