3" Wildman Darkstar Build - Brightstar
This project was the second Wildman Darkstar rocket I built. Since I painted it bright yellow, I dubbed it Brightstar.
The Darkstar line of rockets is very popular for a lot of reasons. They are easy to build, fly wonderfully, look cool and, usually, have a distinctive whistle during the boost phase.
This project was built as a standard dual deploy rocket with a primary and backup flight computers.
Parts List and components
Initial Build Notes
As noted on the Darkstar fron page, you need to check all the ends of the tubes, etc, for smoothness. As these photos show, you will usually find one end of each tube to have a bump. I used a sanding block with 180 grit sandpaper to get this one smooth.
One other tip, once you smooth the ends and match pieces, label the joints to ensure you know which pieces match up to each other.
The main differences between this build and the 2.6″ build are:
- Use of an Aeropack tailcone retainer
- Nosecone built out for electronics
- Redundant flight computers
Before I started the build, I used the fin slots to mark the couplers and motor mount tube. I also used anlge aluminum to draw lines down the booster tube along the fin slots and half way between the fin slots.
Motor Mount Build
I filed out the notches in the forward centering ring to accommodate the 1/2″-2200# tubular Kevlar bridle. A Permagrit file made it an easy and quick process.
Then I measured out the right distances for the tailecone retainer and the front CR. The MMT for this kit is quite short. With the tailcone retainer on, there is less than a 1/4″ of the MMT extending past the forward CR in order to get the CR past the end of the fins slot. That will be fine, although some people may not be happy with that, so you may want to factor that into your planning for this kit and get a longer MMT.
Once I had the right positioning for the forward CR, I tacked it on with CA and taped the tailcone retainer in place for the duration of all the fitting that needed to be done.
With the forward CR in place, I measured off the correct length of tubular Kevlar for the bridle. The goal was to ensure the loop ends up just below the lip of the fin can. I used the fins slots to mark the fin lines on the MMT and extended the lines down the whole length of the tube. I used some 18mm Tamiya tape to tape off the fin areas. I used some CA to stiffen up the ends of the tubular Kevlar and cut the ends clean.
I had already sanded all the parts, but I always like to sand again right before I epoxy anything to the FG tubes, so I sanded the areas for the ends of the bridle. Finally, I epoxied the ends of the Kevlar to the MMT, being careful not to get epoxy near the fin lines or down by the middle CR line. I taped the Kevlar in place and will let it cure overnight. For this, I used Aeropoxy 6209.
Once the epoxy under the bridle cured, I coated the whole thing with Proline 4500 and also added fillets to the forward CR with Proline.
The Proline on the MMT tube cured and I moved onto sewing the loop at the end of the bridle. Once the loop was sewn, I secured it with some heat shrink tubing. (NOTE: As with the 2.6″ build, I neglected to put a swivel in the Kevlar loop. This should be done before you epoxy the ends of the Kevlar to the MMT).
I resanded all the lines where the fins will contact the MMT and tacked the rear CR on with some putty, so I could pull it out later.
I placed a good line of epoxy around the inside of the tube just forward of the front fin slots and then installed the MMT so the forward CR was epoxied just at the leading edge of the slot. I will keep the rear CR on until after the forward fins are i
Booster Section Build
When I test fitted the fins, the tabs were originally a little less than 1/4″ too tall (so the fins stood proud of the body tube). I thought maybe I was doing something wrong and tried all sorts of refitting and moving things around, but found out other people had encountered the same issue, so I understood this was not necessarily uncommon for these kits. A quick trip to the miter saw with a cutoff blade (very, very much suggest you cut these outdoors with a respirator – it produced a huge amount of FG dust, even with two shop vacs running on the saw – or use a wet tile cutter saw) trimmed them to proper length and I cleaned up the edges on my belt sander. After that, they fit perfectly.
