6" Wildman Darkstar Build

This project was the fourth Wildman Darkstar rocket I built. It was dubbed Red Giant Star.

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.

Build date: October 2021

Electronics: Primary: Eggtimer Proton
                     Backup: Missile Works RRC2L

Dry weight: 41.5Lbs pounds (18,816g)
Length: 139 in (3517mm)

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Documentation & Rocksim File

Rocksim File:

Parts List and components

Here is a photo of the parts you get plus some of the items I added, such as the Aeropack retainer, a Onebadhawk bridle and a thrust plate I CNCed. Although the photo shows the stock bulkheads from Wildman, I later CNC’ed custom parts for the Ebay and nosecone, which you will see later in the build.
As usual, start by washing all these parts and sanding with 220 grit. I highly recommend a good random orbital palm sander, as these parts are quite large.

Initial Build Notes

Much of the build will be similar to my earlier Darkstar builds, but there have been some improvements to the process. First and foremost, I acquired a Shapeoko 3 CNC machine since the last Darkstar build and now fabricate a number of my own parts, which allows me a fair bit of flexibility. The Ebay and nosecone builds, in particular,arevery much different than the earlier Darkstar builds.

While you can definitely fly this rocket on some very cool Level 2 motors, I think of the 6″ diamter rockets as the real entry point to Level 3 building. As such, I built this rocket keeping in mind that I would like to fly it on at least N motors eventually.

I should note that the original booster tube I received was quite misshapen around the fin slots. Tim at Wildman replaced the tube and the second one was excellent.

I started this build off by CNCing a thrust plate out of 0.19″ aluminum to hold the Aeropack 98mm retainer. The flange holes were CNCed in the precise location and tapped for the 8-32 cap head screws.

The new booster tube Tim sent me was in great shape, but still needed some slot cleanup. In the photos below, you can see the slots were about 1/4″ short. I used a tube marking guide to draw a line around the tube at the front and rear of the two sets of slots and cut out the necessary material with a dremel and file. Pretty quick work, but necessary prep before starting the build.
This was also a good time to draw all those lines down the tube along the fin slots and between the fin slots.

Motor Mount Build

One difference in this build compared to the previous DS builds I did is that I am using one of Teddy’s bridles from Onebadhawk. Teddy makes way better kevlar products than I could ever do on my own, especially for a bigger rocket. For this build, Teddy recommended he sew the bridle straight onto some 5/16″ welded eye-bolts. Never one to argue with Teddy’s wisdom on recovery items, I agreed. So, unlike the previous builds where I carved a slot in the forward CR and epoxied the strap right to the motor tube, this needs just a slight bit more planning.

I measured the CR locations, then found the center line on the forward CR to drill the holes for the eye-bolts. I drilled the holes on my drill press and, when I fitted the bolts, I realized the washers that Teddy sent were just a bit too wide for the CR. He recommended I grind them down, but, luckily, I had some nice smaller ones from McMaster-Carr that fit the CR perfectly and were a bit thicker. So, I JB welded the underside hardware and tacked the forward CR to the MMT with CA. I am not so worried about the top of the hardware right now because I will pour an epoxy dam in front of the CR later.

One note – I also used some Loctite on the bolts. You really should wash your hardware with acetone before you bond it (with either JB Weld or Loctite). The hardware comes with oil on it to prevent corrosion and that oil has a tendency to make the bonding agent less likely to stick.

Once the CA was cured, I added some 5 min epoxy on top of the CR to hold it in place.

Couple house keeping chores before we get the MMT tacked in and start gluing up fins:

First, need to get the hole in place for the rear rail button. I have been shifting towards using Rotaloc Adhesive Mount Nuts from McMaster_Carr for rail button mounting. For a bigger rocket like this that will often have to go to the away cell, I am using the 1/4″-20 adhesive nuts with a large flange:

https://www.mcmaster.com/98007A029/

You can get the nuts in a bunch of different thread and flange sizes. The 1/4″-20 mount allows me to easily switch between Unistrut and 1515 buttons (I do not plan to need 1010 buttons on this rocket). For smaller rockets, I use one of the 8-32 sizes to switch between 1010 and 1515. One mount, multiple buttons.

One issue, though, is that these adhesive nut flanges are large and flat and the tubes are curved. I gently bend the flange out in a vise until it fits nicely along the tube. I am not gluing these in right now, but it makes it easier to drill the 1/2″ hole and fit the nut before you install the MMT.

