High Power Rocket - 3 inch shipping tube by JRad

Last crawled date: 3 years ago

CAUTION You WILL need to add ballast weight to the nose cone tip to make this design stable. I fly a pretty heavy Arduino based flight computer in the front of mine, and I STILL need some ballast weight. I’ve attached the open rocket design I used for simulation so you can adjust and measure and simulate as needed.
All of these parts should print fine without supports (except my custom scaffolding on the fins) although you might have to rotate some of them. I print all my parts at 10% fill with ABS (even the motor mount) and I haven’t had any flight failures up to an H123 motor.
Here are the parts for the rocket I built to get my level 1 high power certification. It’s designed around an Aerotech 38mm RMS motor.
I would recommend dual deployment, but I did my certification flights without it, I just had to do a little more hiking.
Other parts you will need:
3” paper shipping tube for the body tube, preferably 36”.
6-32 countersunk screws x2 – for the rail buttons. I could only find 1/2” length at my HW store so I had to trim mine down.
6-32 t-nut. The kind that’s meant for furniture and brad nails (no teeth). These need to be made of really thin metal in order to fit into the rail buttons. Make sure to test fit the buttons before you go gluing them into place (made that mistake before). I’ve found the t-nuts at Home Depot are too large, but the ones at my local Lowe’s fit great.
Nuber 8 eye bolt for shock cord anchor. There is a hole in the front of the motor mount for it to screw into.
Shock cord – I just use Kevlar kite string from Amazon.
Parachute – Many options. I’ve flown with as small as a 12” ‘choute, but I did get some fin damage.
Quck-link – for quickly changing out parachutes. Make sure your shock cord and chute are both attached to the strong quick-link since the nose cone loop is not very strong.
Epoxy – lots of epoxy. I use 5 min epoxy for everything except laminating the body tube.
CA (superglue)
Ballast weight for nose cone – I like to use BBs and epoxy.
Order of operations:
Before you go printing a bunch of parts that may not fit, print the “3in – Test Fit” part and test it against your tube. There are two diameters for inside components. Loose for Nose cone, and tight for motor mount and ejection baffle. You should be able to scale the parts up or down a bit if need be.
You can slot the body tube with a hobby knife before, or after you glue in the motor mount. I usually do it before so I can keep the epoxy out of the grooves better, just be sure to wrap it in paper and wrap it tight with tape when you glue the motor mount into place so the airframe walls are firm against the mount. Slide the motor mount into the tube while slotting to support the tube so you don’t bend it.
Assemble the ejection baffle outside of the rocket with CA. Glue the baffle into the body tube with Epoxy so it is far enough forward that you can get your motor in w/o bumping it. It’s best if you feed your shock cord through the ejection baffle before installing it, but if you forget you can fish some thread through it w/ a small nut tied to the end and use that to pull your shock cord through.
Bend the 6-32 t-nut flanges so they match the curve of the body tube. Drill holes for the t-nuts. One should be near the end of the motor mount clearance slot, and the other should be somewhere near the front of the fins. First drill a small pilot hole, then put some CA in the hole and let it soak into the paper and dry. This will make the paper brittle so you can drill through it without tearing up the tube. Glue the t-nuts into place with epoxy. Screw the rail buttons on while the epoxy dries so that the t-nuts are pulled tight against the inside wall. Be sure not to glue the buttons on! They only last for a handful of flights before you have to replace them. Only use a little epoxy, you don’t want to block the motor mount from sliding into the airframe.
After the ejection baffle and rail buttons are installed you can epoxy the motor mount into place. Glue it together out of the rocket with some CA (superglue). Use the fins to align the two sections, but make sure there isn’t any glue in the fin grooves so you can get them back out. The #8 eye bolt anchor screws into the front of the mount.
Other assembly notes and hints:
Body tube – It’s just a simple 3 inch paper shipping tube. I pick them up at Office Depot, but any should do. I did my certification flights with nothing more than primer on my body tube. Recently I’ve been
laminating the tube with a good laminating epoxy (meant for fiberglass). The epoxy significantly reduced “zippering” of the body tube, but I still plan to try actual fiberglass laminating soon.
Fins – If they don’t fit into the grooves right off your printer, don’t fear, they usually don’t. The root tabs are designed to be just a little larger than the grooves so they can be sanded down a little for a nice snug fit. I usually just have to sand the bottom of the tab a little, and then clean up the long edges. I had a HELL of a time getting these fins to print without getting separation between a layer or two. I had to add some print bed anchors as well as support scaffolding to get good consistent prints. Using the right ABS makes a world of difference. Filament from Fillament Outlet on Amazon works great for me. I haven’t had a failed fin print since I started using that brand. I like the natural (white) the best.
It is also importand that the fins be printed so that the layer "grain" is parallel with the leading edge of the fin or they will snap right off.
I think the rest is pretty straight forward, but feel free to ask any questions in the comments and I’ll do my best to answer.
I’ve flown this design about 7-8 times now (including my two level 1 high power certification flights). I think it’s pretty well dialed in so that’s why I’m putting it out for other people to use.
ENJOY!
Jared
Video of a launch of this design:https://youtu.be/FuZghXuwPnQ