Next step was to get the holes “drilled” into the fins slots for the internal fillet epoxy injections. As I have noted in other threads, I prefer to sand or grind any holes in FG tubes, when possible, rather than using a drill bit. For the fin slots, it is easy because the slot is already cut. I first used a conical grinding attachment on a dremel to make the first cuts, then expanded the holes with a round grinding attachment. I just check the hole size against the size of the nozzle on the 10ml syringes I plan to use to know when the hole is big enough.
With the forward CR secured and the MMT in place, it was time to get the forward fins on. I resanded the fins along the tab and fillet areas and then epoxied each fin in with quick cure epoxy. The main structural strength will come from the injected fillets later. We want a good bond with the forward CR in order to ensure a good seal later on during the injection process or the epoxy will leak all over the place. So, make sure to butter up the leading edge of the fin tab as well as the root edge and make sure when you install the fin, it is tight against the forward CR. At this point, I only butter up the root edge to very close to the trailing edge of the tab – I don’t want to get too much epoxy there yet because the middle CR needs to butt up against it tightly and we will do that in the next step.
For the forward fins, I used my guillotine fin jig along with a 3d printed jig from Badass Rocketry. I waited about 15-30 minutes between each fin to ensure they are nice and solid before taking them out of the jig.
When the forward fins were cured, I epoxied in the 2 middle CRs. First, I used a long thin stick to put a good ring of epoxy around the airframe and MMT just aft of the forward fin tabs. I also ensured I got a good amount of epoxy on the fin tabs themselves to ensure a good seal. Then I used two thin sticks to push the CR in place and butt it up right against the fin tabs. For the other center CR, I put a good ring of epoxy around the tubes at the front of the rear fin slots, then pushed the CR in place until I could just see it at the edge of the fin slots. Once the epoxy was tacky, I took a small amount of laminating epoxy (very low viscosity) and used a syringe to inject a very thin layer on the CR to seal it in place.
When all the epoxy on the middle CRs was cured, I installed the rail buttons. I used the lines I had drawn down the whole tube between the fins. I installed both 1010 and 1515 rail buttons. The rear buttons were placed 1 inch from the end of the airframe and the forward buttons were placed 3-1/2″ from the from of the tube. I used weld nuts to hold them in place. I tacked the weld nuts in with CA and covered the back of the nut with a circle of tape, then epoxied the nuts in from inside the tube and set the whole thing aside to cure for the night.
With the rail buttons on and all the middle centering rings in place, I moved on to the rear fins. As with the forward fins, yopu need to butter up the front of the tab as well as the root edge in order to ensure a good seal with the CR. Rear fins are easy to line up using the medium size guillotine jig – just make sure they are perfectly in line with the forward fins.
The next step was to install the rear CR and seal the fins. First, I used some quick cure to get a generous amount of epoxy around the aft end of the airframe and the ends of the rear fins and seated the rear CR in place. Once that epoxy was leathery, I added a generous layer to fillet the end of the tube over the rear CR, being careful not to get any on the area where the retainer will go.
I then put a very small fillet of quick cure around the base of each fin to help seal them and keep the injection epoxy from leaking out.
I then taped all the seams and leveled the bird out on my stand. I mixed up about 30 ml of Aeropoxy 2032/3660, added some milled FG and some fluorescent yellow dye. I am planning to paint this rocket yellow, so may as well go with yellow in the epoxy and the dye helps me see of there are any leaks. I injected the first section of the fin can and put it aside to cure over night.
I ended up having a leak overnight. Turned out that I overlooked the extent of the gap the the taper on the leading edge of the forward fins and the trailing edge of the rear fins. Not difficult to fix – I sealed up those gaps with epoxy and continued with the injections. Since it takes a good 24 hours or so for this epoxy to cure well, it took a couple days before I could move on to the external fillets.
With the internal fillets injected, I proceeded to the external fillets. I used RocketPoxy with a little yellow dye. For each fin, I like to mix up the Rocketpoxy first (about 20g for this size rocket) and then resand the area, draw my lines, tape it off, etc. In the time it takes to do all that, the RocketPoxy has just about the right amount of time (at room temperature) to gel a little bit to the right consistency.
