3D printed Pringles Can "Rear Eject Bomb Rocket MK II" Build Thread (3D printed "Kit" build)

[KenECoyote]

Hi Everyone!

I realize most don't have a 3D printer, but I figured this may provide some insight into this new facet of rocketry while being a build thread of a cool and unique rocket.

Summary: I found some cool Pringles Can rocket designs on Thingiverse and will be printing, building and (hopefully) launching it. If successful, I will try other designs.

3D Project Information and details: Rear Eject Bomb Rocket MK II by Aslansmonkey - Thingiverse

Obligatory Background story:
I got a 3D printer (FlashForge DreamMaker) about 6 years ago on a crazy Black Friday Special along with tons of clearance filament and had lot of fun making cool things along with my daughter, but never really got to use it for rocketry. I then had a lot of life changes...a major job change, my daughter leaving for college, my stepping away from rocketry for a bunch of years and so the 3D printing got mothballed. Additionally I was last having significant issues with the 3D printer (it was a dual nozzle model and one nozzle would drag across what was being printed by the other nozzle, ripping things apart...ugh).

Fast Forward to 2021 and I got back into rocketry - and I had missed it so! Then last month my niece reached out to me to print her some device for her Comicon costume and it got me to try to fix the 3D printer and I was successful. I thought I'd have to adjust the problem nozzle height, which is difficult, but instead I just lowered one side of the printing platform more than the other and that did it! DUH lol. Since then I've been printing some fun stuff and found some cool rocket designs for free download.

Pictures of completed 3D Project from Designer Aslansmonkey on Thingiverse (showing my end result goal):



Note: This will likely be a slow build (it can take hours to print just one part) and I'm not sure if I'll have it ready for my club's last launch, so thanks for your patience!

 

[KenECoyote]

Some important notes:

You need a 3D printer. For those not familiar, I consider 3D printing a bit like learning to cook/cooking...it's not just hit a button and bam! (at least in my case). It involves trial and error, temperatures, watching the thing print and often having to print something a few times before it comes out right. Also for me it takes a LOT of time. I'm currently printing a Pringles-size nosecone in standard definition and it's taking 5.5 hours.

With 3D printing using another's design, you often have to adjust for your printer and materials (I use PLA and ABS...PLA is easier, but not heat resistant and can deform in the sun, so ABS it is!).

I've found that many 3D designs/plans/kits don't offer a lot of instructions, so oftentimes you have to try to figure assembly and other things yourself. It is often helpful to look at the designer's other designs since earlier versions may give more detail and build steps and later ones skip that. YMMV

This rocket "kit" was based on the older Pringles can where the Pringles guy has a brown mustache and hair. The new cans use thicker cardboard, so if you're using that, you may need to reduce the size of the parts to 99% or so (read the designer's details).

Building a 3D rocket as well as a Pringles can rocket are new to me, so some things I'm learning as I go.

 

[KenECoyote]

My printer! I got it in 2016 on Black Friday Special for about $250 and thought that by now it'd be obsolete, but apparently it's still sold on Amazon for $500-$700!



I've already printed out the parts in ABS over several days...

I chose Purple ABS filament because that was the spool I could readily find and I planned on painting everything anyway. Plus it matched an "old" Pringles can I found at home!

Note about ABS printing: It's a bit harder to print than PLA since it needs a heated bed to print on and hotter settings on the nozzles. While a friend told me to use plate glass as a bed, I found that just using a glue stick (ordinary Elmer's School Purple stuff) works great! Yes, the secret to 3D printing for me is a glue stick LOL.

 

[KenECoyote]

Here's an example of things that can go wrong during the print. This was a new error for me...



From what I recall, this was a 3.5 hour print and it was going pretty well for a long time, so near the end I didn't check on it so much. When I did, to my horror, the platform (which automatically lowers as the print gets "taller"), had one edge caught on one of the filament rolls (which apparently fell off the spool holder and was pulled crooked) and so the platform was wonked seriously leaning to the right, causing the printing to be skewed. UGH.

