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Author Topic: Flywheel blasters: the goal of faster darts  (Read 1619 times)
shandsgator8


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« on: December 12, 2015, 05:33:22 PM »

From my online research and limited experience with flywheel blasters, it seems like everyone wants higher FPS darts coming out of their flywheel blasters. Based on my limited testing and observations, if the dart moves too fast, the darts are inaccurate and have no precision (imagine using old school Nerf streamline darts in a singled Titan). Using the same setup, slower moving darts have higher accuracy and better precision, although generally get less range. Therefore, I have concluded that there is a "sweet spot" between FPS/range and accuracy/precision when using standard Nerf Elite darts of Koosh darts (Gen 3). However, I've never see anyone reference this idea. QED: I'm missing something here.

Does anyone know what I'm missing or can shed some light on my ignorance?

Also, does anyone know if the Stryfe and Rapidstrike use the same flywheel motors?

Thanks.
« Last Edit: December 12, 2015, 05:41:25 PM by shandsgator8 » Logged
irishknots


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« Reply #1 on: December 18, 2015, 10:46:54 AM »

You are dealing with two variables there: Dart stability and Flywheel ceiling.

In order for darts to be ballistically stable i.e. fly straight and track, they need to have aerodynamic stability where the center of gravity (mass or where the dart balances due to weight) is at least .5 inches in front of the center of pressure (essentially the middle of the dart). This is basic rocket design and has been used for a long time. Many generic chinese darts, such as the "Koosh" darts sold on ebay, are more stable than elites due to their higher tip mass, and their CG is well ahead of the CP. You can indeed shoot these darts out of any 100+ fps blaster ideally without any issues. As your darts gain velocity, the properties of air become more like a fluid and the more important the stability of the dart is. If  you have fired a Koosh dart (Gen 3) from a high powered springer, you should see that the darts are still much more accurate than almost any other dart, limited experience with FVJs not withstanding.

Flywheels are a different issue all together. If you are seeing darts flying unstable from your blaster, there might be a misalignment in the flywheel cage, front barrel, or magazine well. Do realize that with single stage flywheels, you do have an approximate max velocity of around 120 FPS (Assuming single stage means only 1 set of flywheels + cage). Flywheels also have to be balanced between the top and bottom wheels (Stryfe wheels tend to be the best of the best in terms of straight from the factory balance). Take a look at torukmakto4's blog TheDartZone and read where he discusses how alignment issues easily mess with blaster performance in flywheels.

The stryfe and RS motors are not the same IIRC, I think the RS motors have a higher torque value.
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shandsgator8


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« Reply #2 on: January 12, 2016, 09:26:49 AM »

HvZ forums are back up!

Thank you for the informative post.

As a small update, I modified a Stryfe with MTB Rhinos. I tested them with a 6 cell and 8 cell NiMH AA eneloop pack. The 8 cell pack shot the darts noticeably faster, but the darts were MUCH more inaccurate. You could compared the performance of my darts (Gen 4 Koosh) to stock nerf Elites...ok, not that bad, but comparable.

The 6 cell pack shot the darts well, although not as well as fast as the 8 cell pack. However, the darts were MUCH more consistent. My current Stryfe setup uses a 6 cell NiMH pack instead of the 8 cell pack.
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torukmakto4

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« Reply #3 on: January 16, 2016, 11:02:26 PM »

From my online research and limited experience [...] it seems like everyone wants higher FPS darts coming out of their ...blasters. Based on my limited testing and observations, if the dart moves too fast, the darts are inaccurate and have no precision (imagine using old school Nerf streamline darts in a singled Titan). Using the same setup, slower moving darts have higher accuracy and better precision, although generally get less range. Therefore, I have concluded that there is a "sweet spot" between FPS/range and accuracy/precision when using standard Nerf Elite darts of Koosh darts (Gen 3). However, I've never see anyone reference this idea. QED: I'm missing something here.

Does anyone know what I'm missing or can shed some light on my ignorance?

You aren't missing much in terms of stability and velocity for the majority of superstock darts, especially the older and less favored types like Streamline and Elite. All I would consider you to be overlooking, and this does get partially into personal preference and situational factors, is that maximizing precision (minimizing spread) is definitely not equivalent to maximizing combat effectiveness of the superstock blaster system. Targets don't sit still in the open 30 feet away. Trajectory flatness, maximum and effective range, retained velocity, and time on target are considerations that favor the use of the highest legal/safe velocity available. Coming up with an effective solution means balancing those with accuracy issues, similarly to the selection of ammunition to balance aerodynamic efficiency and velocity retention with stability.

Nowadays with the much improved darts in .50 cal (such as koosh, ZS Elite, USD, USC, FVJ, FVN/Hardball, ACC, Kforce, and even standard Hasbro Elite to a large extent) which are much more suited to the 100-130fps band, if you ask me, the accuracy problems are dead and gone, and the best bet is to milk those safety limits for every last joule you can put on darts. Velocity gets hits. What would you rather have, a 70fps stock rampage, or a 120fps RS build? Who can take a quick aimed shot across a 45 foot clearing and hit the enemy as they pass a doorway without tons of unintuitive elevation and lead? If both of these players engage each other simultaneously, who is advantaged? Who can reach a horde at 30 yards for area effect? Who is least likely to have a dispute with a zombie? (But who is best at plinking cans off the fence in the backyard?)

flywheel blasters

This opens a whole other can of worms due to the physics of these beasts. There is a proper document by rhino_aus (the Rhino motor guy) describing what I cover below out there but I forget where.

