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Model Rocket - B & C Engine Size

by NEATman, published

Model Rocket - B & C Engine Size by NEATman Dec 27, 2011

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UPDATE - I've added "Rocket 2 - Payload.stl" It's the same size rocket, but with a payload section at the top. It also has a new lighter weight motor retention system, made from a cleverly bent large paper clip to keep the weight down. To assemble, straighten a large standard paper clip. Bend the "U" at one end, insert downward, from the nose cone end toward the tail end. Then bend the paperclip out sideways, and add the knee bend and loop at the end. It acts like a torsion spring to retain the rocket motor.

I tried unsuccessfully to properly print out the rockets that were here on thingiverse, so my son and I designed our own in solidworks. I think it was mostly due to learning the limitations of our TOM, and not a problem with the existing designs. You will notice that this is a "all at once" print, where you print the fins, tubes and nose cone all at the same time. There are connecting ribs between the parts so that the fin section will stabilize the other tall thin parts - you'll notice in one of the pictures that the print failed near the end when the tall skinny tubes were tilting around on the ABP conveyor belt.
It is currently just a simple design, but I hope to design a version that will include a mount for a "Spy-pen" camera to take video, and possibly one that will launch gliders when the nosecone is ejected, perhaps a propeller retrieval option for the nosecone - and any other wild ideas my 4 & 7 year olds come up with...
This was printed on a Thing-O-Matic, with a MK6 extruder, ABP (which made the first attempt unstable), the layer height is .35mm, feedrate of 30, and we used white ABS so the kids could color the sections with markers.

I have added a STL without the connecting ribs - just make sure you have a solid foundation - the incomplete print in the pictures was because the conveyor belt on my ABP was too "floppy" when the parts got that tall.


1.) Download file & create g-code
2.) Print parts
3.) Trim away connecting "webs" - these add stability during printing
4.) Assemble - glue sections together, leave nosecone a light friction fit (sand as needed) - Paint if desired - use 2 drywall screws for the original design in opposing holes to secure the motor - use one of the remaining holes for the guide rod on the launcher. For the newer design, bend a large paperclip as shown.
5.) Launch! (if you lose/break/destroy it, repeat steps 2-5)

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is any one elas have the payload like tiny if so do yo know what to scale it to to fix it

Hi, nice model!

Are you able to upload the individual parts for Rocket2-Payload-_no_supports.stl ? I want to scale it up but then I can't print all pieces at once.

Comments deleted.

Is this an 18mm mount or a 24mm mount for the motors?

It is sized for a B or C motor, Ø18mm x 70mm long.

how much would i have to scale it so it can hold 24mm motors?....

24/18=1.333333333 It was a tight fit at 18mm, so you should probably scale it up by 1.35 to have a little more clearance. The trick is, the 24mm motors are also 70mm long, so if you scale the whole thing up by 1.35, the motor will enter into the tube too deep. If you only scale X and Y by 1.35 and you don't scale the Z axis, it should be the same height rocket, but bigger in diameter to allow the use of the D size Ø24mm x 70mm long motor. I found the dimensions for the different motors listed here: https://www.apogeerockets.com/Rocket_Motors/Estes_Motors
Interestingly enough, if you want to try this rocket with E sized motors, Ø24mm x 95mm long, you should be able to scale all three axes by 1.35 and get a Ø24mm hole that is 95mm deep.

I was going to put a G in it so I don't kind the z axis.

Really nice model, do you know the stability margins? I would like to know how stable it is. But it seems great!

Great parts, but it would be nice if on the non-payload rocket, there was some kind of a mount for the parachute built into the body tubes., like the payload one has.

Can you post .stl versions of the individual parts please?

I finally got around to editing the footage and posting it on you-tube. There is a link in the 'about' back to here. The actual launch is 26 secs in, prior to that is some build shots on our Uprint.


It's all fixed up again and ready to fly, modified with Superglue rather than d/s sticky tape !!

We printed a 'fresh' version which has been sent down to the Science Museum in London and should be on display in the Autumn with a credit to NEATman :)

Thanks for sharing the video & pictures David.
The superglue should do a far better job of holding it together. I have had great success solvent bonding ABS together with acetone as well.

