After being a bit disappointed with the speed that the Eccentric dropped off the page I am hoping that this will generate more interest. Being the last in my 7 original projects I think it is the most innovative and practical of them all.
Often people have tried to create a semi-automatic blaster that still achieves reasonable ranges, most notably in the case of cheesypiza001 who completed a design similar, but significantly more complicated than this one, and to my knowledge never completed a practical blaster off the concept. Major props to him because it was after reading his posts that this idea formed in my head.
Interestingly, like the Eccentric this build was originally going to be put into a maverick for feeding. After the failure of the Eccentric however I decided to save myself the trouble and go with an RSCB.
This is the continuation of the Mirage series, and although it started out as just a proof of concept, this design proved so effective that even the prototype is a VERY practical and respectable blaster. I will be applying the same pneumatic setup to a more efficient loading system and a nicer shell in the final iteration of the Mirage which I am working on now!
For those of you wondering about the name, Mirage is just the series, and SS stands for small and simple.
After some trial and error, and a lot of waiting for materials I came up with this:
Again, its ugly but I am incredibly excited about this concept.
Three components make up the propulsion setup.
-A Magstrike pump and bladder
-A modified hornet sliding valve (NOT the blast valve)
-A Big salvo tank (any back pressure tank will work, but this was chosen because it has a good amount of volume. Enough for greater than 100' ranges, but not so much that it is ridiculous to prime)
The operation is based off of the properties of a back pressure tank. If you know about how these work skip the next paragraph, if not read on.
A back pressure tank like the one in a Drain blaster, big salvo and hornet are triggered by changes in pressure. When they are pressurized, and you let some air out of the back the lower air pressure in the back of the tank pulls the valve backwards, releasing the rest of the air out the front firing the dart.
Normally these tanks are pressurized with a pump, released, and then pressurized again. In this case all of this is done beforehand and stored in the Magstrike bladder (the green sock in the image. The sock is just to protect the bladder from the sun).
The pressurized air then equalizes the pressure in the bladder, and in the BS tank when the trigger is at rest:
When the trigger is pulled, and the plunger in the valve slides past the port connected to the BS tank pressure is released and the tank fires:
As the trigger is held down, it DOES NOT slide past the port which the bladder is connected to and so no air is lost other than that from the BS tank. Pressure from the bladder then pushes the plunger back to its original position and the process repeats. No return spring is needed, and this way when the pressure is too low the trigger stays compressed acting as an indicator for pressure levels. This way true semi auto is achieved. The bladder is fully pumped, and then a burst of air is released (equivalent to a normal BS firing) with each squeeze of the trigger.
The valve itself is the only modified component in the whole blaster. I simply cut it shorter and attached it to the trigger. I connected the last two connection ports. The first to the BS tank, the second to the Bladder and pump. Also, because there is actually a check valve in this valve, there was no need to plug the back of the valve (where the unconnected tubing sticks out):
The rest of the build is purely about quickly putting together a test rig. A 12" RSCB constructed exactly like that on the Eccentric:
This RSCB was actually developed for this build, and used on the Eccentric first. I needed an RSCB fast and efficient enough to complement the Semi automatic capabilities of this setup. See the Eccentric post for details on construction. Even the style of construction is the same. The tank is glued directly into the RSCB vertically, and the handle is Zip tied on. The trigger is equally simple. A hole drilled (by hand ) through the handle with a hex wrench going through it acts as a guide for the valve's sliding motion. The PVC scrap is just for comfort.
The result surprised me a lot. Despite the sub-optimal barrel length the first shot clear 80 feet while the last goes about 70 (on average. Level with streamlines) and the ROF is incredible. I won't even try to put a value on it, but even with an RSCB its fast (Although the RSCB was just for testing purposes. The final Mirage will use a breech new feeding system I am developing).
The biggest surprise however was that with a full fill of the MS bladder at 20 pumps I can fire the blaster 6 times at full force. At just 15 pumps I can empty the RSCB (with 4 streamlines in it). (this goes to show just how inefficient the MS valve actually is)
It is also small and maneuverable!
Next to a BBB:
Of course I'll let you see all of this for yourselves:
Overview of blaster
Humble beginnings (The very first valve test)
Feel free to ask any questions as this may be a bit confusing. Again, comment on the clarity of the writeup because there always will be more to come.
As far as I can tell this is the first semi automatic setup that is this simple and effective and I am surprised that no one has done it (or documented it) before. If anyone has and I have missed it major props to you!
Edited by Boot, 02 December 2010 - 05:29 AM.