Winner of the Instructables 2016 3D Printing contest!

The Arcus is a fully 3D printable rubber band Gatling gun that is capable of delivering 48 rubber bands downrange in mere seconds.

Unlike almost all of the other rubber band Gatling guns out there The Arcus uses the energy from the rubber bands that it is shooting to spin the barrels. The Arcus also features the arm mount system, meaning that to hold it you put your arm through the center and the barrels will spin around your arm. A cam system is used so that when you pull the trigger the barrels will start the rotation.

All of the parts are designed to snap together, no screws or glue will be required, because of this it can be taken apart and reassembled as many times as you want. The only other thing used in the assembly besides the printed parts is rubber bands. All of the parts are designed to be printed without any supports, and all the parts will fit on a print bed of 200mm X 200mm. This assembly is designed to work with #64 Rubber Bands with six Rubber Bands loaded onto each firing block.

Here are some articles that have been written about the Arcus:






My Settings for printing:

Printer: Ultimaker 2

Material: ColorFabb XT White

Layer height: .15mm

Wall Thikness: .8mm

Fill density: 25% (unless otherwise stated on the part name)

Nozzle size: .4mm

Step 1:

Print all the parts. The file name says the number of times that part is to be printed. Some of them also say a cretin fill setting, If it does not say a fill setting then it should be set to 25%. After printing clean off all excess burrs and bumps. All of the parts are designed to be printed in the orientation that they are set in the STL's

Before printing make sure that your printer is calibrated correctly and is printing true circles, the bearings will not work if it is off.

Step 3:

insert 8 of the Bearing Wheels into the Back Inside Plate

Step 4:

Put the Cam Stick into the notch in the Back inside plate and then put the back outside plate over it.

Step 5:

Put the Back Plate Top onto the Back outside Plate and then put the clicky ring onto the posts of the back outside plate

Step 6:

Insert the Temporary Holders into every other hole of the Back outside plate. These will not be part of the final assembly but are needed now to hold everything together.

Step 7:

On the back insert the two Long Screws through the Back Bracket and then through the back inside plate, the slot in the Back Bracket must line up with the Cam Stick. Then insert two Short Screws through the other two holes of the Back inside Brace.

Step 8:

Insert one of the Cam wheels into the bottom hole of the Cam Stick.

Step 9:

Slide the Cam Holder onto the four screws, the Cam Stick must line up with the slot on the Cam Holder. Add a cam wheel to the top part of the Cam Stick.

Step 10:

On the Cam assemble the Cam Pusher Holder and the Cam Pusher Insert.

Step 11:

Insert the Cam Pusher Spring in the notches in the Cam and the Cam Pusher Insert. Push a Small Pin through as shown to lock the assembly together.

Step 12:

Insert 4 Cam Wheels into the side of the Cam Holder. Slide the whole Cam assembly over the Cam Holder, the Cam Wheel on the top of the Cam Stick needs to go into the slot on the inside of the Cam.

Step 13:

Insert 4 Cam Wheels into the last 4 outside holes of the Cam Holder.

Step 14:

insert the Cam Wheel Holder and then the 4 Core Bars. The Core Bars will only screw in on one end.

Step 15:

Install the Trigger Bar using a Small Pin. Make sure that the notch is pointing down and is at the back as shown.

Step 16:

Slide the Front Outside Plate over the 4 Core Bars and let it hang lose for now. The flat on the Front Outside Plate needs to be towards the back.

Step 17:

Insert 4 Short Screws through the Front Inside Plate and the Grip as shown.

Step 18:

Install the assembly onto the 4 Core Bars.

Step 19:

Use the printed Tool to tighten the four short screws.

Step 20:

Insert 4 Bearing Wheels into the holes in the Front Inside Plate. Slide the Front Outside Plate forward onto the Bearing Wheels.

Step 21:

Install the Trigger and connect it to the Trigger Bar using Small Pins.

Step 22:

Attach a Rubber band to the two notches on the Bearing Wheel Holder and the notch on the Trigger Bar.

Step 24:

Insert the Star Bearing into the Star.

Step 25:

Add the assembly to the Firing Block using the Big Pin. The pin will not snap into anything yet.