So, simple procedure:
- Mix 20g of RocketPoxy
- Sand the fillet area on tube and fins
- Mark off the edges of the fillet using a 1/2″ piece of PVC (for this rocket, that turns out to be about 5mm)
- Extend the line along the whole fin section
- Tape off the lines
- Apply epoxy
- Smooth out the fillet
- Give it about 10 min and pull the tape
- Smooth down the edges a bit with an alcohol dipped finger tip, while the epoxy is still flexible
- Put aside to cure
For this build, I used an Additive Engineering 75mm 3D printed sled. It is a nice sled with a good selection of pre-drilled holes. I am installed a Stratologger CF as the primary altimeter with a Raven 4 as backup. The sled was too narrow to fit both side-by-side, I thought about using the NC for a HED backup, but I would like to save that for a tracker. Luckily, the two altimeters are very small and they fit nicely in a top-bottom config. By using a modified Featherweight “Power Perch” with the included LiPo, it also means the Raven is self contained and will use a magnetic switch, so no need to install a second battery or switch. Nice.
After test fitting the two altimeters in various places and configs on the sled, the best organization seems to be to have the Raven on “top” (the side with the switch bridge) and the Stratologger on the “bottom” (side with the 9V battery compartment).
Installing the Stratolooger was the easy part. There were already a set of pre-drilled holes that lined up with the SLCF mounting holes, so I screwed some 4-40 mounting posts in and secured the altimeter with 4-40 screws. I then soldered wires onto a Shurter rotary switch (note, they need to be soldered on perpendicular to the switch cylinder, or they won’t fit on the sled). Routed the wires cleanly to the switch and installed the wires using ferrules. Also, I measured out the required length of wires needed from the battery mount and installed the battery wires to the altimeter, also with ferrules.
The Raven was a little bit more difficult to install. A couple issues came up.
First, the whole Power Perch assembly would not fit on the sled, so I only used the battery retention pieces and the port “dongle” that plugs into the ports of the Raven that also provides the magnetic switch and receptacle for the LiPo battery.
Then, I also realized nothing really sat flat on the sled. All the various parts needed to be off the surface, so I used 4-40 posts. This required me to drill some extra holes for the post.
The next problem came when I realized that, by using the posts, the Raven itself was slightly raised compared to the port connector, so if I just screwed the Raven to the mounting posts, it would be flexed since one end would be higher. Fixed that issue with some washers between the Raven and the 4-40 mounting post.
The next problem was that, by raising the whole assembly using the mounting posts, the LiPo would be hanging in mid-air. Luckily, the distance between the battery and the sled was exactly 1/4″, so I cut piece of plywood to fit under it. I epoxied the shim onto the sled and the battery sat perfectly flat.
Finally, the screw provided with the power perch to mount the rotating battery retainer arm was too short to use in this config, so I used a longer screw I had on hand.
When complete, the whole assembly sits nicely and is very secure. Added bonus, the position of the battery snugs it right up to the coupler tube when installed, so the tube should hold it in from a side-to-side perspective and the retainer arm should keep it secure longitudinally and vertically. As noted earlier, this whole thing is self contained – no switch or battery wires to run to it. Just run the wires to the terminals on the bulkhead.
To install the bulkhead terminals, I used a wire wrap tool to wrap the terminals with 24 gauge wire and then soldered the wire on.
I drilled the holes in the bulkheads and had to file them a bit to fit the solder connection points. Then I fed the wires through the holes and epoxied the terminals in place with quick cure epoxy. They epoxy also serves to seal the holes from any ejection charge gasses.
I used the small charge wells from Rocket Junkies. I installed them with the included hardware and also sealed the bottoms of the wells with some Fabri-tac.
I secured forged eye bolts in each bulkhead with 1/4″ nuts/washers and Loctite red.
