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Member Since 22 Apr 2009
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#363625 Project 8

Posted by snakerbot on 06 January 2019 - 09:48 PM


This is what I’ve come to call “Project 8” or just P8. It is a fully 3D-printed, magazine fed, fully-automatic blaster heavily inspired by/based on Torukmakto4’s T19. It uses the same Hy-con geometry wheels, but with the 11mm gap instead of the base 9.5mm. The important parts of the flywheel cage geometry such as spacing and bore diameter are the same, although both parts of the flywheel cage have been modified somewhat.


It also uses the same stepper motor bolt drive, although again, some slight geometry changes have been made to fit them into this blaster.

Flywheel motor controllers run the same build of SimonK that the T19 does, but with the motor speed governed at 21,291rpm instead of 25,510. The slower speed at the larger gap flywheels are meant for 150fps games, and although there wasn’t a chronograph at the last game, a test cage with the same geometry was getting ~145fps with community bin accufakes and ~150fps with community waffles. The new wheels were printed with different settings that better matched the intended profile, so I dropped the speed by about 5% (to the current speed) just in case it was shooting too hot.


The core arduino code is near-stock T19 “Core 26.1”. The only change I made was to reduce the base feed delay from 185ms in non-turbo mode and 180ms in turbo mode to 145ms and 140ms, respectively since the flywheels don’t need to reach quite the same speeds.


Essentially this is a T19 in a differently shaped body. I did not really intend this to be so, but once I started doing the CAD, the design took on a life of its own and this is where it ended up. In general it features smoother contours than the T19, especially on the user contact areas, where the grip, the stock pad, and the front of the magwell are all very heavily radiused. It also has large windows on the left and right sides of the magwell so I can see how much ammo I have left in the magazine. The breech is also not a fully enclosed breech like the T19, although the jam door, when closed, serves the same purpose a closed breech does, aligning the dart with the bore. This jam door was really intended to be a top loading door more than a jam door, but I’m not sure I’ll ever actually use it for that. I used to top load my rapidstrike, but it lost that ability about seven months ago and I can’t say I’ve missed it.


Issues as they exist right now:

- It’s pretty large and heavy. Not unreasonably so, but a hypothetical Project 9 may make an effort to be lighter.

- The weight balance is a little off. The center of gravity is about an inch behind the handle with the battery in place. Not a huge deal, but noticeable in some circumstances.

- The magwell required huge amounts of sanding, filing, and scraping to make the mags drop free. I’ll edit the CAD eventually, but I haven’t yet.

- One of the screws in the handle digs into my knuckle if I hold it in certain ways.


And so you can see it in action, here’s a video of the CTF rounds we played at the last HANU game where I used this blaster.



More info on the T19 can be found at Torukmakto4’s blog:



The cad files and code for P8 are available here:


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#358519 Uploading attachments to PMs

Posted by snakerbot on 12 March 2017 - 03:10 AM

I was having a private message conversation with another user and needed to include an image, but couldn't upload the image as an attachment, at least not that I can see. We can include attachments in messages, but only if they've been uploaded in a topic post. I found that I could begin to post a reply to a topic and upload the attachment from there, then cancel the post before actually posting anything, and then attach that image to the private message, but a way to upload directly through the messaging window would be helpful.


Actually, I don't even see the uploader down below this editor. I know I've attached images both to replys and to new topics. Under what circumstances does it show up?

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#355121 Extension Spring Rainbowpup post-construction writeup

Posted by snakerbot on 20 July 2016 - 11:15 PM


I had planned to do a full writeup with step-by-step instructions and pictures and all that, but as months of non-work turned to years of non-work, I decided I should get this out to the community in whatever form it took. By now nothing in this blaster is in any way new or revolutionary, (with the possible exception of the Dura brand PVC bushing trick) but I want to have this information out there.


I’d like to give credit to the rainbow clan for the rainbow catch, Ryan and Kane for the BullPAC and the original Rainbowpup, Carbon for the Snap/Revolution, Ryan for the original catch and handle templates, and Diamondback for the slightly modified ones.


In lieu of an actual writeup, I’m uploading the .dwg and template file that I have now. They are included as attachments at the bottom of this post. If you don’t have autocad, you can download draftsight for free at http://www.3ds.com/p.../free-download/ and it’ll do all of the same things. Alternatively you can find various free viewers (not editors) at http://www.autodesk....cts/dwg/viewers. I’m also including various pictures of the only one of these I still have, so you can get an idea of what the actual parts look like, especially where I wasn’t super detailed in my .dwg. The pictures I include are of a somewhat earlier revisions than what the .dwg shows, so be aware of that.


