19 replies to this topic

[Phil]

So I'm in the process of making a home made nerf HMG, and I wanted a longer barrel, but yet have the same, or greater distance in FPS of the dart. I also came to realize that longer barrels would decrease the muzzle velocity of the dart. But what if you made one without a barrel at all? Would it work if you lined one one fly wheel to the next? I mean you would have the illusion of a barrel, you could design a LEWIS gun, or a MAXIM machine gun type of barrel, but they would just be fly wheels.

And if they were all flywheels how many volts would you have to run to achieve 200-250fps?

Warm regards,

Phil

[jwasko]

Your post is a little confusing, but here's some info.

1. You don't really need (much of) a barrel on a flywheel blaster.

2. If you want a long barrel for aesthetics, you could just make one that's a very large diameter to minimize the amount of drag it has on the dart. However, there is still the possibility that the dart could hit the wall and thus it could still decrease your average FPS.

3. A single set of flywheels is going to max out at around 110-120FPS no matter how many volts you put into the motors. In order to have a flywheel gun shoot 250FPS, you would need several stages of flywheels that continue to accelerate the dart as it goes down the "barrel." I'm pretty sure no one has ever done more than a two stage/four motor flywheel system (often referred to as an "afterburner"), but according to physics models you would need about a 5-stage flywheel system to reach 250fps. See the table in this blog post. A person better educated in motor electronics than I could tell you the battery requirements for all of that.

Ironically, a 5 stage flywheel system would probably necessitate that long cosmetic barrel that you wanted in the first place.

Per the previously linked blog post: "A completely homemade system with 10 flywheel pairs, a generous 0.25 inch gap between flywheels, and flywheels that are 1.25 inches in diameter would be less than 15 inches long, and could fling stock Nerf darts at about 350 fps if my calculations are accurate."

Edited by jwasko, 15 June 2015 - 07:55 PM.

[meishel]

You don't really need a barrel after the flywheels, but a very short one does help stabilize the dart a LITTLE bit because as it leaves the flywheel sometimes the dart will try to bend up or down as it's coming out of the flywheels. Anything more than a couple inches is going to have little to no benefit and only serve to slow down the dart. You also want a loose fitting barrel IF you have one. In terms of performance out of multiple sets of barrels, that I know of, there is not chrono data for anything over a 2 stage system. I hit 173 FPS high on my 2 stage system, and with decent darts I can hit 155 FPS average (in my video I was at 152 average due to gluing issues and feeding issues). I plan on building a quad stage blaster soon for a friend. The issue you would run into with multiple stages, is that you need very high RPM motors to get extremely high FPS numbers. I did a test with a 2 stage system with all motors running at 37,000 RPM and I averaged 135 FPS. My Hailfire is running 47,000 RPMs on the second stage of motors, so that explains the huge performance increase. If you want to keep scaling performance upwards with each stage of flywheels the RPM needs to increase as well. I get drastically less foam build up on the second stage of flywheels on my hailfire as I do on the first set. This means I'm not getting nearly as much dart slip as I do on the first set which means there may be a performance increase by increasing the RPM of the second stage motors.

tl;dr you'd likely need 90k+ RPM motors on the 4th stage of flywheels to hit 250 FPS. I could be wrong, but we should find out in 3-6 months unless someone beats me to it.

Here's my hailfire build:

Edited by meishel, 15 June 2015 - 08:02 PM.

[jwasko]

47,000 RPMs on the second stage of motors

Well. Shit. Toruk's model didn't have 45k RPM until stage 5 or so.

What motors do you plan to run at ~90k if you don't mind my asking?

Edited by jwasko, 15 June 2015 - 08:23 PM.

[Phil]

Your post is a little confusing, but here's some info.

1. You don't really need (much of) a barrel on a flywheel blaster.

2. If you want a long barrel for aesthetics, you could just make one that's a very large diameter to minimize the amount of drag it has on the dart. However, there is still the possibility that the dart could hit the wall and thus it could still decrease your average FPS.

3. A single set of flywheels is going to max out at around 110-120FPS no matter how many volts you put into the motors. In order to have a flywheel gun shoot 250FPS, you would need several stages of flywheels that continue to accelerate the dart as it goes down the "barrel." I'm pretty sure no one has ever done more than a two stage/four motor flywheel system (often referred to as an "afterburner"), but according to physics models you would need about a 5-stage flywheel system to reach 250fps. See the table in this blog post. A person better educated in motor electronics than I could tell you the battery requirements for all of that.

Ironically, a 5 stage flywheel system would probably necessitate that long cosmetic barrel that you wanted in the first place.

