Modular 3D Printed Rocket, 2" tube, payload nosecone, C/D/E motors

UPDATE 2025-08-26: watch this space. DO NOT PRINT THIS YET. I am in the process of test printing the new engine retainer pieces and tail fin cans, and am actively adjusting the fit tolerances to make it.... actually possible to use. The ideas seem to be sound. The parts tolerances., not so much.

UPDATE 2025-08-25: I've added a second fin-can with 38mm fins vs. the original 50mm fins. This brings the stability just below 2 cal (assuming a small beanie baby keyring sized payload in the nosecone payload module). The original stability would have likely been prone to weathercocking. Without a payload, the 50mm fins are just over 2cal.. so, some weathercocking still possible.

This started off as a remix, to include a payload bay, and then grew into a full clean slate redesign based on the ideas of the original rocket I downloaded here in the first place. so... while the look is similar still, and you will see many similarities to the original, no STLs are from that source anymore, and all parts were modelled from the ground up in cad/cam for this 'remix'. But credit where credit is due, so inspiration is at https://www.thingiverse.com/thing:8754 and this is tagged as a remix nonetheless.

Preface: I have no idea what I'm doing. I say again, I HAVE NO IDEA WHAT I AM DOING. Mostly. But if you fly this, you are absolutely doing so at your own risk. I have not flown this yet, due to... real life, and OCD levels of wanting things to be perfect first, and such.. so If you do leroy jenkins your way forward and fly it before I do, I suggest you start small. ie: maybe a C6-3 or something. Open Rocket suggests this should be stable-ish, but real life has a way of not always following the simulations. The plan is to eventually, after a few training hops, absolutely send it with an E12-6 motor, which... according to the various motor simulations in OR, and some conservative weight estimates... should give it a solid 230m+ altitude. Or it may veer off sideways into the crowd. Remember that "at your own risk" bit I said up there? This very much applies. With a C11-3, it should do about 45m. You don't want too much delay, or it may not deploy chute until it's already hurdling its way back to earth at high velocity.

So... Why remix the original? My daughter has a tiny stuffie giraffe. She loves it, and it can do anything. The stuffie has, in fact, now started its own space program, and this is it's first training rocket. The re-design for this started simple, just adding a payload nose to the original on thingiverse, but as real life kept holding me back from actually building it, I just kind of kept adding more and more features at silly hours of the evening after everyone had gone to bed, and.. It sort of turned into it's own entirely new beast now. And yes, I'm fully aware that most of the features here are.... probably completely pointless.

I'm just hoping it goes better than her first couple of Kerbal Space Program rockets. (and so is she, she loves that stuffie).

Intended (and modelled in OpenRocket) for 5 mid-section modules, one nosecone payload bay for said tiny stuffie to travel in, and one tailcone / motor mount assembly of course. I've seen some people build the inspiration rocket with a mid-section fin-can to look all cool like an air to air missile. I don't suggest you do that, ORK suggests it would be wildly unstable.

I'd like to modify the diameter transition piece to hold a tiny action camera, but... work in progress.

I've used a baffle to make the ejection charge parachute-safe (ish?), vs. using lots of wadding. I read something somewhere that this was an option, so.... I decided to design one and try it.

I also made some attempt at cooling the motor mount assembly. it looks pretty slick. But.. I doubt it will be remotely effective. Most of the heat transfer from the motor into the printed parts would be after parachute deployment, during the long float back down to earth, until you are able to rip the hot spent motor out of it. With the low airspeed there, it probably won't have much airflow actually moving through the cooling channels. But I like the look, so I'm going with it. This may be a fly-once model, due to heat damage to the printed material. We shall see.

I'm intending to use a piece of bent wiper blade insert as a motor retaining clip. There is a cutout for it in the screw-in motor mount. small bend at the top to catch on the motor adapter, small bend at the bottom in the opposite direction to hang onto the motor itself. You will also need some 2/2.5mm wire for the parachute loop that passes through the ejection charge baffle. Both that pin, and the motor retaining clip are modelled here, but.... do not print them. Unless you want a template to bend your metal parts against for comparison. The metal clip supplied is for 24x95mm engines, ie: E11 series.. some D's and some C's. For 24 x 70mm or 18 x whatever's, you may need to make an adapter or something for now. I'll get to it myself and add some here at some point... just... not right now.

I'm planning on sewing a pair of hemispherical parachutes from lightweight kite-fabric. This ridiculous insistence of mine that everything be super-slick is why this thing hasn't taken off yet and my daughter will probably outgrow her stuffie before it ever does, but you may be less discerning and do just fine with a half garbage bag or something.

And, one caveat. Today I glued an early PLA test print of this rocket together that had been sitting on a shelf with the sections just friction fit together for the past 2 years, being played with intermittently. It seems the thin-wall design versus the original I remixed it from has cracked a bit at the tight overlap joints. Now, it was just friction fit together for display, and was getting played with intermittently by a 5/6 year old for several years, so... maybe it's not as big of a sign of weakness as I think it is, but... buyer beware. This is a thinner-wall rocket for weight savings versus the original I remixed from. I wanted it lighter, but... we'll see if it stands up to the rigors of actual flight sometime soon I guess.