Level 2 Project - Another Darkstar 3 Build

[NateB]

These are popular rockets and there have been plenty of build threads on them, including the stickied thread in this sub. I want to get my Level 2 so I can fly small sugar motors at launches, I used a Darkstar Jr for my L1, so why not fly the 3" one for my L2? I'll be catching this build up with my Interceptor AAD-75 and they will share some of the recovery gear and electronics. I'll be building this to fly dual deploy with the payload section and HED with just the booster. This should give me the versatility to fly this rocket with a medium H and up motors.

First things first, as always, I washed and dried all of the fiberglass parts then weighed and measured everything to start building my Open Rocket sim. I ordered this kit during the Black Saturday Sale in 2021. Parts can change over time, so I prefer to create a sim from scratch for each build. This won't be a super fast build, but I'd like to get the paint finished by the end of the Summer / Early Fall when the humidity is lower and the temperatures are still warm. I don't have an estimated launch date yet, maybe this Winter or next Spring before the crops are planted.





The first steps with the actual build were to make sure one end of the motor mount is square. There's some compression in the picture above, but you can see a small lip on one layer of the fiberglass which was easily sanded down. The fiberglass surface where it mates with the retainer body is roughed up with 60 grit sandpaper and the retainer body is attached with JB Weld. For the rest of this build, I'll be using RocketPoxy for permanent joints and CA glue to tack things in place that might need to be adjusted before using epoxy.

 

[kenstarr]

Ooh! I like me a Darkstar. I've got a 4, 3, and a scratch built 5mm carbon fiber micro maxx. Make sure to post lots of pics of your av bay setup.
Ken

 

[NateB]

Ooh! I like me a Darkstar. I've got a 4, 3, and a scratch built 5mm carbon fiber micro maxx. Make sure to post lots of pics of your av bay setup.
Ken

The AV Bay will be pretty simple, but I'll post pictures. My plan is an Eggtimer TRS with 2 batteries and 2 surface mounted screw switches. I have a pair of the ejection charge wells and a sled from Additive Aerospace.

 

[NateB]

This is my first time using a tailcone retainer, so I'm taking my time to make sure it fits properly with my motor cases and adapter.

I have a Loki 54/950 case in the motor mount for test fitting. Most flights will probably be with a 38mm motor.



When the motor is installed, the tailcone needs to be flush with the end of the body tube.



I also want the centering rings to be snug against the fin tabs for when I add the fin pockets and fill them with epoxy. After measuring, looking, and remeasuring, I marked lines for the centering Rings, sanded the motor mount where they will be attached, and tacked the CR in place with 2 drops of CA.



I use the fins as guides for CR placement and repeat. The forward most CR is left off for now. I still need to cut out a space for the shock cord harness.



You can just see the CT through end of each fin slot. This is perfect and will keep the epoxy where I want when I attach the fins.


I wanted to verify that the 38/740 motor case with the adapter also fits. Now I'm ready to move on to permanently attaching the centering rings.

 

[NateB]

I made a little more progress today. I cut notches in the forward centering ring for the recovery harness.



I also used a few fin guides to mark where each fin will seat against the motor mount.

 

[NateB]

The next steps don't make for the most exciting conversation. I started to cut 1/16" plywood for fin pockets. Each strip was cut to size and sanded to fit in place around the fins. I tacked them in place with CA and verified that each pocket would line up with the fin slots. Once I was happy with the positioning, I attached them permanently with RocketPoxy fillets.

 

[NateB]

I'm wrapping up the fin pockets and motor mount. The recovery harness is simply epoxied to the motor mount in a Y shape. Make sure it fit it fits between 2 fins without interfering with the fin roots and fin pockets. For now, the forward centering ring is tacked in place with a few drops of CA.



Strips of basswood for the upper set of fin pockets were cut to size and tacked into place with CA. Take care to ensure they are all aligned. Proper Planning Prevents Poor Performance.



One the upper set of wood strips are in place, I again verified that everything lines up before attaching them permanently with rocketpoxy.