Per the previously linked blog post: "A completely homemade system with 10 flywheel pairs, a generous 0.25 inch gap between flywheels, and flywheels that are 1.25 inches in diameter would be less than 15 inches long, and could fling stock Nerf darts at about 350 fps if my calculations are accurate."

i dont think standard darts will reach those speeds, unless you add weight to them if im not mistaken?

[Draconis]

i dont think standard darts will reach those speeds, unless you add weight to them if im not mistaken?

You are mistaken. The relationship is Force = mass * acceleration. If you are looking for acceleration, then a = F/m, so that lower mass allows the object to accelerate more quickly with the same force. Once travelling at a velocity, greater mass lowers the deceleration of the dart due to air drag.

[Birch]

To get your desired fps, size up the flywheels by a centimeter or two, this will greatly increase the speed at which the edge of the flywheels is spinning, thus giving greater dart fps. You'll need to find some relatively high-torque, high-rpm motors. Look into 180 sized motors instead of 130.

[Phil]

To get your desired fps, size up the flywheels by a centimeter or two, this will greatly increase the speed at which the edge of the flywheels is spinning, thus giving greater dart fps. You'll need to find some relatively high-torque, high-rpm motors. Look into 180 sized motors instead of 130.

can you provide the links to the suggested models?

[jwasko]

I would have suggested Mabuchi FK-180SH-3240, but the supply dried up a few months back. Blade 180s (which are basically the same thing but more expensive) or Xtreme Pro 180s are still available.

The Blade 180 part numbers are:
EFLH1210 or
EFLH1211 or
EFLH1210B or
EFLH1211B
Just do a google and/or ebay search for "Blade 180 motor" and/or one of those part numbers.

There are some 130 size motors that supposedly offer good performance: the "Falcon" 130 and also "Meishel's" motors, but I'm not sure how they will work in this particular setup.

Falcons: http://www.aliexpres...1949808946.html

Meishel's: http://www.ebay.com/...oy/221639931485

Since you need higher RPM I guess that the Falcons would be better between those two.

Edit: Actually just watch this video by Foamdata. Goes over pretty much all the current options.

Edited by jwasko, 16 June 2015 - 07:27 PM.

[Borgador]

Why hasn't anyone tried brushless motors? Hobbyking and eBay have tons of cheap outrunner brushless motors and ESCs. It looks like you could build a simple servo controller for the ESCs with a 555 timer chip and a few resistors and caps. Plus with an outrunner motor you should be able to just screw the flywheel right to the motor. Brushless motors can take much more voltage and are more durable too.
Just wondering?

[Lunas]

Why hasn't anyone tried brushless motors? Hobbyking and eBay have tons of cheap outrunner brushless motors and ESCs. It looks like you could build a simple servo controller for the ESCs with a 555 timer chip and a few resistors and caps. Plus with an outrunner motor you should be able to just screw the flywheel right to the motor. Brushless motors can take much more voltage and are more durable too.
Just wondering?

they have

https://www.youtube.com/watch?v=IeA81xYm8bg

https://www.youtube.com/watch?v=LhFn7DkRkiM

[meishel]

Well. Shit. Toruk's model didn't have 45k RPM until stage 5 or so.

What motors do you plan to run at ~90k if you don't mind my asking?

Brushless motors. I don't remember the exact model I planned on using. The project is in Limbo until I hear back from DrSnikkas. I'm in talks with a friend to design me a flywheel cage from scratch, 3d print it, test it for fit/function and ship it off to china for mass production. I'm also talking with some people about custom flywheels.

To get your desired fps, size up the flywheels by a centimeter or two, this will greatly increase the speed at which the edge of the flywheels is spinning, thus giving greater dart fps. You'll need to find some relatively high-torque, high-rpm motors. Look into 180 sized motors instead of 130.

This would work in a multistage system, a single stage system with larger flywheels will still have to overcome dart slippage. A bigger wheel would have a slightly larger contact patch with the dart which would increase the amount of friction, but I can't see a single stage breaking 140 fps. Also, bigger flywheels = bigger blaster. Flywheel blasters are already kind of bulky, especially if you make them multi stage.

Why hasn't anyone tried brushless motors? Hobbyking and eBay have tons of cheap outrunner brushless motors and ESCs. It looks like you could build a simple servo controller for the ESCs with a 555 timer chip and a few resistors and caps. Plus with an outrunner motor you should be able to just screw the flywheel right to the motor. Brushless motors can take much more voltage and are more durable too.
Just wondering?

The main reason people don't mess with them is price. To get a decent Kv motor that's capable of the RPMs we need, you're looking at $9+ per motor and $10-11 per ESC. That's $40 on a blaster for JUST the motors. Throw in a LiPo pack, wire, switches, and you're blowing most people's budgets. Especially considering there are reliable brushed motors that hit the glass ceiling for far less money.