Very happy and honored to hear one will be on display in London.


Hi NEATman,

A photo of the finished rocket from our uPrint:


The flight went well except for the double sided sticky tape fail which meant it did a core sample. Despite a 200m fall the tube was undamaged and I've redone the elastic and will fly it again when the weather clears.

NEATman - can you drop me an email on [email protected]://-alchemy.co.uk-alchemy.co.uk - A major UK museum has asked us for 3D Printed objects for a display they are working on and I wanted to credit you if we send a print of the Rocket.



Hi David-

First, Cool website - You have got some great machines there!
Where I work, we have several 3D printers, Stratys, Objet, EOS & a new metal SLS machine! Unfortunately, I can only use them for business related projects. At home I only have a old Thing-O-Matic, which explains the build envelope of this rocket.

Happy to hear you have flown one of these, and very impressed to hear it created a core sample and survived!

Second, I sent you an e-mail earlier today with my contact info. I would be honored if you included one of my models in a submission to the museum.



Cheers. Thanks for the email, I've replied. Looking forward to the other project you mentioned !

I printed this on our U-Print and it's come out very nice. I'll link to some video when I get chance to fly it.

clips to hold rocket engines are the product of an old way to do things. How about making a holder that is merely slide and lock or a barbette mount such as insert and twist to lock (artillery is done this way) Try just printing the holder in!

While the clips are an old way of doing things, I thought the use of the large paperclip as a torsion spring was a novel and lightweight way to retain the motor. I've never seen that design on any other rocket. I agree, that a printed solution would be even easier. Feel free to make a remix or derivative of this model. Let me know if you would like a STP or IGES version of the files.

RepG states there is a hole in the triangle mesh. Seemed to generate fine, though. Rocket 2 Payload No Support.

Thanks for letting me know. I didn't see that with Replicator 47, and it seemed to print well on my machine, and old ToM running Sailfish.

I printed and flew this rocket (actually several copies). Of five launches, we had two successes, one lawn dart, one lost in the distance, and one stuck on the pad. Here are my observations:

1) I printed this on an Up, with 0.4mm layers in "fine" mode. On those settings, the fit between the body tubes was extremely tight. I snipped off most of the coupling at the top to ensure the nose cone would pop off properly.

2) Attaching the shock cord to the inside of the body was a challenge.
Eventually, I just jammed it in one of the body joints (making it even tighter). Worked just fine.

3) The holes for the launch rods are marginal--they should probably be closer to 5-6mm diameter to ensure the rocket doesn't get hung up on the pad. The launch lugs on kit rockets are actually pretty

4) The rocket diameter is too small for even a small parachute. I used a streamer.

5) I had to add a lot of weight to the nose cone for stability. Be sure to do a swing test before launch. Good news is that it's easy to jam play-dough into the nose with a pencil eraser.

5) If you launch t
his with a "C" engine, YOU WILL NEVER GET IT BACK. :)


Great looking prints
amp; Great observations.

I haven't launched one yet - too many other priorities
amp; nasty New England weather, but I have a couple printed and waiting for next month when I head to a frozen lake for a launch. It worked out last year, just a bit of snow-shoeing involved in the recoveries. I should post a picture of the launcher we made - it attaches to the top of our tripod so we can angle the rocket into the wind, ans it also gets the tip of the rod up so high that no one can poke out an eye!

1.) Tight fit - It is modeled line-on-line (no clearance) and depending on how the different machines print, it could make for a tight fit. I had to do some light sanding to make mine fit before I glued it.

2.) I should add a rib across the tubes to attach the shock cord. Although, jamming it b
etween the tubes works! I did the same thing...

3.) I had already increased the diameter of the lug holes to match an Estes rocket I have - perhaps I need to go a little more on two of the holes - if all four are enlarged, a larger screw would need to be used to retain the motor.

4.) I was als
o planning on using a streamer - I should have mentioned that. Oops.

5.) I also didn't do the balance test - the weight of the fins
amp; motor at the back and the equal density tube through the middle section would make it quite tail-heavy as you observed. The clay/play-dough in the nose cone trick is a great suggestion.

