3D Printed Roma: Negative Pressure Canister Cannon Tested at Maker Faire

Dear Big Gun community,

3D-printed cannon are now a reality. Western Warship Combat Club has tested 2 separate designs. The first, by Alden Bedard, is patterned after the traditional Indiana-style guns we're all familiar with. These have been tested thoroughly in battle for two years.

The second, designed and engineered by Jeff Krolik, is a canister-style, negative pressure cannon with a relief valve that prevents the cannon from firing in the case of a loss of pressure to the system, such as when occurs when a safety switch is tripped.

The files and instructions/drawings are undergoing final revision, and should - if all goes according to plan - be released to the Big Gun community, free of charge, in the next 30 days. I'm happy to report that Jeff installed 3 of these triple, 1/4" turrets in his brand-new Roma, introduced in combat at this past weekend's Maker Faire in San Mateo, California. The guns survived the weekend intact, and final tweaking to the design is currently underway, prior to completing the documentation.

Please note the attached photos. All construct assemblies in gray are 3D-printed: superstructure, secondaries, all the various cosmetic details, the turrets, gun houses, gun bodies, servo brackets, depression brackets on the barrels, magazines, pump housings, gear housings. There are no wooden parts in this ship.

Questions of a technical nature around the Roma's 3D printing and negative pressure cannon engineering should be directed toward Jeff Krolik.

Best regards,


Rob

1:144 Roma: First battleship built by WWCC club member Jeff Krolik. Most parts are 3D printed.










Roma Superstructure. All parts 3D Printed

 

Well done, Jeff! She is absolutely gorgeous, inside and out. The detail is impressive.

And Kudos on designing and printing the cannons! An outstanding achievement! I look forward to hearing more details on this...

 

Thanks guys. The detail is easy to do, but as you can see the prints are not perfect by any stretch. A real detail modeler would cringe at the printing artifacts, but it doesn't bother me because I'm far enough away when battling to not see them.

I've been working on the guns for about 6 months while lurking this site ;-) I really appreciate all of the cool stuff that goes on here. The guns are designed to be really reliable. For that, I'm using an industrial control valve called a Quick Exhaust Valve (QEV). The concept came from the guys that make potato cannons, where they are used in most guns. Here's a cut away view of the valve:


Propellant is connected to the port on top. The side port is connected to the accumulator, and the bottom port is the exit to the barrels. The way it works is that the rubber seal (orange) is pressed against a seal leading to the exit port when pressure is maintained on the input. When the pressure on the input drops, the seal on the exit port is broken and the gas in the accumulator dumps to the barrels very quickly. That's the upside of this component; when it opens, the flow out to the barrels is very fast, giving good power. On the reliability side, there are no springs, and the only moving part is that little orange seal. Industrial control components are extremely reliable, so we should be good here.

 

While the guns are mostly 3-D printed, the accumulator, control valve, and barrels are not.



This is a view of the bottom of the gun, where you can see the bottom of the aluminum accumulator. The accumulator is made from a piece of 4" x 3.5" aluminum pipe, and 1/4" aluminum plate to close up the ends. I used the aluminum brazing sticks that can be bought at harbor freight to braze it all together with a MAP gas torch. (This is really cool because you can join aluminum for about $35 all in) The input port of the QEV from the previous post can be seen in the middle, and is sealed in the aluminum plate with an O-ring so it can be opened and serviced if needed.

 

It's a
Legris 7982 18 18 Nickel-Plated Brass Quick Exhaust Valve, 3/8" NPT Female

on AMAZON here:

http://www.amazon.com/gp/product/B009XIU2Z8/ref=oh_aui_search_detailpage?ie=UTF8&psc=1

for $17.42

 

On the 3-D printed side,
The aluminum accumulator is attached directly to the magazine with 10-32 screws. The accumulator/magazine assembly has a bearing race on the bottom, and sits on a matching bearing race on the Base, so it is free to rotate. It's all held together with the Accumulator clamp that also provides a timing belt pulley. The whole thing is turned by the Rotation Drive, which has been hacked to run off of an external potentiometer that is turned by a compound gear drive. The whole thing rotates about 270 degrees, and is proportional to stick position. I like this because when you release the rotation stick, it re-centers on the ship midline.