Parts needed.



Here’s the part I think is least clear in the .dwg: what I call the seal block. This is what seals the plunger rod. It’s made from a 3/4" to 1/2” PVC bushing nested inside a 1” to 3/4” bushing with a 9691K53 U-cup seal sandwiched in the middle. I cut down the outer lip of the U-cup to about half height. The PVC here stops the plunger when it hits home. I use SCH80 PVC since the thicker walls provide a little more surface area for the plunger head, but I don’t think it’s that important.






The rainbow catch is directly in front of the seal block.



Here’s my plunger head. It’s a little longer than the one in the .dwg, but concept is similar enough. You can use whatever you like here to interface from the nylon plunger rod to the skirt. The .dwg and parts list use a U-cup since it’s cheaper, but I used a skirt for this one because this was the first one of these I made. Use whatever you like, but keep in mind the skirt is 1/8” taller. Those grommets there provide a little cushion when the plunger head hits home.



This is the front of the plunger rod. I use a really long eye bolt to mount both the spring and priming disk to, as well as providing room for the catch, which works against the front surface of the nylon rod.



You can use a long set screw or cut the head off a regular screw to support the spring at the front. I use these things called weld nuts to hold the spring centered on the screw.



The priming grip is simple enough, but I want to point out the screws that poke in through the slots and push on the priming disk. That is how this blaster is primed. Also, the slots on the top and bottom need to be the right size to be out of the way. The .dwg shows the priming slide being stopped when the bottom slot hits the front of the handle/trigger block, but this one here stops when the plunger bottoms out against the catch. An important thing here is that you can’t really use thinwall 1-1/2” PVC for the pump grip. The walls are too thin and flex inward with those slots cut.



Finally, the redirect. For the actual elbow part I use a 1/2” CPVC street elbow, with the spigot end hammered into a short piece of 1/2" PVC to interface with the wye. The socket end has a short piece of CPVC in it. I just drill a hole in the coupler and plunger tube and insert the CPVC into that, but you can do various things here. I use a 5/8” forstner bit and my drillpress to make this hole, and it seals perfectly without glue, but you may or may not be able to do this, depending on your tools.





The template file is attached to this post. I can't attach .dwg files so I put it on google drive: https://drive.google...Ym9VaGtfSkZSLW8

Attached Files

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#353681 Constant Force spring blaster infodump

Posted by snakerbot on 22 May 2016 - 09:51 PM


A while back I posted this in the homemades pictures thread.  In short, it was a blaster whose energy source was a constant force spring, like the kind used in Raider drums or your tape measure.  Specifically it was 9293K12.  For those who are not familiar, a constant force spring is a flat piece of metal wound in a coil around some sort of central shaft or bearing.  When you pull on the free end, the coil rotates around this shaft and unwinds.  Because pulling the free end farther only unwinds more of the spring, it doesn’t get any harder to pull as you pull it farther, hence the ‘constant force’ descriptor.


The origin of this experiment is several years ago when a poster on this forum (I can’t remember who it was or what the original context was) offhandedly mentioned constant force springs.  Fast forward several years and I have a job, disposable income, and boredom, and decide to give this a shot.  The original plan was to build a new blaster to run the experiment with, but I got lazy and retrofitted my extension spring rainbowpup instead.  Because of the nature of constant force springs they can really only be put into rainbowpup/eslt/whatever type blasters with plungers that are pulled instead of pushed. 


I’m going to drop some physics on you guys here.  I wasn’t sure exactly what spring to get, or how strong it should be.  Constant force springs really are a completely new area, so there are no “standard” springs or rules of thumb or anything.  Constant force springs don’t have a “spring constant” like compression or extension springs do.  So how to compare?  I didn’t come up with a good answer to this until much later.  What I eventually did was just guess and pick a spring whose draw force was about halfway (a little more actually) between the no-extension and full-extension force of the 9432k125 I found for my rainbowpup.  After buying the spring I realized that the best comparison was probably energy release.  The potential energy stored in a compression or extension spring is given by the equation E=0.5Kx^2 where E is the potential energy stored by the spring, K is the spring constant, and x is the displacement of the spring.  The potential energy stored in the K125 spring at the 6.5” of draw I use is therefore 65.4875lbf*in or 7.4J.  The potential energy at rest (I use no pre-extension) is 0J.  So the total energy released during firing (not all of which goes into the dart) is 7.4J-0J=7.4J.  So for the most equal comparison I should find a spring that can release 7.4J over 6.5in of travel.  Turns out by complete accident, I hit that on the nose with the spring I bought.


