Bull Pup 12D

thingiverse

This is a more advanced build and will take a short while to make. This is a model of the Bull Pup 12D air to ground rocket. It is fully printable. It is balanced correctly as built. I have flown both vase and standard mode versions successfully. It is stable but it needs a C6-3 for the non-vase mode version. You can make it as a static model since it closely represents a scaled down version of the real air to ground rocket with the Estes fin alignment (nose canards dropped down). You can move the nose canards back up if you want it closer to the real one. Making the Bull Pup 12D with a 3D Printer This tutorial assumes you have simple hobby tools and CA glue This is a tutorial on how to print my version of the neat looking Bull Pup 12D with 18mm motor. Why? Well… because the commercial kits for this rocket are tedious to make and after you are done, you don’t feel like flying it and risking damage. This model is built in four major sections so a bad crash might still be recovered without starting from scratch. It is heavier than I like but it still is sexy. The decals on this model were made with a Brother label maker. It was a stretch in some cases but the result was still satisfactory. Since I copied the verbiage from the Estes model kit, I can’t repeat it here but there are lots of examples on the web of what to put on it. In the end, you may find it feasible to just buy the Estes kit (16 bucks on Amazon as of this writing) and use the kit decals. However, if you plan on flying this model, I would forego the decals for the first flights. All printing was with PLA with 100% infill for the motor can, motor can rings, and launch lugs. The nose cone was set to 0 fill (need the inside space for counter weight). Everything else was 20% infill. I used a .4 nozzle and .20mm quality with no special slicer options other than the infill. No supports were used for any of it. YMMV I made three fully functional ones. One is a static display and two are flyers. The first flyer was made with light weight PLA and then later in vase mode with regular PLA with the main tube made from PETG. The vase mode version made it very high on the C6-3 - the sim said 800 feet and I believe it exceeded that. There are some parts differences for PLA vs LW PLA vs PETG vs Vase mode so you may have to adjust. Nose Section Print the top body tube first so you can fit the nose cone. The tubes, motor and fin can and fins are all made with PLA or lightweight PLA (your choice). The nose cone should be printed with normal PLA and ZERO fill! The nose with zero fill has a thin membrane just inside it – you may have to break this and clean it off to make room for the clay/putty counter-weight. Orient the back piece on the slicer so the nose cone lugs are facing down. The nose section was made using the Customizer Model Rocket Nose Cone Factory (https://www.thingiverse.com/thing:3249782 ). I started printing it in red and then swapped color about 1/8” into the Ogive section. You can also just print it all white and use some Duck Tape (not Duct Tape) to make a red strip where the nose fits the main fuselage. Duck Tape is cheap and thin and makes acceptable pin striping. If you can’t get or order Duck Tape where you are, then use any thin colored tape. The STL for the nose cone is closed in the back. If you are going to fly it, you have to leave the nose cone open so you can put balancing putty (Sculpy, modeling clay, plumber’s putty or similar) in the nose to get the balance right. After you get it balanced, you can close the nose cone with the bottom sleeve shown above. Depending on your printer, the nose cone sleeve may be tight and might need to be filed so it is loose enough to come off easily. I used a Dremel sanding sleeve to shorten the work. Getting this section right can be tedious so put on your Maker Fu and take your time. After you get the weight in it and seal it up, the nose cone should pass the blow test – you should be able to blow the nose cone off with a puff of breath on the rear of the rocket. The amount of balancing weight is quite a lot so that will also dictate the motor you need to use. I used 1.5 ounces on the PLA only and 1 ounce for the Vase mode. EDIT: Use a C6-3 not a C6-5. The CG on the Estes model is at 7.1 (180.34mm) and the CP is at 10.36 (263.14mm) from the nose. The CP is about 3/8” from where the top tube mates with the fin can tube. Getting the CG right can be a challenge but close still works. Just try to be ~2 fuselage diameters from the CP.   Main Tubes The two main tubes are straight forward. No supports. The shorter of the two is on the bottom and it becomes the fin can. For flying, you need to tape the two tubes where they meet although you could also glue them. If you have decals then gluing is the preferred method. However, if it crashes and you destroy one of the main tubes, you will have to print both of them. DO NOT GLUE THEM UNTIL AFTER YOU ALIGNED THE TOP FINS WITH THE BOTTOM FINS (Last step). Motor Can The motor can is glued to the tail cone and NOT to the main fuselage tubes. The support ring for the tail cone is glued to both the motor can and the tail cone. There are two support rings – only one fits the tail cone. For flying, you need to tape the tail cone onto the fin can. Add a bit of CA to the top of the wire on the motor can itself to stabilize the wire. The motor can is printed with no supports. There is a hole that runs through the motor can that is meant to hold a piece of music wire that makes the motor holder. Note again that the motor can is only glued to the rear nozzle fairing. The rings are meant to hold it steady in the main tubes. When putting in the wire, bend the top part first so it locks into the two holes at the top. Then measure the wire, release it from the holds and bend it as close to the end of bottom of the can as possible and also bend it at an angle so it isn’t in the exhaust stream. The ring at top and bottom will hold the wire in (permanently). If the top ring is loose in the main tube, add tape (or wet the edge with CA and cure it - don't glue the top ring to the main body. Drill a hole in the top of the motor can and below the first ring and angled up at 30 degrees or so. This will be to tie a length of Kevlar line that goes to the parachute and nose shock cord. Bore the hole as close to the top ring as possible. 2mm or 3mm max. I have started putting a drop of CA on all Kevlar knots - I had two unravel on the same day. Fins Use a fin guide. One is included with the STLs that is from Thingiverse Parametric Hobgoblin Fin Alignment Tool (https://www.thingiverse.com/thing:5371861/files) and set to the right dimensions. Use CA glue to put them on. After the glue is set, go back and run a thin bead on each of the fin roots Do the bottom first and then assemble the tubes and do the top. The top fins go to just the edge of the top tube. The bottom fins are set 19mm from the bottom of the bottom tube (not from the tail cone). Twist the two main tubes until the bottom and top fins align. Now you can glue the two main tubes together if you want.   Finally – If you are going to fly it: EDIT: Use a C6-3 Print out a couple of lugs (included in the STLs) and glue them – align them for your launch pad. Go over the edges of the lugs that are touching the tube with another bead of glue after the first coating of glue sets. Thread a Kevlar cord through one of the holes in the motor can or drill a 2mm hole in the top support ring. Tie a knot, maybe like the one above, so it can’t go back through. Put a bit of CA on the knot - Kevlar likes to unravel normal knots.Give yourself at least 12 inches of Kevlar, add a foot of elastic for shock cord, thread it through the main tube and out the top. Tie the elastic onto the chute and a string to the nose code from there. Use your favorite method or look up how with just about any Estes model. Use at least four or five squares of fire proof wadding so that it covers the inside seam where the two main tubes are joined. This rocket made with only PLA and not vase mode is heavy (5.2 ounces wet) so it requires a bigger chute. I would recommend something in the 15 to 19 inch range. That may need tweaking but it should get the rocket down safely. You can tweak it after you fly it the first time. The Vase mode version (made with PETG) is almost 2 ounces lighter and only requires an ounce of counterweight. It will fly well on a B6-4. Vase mode main tubes will warp on the first flight unless you make them from PETG and insert a few turns of heavy typewriter paper inside the tube. Have fun! PS: If you have trouble with any of these parts, please advise me. I've made five or six of these and I have a slight variation of each one. The STLs included will work but you may have to tweak them a little. Be patient - the model will fly well.