 

[KenECoyote]

So I decided to print another nose cone and while it was printing, I tackled possibly fixing the wonked one. I then figured I can also add a bit more weight while fixing the tip so I can launch on bigger motors if desired. The designer also has an "F-Bomb" rocket that (last I read) he had only launched on Es and asked that if anyone launches on F/G to post, so maybe I can use this weighted nose cone for a future build of the F-Bomb.

First attempt to fix was to soften the tip over the stove (the filament is melted to form the item, so it can also be melted again to reform). That and using a putty knife worked pretty well to get the tip straighter, but there was a hole on top and I also had to file/sand. In between, I temporarily taped the hole on top, forming a "tip" of sorts and filled the inside with epoxy and some bb's.


NOTE: The weight/BBs and Epoxy are NOT needed for this build and I'm doing this for a separate/future project to make use of a poorly printed nose cone.

I then used Bondo to form more of the tip. I was planning on applying to the entire nose cone as surface filler to cover up the linear filament texture, but unfortunately I used too much hardener and it hardened too quickly...I was only able to cover maybe 1/4 or less, but I think I did the tip pretty well. Next I filed and sanded it to be more "tip-like". BTW it's amazing how a nose cone tip being a little bit off can be so noticeable... probably because we're so used to seeing perfectly formed/molded ones.

Here's what the "fixed" nose cone looks like and I'll be doing a bit more filling and sanding in the future followed by priming and then painting.

 

[KenECoyote]

Onto the actual building!

(Note: I'd suggest cleaning the Pringles can first to get rid of the oils so the glues stick better...not sure of the best way, but I used a paper towel dampened with a bit of dishwashing liquid and water mix and then wiped again with a paper towel that just had water. )

So a Pringles can has a metal bottom as well as a "fat lip" . I wasn't sure if I was supposed to cut them off or not. I first tried using a can opener on the metal end and then test fit one of the parts on that, but it wouldn't fit. I then messaged the designer on what to do, but already figured I'd have to cut both ends (still wanted to check since I don't know where I'd find another old Pringles can). The designer replied to cut off the ends with an Xacto knife.

So off with the ends!

 

[KenECoyote]

So with that out of the way, I wanted to start gluing...at least that's "building"!

Lacking step-by-step directions on hand, I decided to first tackle the most obvious and that was the nose cone and upper nose cone mount (remember this is a rear-eject model). Of note is that this design has a screw on/off type nose cone so you can add an altimeter.

Side note is that printing threaded parts can be tricky. Basically with 3D printing, melted material is layered on, so any overhangs need support of sorts otherwise it just falls and droops making a mess. I added "automatic supports" from my FlashPrint (software that came with my printer). It adds little balls or trees to support the overhangs. With threads, it becomes a bit of a mess and needs a lot of cleaning after. Still, the end result is worth it imo since it's cool

Here's an example of support trees added to an overhanging lip where you can also see some of the little support balls on the lower threaded section (nose cone for a future "Snake Eye Bomb" rocket from the same designer):


So I cleaned the threads, made a few test fits and then looked up glues for ABS...turns out it uses the same stuff most of us use - plastic model cement, epoxy and super glue all work! So I glued the "Nosecone_ScrewtopInner" to the "Centering_Ring_BT-60" using Testors plastic cement.

I should also note that I test fit these parts into the bt first. The Centering Ring was a little loose and the Inner Screwtop was a bit smaller than that.

 

[KenECoyote]

I then applied a bead of the same liquid cement to the inside edge of the nose cone and pressed the "Nosecone_ScrewtopOuter" in until it was flush with the bottom edge of the nose cone.


Next I added CA/super glue for an extra measure of "stick"...a few drops to the inner edge of both parts and then letting it drip while rotating the part allows it to flow/fillet in for a nice secure bond.



This step may be a bit out of sequence, but it's ok to do at this point...I sanded the nose cone shoulder until it fit into the bt (originally it was a bit big). I also filed and sanded a rounded lip so it's less likely to crush the cardboard edge that sticks up in this design.