[Phil]

I would have suggested Mabuchi FK-180SH-3240, but the supply dried up a few months back. Blade 180s (which are basically the same thing but more expensive) or Xtreme Pro 180s are still available.

The Blade 180 part numbers are:
EFLH1210 or
EFLH1211 or
EFLH1210B or
EFLH1211B
Just do a google and/or ebay search for "Blade 180 motor" and/or one of those part numbers.

There are some 130 size motors that supposedly offer good performance: the "Falcon" 130 and also "Meishel's" motors, but I'm not sure how they will work in this particular setup.

Falcons: http://www.aliexpres...1949808946.html

Meishel's: http://www.ebay.com/...oy/221639931485

Since you need higher RPM I guess that the Falcons would be better between those two.

Edit: Actually just watch this video by Foamdata. Goes over pretty much all the current options.

http://www.horizonho...x-2-3-eflh1211b

wouldn't this model be a problem? it has the teeth, and it seems like the metal pole that's sticking out of the motor, connecting to the teeth is larger than the hole of the diameter of the spin wheel?

[jwasko]

The cage seems easy enough to fabricate - just attach motors to flat material like this- but cheap flywheels (even if they are just equivalent to what is in a Nerf blaster) would be great for multi-stage systems.

This would work in a multistage system, a single stage system with larger flywheels will still have to overcome dart slippage. A bigger wheel would have a slightly larger contact patch with the dart which would increase the amount of friction, but I can't see a single stage breaking 140 fps. Also, bigger flywheels = bigger blaster. Flywheel blasters are already kind of bulky, especially if you make them multi stage.

Not sure if Birch was specifically talking about bigger flywheels in a multi-stage system or not, but doing so would certainly broaden the pool of motors that can reach the reuired surface velocity for later stages. Nerf flywheels are 1.25" in diameter I think. On a 3S (11.1V), an Fk-180SH-3240 motor does 47,730RPM (by the spec sheet). So increasing that diameter by a mere 0.25" to 1.5" would be like having a 57,000RPM motor. That would only make the cage 0.5" taller (because 2 flywheels).

If I'm doing the math right, you'd need 2.5" flywheels on Fk-180SH-3240 motors to be roughly equivalent to the aforementioned 90,000RPM motors on 1.25" flywheels. That would only make the cage/blaster 2.5" taller (or wider), which doesn't seem too horrible I think.

--Unless I'm wrong about stock flywheel diameter and then that was mostly pointless rambling--

Phil, you can pull the pinion gear off (carefully/without bending the shaft). Not totally sure if that is the right diameter (or indeed even if it's the right kind of Fk-180) or not because there are no specs on that site but it at least has the right part number.

Edited by jwasko, 17 June 2015 - 11:12 AM.

[meishel]

With 2.5 inch flywheels, you'd be looking at a blaster height of at least 5.5 inches, which is starting to get rather tall, especially for the last stage which means the end of the blaster is thicker than the rest of the blaster. That sticks a lot of weight out over the end of the blaster. I'd prefer the smaller flywheels if possible to keep the overall size down since dealing with 4 stages of flywheels is already going to mean a large amount of weight.

Edited by meishel, 17 June 2015 - 05:12 PM.

[Lunas]

it is kinda nerdy but i wanted to do a brushless for the startup sound turn on the gun for the 4 startup beeps then the motor sounds...

[TheNerfZilla]

With 2.5 inch flywheels, you'd be looking at a blaster height of at least 5.5 inches, which is starting to get rather tall, especially for the last stage which means the end of the blaster is thicker than the rest of the blaster. That sticks a lot of weight out over the end of the blaster. I'd prefer the smaller flywheels if possible to keep the overall size down since dealing with 4 stages of flywheels is already going to mean a large amount of weight.

I know this might not work, but couldn't you use a rayven shell for the bullpup magwell to do away with the large barrel.This way, the weight would be mostly over your hand, eliminating the inherent front-biased weight you would get otherwise.

[meishel]

I know this might not work, but couldn't you use a rayven shell for the bullpup magwell to do away with the large barrel.This way, the weight would be mostly over your hand, eliminating the inherent front-biased weight you would get otherwise.

Yes but it would still be large and unwieldy. It would likely be unbalanced (As flywheels become larger the balance becomes more of an issue, and it would need to be perfectly balanced at those speeds). I mean, I hope someone does it, because it might be a cheaper solution than what I'm planning on doing, but eh. Also, for the record, the project I'm planning with 4 flywheels is a bullpup.

[Phil]

i think this weapon system is only viable as a deploy-able with a 3-4' tripod. you also have to consider the powers supply for all those fly wheel, it's gonna be heavy.

[Zorns Lemma]

Don't call foam blasters "weapon systems" and if you need a tripod for one then your expectations of what we do here do not match reality.