18 replies to this topic

[Landru]

I play Humans v Zombies at Penn State and decided I needed more firepower this semester. I subsequently modified a RapidFire 20 to be charged with an air compressor in my backpack, as well as greatly improve range and accuracy.


With all modifications, I can:

Average 70ft with stock taggers

Average 105ft with my hemispherical tipped Stefans.

Charge the air tank 10times to 100psi before recharging the battery

Fire about 100 darts per charge

Fire 20darts/s



Details:

The backpack containing a compressor, batteries, and air tank was the most significant improvement from the stock gun.

Two 7.2v NiMH remote control car batteries power the compressor. The batteries are wired in series for a total of 14.4v at 3000mAh of capacity. An easy to reach push button switch on the gun is wired to a BNC cable which connects to the batteries and compressor. There is also a ‘stealth’ switch on the gun which prevents the compressor from turning on by accident.

The compressor was purchased years ago for water bottle rockets, but similar ones can now be found at Harbor Freight for under $20.

The air tank used is a 2L soda bottle. They are durable, reliable, do not leak, and are dirt cheap. A custom brass fitting attaches to the bottle cap and connects the bottle to a standard 1/8in NPT fitting. There are a variety of fittings used on the system, but the push to connect is my favorite. The only reason others were ever used was local availability. The bottle connector leads to a ‘T’ which connects a bicycle valve and the tube to the gun. The compressor attaches to the bicycle valve. The air tube attaches to the gun through a quick disconnect fitting which I found at a local scrap yard. Standard compressor quick disconnects will work also, but tend to leak. Once the air hose is inside the gun, another ‘T’ connects a pressure gauge to the air line. The commercial home depot tubing is connected to the stock RF20 tubing by a barb fitting AND small hose clamps.

The next gun modification is of the firing mechanism. I carefully pried the clear plastic from the red piece at the base of the piston tube and opened the mechanism. I then compressed the spring back about 1in and put a large quantity of masking tape above it to pre-compress the spring and raise the minimum firing pressure to about 40psi. As a result of the higher firing pressure, the cone shaped red piece at the tip of the mechanism also needs to be replaced with something slightly wider. If it is not, the black rubber piece fails to make a reasonable seal. To replace the red cone, cut it off, careful not to damage the black gasket. Remove the rivet, and drill out the hole to 5/32 and replace the entire cone with a single 12-whatever machine screw. The head of the screw should be slightly wider than the base of the red cone for it to work correctly. The screw will self tap into the hole with some minor effort. Do not tighten the screw onto the gasket; only make it very close to touching. If the gasket is compressed it will expand outward and get stuck in the clear tube.




The next modification is simply cutting 20 pieces of 17/32 brass and press fitting them into the barrels. Removing the turret and using a large clamp to press fit the barrels can make things easier.

The final functional modification is replacing the trigger with something sturdier. Because the gun runs up to 100psi the trigger will fatigue and break within the first hr of use from the increased force needed to push down the firing pin. I made a paintball style aluminum trigger; reinforcing the existing trigger with embedded paperclips or dremeling a new one from polycarbonate may work too…


Finally I removed the black shell and cut off any excess parts to make it more manageable.

Feel free to ask questions, but I don't get on too often between dodging zombies and finishing a degree in mechanical engineering.

[nisaburo]

Very nice job, however I, and I'm sure many others around here, will suggest that make a proper air tank. Captainslug has plans on the site to build a pvc hard tank. How long does it take to fully fill the tank? The masking tape increases your ranges but lowers your ROF, correct? By having an external tank you could stand to eliminate a lot more of the shell making the gun more compact and sleek, you would just have to move or replace the grip and it could almost be the size of a maverick. Add a drop clip mod to this and you'll never have to be worried about being ambushed by those pesky zombies!

[NerfGrassHopper]

Awsome, have you used it in a war yet?

[VACC]

Very cool. The only question I would have is....doesn't 20 darts/s make it pretty dificult to stay loaded? You can't possibly aim and spray at more than 3 or 4 targets in a second, and probably can accuratey hit less than that at more than 10 feet. I would think that 100 ft and such an accompanying rate of fire would actually a bit detrimental for your purposes. Than again, dialing the psi back a bit isn't a problem I supppose.

I, too, would recomend installing a drop clip system, only because you've done everything else, and adding the option to quickly swap out a preloaded barrel assembly or two would make you pretty much unassailable on open ground, annd prevent you from having to run imediately following your 1 second of glory. However, I do recognize that this would require you to purchase another rf20 or two, and the rest of your rig seems to be built for economy. Than again, I'm sure it wouldn't be the first time a rf20 got returned to the store without some vital components. No, that would be Wrong!

VACC
~strongly in favor of "the man"~

[Split]

Wow. Great work! I figure that you just removed the bladder (fifth picture shows the tube it routes just completely bypasses the original bladder area). Is that correct?