The potential energy of a constant force spring I couldn’t find online or in my machine design textbook, so I derived it.  (If someone finds a mistake in this result, please let me know, that might explain some things).  What I got was E=Fx where E is the energy released, F is the spring force, and x is the displacement.  So our total energy here is 68.9lbf*in or 7.78J. 

Note that the displacement term in the compression/extension spring is quadratic, while the displacement term for constant force springs is linear.  That means that for higher draws, the constant force spring falls behind in energy very quickly, but for this blaster/spring combo, I had almost exactly the same energy, so I moved forward with this.

spring energy graph.png


So theory over, let’s talk practical application.  The edge of the spring needs to line up with the plunger rod, because that’s where the free end comes off.  To accomplish this, I used a 1.5” pvc tee and carved it to the nines so I could mount the spring a little off to the side.  I drilled a hole through the tee and used sliding door bearings to hold the spring.  I ground them down so one edge of each could fit into the ID of the spring. 




For attaching the spring to the plunger rod, I used a section of ½” nylon rod (the same material used for the plunger rod).  One end was threaded to screw onto the end of a small stud with the priming disk on it.  The other end had a slot in it, into which I inserted the spring.  A small screw goes through a hole in the end of the spring (the spring comes like that) to affix the two together. 




Assembly is a bitch.  To get the spring into the tee, I had to hold it in place and slowly thread the bolt down through the tee, alternating between rotating the bolt a turn or two and then going back and rotating these nuts a turn or two.  Once that was done, I inserted the plunger extension into the front of the blaster body.


That is where it sits at rest, so I had to stick my finger in the tee at the front and force it down towards the plunger rod. 


Then I turned the plunger with my other hand to thread the two together. Not fun.



So how does it shoot?  Not well.  I’m not sure of the exact reason now, but this blaster had trouble.  About one in five darts didn’t leave the barrel.  The ones that did didn’t seem to shoot as hard.  I don’t have a chronograph, but range tests show a clear drop off. I have a couple theories for why this could be.  First, while this spring is labelled as ‘constant force’, it isn’t like that, not quite.  Constant force springs take a small amount of travel before they reach their listed force.  I guess this is due to the shape of them or something.  I have a couple inches of pre-travel built into this setup, but maybe it isn’t enough.  Further, there is almost certainly more friction in this setup compared to an extension spring.  The bearings I used are a source of some of this, and the priming disk in the middle of the plunger rod is surely rubbing against the inside of the body because of the shape of the spring pushing it sideways.  There is also a possibility that the spring, which is 1in wide, is scraping on the inside of the front body of the blaster.  One final reason is that the process of disassembling this blaster and replacing the spring seems to have messed up the rod seal a little bit.  I’m not sure why, and it doesn't seem bad enough to account for all the problems I see.


I said in the pictures thread that “this is the weirdest thing ever”. What did I mean by that?  Well, it primes like nothing else I’ve ever used.  I’m not even sure how to describe it.  “Light” is almost right, but that isn’t really it.  I end up smashing the priming handle hard against its stops almost every time I prime it.  It’s like I begin to prime back and am expecting a certain amount of force based on how much resistance at has at the beginning, but then it throws me for a loop because that extra resistance doesn’t come.  I’m sure I could get used to it eventually, but it is pretty weird at first.


So, difficult to assemble, expensive ($10.83 for one spring!), weird to prime, and not shooting quite like you’d expect.  Are there any upsides?  I don’t know.  If you could find the right spring, and get the geometry correct (no grinding), you could make one of these that shot pretty well and maybe felt like it had a weaker prime, but I don’t consider that worth it.  Extension springs already have pretty light primes for how well they shoot, and I don’t see this offering enough advantages to overcome the disadvantages.  I’ll leave the blaster as-is for a little while if anyone wants more pictures or wants me to do any more tests, but I don’t see a good reason to keep it as it is forever.


Crossposting additional pictures from the homemades pictures thread here, so it's all in one place.


Not primed:




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#351288 Homemades Picture Thread

Posted by snakerbot on 01 February 2016 - 09:23 PM

This is the weirdest thing ever.



Yes, that is a constant force spring.

Not primed:




Postmortem coming eventually. 

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#344588 Homemades Picture Thread

Posted by snakerbot on 25 January 2015 - 09:01 PM

Posted Image
A bunch of boredom on a Sunday with neither football nor Nascar led to this. Stupid simple snap crossbow. I didn't even bother with routing the airflow. It just goes around the bow arms, which are one solid piece all the way through.
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