For the fins, I am not making actual glue wells like I do in my 8″ and larger rockets, but I am planning to inject a fair amount of epoxy at the fin root, so I drilled some 1/8″ holes along the bottom to allow the epoxy to have a more mechanical grip.

With those tasks done, I tacked the MMT into the booster tube. At this point, the only glue point is the front CR. None of the other CRs are in place yet. The rear CR is just there as a placeholder to keep the MMT centered while the epoxy on the front CR cures. Some holes and zip ties make it easy to remove the rear CR.

Booster Section Build

With the MMT tacked in, I tacked in the forward fins using 5 min epoxy on the leading edge of the fin tab and the fin tab root. Main intent here is to ensure the fin is securely tacked in and the edges are sealed so I can inject a robust pool of epoxy later. I do have some fin jigs I CNCed for another 6″ diameter project, but once I get to 5″ diameter and larger rockets, I find it easier and quicker to just ensure the tube is level and plumb, then clamp it down and then you can be reasonably sure the fin is straight if it is line up in the slot properly and plumb. So far, this method has worked well in a number of rockets and I have not had an issue with misaligned fins. For smaller rockets, I usually use my guillotine jig.

Once the forward fins were securely tacked in, I epoxied in the CR that goes right behind the fins and then injected a shallow pool of epoxy behind the CR. 60ml of West 105/205. Once that pool cured, on the forward end of the fins, I drilled and inserted 3 x 1 inch long #8 screws just above the forward CR and poured a 100ml epoxy dam in front of the CR. The screws ensure the epoxy has more mechanical grip on the body tube. The epoxy dam also covers and locks in the eye-bolt hardware.

In the past, I have struggled with using long flexible tubing to inject epoxy that far down a tube. The tube wants to curl up and get epoxy all over the place. I realized the solution was to simply tape the tubing to a long piece of dowel. Tape the tube to the dowel and then tape the tube to the syringe. Then I just pour the epoxy in the syringe, plunge and refill until all the epoxy is used up.

I drilled 1/8″ holes next to each fin, levelled the rocket and injected 30ml of epoxy to the root of each fin.

I epoxied in the forward CR for the rear fins and then adhered the Rotaloc nut to the frame before installing the rear fins. For this, I first tack the nut in with a bit of 5 min epoxy and attach the rail button to keep the nut tight and centered while the epoxy cures. Then, I take the button off and slather on a healthy bit of JB weld. I go ahead and cover the whole thing, threads and all. I get some of the JB weld up in the threads and also fill in the gaps the nut leaves on the outside of the body tube. This may seem counterproductive to fill in the thread portion, but, as much as I like these Rotaloc nuts, I have found their weak point to be the weld connection of the nut to the baseplate. It can and has snapped off. JB weld is easy to drill out and tap, so I just fill it all in and then drill it out and tap it later. The 1/4″-20 screw then engages not just the nut, but the JB Weld as well.

To install the rear fins, since I was comfortable that the front fins were straight, I used the simple method of clamping some aluminum angle to the front and rear fins when I tacked them in. Once the root edge epoxy was cured, I injected some internal fillets.

Once all the internal fillets were cured, I mixed up a batch of epoxy thick with colloidal silica and generously filled in the spaces internally the injections didn’t hit near the aft end and proceeded to smear a bunch of epoxy on the tubes and end of the fins to adhere the rear CR in place. I cut some notches on the forward side of the thrust plate to give the JB Weld a little more to hold onto, then mixed up a healthy batch of JB Weld. I smeared it all over the aft end of the rocket, installed the thrust plate, and held it in place by inserting an Aerotech 98mm case. I used the rest of the JB weld to make a small fillet along the outer edge of the thrust plate.

I drilled and tapped the rotaloc nuts for the rail buttons which allowed me to securely switch between Unistrut and 1515 airfoil.

Finally, I got all the external fillets in place.

EBay Build

With the booster pretty much complete, I moved on to something (arguably) more interesting – the Ebays.

The basic config is an Eggtimer Proton for the primary computer and a Missile Works RRC2L for backup. I decided to go with separate batteries for the logic and deployment on the Proton. I love the eggtimers, but those WiFi models suck down a lot of juice. I have had a Proton drain a 2S 7.4V 400mAh LiPo in less than two hours. Considering I have had times when a rocket could easily sit on the pad for 90 minutes (happens a lot at big events like Red Glare), I wanted to make sure I could vary the logic battery as necessary and keep the deployment channel “pure”. So, I will use a LiPo for the Proton logic and an Energizer Lithium 9V for the deployment charge. The RRC2L will get an Energizer Lithium 9V.