Would you sell one of those molds for the hemisphere dart tips?

20 darts per second is insane, but pretty believable at that pressure. 50 clips before recharging the battery? Very nice work.

[Landru]

It is set up for replaceable clips, just need to work on the seals.

It has been through quite a few battles with most of the modifications. it's always a work in progress.

[BobRedshirt]

This is awesome. I, for one, would love to see a video of it working, if that's at all possible.

[slienced assassin]

This has to be one of the best rf20s I have ever seen. Great job.

Edited by slienced assassin, 18 March 2009 - 05:02 PM.

[eddieoctane]

I want to go on the record saying that this thing, along with the 3 other guys who just run around with RF20s, make games like capture the flag rather lame. That being said, I have seen this thing first hand and it is damned impressive. PSU engineering FTW.

It's hilarious that you just now post this thing, Landru. I am waiting for that bottle to pop one day, though. Not that i want you hurt, I just want to see the look on your face when being rushed by zombies and the bottle finally gives out.

[GodOThunder8882]

I'd use a Coca-Cola bottle, Coke is better.

but seriously, amazing job. I'd love to have one of these of my own, so I'll have to try this.

[John Q]

Talk about some real firepower, now all you need is some solar panels on your backpack so your batteries can stay charged on the move

It would ease my heart to know that you end up replacing that plastic bottle with something a little more durable in the future!

[Forsaken angel24]

Very nice.
I love the trigger.
I would also love to see a video of it in action.

[CaptainSlug]

What you need to do now is attach it to a Big Blast

Edited by CaptainSlug, 18 March 2009 - 11:57 PM.

[Banshee]

Sorry to turn the thread to CaptainSlug, but I have a question about your "Big RF20 Blast". Where is the pump for the RF20? Is it linked together with the Big Blast pump? If so how did you manage to keep the Big blast tank from over pressuring as you filled the RF20 bladder? And lastly, how many pumps does it take to fill both?

[VACC]

Banshee, on Mar 19 2009, 01:43 PM, said:

Sorry to turn the thread to CaptainSlug, but I have a question about your "Big RF20 Blast". Where is the pump for the RF20? Is it linked together with the Big Blast pump? If so how did you manage to keep the Big blast tank from over pressuring as you filled the RF20 bladder? And lastly, how many pumps does it take to fill both?

Look here. No more questions on that subject in this thread, please. I'd recomend you read the ENTIRE thread I linked thouroughly before asking any questions about it anywhere else either. Everything you could possibly want to know is described there.

Carry on.

[Landru]

In the final version I plan to use mountain dew bottles. While you can probably fit more air at higher pressure in a hard PVC tank, the external soda bottle tank is extremely robust and will take large mounts of abuse. Also there were no leaks, first time. It is also easily replaceable if it were to leak.

I usually use it in a semi-auto style of fighting with 1-2dart bursts so as not to rapidly deplete the ammo. Full auto is only ever useful in assassins or other 1v1 style games.

As for the hemispherical dart molds, I'd be willing to sell an aluminum 5 dart mold for 10$. PM me. There wasn't much interest for them over on the HQ and then my account crashed so nothing ever came of it before. The dart basically looks like this: http://i211.photobuc...13/NewDarts.jpg

[oodalumps]

Landru, on Mar 18 2009, 01:28 AM, said:

Average 70ft with stock taggers
Average 105ft with my hemispherical tipped Stefans.

Not to come off as an asshole, but are those flat ranges? It's hard to see 2.5" of barrel getting 105' flat average with just extra spring compression. If it does get those ranges, I imagine the darts would explode as they leave the barrel (like when you put a short barrel on another high-powered airgun).
The ROF is understandable with how much pressure you put in it. But how did you get the piston to work with that fast of airflow? On my rf20 (even with the piston expansion), when it's fully pumped I have to turn down the airflow or else the piston doesn't retract far enough for it to catch the rotation mech before it tries to go forward again.
If you got everything to work as you say, congrats, I would be quite jealous after all the seemingly needless stuff I did to mine. All I needed to do was band the piston and use 17/32 barrels and I would have gotten the same range? I guess FA's magstrike shot pretty far too.

[Landru]

The range is not flat. it is the max range. Video to come soon.

I have a few different guns and this one just happens to work at the increased speed, but just barely. Maybe just random luck.

[VACC]

This thread seems to have died down, but I would like to make one more comment on it before we move on. The subject of safety concerning soda bottle air tanks has been broached in another topic. It has been pointed out that Soda bottles should not be considered a reliable air tank for anything more than 60 psi. While they may indeed be able to hold more preasure they should not be considered reliable or safe in such instances. They are designed to contain liquid, which is not nearly as dangerous in the case of a rupture, and are manufactured to great variances in specifications. As such, Nerfhaven recomends that you search further to find more reliable and, most importantly, safe mediums of air preasure storage.

VACC