I had better print more, as I have a bulk box of "C" engines - and I'm not buying more engines until they are gone!


Good stuff. Please be mindful that as one is pushing the boundaries, the law of man (in this case as promulgated by the FAA), might bring you back to earth.

I love rockets, and have made many custom rockets and parts, but after a few incidents of nose cones not seperating and parachutes not deploying, you really take stock of the missile that is coming down that you have no control over.

In doing my due diligence, retrospectively of course I came ac
ross the ignorance of the law that I was in ignorance of.

Basically, two thing to be mindful is that per 14 CFR § 101.22 (a) Class 1—Model Rocket means an amateur rocket that:...... (3) Is made of paper, wood, or breakable plastic;

§ 101.23 General operating limitations. (a) You must operate
an amateur rocket in such a manner that it: ......(4) Does not create a hazard to persons, property, or other aircraft.

Anyway, I would say adding a Section 4a stating that weights should kept light and the rocket should be able to be crushed if someone accidently sat on it, and maybe stating that
this is only for use a Class I rocket. A Section 4b would delve into what recovery systems are suggested for use (or how one would go about implement it).

I hope I did not kill the buzz. It really is exciting and I too hope to add some designs. I mean imagine, no more have to glue tailfins. And fo
r every rocket made/launched the enigine is the most expensive part.

Just -

Not a buzzkill at all.

Thanks for the disclaimer reminder - Users of this rocket must follow all of the standard rules of Estes model rockets - I believe that the rules come in every package of rocket motors.


Actually it's the NAR safety code, and local laws and ordinances. In CA we have to get a fire permit to legally launch, which is why the clubs are so popular.

Can you add an STL file that doesn't have the connecting ribs.

It's almost impossible to separate the pieces.

Fantastic Work!

Being able to print rockets was one of the reasons that I got my printer - I just haven't designed any of my own yet.

I am curious to see how they will scale - Is printing an HPR rocket possible?

Skeinforge 35 doesn't seem to like this STL very much. Even after running it through Cloud.Netfabb to repair the file, it still is choking on it. :\

Please try the latest uploaded file - let me know if it works for you.


I flew both small and large model rockets (E class engines and higher) so a couple notes:

1) You should spec slow dry epoxy (1 hour+) or stronger cement for bonding the pieces together, or else the rocket will not survive the engine's ejection charge.

2) I would probably recommend only printing this in ABS, not PLA, especially anything near the motor area.

Looks neat otherwise!

Considering that most epoxies will NOT adhere to ABS I would recommend using ABS cement or acetone. It softens the plastic and allows it to permanently adhere to other ABS. Too often I have used even slow dry epoxy to only have it break the first time there was ANY stress on it.

This looks great but I'm having a problem with the scale. When I import it to RepG it's tiny. When you export as stl from Solidworks make sure the scale matches the drawing. Could you upload the Solidworks file? Looking forward for this build.

OK - I had uploaded an older version that had not been converted to inches, and I rotated it and centered it on the build platform. Please let me know if this latest version would work for you - I did the scaling, rotating and moving within ReplicatorG-0025. Also, see the attached solidworks assembly and parts. Feel free to modify to suit your needs.


neither skeinforge (SFACT) or slic3r seem to like this STL. Both return immediately for me. Anyone else having better luck?

Do you have an OpenSCAD file for this?
thanks! hb

There is a small problem in the 'skin' and 'comb' plugins in the latest replicatorg (skien 47).

It's a known bug, and a solution has been found. If you're brave enough to edit the python code:

If you edit the file

On line 149 it says "end = self.boundary.segment[1]", as far as I can see
this should be "end = self.segment

This code normally never seems to trigger, only when there are really small
or thin areas to be found.

Hi hb-

I used ReplicatorG-0025. I had to rotate and center it - I'll try to save and upload that version now. This was modeled in SolidWorks 2007 - I could post that format, or any other that SW07 can save - let me know what would work for you.


Yeah holy crap I'm going to have to start buying model rocket engines again lol

Any designs for a printable launchpad base?

Nice build. I will print in the next few days. Well done.......... you enabler.......