Designer's pic of the same parts (notice the bt sticks up past the base of the yellow screw threads):


UPDATE & NOTE:
The design Build Notes mentions "1) The parachute attaches to a screw eye threaded through the center of the "Centering Ring" part, which goes on top of the BT-60 tube. Tie kevlar line to this and run it through the tube. This line WILL be exposed to exhaust gasses. I also used a piece of nomex cloth against the inside of this centering ring to protect the plastic. " I was going to follow this; however the pic above seems to show just a knotted piece of kevlar, which I think would be better and easier to replace, so I figured I'd go that route. I think the eyelet shown on top of the CR is for anchoring an altimeter.

 

[KenECoyote]

I then screwed the nose cone onto the CR/ScrewtopInner assembly in preparation of gluing it into the bt. I did a test fit and it was good.


Using a Dremel, I sanded a bit of the inside of the can (where the CR would glue in) to provide a better surface for the top CR to bond to and used some 6min epoxy.

BTW The hole you see below the nose cone shoulder is one of 4 and is meant to be vent holes for an altimeter and also serves as a drilling guide from the inside to drill the hole through the bt. Very nice!

So now I'm waiting for the epoxy to dry (make sure it doesn't drip down to the threads!). I have errands to run tomorrow, but will update when I work on this again. If you have any specific questions please post here or feel free to PM me; however note I'm far from a 3D printing expert.

 

[GlenP]

Very cool. Since the Pringles can is lined with foil, that might make a good ring-fin-can for an Augie type of ducted & CHAD staged rocket also.

http://www.spacemodeling.org/jimz/eirp_28.htm

 

[KenECoyote]

Very cool. Since the Pringles can is lined with foil, that might make a good ring-fin-can for an Augie type of ducted & CHAD staged rocket also.

http://www.spacemodeling.org/jimz/eirp_28.htm

Thanks and cool thought! While the foil is pretty thin, it should still be better than just plain cardboard tubing.

 

[KenECoyote]

I wanted to add that while the design is provided free to download and build (so awesome!), Thingiverse does have a button for you to "Tip Designer" and I try to whenever I can if I'm printing their design.

It supports designers you like and can also encourage them to make even more designs. If you think about it, the "kit" is pretty low cost* if you already have the tools and materials.

*This has actually been very helpful given I lost my job unexpectedly this year and now have less money, but more time. On the bright side I'm really enjoying this extra time!

 

[cwbullet]

Nice build thread.

 

[KenECoyote]

Just a quick update...

Remember me saying "make sure it (the epoxy) doesn't drip down to the threads!"?

Um...err...I may have had some epoxy drip onto the nose cone since it seems stuck.

I have a few ideas on how to "unstuck", but wanted to pass it along since it's one of the things most (almost all?) of us have come across while building rockets. Will report back later on this.

In the meantime, here's a pic of a dry assembly run of the main rocket using a BT-60 tube (sans rear-eject pod):

Does this pic make you hungry?

Side note is that I just realized that I should be accounting for the main chute retention...the last rear-eject rocket I built was the small Estes R2-D2 model, so I wasn't thinking about chute anchoring while I was working on the nose cone and upper CR gluing.

 

[KenECoyote]

I was planning on painting and finishing the rocket before launching it, but tbh I kind of like the way it looks now!

 

[KenECoyote]

Side note and my take on this design:
While I'm not a big fan of rear-eject pod rockets after my experiences with that old Estes R2-D2 (I wasn't crazy about the limited space for recovery as well as it being "fiddly"), in this case it makes sense imo. The end result of a good launch and ejection event is that the "bomb" comes down nose first on it's own chute and that looks very cool!

 

[KenECoyote]

Update on stuck nose cone!

So my plans today changed slightly and I was able to tackle the "sticky situation" .

I figured there wasn't too much glue that made it's way down since I was somewhat careful even though I still misjudged how much the epoxy would seep through. I had a 2-stage plan of attack thought out...

1) First I'll try these...a rubber strap wrench along with rubber gloves for grip. The strap wrench should work since the part I'm putting it on is supported on the inside by the upper CR and since that part is ABS, it's very strong (I wouldn't try this on cardboard CRs lol). The strap wrench should also prevent damage to the outer bt (unlike a pipe wrench, etc.). Luckily I was able to find Mr. Strappy - one of those tools that I have which I rarely use and when I need it I can't find it, but come across it every few years ....however the planets aligned this time and I found it!