Step 26:

Insert the Rocker into the Firing Block and secure it with a Small Pin.

Step 27:

Screw in the Outside Bar and the Tip. They should line up as they are shown in the picture when the are fully screwed down.

Step 28:

Insert a Rubber Band between the notch in the Rocker and the front part of the Firing Block as shown.

Repeat steps 24 to 28 till you have all 8 of the Firing Block assembles.

Step 30:

Insert the Brace onto the post on the Back Outside Plate. The Brace has a short side and a long side, the long side needs to go onto the post of the Back Outside Plate.

Step 31:

Install the Firing Block Assembly as shown in the video.

Step 32:

Push a Small Pin through the Tip and The Front Outside Plate.

Step 33:

Push a Small Pin through the brace and the Firing Block

Repeat steps 30 to 33 until all 8 Firing Block assembles have been installed.

<p>So I finished my first Arcus, and it works fairly well, but I do have a quick question. All the wheels fit tightly in their assigned holes, they fit but are too tight to spin. Should the wheels fit tightly or should I open up the holes so that they can spin?</p>
<p>They should be spining freely in the holes. Try cleaning out the holes with a Xacto knife or something.</p>
<p>I've been printing Darth Vader Heads and Creepers for too long. I didn't realize how badly my printer is calibrated. Looking forward to dual arm mounted rubber band cannons!</p>
<p>Does the Cam Stick need to be able to slide freely through the Back Bracket, or is it tight by design? I can't wait to put it together, but I've already tried once, and at the step installing the trigger, I realized that my Cam Stick was very stuck and would not move when I pulled the trigger. But even after cleaning/sanding the Cam Stick and Back Bracket, it's still tight. Please let me know. Thanks for this design, we can't wait to use it!!</p>
It should slide freely through the back bracket I'm not sure why it is tight for you. Are all of the other pieces fitting for you?
Yes, so far everything else has fit pretty well. I guess I'll sand/cut the bracket more to allow it to slide through. Is there a reason the tab on the Cam Stick is a bit curved?
Yup it is curved for a reason. Hope that the extra sanding works for you, let me know if you have anymore questions.
<p>What's the reason? Thanks!</p>
<p>It engages the rockers to fire the rubber bands</p>
<p>I don't have a 3D printer but my local university has a couple of 3D <br>printers that people can use and they charge by the gram, so I was <br>wondering what the complete weight is</p>
<p>Its pretty heavy lol my scale says 1090 grams</p>
<p>$109 -_-</p>
<p>So I stumbled onto this a couple of days ago and I really want one. Unfortunately I don't own a 3D printer and I certainly don't have the thousands of dollars to order the parts online. Does it REALLY cost that much to print stuff? I'm trying to see if I can find a place here in San Diego that rents out the printers, but I honestly don't know the first thing about printing.</p>
<p>Who quoted you thousands of dollars to print it? That seems like way too much.</p>
<p>I still haven't heard from the local prototyping companies yet, but I'm hopeful that I can find a better price from a local source rather than those crazy online prices.</p>
<p>I tried to load it to 3dhubs, based on calculation there usually cost like that.<br></p>
<p>Wow I just checked it that way too! that is a lot lol ive never had a need to use that service so I had no idea. Check your private messages ill see if we can work something out.</p>
<p>Waiting for long enough rubber bands<br>material PLA (0.15mm layer height)<br>printed by ATOM3dp 2.0</p>
<p>Looks Good! How does everything work with PLA? I havent tried making it with that material yet.</p>
looks fine, my friend already running it with PLA.<br>I am still waiting for the rubber bands from him.<br>The only strange thing is outside bar &amp; tip.<br>The tips screw tight but not at the right place.
<p>How far off is it?</p>
<p>From above photo, it's already tight.<br>But still need about maybe 30~60 degree tighter to near the expect place.<br>It's 100% print , but looks got similar case like above comment that shrinked?</p>
<p>Works awesome, so fun!</p>
<p>Looks great! glad that you like it and thanks for sharing!</p>
<p>Thanks buddy =)</p><p>http://bastienbonard.org/?p=16235</p>
<p>Looks great! Thanks for sharing that :) How does it shoot?</p>