I started out by CNCing the bulkheads out of aluminum and tapping the holes for the terminal blocks and the charge wells. Then I CNCed all the sled parts – the sled itself, the end brackets and a switch bracket out of 3/4″ basswood.

I cut out some aluminum angle and drilled holes to attach the pieces to the sled brackets. I used 4-40 bolts and nylon lock nuts to attach the aluminum brackets. I lined the brackets up on the sled and secured the sled to the brackets by drilling holes through the aluminum and sled and securing with 4-40 bolts and lock nuts.

I reinforced the wood bracket by “painting” epoxy on the section that would be drilled for switch holes. Once cured, I measured the holes for the switches and drilled them out on my drill press. I am using screw switches from Binder Design. They have a little notch in the switch housing, so I needed to elongate one end of the hole with a Dremel, then the switches fit perfectly. I am only using 2 switches right now, but I drilled a third placeholder in case I need to add a switch later or if I want to add an indicator light, beeper, etc. I will epoxy the switches in later, once everything is tested.

I know there are folks who don’t like terminal blocks, and I get it, I have had those cheaper white plastic ones completely get blown apart!! For all my terminal blocks, one thing that has made them much better to use is a healthy covering of green frog masking tape over the whole block. Since I started doing that, even the white ones no longer break on me.

For this build, I am trying something new (for me) from McMaster-Carr this time around. These are some pretty industrial looking terminal blocks. They have very secure screw-down terminals, made of some heavy duty plastic, you can get some cool marker strips to label the terminal and you can get covers to help protect them from the black powder charges. Also, you can get them as small as 2-circuits and as large as 20-circuits if you need to do some crazy large amount of air-start/cluster/staging from one terminal block. I am looking forward to trying them out. Here is the link for them – the marker strips and covers are in each line after the link for the terminal block itself:

https://www.mcmaster.com/terminal-blocks

The other nice thing about McMaster-Carr parts is they give you the schematics on the site which make it easy to layout the part in CAD for CNC. Even better, if you use Fusion 360, you can download the part directly from McMaster-Carr using the Fusion 360 interface and place the part on your CAD model. Using that method, I was able to have the holes for the terminal block perfectly positioned when I CNCed the bulkhead and then I tapped the holes for 8-32 screws and easily secured the terminal blocks to the bulkheads. While I was at it, I had also tapped the holes for the screws that came with the Binder Designs charge wells, so I screwed those in as well. I secured all the bolts on the other side of the bulkhead with nylon lock nut

I put aluminum brackets on either side of the switch bracket to hold it in place and tapped in holes for the standoffs for the Proton and the RRC2. Once that was done, I marked out and drilled the holes in switch band for the switches and vents.

My first attempt at installing the Proton did not go well. I had previously assembled and tested the Proton, so that wasn’t an issue, but I built it a while ago and had soldered a bridge between the DP+ and B+ pads because I figured I would probably use it in single battery mode. No big deal, get out the solder wick and remove the bridge. Then I soldered JST connectors to the proper pads for both the deployment and logic batteries. Then I installed the board back on the sled and went to attach the leads from the terminal blocks. Here I ran into the next issue – when I assembled the board, I chose to use the green terminal blocks that come with the kit. Frankly, I must have really messed up that soldering job. Of the 12 ports, 9 of the screws would not screw down. I must have melted them or something, who knows. So I took the board off and started trying to de-solder each connection. In doing so, I managed to break one of the terminal blocks off. It didn’t damage anything, but it was a lot harder to de-solder. After about an hour of wrestling with the damned things, I finally got one off and all the solder off the board. I cleaned up the pads and soldered 4 wires to two of the channels. I reinstalled the board on the sled and then realized I had put male JST connectors on the battery pads and they needed to be female. And to add insult to injury, I had installed the board with the “UP” arrow pointing toward the aft end of the Ebay and the battery wires would be the wrong length if I turned the board around.

At this point, I was tired and frustrated and realized I needed to walk away for a while. I went and had some dinner, watched some TV, etc, then came back with fresh eyes. I de-soldered the JST connectors, soldered the proper ones on and did a thorough check to make sure I didn’t miss anything. I installed the board back on the sled in the proper orientation and proceeded to wire everything up. I finished up wiring the RRC2 and the batteries and the final pictures are below.