If this doesn't work, I'll try the more extreme "2)" which would be to drill holes through both parts and using rods/screwdrivers, wrench them apart. This should be fine since I can easily fill in the drilled holes after.

However Stage 1 plan worked! Here's the result showing how a little bit of epoxy made it's way around a thin sliver of the bottom of the nose cone (still that was enough to make it require some heavy effort to twist it apart):



Woo hoo!

 

[Aslansmonkey]

Side note is that I just realized that I should be accounting for the main chute retention...the last rear-eject rocket I built was the small Estes R2-D2 model, so I wasn't thinking about chute anchoring while I was working on the nose cone and upper CR gluing.

There's a part called the centering ring. It should be on top of that inner tube. There is a little hole in that part that is there for you to put a screw eye. Actually, looking at mine I realized I just ran the kevlar through the hole and knotted it and skipped the whole screw eye, so you can do that too. The kevlar shock cord for the main chute runs from that part out the bottom of the inner tube and the chute attaches to a loop you put on the end of it. I used a kevlar cord leading to an elastic cord leading to the chute so I could use less overall cord length.

The motor pod has a middle centering ring and the main chute is meant to be folded and put above this center ring while the pod chute is folded and put below it. It helps to have a stick or something around when packing the chute for this thing, btw. Just makes it a little easier. When the pod ejects it drags out the main chute as well as it's own chute.

Sigh, here I am explaining it and the rocket is literally sitting within reach...lemme take a picture...

The original design just used a streamer on the motor pod, btw, and if the ground you launch over is soft enough, that's an option. But the pod falls fast enough that way that it will break if it hits something hard.

As a side note, I have plans to upscale this thing to a 29mm motored version, if I can get my son and grandson to drink Nestle's quick faster (because I'll need two cans for that idea). I may also re-design this kit some day to use readily available purchasable parts from Apogee and submit it to them as a design like I did with a snake eye design. This rocket could easily be converted to a "non-3D printed" design. But that's likely a winter project.

Right now I am working on a 13mm motor version of my snake eye rocket design, because I like the challenge.

 

[KenECoyote]

There's a part called the centering ring. It should be on top of that inner tube. There is a little hole in that part that is there for you to put a screw eye. Actually, looking at mine I realized I just ran the kevlar through the hole and knotted it and skipped the whole screw eye, so you can do that too. The kevlar shock cord for the main chute runs from that part out the bottom of the inner tube and the chute attaches to a loop you put on the end of it. I used a kevlar cord leading to an elastic cord leading to the chute so I could use less overall cord length.

The motor pod has a middle centering ring and the main chute is meant to be folded and put above this center ring while the pod chute is folded and put below it. It helps to have a stick or something around when packing the chute for this thing, btw. Just makes it a little easier. When the pod ejects it drags out the main chute as well as it's own chute.

Sigh, here I am explaining it and the rocket is literally sitting within reach...lemme take a picture...

The original design just used a streamer on the motor pod, btw, and if the ground you launch over is soft enough, that's an option. But the pod falls fast enough that way that it will break if it hits something hard.

As a side note, I have plans to upscale this thing to a 29mm motored version, if I can get my son and grandson to drink Nestle's quick faster (because I'll need two cans for that idea). I may also re-design this kit some day to use readily available purchasable parts from Apogee and submit it to them as a design like I did with a snake eye design. This rocket could easily be converted to a "non-3D printed" design. But that's likely a winter project.

Right now I am working on a 13mm motor version of my snake eye rocket design, because I like the challenge.

Hello! I read about the screw eye, but also studied the picture up close and saw the kevlar line with a knot used instead and personally felt that was a better option since it makes it simpler to replace the kevlar line if it gets too charred (I actually have a rocket that this just happened to). Sorry, I wasn't aware you were already on here (been out of the forums for a few years and only made it back this year and just in my usual haunts). I'll have to do some back reading!