 

[NateB]

The motor mount is almost complete. I lightly sanded the motor mount where the fin pockets, centering rings, and Kevlar harness will be joined. The Kevlar is secured with a generous amount of epoxy and small fillets are added around each fin pocket and both sides of the centering rings. This will cure overnight and then I can move on to installing the motor mount and lower finset into the booster body tube.

 

[kenstarr]

It's looking really good! I like your harness attachment method.
Ken

 

[NateB]

It's looking really good! I like your harness attachment method.
Ken

Thanks, that method for harness attachment is from the instructions for all the Wildman kits I have built.

 

[NateB]

Now for mounting the motor mount into the booster section. The tailcone retainer has a groove which mates up with the end of the body tube. It has to be in the right place to prevent a gap when it is closed. I inserted my motor case, screwed the retainer in place, and applied a thin layer of epoxy to the outside edge of each centering ring.



Slide the motor mount into the body tube and make sure the tailcone retainer is fully seated in place.



Remove the tailcone retainer and clean up any epoxy that may have gotten in the grooves of the retainer.

I also added a small fillet between the lower centering ring and the inside of the body tube. Again. Taking care to clean up any epoxy that dripped where I didn't want it.



I set everything aside to at least partially cure. It may not seem like much epoxy holding the motor mount into place, but the the fin pockets are filled with epoxy and cured, it will be strong.

 

[NateB]

Today I was able to move on to the lower fin set. First, the tabs were just a bit long. I could certainly cover this with the external fillets, but I decided to cut a little of the excess tab off.



I masked off the fin slot I was starting with to make clean up easier later. I also made sure to rough up the fin tab area with some coarse sandpaper before gluing the fin in place.



I never estimate the right amount of epoxy. I mixed up 40 grams and it was too much. I'll try half that with the next fin. Next, I spread epoxy into the slot with my stir stick.



I used the stir stick to push epoxy down into the slot. It doesn't gave to be entirely full, the fin will take up some space.





Next, I inserted the fin into the slot. You can see a small fillet of epoxy pushing out of the slot. This means the fin pocket is full and will make a strong joint once it cures.



If the centering rings are a tight fit to the fin, give the fin a few taps with a mallet to make sure the fin tab is fully seated against the motor mount.



Almost finished now, the tape is pulled and any excess epoxy is cleaned up with a paper towel dipped in rubbing alcohol.



Last, I'm using the fin guide to hold all 3 fins in place. I only have epoxy in the one, but I want to make sure it cures in the right position. Double check that there isn't too much epoxy on the fin so you don't glue the guide in place.



I like to let them cure for 4 or 5 hours before moving to the next fin so the epoxy doesn't run out of place when I rotate the booster. The same steps will be repeated for each fin and they will fully cure before I start the upper fin set.

 

[NateB]

The upper fins are attached the same way as the lower set. I roughed up the fin tab, filled the fin pockets with rocket poxy, push the fin in place and tap with a mallet when needed to make sure it is fully seated, and any excess epoxy is wiped up with a paper towel dampened with alcohol. To ensure the split fins stay aligned with each other, I use stir sticks and binder clips.



You could do this all at once, but I still worked on these one fin at a time. Once all the epoxy is cured, it looks good to me.

 

[kenstarr]

Awesome! That rocket is going to fall apart before those fins fall off! I'm not even sure if you would need to do external fillets. At least not very big ones. I just took my first dip of rocketpoxy last week and after looking over the specs, it's some good stuff.

 

[NateB]

I do not think I will need large fillets either. I will be adding some, but I'll look at my tools and eyeball what I think looks best. Right now, the fins are sturdy. I think I will have to order some more Rocketpoxy before I work on them.

This build is almost caught up to my Interceptor where I'll continue them together. My next steps are to mount the switch band in place on the coupler and start drilling holes for screws and shear pins.

 

[NateB]

I have a small update this evening, but it's an important step. I want to be able to use this rocket for HED and traditional dual deploy. The vent band placement is important so the coupler with the AV Bay inside fits into the nosecone.

If anyone is following along, remember to include the bulkhead when you measure for the vent band.



Slide the coupler with the bulkhead into the nosecone until it stops. I pull back just a little bit to make sure everything always fits. It will be secured with shear pins anyway. A wrap of tape will mark the spot and keep the vent band in place when you apply epoxy.