Those Stryfes and such (i.e. "Nerf-design flywheel systems") you see shooting 100-130fps are operating in dynamic friction. The flywheels turn at a surface speed significantly in excess of the maximum velocity a dart can obtain during its contact with them ("critical velocity" which is first reached at "critical speed", approximately 25,000 rpm for the 1.25" 10mm gap system and a typical dart). This mode of operation i.e. "supercritical" is key to flywheel launchers, in my opinion, being viable in the nerf hobby as anything more than a niche or high-priced product.

The reason behind that is simple: As long as flywheels maintain at least critical speed, velocity and flywheel speed have no relation. Since the dart is always skidding on the flywheel surface, the difference of speed between the two is largely insignificant to the force applied on the dart, and so as you shoot and the motors (which are PMDC with linear torque curves) operate under variable loads and hence vary in speed, the velocity of darts doesn't change in response. Supercritical flywheel guns have a definite capability to support ROF, corresponding to the maximum load under which the motors can maintain critical speed; for instance one can calculate 15rps for the Rhino/3S lipo system and 35rps for the FK180SH-3240/2S lipo system both with Nerf geometry and standard ~1.2g darts. Exceed that, which for these setups is not easy, and velocity starts drooping.

Supercriticality also moves the critical speed far enough down in the torque curve that the torque at that speed is high and the total time to accelerate from rest to that speed is only a small fraction of the time to reach full speed - hence quick response. You need not rev one to full speed to get a 100+ fps shot off.

By contrast, i.e. a stock Nerf flywheel gun operates in static friction mode i.e. rolling contact and hence has a supportable ROF of zero rps and a theoretical full-velocity response time of either infinity or 5 time constants (depending on who you ask) - in other words. equating flywheel speed directly to dart velocity is not good. Well, enough theory. Grab a stock Stryfe and rip on it, watch the darts fall shorter and shorter. That is subcritical operation and it is bad. M'kay?

And what that means? You CAN'T, properly speaking, "turn down" a flywheel blaster's velocity without a major tradeoff to other aspects of performance. And that is part of why they all shoot full velocity - because they can do it consistently, and consistency is practical accuracy.

As a small update, I modified a Stryfe with MTB Rhinos. I tested them with a 6 cell and 8 cell NiMH AA eneloop pack. The 8 cell pack shot the darts noticeably faster, but the darts were MUCH more inaccurate. You could compared the performance of my darts (Gen 4 Koosh) to stock nerf Elites...ok, not that bad, but comparable.

The 6 cell pack shot the darts well, although not as well as fast as the 8 cell pack. However, the darts were MUCH more consistent. My current Stryfe setup uses a 6 cell NiMH pack instead of the 8 cell pack.

The 6 cell is subcritical. The 8 is super. That is the major difference. The 6 should get about 90 fps. The 8, 100-120.

Fortunately, Rhinos and a 6 cell nimh pack will give plenty of torque and since it's a semi-auto and probably doesn't see major ROF you should be able to get away with that. The question is whether it really serves your needs. Can you make it start drooping by shooting as fast as in a game? Can you get a ~80% velocity response shot off from standstill?

I still think you should take the 8 cell into combat, as the 120fps is where it's at. Again, it IS personal preference and situational. Some people (see: BURN and their AR equipped rampages) prefer about 90 fps for better accuracy. I find it lacking reach and hitting power.

Also, does anyone know if the Stryfe and Rapidstrike use the same flywheel motors?

Thanks.

They both accept 20.4mm flat can motors.

They both come stock with FA130 motors.

The stock FA130 motors are not the same motor. The Stryfe motor is the common Nerf semi-auto motor (Demolisher, Rapidred, Cam, Stryfe, E-Ray, blah blah blah). You usually run it on a 3S lipo for superstock. The RS motor is a lower turn (hotter) wind. You usually use 2S for similar speed to the former, and it does make more torque, 3S blows them up, and they don't last but a year with stock metal brushes.
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shandsgator8


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« Reply #4 on: January 18, 2016, 04:01:56 PM »

Torukmakto4,

I was wondering if you would respond and I appreciate that you did. Your response was timed great because I just came from a superstock Nerfwar yesterday where engagement distances were about 25 to 45 feet with tons of cover. I used my 6 cell Eneloop custom made battery pack in my modded Stryfe (rewire, MTB Rhinos, and upgraded microswitch). To put it shortly, it performed extremely well. Firing off darts as fast as I could pull the trigger produced only minor reductions in dart speed. Basically, firing the Stryfe as fast as I could provided performance that was close enough to that "first shot" when the flywheels have plenty of time to reach full speed. So as you predicted or alluded to, the Eneloop battery and MTB Rhino combo had enough torque to provide the rapid fire performance I wanted.

As for dart speed, someone had a chrono at the event and I was hitting over 100 FPS (about 100-105 FPS) when the flywheels were fully spun up. I did not do any testing for when I was firing in rapid succession, though. Based on what you said, I bet I was hitting between 80 and 90 FPS when shooting as fast as possible. Note that this testing was done when the battery was below freezing (it was snowing while we played). Playing in the summer time will hopefully produce a tad more power from this setup.

I can see how, based on preference and type of Nerf wars a blaster will be used in, that higher FPS with larger grouping could be advantageous. This is something I will look into and may experiment with at the next superstock Nerf war I attend.

Thanks again for your response!

« Last Edit: January 18, 2016, 04:07:40 PM by shandsgator8 » Logged
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