Also now that you mentioned it, I vaguely recall reading about your Snake Eye bomb on one of the Apogee newsletters...here it is for everyone else:
Newsletter551.pdf (apogeerockets.com) . I had read it in passing and made a side mental note to maybe try it since I thought it was very cool, but my rocket-filled brain only held so much and had forgotten (plus that sounded like quite an involving build, so I put that on the long term "to-do" list). That explains why the SE design on Thingiverse seemed vaguely familiar to me. Also fyi that I've already started printing that one out...really love that and would like to try it as well after this one.

An upscale would be awesome! I normally test my designs in minature and upscale as I go. I think 29mm would be great. Last night I was actually wondering about a HP version of the Snake Eye...I haven't seen that yet and I'm sure it would be amazing and quite a sight at the field.

 

[Aslansmonkey]

The problem with the snake eyes is that they work great if the ejection happens VERY close to apogee, but they tend to take damage if the petals deploy at speed (either going up or down). I'm not a Tripoli member though I've been to HP launches locally. I'm more interested in the design process and have enough other expensive hobbies that I can't really jump into HP rocketry. But a HP Snake Eye would most likely need an altimeter tied deployment method as you'd have to be certain the petals deploy at the slowest speed range. That also means the rocket falls at max recovery deployment, so high flights would be problematic. Materials at that scale are all heavier as well. None of this makes it impossible, but the challenges are greater.

I find the larger I make them, the more prone they are to needed repairs, or at least need to be examined, between launches. The one I designed for Apogee Rockets functions the best and really floats on recover, but it's also the most prone to damaging itself. I expect the 13mm one to be the most robust since there is so little weight and the parts are really over engineered at that scale.

The Pringles snake eye seems pretty robust so far, though, but that one benefits from lessons learned on all the earlier designs. And I've only launched it twice so far.

An upscale of the rear eject bomb, on the other hand, should be easy. And you could use a drogue and chute release for recovery for high flights. Mainly I'm just waiting on the body tubes for that. Currently I plan to use two Nestle Quick cans for the outer body, a Pringles can for the inner tube, and a 28mm motor tube for the pod. There should be plenty of space between that motor tube and the pringles can for a 30 to 36" chute. Right now that rocket is in the "thinking" stage, though. For instance, I'm trying to think of a way to make it withOUT an ejecting motor pod.

 

[KenECoyote]

The problem with the snake eyes is that they work great if the ejection happens VERY close to apogee, but they tend to take damage if the petals deploy at speed (either going up or down). I'm not a Tripoli member though I've been to HP launches locally. I'm more interested in the design process and have enough other expensive hobbies that I can't really jump into HP rocketry. But a HP Snake Eye would most likely need an altimeter tied deployment method as you'd have to be certain the petals deploy at the slowest speed range. That also means the rocket falls at max recovery deployment, so high flights would be problematic. Materials at that scale are all heavier as well. None of this makes it impossible, but the challenges are greater.

I find the larger I make them, the more prone they are to needed repairs, or at least need to be examined, between launches. The one I designed for Apogee Rockets functions the best and really floats on recover, but it's also the most prone to damaging itself. I expect the 13mm one to be the most robust since there is so little weight and the parts are really over engineered at that scale.

The Pringles snake eye seems pretty robust so far, though, but that one benefits from lessons learned on all the earlier designs. And I've only launched it twice so far.

An upscale of the rear eject bomb, on the other hand, should be easy. And you could use a drogue and chute release for recovery for high flights. Mainly I'm just waiting on the body tubes for that. Currently I plan to use two Nestle Quick cans for the outer body, a Pringles can for the inner tube, and a 28mm motor tube for the pod. There should be plenty of space between that motor tube and the pringles can for a 30 to 36" chute. Right now that rocket is in the "thinking" stage, though. For instance, I'm trying to think of a way to make it withOUT an ejecting motor pod.

Excellent thoughts and observations! I hadn't given thought to the petal deployment having to be done at apogee.

On the current build, I was partially mulling over whether this design can be made non-rear eject as you've noted, but also realize it would be difficult without significantly changing it (ex. it wouldn't look like a bomb coming down on a chute). Plus I like to try to build something stock/as designer intended before I try a modification...despite how I carry myself here, I usually don't know better than the person who designed the rocket.