Next, I remove the vent band and scuff up the coupler and inside of the vent band with sandpaper.



Mix up some epoxy and apply a thin layer.



Slide the vent band into place and give it a spin to help spread the epoxy evenly. A small fillet epoxy will likely push out from the vent band and on the tape. Pull the tape and clean everything with alcohol.





I also add another strip of tape to what is the nosecone side to keep the vent band in place while the epoxy cures. Take a minute to make sure any epoxy is cleaned up and you have a nice joint around the vent band on both sides. This will save sanding later.

 

[NateB]

I've had a lot going on in recent weeks and wasn't able to keep up on this build. My son is back in school now, which means quiet mornings and afternoons so I can work on projects when I'm not working. Today, I started work on the AV Bay by drilling holes to for my screw switches and venting for the altimeter.

I was hoping to prevent the fiberglsss from peeling when drilling the holes. I didn't have the right size of dowel to insert in the coupler as backing, so I printed a band to slip inside the coupler.




The sacrifical band and the drill guide are both held in place with friction and tape. There is a little play with the fin guide, so I used calipers to make sure it was level all around.



I drilled 1/16" pilot holes, the vent holes are 1/8" and the holes to access the flush mounted screw switches are 15/64". After drillomg, each hole was cleaned up with a round file.




Looking on the inside, you can see where some of the fiberglass tore away. I probably should have used smaller steps when drilling the larger holes. The backing did appear to help. I'll print another band that is a little thicker for more support when I drill the holes for screws and shear pins.

 

[NateB]

I made a tiny bit of progress today. I drilled some pilot holes for the rail buttons. These are placed just above the rear most and forward most centering rings. Sometimes I like to mark the CP with the forward rail button, but this rocket will have 2 CP and minimum CG locations depending if it has the payload section or not. I'll make some decals instead.

 

[Hobie1dog]

Thanks for all the pictures . You are doing a great job on this one.

 

[NateB]

I was back in the mood to move on this evening. I'm planning on installing PEM nuts to hold everything together, so I needed to plan where I want all the hardware and drill pilot holes.

I used the fin and drill guide I've been using for this build along with a lot of masking tape to hole the body tube to the coupler / AV bay and the fin guide in place. I want the pem nuts to sit 1" from the end of the coupler so I can press them in with pliers in case I am not able to pull them in with washers and bolts. I measured everything several times and taped the guide in place so it would not wander. I also slipped the plastic backing ring I printed to hopefully keep the inside of the fiberglass from splintering.



I started with a new 1/16" bit and slowly drilled through each layer. I probably should have drilled each hole 1 at a time and installed the PEM nut before moving on, but these guides do a pretty good job keeping everything in alignment. So, I went for it and drilled 3 pilot holes. I did stick an extra bit the first hole, through the drill guide and both layers of fiberglass to keep everything from turning. After the 1/16" holes were drilled, I stepped up to a new 5/64" bit and enlarged each hole.



I pulled the tape and guide off to see how it turned out.



After removing the backing ring, the inside layer of the coupler still splintered some. I'll have to smooth it out with sandpaper before securing the PEM nuts. It's better than nothing, but I still think I can do better.



The inside of the body tube has a pretty clean hole, but still some splintering on one layer of fiberglass. The coupler provides enough pressure against the body tube to drill the layers cleanly. I'll print a slightly larger diameter and thicker/stiffer backing ring to make it fit snug to see if that works better.



That's enough for tonight. It is getting late here.

 

[NateB]

I installed the first set of PEM nuts today. I had a hard time deciding what size to use. I have 2-56 and 4-40 on hand. I think both will work. I used 2-56 on 2 previous builds. A 3" Wildman Interceptor-AAD 75 that I'm building alongside this rocket and a Mach 1 Electron BT55 dual deploy setup. After staring at the full stack Darkstar, I decided to use the 4-40 hardware. I'm sure it's all overkill, but this is heavier rocket than I've ever built. I hope I don't regret this when I ground test. I suppose I don't have to stick shear pins in all 3 holes if I don't need to.