Some highlights:

  • Eggtimer Proton with a LiPo for the logic and a 9V lithium for the deployment
  • RRC2L backup with a 9V lithium
  • Nose end bulkhead fixed in place, all wires from those terminal blocks directly wired to the boards
  • Aft end bulkhead removeable, leads have 3M quick connects in the middle
  • All batteries on opposite side of sled from electronics to help protect them if one gets loose
  • LiPo zip tied to sled
  • 9V batteries in modified battery boxes. I remove the switches and hard wire leads to the terminal connectors. Battery box covers are held in place with a screw during flight so the 9V batteries are completely enclosed
  • Pictures show 400 mAh LiPo for testing, actual flights will use an 800 mAh LiPo

Once completed, I did continuity tests and a test ematch fire on all channels.

Lesson here is to ensure you don’t work on this stuff when you are tired and trying to rush. As we used to say in Special Forces, “Slow is smooth and smooth is fast”.

With the holes drilled in the switch band, I can easily access the screw switches when the ebay is assembled.

Nosecone

For the nosecone bay, I mounted a Featherweight GPS to a 38mm ebay sled from Additive Aerospace. Works okay. Main intent is to be able to more easily move the tracker from rocket to rocket. The plastic mount is held to the sled with two 4-40 bolts. I plan to add these mount holes to the sleds on my other rockets that can handle it. I also put a mount in for the Marco Polo tracker, which I will use for lower altitude flights.

For the sled, it is just a piece of .08″ thick FR4 sheet with 1/2″ tubes JB welded to the bottom and then laminated with a piece of FG cloth.

The sled slides onto the bay rails. The rails are 5/16″ nylon all-thread. I am honestly not sure how these are going to hold up. First time I am trying nylon. The nuts are made from fiberglass. The intent was to try and get as much metal out of the main part of the bay to avoid interfering with the GPS tracker. The bulkheads are CNCed FR4. The nosecone isn’t particularly heavy, so I am hoping that 4 pieces of 5/16″ nylon holds everything together. If it fails, well, that will answer the question. More likely, if it doesn’t work well, the pieces of nylon will deform, start to strip, etc rather than all out failure. If that happens, I will come back later and replace the nylon all-thread with metal.

As noted earlier, in order to ensure I can remove the nosecone bay later (especially if I have to replace that all-thread), it is held into the nosecone with 6-32 PEM nuts.

PLACEHOLDER FOR FUTURE AVIONICS BUILD – sled broke on first flight

Odds and Ends

I tapped in 2-56 shear pins for the booster and 4-40 pins for the payload bay. I also installed 6-32 PEM nuts to hold the ebay to the booster and the nosecone ebay to the nosecone. I also Dremelled in all the necessary witness marks.

Painting and finishing

As of February 2022, this rocket still needs paint and decals. Waiting for warmer weather to get this done. In the meantime, she flies naked!

Ground testing

The charges for the ground testing were calculated using the calculator at Insane Rocketry’s site: https://www.insanerocketry.com/blackpowder.html

3 grams FFFFg worked great for the drogue. 4g for the main was slightly less than authoritative. I upped the primary charge to 4.5g for the flight.

Pictures & Flight Videos

The initial flights were conducted on 25 October 2021 at URRG. That weekend, it flew on a K1999 and an M1780. Both flights were excellent, but there were a couple issues.

I used a 24″ Skyangle drogue and it was too small. You can see in both videos the booster was WAY above the nosecone/payload bay while under drogue. It didn’t cause a problem on these flights, but it obviously could be catastrophic in the future. 

On the second flight, you can see in the video at the end there was an issue with the main chute deploying. It looks like a tangle, but it isn’t. What happened was the deployment bag completely ripped out at the end where the pilot chute pulls it off the main and the parachute was pulled through the rip for a couple feet. Luckily, it acted more like a slider – when the parachute fully opened, it pushed the bag off and fully inflated.

The deployment bag is from Skyangle and is the one sold to work with the Skyangle Cert XL chute I used. Post-mortem showed the bag had some really awful stitching at the end. Inspecting the other Skyangle deployment bags revealed the same. I talked to Teddy at Onebadhawk and I am going to have him sew the end closures with Kevlar thread. That should prevent that problem again.

On a positive note, the nylon rods, nylon wing nuts and fiberglass hex nuts in the nosecone worked beautifully! No problems at all – everything looks great. I will keep an eye on them for wear over time, but with two flights logged, no issues yet. Featherweight altimeter worked great (didn’t need it, first flight almost literally landed on the pad) and I tried a flight with both the Featherweight GPS and the Marco Polo transmitter – no issues, they did not interfere with each other.

On subsequent flights, I used a Fruity Chutes 30″ Iris as a drogue and it worked perfectly. I also switched to Fruity Chutes deployment bags and they seem to be much better than the Skyangle bags.

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