Also I agree with the notes about upscaling...on a small scale the materials are more robust and as you go bigger, you then have to take much more things into account. Size scales up easily, but strength doesn't scale up the same since we're not enlarging molecules lol.

 

[Aslansmonkey]

The whole beauty of this rocket is that it DOES fall nose first like a bomb. It could easily be converted to a regular rocket by using a centering ring instead of that bulk head at the top and just gluing in the motor pod. The nose cone would need to be altered a little to provide a shock cord attachment mount.

But the "F-Bomb" rocket I made out of a pringles can is pretty much the same idea and flies really well. It's actually the inspiration for this rocket as when I showed the F-Bomb to my son he said "Wouldn't it be cool if the parachute came out the bottom and it fell like a real bomb?" I say "Why yes, that would be cool." Then I looked around, noticed I had another Pringles can and a paper towel tube and too much free time and this rocket was born. I've since made two 13mm versions and an 18mm version, all rear eject. Because, too much free time, and I couldn't bear my 3D printer not making something, apparently.

I'm probably going to do a build thread on the 13mm snake eye because I've yet to assemble the thing and because the same principles work on all my snake eyes. Most of the steps will be posted at once, though, because I have all the parts printed.

 

[KenECoyote]

But the "F-Bomb" rocket I made out of a pringles can is pretty much the same idea and flies really well. It's actually the inspiration for this rocket as when I showed the F-Bomb to my son he said "Wouldn't it be cool if the parachute came out the bottom and it fell like a real bomb?" I say "Why yes, that would be cool." Then I looked around, noticed I had another Pringles can and a paper towel tube and too much free time and this rocket was born. I've since made two 13mm versions and an 18mm version, all rear eject. Because, too much free time, and I couldn't bear my 3D printer not making something, apparently.

Haha, great story! I actually find the fact that these are made of Pringles cans very cool. Being a maker, it's great when you can repurpose ordinary items (or junk ) into something pretty cool.

I'm probably going to do a build thread on the 13mm snake eye because I've yet to assemble the thing and because the same principles work on all my snake eyes. Most of the steps will be posted at once, though, because I have all the parts printed.

That'd be awesome and I'll definitely subscribe!

 

[Aslansmonkey]

I should have added that the reason this design is "Mk 2" is because the original design used a paper towel tube as the inner tube and as I didn't have any BT-50 at the time I made my own motor tube by wrapping some card stock around an E-Engine blank I'd designed. There was a lot of scratch building on that one. The Mk2 design uses a regular body tube instead of the paper towel tube. I still have the Mk1, but it's retired in the garage with no chutes in it. Technically it's still flyable, but this design is better.

 

[KenECoyote]

For everyone else, I'd like to add another cool facet of this 3D printed rocket...spray stencils are also provided that you can 3D print and use to add the lettering to the bomb, making that part MUCH easier.

Stencil for the nose cone:
.

Stencil for the bt:


I believe decal images are also available, but I think this is cooler. I have a built olive drab TLP Flail rocket that I've been wanting to add stencil bomb markings on, but haven't found the right stencils/font/etc., so this is so awesome to me.

 

[Aslansmonkey]

I don't know about the others, but I'm still waiting to see the finished model and see it fly!!

Any updates?

 

[KenECoyote]

(dupe due to bad connection)

 

[KenECoyote]

I don't know about the others, but I'm still waiting to see the finished model and see it fly!!

Any updates?

Hey! Sorry, no substantial updates because I'm currently away this week.

Will update next week and no worries because I do plan on getting one of your Pringles can rockets ready for my club's last launch early next month.

 

[Aslansmonkey]

Hey! Sorry, no substantial updates because I'm currently away this week.

Will update next week and no worries because I do plan on getting one of your Pringles can rockets ready for my club's last launch early next month.

Good to hear.

I'm almost done with that 13mm Snake Eye design...actually, I'm almost done with my second one. With any luck I'll fly them this Saturday then I'll post the thing and post a build thread on it (I took a bunch of photos building the second one). The second one uses only half the fins as I hope it helicopters down. I'll video the launches, of course.

 

[Aslansmonkey]

Hey Ken, when's the launch? Waiting on updates here.