I drilled the pilot holes last night with my hand drill and the fin/drill guide. I decided to use my drill press tonight to ensure the holes are square to the coupler. This will make the PEM nuts press into place better. If you're wondering, use a #19 drill bit for a 4-40 PEM nut.



I used another 3D Printed backing ring that was a little larger and stiffer than the other ones I made. This one worked well. The holes are clean and only required a quick pass with a round file and light sanding with medium sandpaper.





Next I inserted the PEM nut in thr hole and pressed it into place using vice grips. I used a sacrificial piece of paper on the outside of the coupler to prevent the jaws of the vice grips from marring up the fiberglass. I tried to use a bolt with a few washers to pull the PEM into place and pressing it in was much easier. I learned this with the other two builds. The 4-40 size are quite a bit easier to work with than the 2-56.









Some of these pictures didn't turn out great. If someone needs a different angle or more clear view let me know and I can try to take more. I have 9 more to drill and press into place.

The pilot holes in the body tube were enlarged with a 1/8" bit amd cleaned up with a round file to accept 4-40 screws or nylon shear pins. The countersunk washers are more for appearing aerodynamic than any hopeful performance gain. This is a heavy build already.

I placed the coupler into the body tube and everything lined in as planned. Now I can move on to the rest of the hardware.

 

[pathtouch]

Where’d you source your nuts from?

 

[NateB]

Where’d you source your nuts from?

I bought the PEM nuts, bits, screws and shear pins from McMaster Carr.

https://www.rocketryforum.com/threads/pem-nut-kits-and-shear-pins-kits.165818/page-2#post-2154846

If you are not interested, no worries, Mcmaster Carr part numbers are below for reference.
View attachment 471696

 

[pathtouch]

I bought the PEM nuts, bits, screws and shear pins from McMaster Carr.

https://www.rocketryforum.com/threads/pem-nut-kits-and-shear-pins-kits.165818/page-2#post-2154846

Thanks! I tried the Amazon route but wasn’t happy with how shallow the shoulders were on those ones.

 

[rfjustin]

Thanks! I tried the Amazon route but wasn’t happy with how shallow the shoulders were on those ones.

Yeah be careful there, make sure it states what panel thickness the nut is intended for and match that up as close as possible to thickness of the (presumably) fiberglass tube.

 

[kenstarr]

I've really enjoyed using PEM nuts as well. I use them for avionics bays as well as rail buttons.
Ken

 

[NateB]

I wrapped up installing all the PEM nuts to allow for this rocket to be flown with head end and traditional dual deploy. Just like I showed previously, I started by carefully measuring the locations for all the holes, taping drill guides into place and drilling small pilot holes before enlarging them.

The trickiest part was ensuring the holes in the bottom of the payload section lined up with the PEM nuts I had already installed in the coupler. With careful measuring, I drilled one hole through the payload tube using my drill guide and then made sure it lined up with the PEM nut in the coupler. I screwed both pieces together to keep everything aligned and then just drilled through the payload tube and into the other PEM nuts with a 1/16" which will fit through the center of the 4-40 nut without marring the threads. It is also instant feedback that you measured everything correctly.

With that out of the way, it was time to assemble everything into both flight configurations.







Now it's time to work on the external fillets and finish up the AV bay before it will be ready for paint.

 

[kenstarr]

That's looking awesome! You won't regret the time an effort you've put into it.
Ken

 

[NateB]

I like using screw switches and mounting them right on the inside of switch band for easy access.

I also want to easily move the sled and altimeter between a few rockers, so I'll use JST connectors for the switches and batteries.


The switches are wired into the positive battery lead, but I want to easily identify which switch powers the GPS and which one powers the ejection charges on the TRS.



Wires stripped, tinned, and soldered to the pads on the screw switches. Heat shrink tubing for added protection.



JST connectors pins are crimped on the other side of the wires.



The metal part just slides into the plastic part and locks in place with a small tab. I had to use a small screwdriver to help slide the metal pins into the connector.



The switches screw into the surface mount.



And the switches are then epoxied in place inside the coupler, making sure everything lines up before it cures. I just used BSI 15 minute epoxy for this step.

 

[NateB]

Now I am preparing for the external fillets by marking and masking the areas for epoxy. This area will be lightly sanded before I apply the fillets.