When I first started measuring everything out, I noticed the kit comes with a short coupler for the AV bay. It is about 6 inches long. As the photos below show, the sled fits in it, but if I want to use the switch as it sits on the sled, the switch would be about an inch from the end of the coupler. Simple solution was to get a longer coupler. I bought one from Wildman and they got it out to me within a couple days. This one is 9″ long and has enough space to accommodate the sled and switch position.
With the new coupler in hand, I laid out the proper distances for the sled on the rails and secured it in place with some 1/4″ nuts which were secured with some Loctite blue.
With the sled in place, I could determine the length of wire needed to use between the altimeters and the aft bulkhead and install the 3M mini snap connectors I use.
Next, with the sled inside, I marked the position of the switch on the outside of the coupler tube and used that to determine the positioning of the switch band. I drew the lines for the switch band and sanded the coupler and the inside of the switch band. I epoxied the switch band in place, using the payload bay tube to ensure the switch band was not crooked.
All other 1/4″nuts were secured with Loctite red.
I assembled the nosecone using a glueless method. Doesn’t get much easier. Trim an all thread to length, attach it to the metal nosecone tip. Insert coupler and bulkhead. Secure with an eye nut. One change from the kit, I am using a 3″ aluminum bulkhead I had on-hand rather than the fiberglass one that came with the kit.
Odds and Ends
I used the very convenient holes on the Badass Fin Jig to mark out the placement for the screws for the ebay/payload bay coupling, the shear pins for the nose cone and the vent holes in the switch band. I also used a diamond wheel on a dremel to cut the witness marks between the switch band/payload bay and the payload bay/nosecone.
I am using the Lumadyne PEM nuts again this build. This time I am using the 4-40 size, as opposed to the 2-56 size I used for the 2.6″ DS. I had a lot of trouble with the 2-56 nuts, but the 4-40 ones are bigger and the tube is bigger, so this time they went in with no issues. The hole for the PEM nuts is 1/4″. Everyone knows how much tear out is an issue with these FG tubes when you drill into them. I am a big believer in using files to get clean holes. I recently got some diamond hole saws in small sizes and decided to try one out for this build. Since they essentially grind/file out a hole rather than drilling it, I was hoping it would cause less tear out. I taped the inside of the tube as normal and used the 1/4″ / 6.5mm saw on my drill press. It turned out pretty well. As long as you go slowly, I got very little tear out. I am not sure how well this would work using a hand drill, the hole saw wanted to skip around on the surface of the tube, but with a drill press, it was easy to keep it on track.
With the holes drilled, I put a little epoxy around the lip of each side of the PEM nuts and set the screw in place while it cured to ensure everything stayed tight and in line.
I drilled the pilot holes for the shear pins on the NC and threaded with a 2-56 tap.
I also spent some time sanding the external fin fillets to get them smooth.
Painting and finishing
I used Duplicolor Filler Primer. I gave it two coats, sanded with 400 grit and recoated.
Color coats were Duplicolor Engine Enamel. 3 coats of each color, sand with 800 grit, then 2 more color coats.
After applying the Stickershock decals, the rocket got 3 coats of Duplicolor Engine Enamel Clear Gloss
The charges for the ground testing were calculated using the calculator at Insane Rocketry’s site: https://www.insanerocketry.com/blackpowder.html.
The calulation for the drogue charge was 1.3g of FFFFg black powder. That charge turned out to be good and was used for the primary charge in the cert flight. The backup charge was 1.6g of FFFFg.
The charge for the main charge was calculated to be 1.5g of FFFFg. This turned out to be a bit weak, so the primary charge used for the cert flight was 1.7g of FFFFg and a 2.0g backup charge.
Pictures & Flight Videos
The initial flight was conducted on 20 February 2021 at MDRA Higgs Farm. It flew on a AT I-599 and had a great flight. One of the switches broke during the flight. It was subsequently replaced and the rocket has been flown many times since then.