<p>I worked a bit on this model to achieve a slightly better result than ricku425. I cleand/drilled/sanded/greased a bit but I think there should be maybe 1/10 mil of mechanical constraint everywhere so it is easily stuck as it is meant to fit perfectly.<br></p><p>But I manage to operate it (a little movement of the wrist) pretty well and one handed, not as nicely done as on your video though...</p><p>Thanks again for everything!</p>
<p>NICE! job.</p>
<p>I couldn't get mine to fire like in the video. There seems to be a crap-ton of friction. Only way to get it to fire was to manually rotate it while pulling the trigger. Then I'd have to manually rotate it in the other direction to get the Cam to spin. All the parts seem to have plenty of &quot;play&quot;, and move really smooth and easy when putting it together. However, put a little tension on the parts, and everything freezes up. Dunno what's wrong, but at least it looks nice.</p>
Hmm did you make sure that all of the extra bumps and burrs where cleaned off of the peices before you put it together? The only other thing I can think of is if your printer is not calibrated correctly and not printing true circles that would make it not spin as well
<p>Circles are +/- .010&quot;. Not sure how accurate it needs to be, but I though that was pretty darn close. Perhaps the next step is to disassemble the entire thing and sand every surface until it's glass smooth, and then wax everything?</p>
Yeah that would be good to try. If you could find out where it is binding that would help. I had it bind on one of the wheels in the cam but I took it apart and cleaned out the cam track a little and it worked a lot better.
<p>what is the best way to screw in the outside bar and tip into firing block?</p>
<p>You should screw both of them down until they are tight. They should end up in the orientation that they are in on step 27 if they are a little bit off it should be fine.</p>
thanks, but when i do that it end up in the wrong angle
<p>Hmmm do you have a picture?</p>
<p>ok , so the tip is not aligned properly as it would be getting in the way of the rubber band...</p><p>btw i scaled all the parts down just a little bit so some of them could fit directly on the heatbed.</p><p>so maybe that affects it????</p><p>thx</p>
That could be the reason for it not working, I had to play around a lot with those threads to get it the right way so if you scale it that could mess it up. I would suggest if you are able to design simple parts that you make a washer to fit in between on of the two points, start with like 2mm and keep on changing the thickness till it looks right. Hope that helps.
<p>ok thanks very much , very helpful!</p>
<p>Ok, everything is mounted but I have troubles... Lots of friction and two questions:</p><p>- why my core isn't spinning when firing?</p><p>- how to put more than 1 rubberband per firing block?</p><p>I made several pictures for you when it's finished =)</p>
<p>OK I made a video showing how to load it up let me know if that helps you!</p><p>https://www.youtube.com/watch?v=fGZw29fSg4Y</p>
<p>you're perfect :)</p>
I'm gonna post a video soon of the loading process, there were some other people that were having trouble with that as well
<p>Thanks a lot!!</p>
<p>Hey, would this work well in PLA. My printer will do all the specifications but the only filament on hand is PLA, any suggestions?</p>
<p>I dont see why it wouldn't work with PLA, I haven't really used it that much myself but I think it should work. The only thing that might be a problem would be the small printed spring that is used on the cam clicker. PLA can be brittle so I would suggest you print out the spring first and see if it would work as a spring or if it just breaks. It should only take you like 2 minutes to print it out. After that I would suggest that you print out a full firing block assembly and make sure that it can hold the tension of 6 rubber bands. </p>
<p>I am printing the complete gun in PLA at the moment. nearly finished. I will report back if there are any issues. I have printed the spring and it seems to have enough flex. I do have some ABS handy if I need it thankfully.</p>
<p>Looking good! I like those colors! let me know how it turnes out.</p>
<p>waiting on rubber bands from Amazon. PLA seems to be working just fine. I had to sand the short and long screws to have them fit better (easier) i may also have to sand the star bearings or pins to have them spin more freely</p>
<p>So, having printed and assembled this beast, it isn't very obvious how one loads it with more than one elastic per &quot;gun&quot;. Can you please elaborate on the actual operation of the arcus once built?</p>

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