 

It can be made even more compact without the rotation drive. For the Roma, the A&B turrets are linked via a drive belt. The B turret ends up being much smaller without the rotation drive.

Here's a link to my CAD files. There should be .STL files as well in case you can't read solidworks.

Dropbox - 3-Barrel 4in Can Gun V1

There are also .PDF's for the aluminum accumulator. The QEV valve is machined down to form a cylinder and is cross drilled with two additional holes to breath better. I don't have pictures or drawings of that right now as my guns are all assembled. I think there's a solidworks model of them in the folder though.

 

I'm running Solidworks 2013. I'll try to export into the format you suggest when I'm back at my computer

 

Honorable mention from Tugboat makes my day! Thanks man

 

I'm incredibly optimistic about all of this. I'm pretty sure we're looking at a renaissance of the Big Gun sector of this hobby, since lack of cannons has really held us back. 3D printing is putting the "maker" back into the picture, and I can see the day coming when printing parts for these ships is as commonplace and easy as printing a paper PDF from your home computer or tablet.

I salute people like Jeff, Alden Bedard, Tugboat and Greg McFadden who have advanced this technology across the hobby! I know I may be leaving guys out, but I don't know all of the names. Consider yourselves honored for all your hard work!

Rob

 

Holy cow, that looks clean cut. Looking forward to finding out the durability. Hopefully no bad sun rot or weakness against BB hits.

 

One of our club cargo ships has gone through 2 maker fair's worth of battling. That's 18 battles with a lot of intensity given the small, enclosed battle pond. Some dents, and minor delaminatikns here or there, but equal or better than foam or balsa superstructures. The guns themselves are protected, and I'm not concerned about them. Mine are printed from PLA, and I haven't seen any issues with temperature instability in the Ca sun. However, if something does fail, I can just print another!

 

We have another set of guns in the club that are 3D printed in a more traditional, Indiana style. They've been in every battle for two years, and work just fine. I'll start another thread about those, but it's obvious to me that we've turned the corner on this technology for RC Warship Combat.

Rob

 

Thank you for sharing the files. It is a very compact and well thought out design.

Are the risers for the barrels just glued in? Do they seal the holes in the side of magazine top, which I assume is there just to clean out the horizontal feed holes?

Also, how do you seal the 6 10-32 screws that penetrate the top of the accumulator?

What o-ring number do you use to seal the magazine base to accumulator and magazine top?

Thank again.

 

The risers have a hole to allow ammo through, but the back wall is solid to close off the clean up holes. I put a 1/4" x 1/4" neodymium magnet in the cleanup hole to maintain ammo position in the riser. I actually put one round of ammo between the magnet and the riser to reduce the magnetic holding force a bit. The risers are epoxied in place, and I fill the horizontal holes behind the risers containing the magnets with epoxy as well.

One of the guns I've made so far, the 6-32 holes went through, and we're epoxied from the inside. The other two guns were tapped with a blind hole so no sealing was needed. The good news here is that the QEV is removable, and so if those holes ever develop a leak, you have access to the inside of the accumulator to seal things up.

I don't use an o-ring to seal between the accumulator and parts on top; instead, I put some RTV in the slots printed into both sides of the magazine base.


BTW, I'm sure there are many improvements to be made here. As you are hinting at, the threaded holes on the top of the accumulator are not ideal, but I couldn't secure the magazine top well enough otherwise. The gun is also somewhat tall, as driven by the height of the QEV used. The inexpensive aluminum QEV's that are on Amazon are my next area of exploration because I can machine them down to a much smaller size and can directly braze them into the accumulator (as opposed to the brass ones used in the present design).