Drone Buster Scratch Build

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Back_at_it

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Time for another scratch build. I can't take complete credit for this design as it is something that I recall seeing at a launch many many years ago before I left rocketry and it stuck in my head as something I wanted to build. I've not been able to find anything on the market that looks like it currently so I don't know where to give credit for the design.

For my build I'll be using the following items.

- Fins and lug standoff cut from 3mm birch ply.
- Estes PSII 2.0 inch body tube cut to 10 inches for the lower tube.
- Estes PSII 2.5 inch body tube cut to 1 inch for the upper ring.
- Estes PSII 2.5 inch nose cone.
- Estes PSII 2.0 to 2.5 inch transition.
- BT50 motor tube cut to 3.75 inches.
- BT50 centering ring for a motor block.
- Centering rings. Ply for the upper, cardboard for the lower.
- 1/4 inch launch lug.
- 500# Kevlar shock cord.
- 3mm bulkhead and screw eye (not shown).

DB_1.jpg

Unlike most builds, I'm going to start with the nosecone on this build. For this step we will need the nose cone and the 2.5" ring. The PSII nosecone has had the shoulder cut down to 1/2 inch.

DB_2.jpg

Since this connection is cardboard to plastic, i'm using BSI epoxy for the bond.

DB_12.jpg

Epoxy was spread on the inside of the ring as well as the outside of the nosecone shoulder. The outside of the shoulder has been sanded with 100 grit to give the surface some texture.

DB_13.jpgDB_15.jpg

The pieces were then connected and the excess epoxy was cleaned up with rubbing alcohol.

DB_16.jpgDB_17.jpg
 
The next step in this build is assembling the bulkhead and inserting it into the reducer.

To begin, a reinforcement plate was glued to the backside of the bulkhead to give the screw eye something to screw into. These were glued together with wood glue and clamped to dry.

DB_4.jpgDB_6.jpgDB_7.jpg

Once dry, the screw eye was inserted and glue was placed on the back to prevent it from coming out.

DB_41.jpg

For the next step, I needed the bulkhead and the reducer. Like the nosecone, the reducer shoulder has ben trimmed down on the large side to 1/2 inch and the small side to 7/8 inch.

DB_22.jpg

The inside of the reducer was sanded with 100 grit then cleaned with rubbing alcohol. The bulkhead was then inserted and BSI epoxy was used for the bond.

DB_25.jpg

Once the initial bond was dry, I went back and added additional epoxy to the backside of the bulkhead and allowed that to cure over night.

DB_26.jpg


More to come tomorrow.
 
With the epoxy cured, the next step was attaching the nosecone to the transition. Epoxy was used to connect the pieces. The shoulder of the transition was sanded with 100 grit and wiped clean before epoxy was applied. A thin coat was applied to the outside of the shoulder while a heavier coat was applied inside the tube.

DB_27.jpgDB_28.jpgDB_29.jpg

The pieces were attached and the excess epoxy was wiped away with alcohol.

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With the cone section curing, I started working on the fins. The leading edge was tapered and I knocked off all the sharp edges off.

DB_19.jpg

The ply used for these fins is extremely smooth. A coat of filler primer should be enough fill any remaining grain in the wood. I taped off a the fin tab and about 1/4 inch of the surface where the epoxy is going to be applied. These were then taken out an shot with a single coat of high build primer and allowed to cure.

DB_21.jpg
 
Next was building the motor mount. The upper ring was was drilled to allow the Kevlar to pass through. The motor tube was sanded with 100 grit to knock off the shine and allow the adhesive to soak into the materials.

DB_8.jpg

The motor tube used was a scrap piece that already had a motor block installed from a previous build so I can skip that step.

DB_9.jpg

The forward ring was installed and two spacers were used to position the ring 3mm back from the edge of the tube.

DB_10.jpg

Next I added 5ft of 500# Kevlar to the mount. The Kevlar was passed through the hole in the upper ring and a double knot was tied. The knot was coated in wood glue and a fillet was done around the base of the centering ring.

DB_36.jpg

I section of heat shrink tubing was applied to Kevlar to protect the first few inches. The motor mount was set aside and allowed to dry over night.

DB_37.jpg

I'll be installing the motor mount today and hopefully get to the fins this evening.
 
Time to install the motor mount. The Kevlar shock cord was passed down through the motor mount to keep it out of the way during assembly.

DB_38.jpg

The motor mount was slid into the body tube making sure to keep the shock code mount away from the fin slots. The mount was slid in until the ends of the tubes were flush. The rear ring was slid in place temporarily to keep the tube centered. This will be removed to allow for internal fillets.

DB_40.jpg

With the mount drying, I removed the tape from the fins. The filler primer is cured and ready for sanding.

DB_43.jpg

The fins were sanded with 220, 400 and 600 grit to knock down the primer and make everything ready for for assembly.

DB_44.jpg

A small area where the fin will attach has been removed from the body tube for better adhesion. The fin will be attached using epoxy.

DB_45.jpg

First fin has been installed and is currently drying.

DB_46.jpg

I should have all the fins attached today so we should be looking at a mostly completed rocket tomorrow.
 
Made good progress yesterday and this morning.

Fins two and three were attached.

DB_47.jpgDB_48.jpgDB_49.jpgDB_50.jpgDB_51.jpg

After letting the fins dry, I was able to get the internal fillets done using warmed T-88 epoxy. The connection points to the motor tube and the inside of the body tube were given a small fillet using a long paint brush. Once the epoxy was in place, I used a heat gun to warm the epoxy to allow it to soak into the materials. This was left to cure over night.

DB_52.jpgDB_53.jpg

With the internal fillets cured, I inserted the rear centering ring then began adding the external fillets.

DB_55.jpgDB_54.jpg

Next up will be completing the external fillets and adding the launch lug. After that it's primer and paint. I will also need to address the nose cone fitment into the body tube. The cone is actually very loose so I'll need to build up the first inch of the tube with epoxy and maybe a little paper stock.
 
Work on the external fillet has continued. I have also attached the stand off for the launch lug.

DB_57.jpg

To address the fitment of the nose cone into the body tube, I coated the inside of the tube with epoxy and added a 1 inch wide strip of copy paper. Once stuck in place, the epoxy was warmed to allow it to soak through the paper as shown. I sanded off the minor rough spots and the cone now fits nice and snug with no wiggle. It's been a lot of years since I've seen a cone fit this poorly and I've used a ton of these tubes and cones so I'm kind of surprised by the fitment.

DB_58.jpg
 
At this point the launch lug has been attached, all fillets on the fins have been completed and I did the first coat of filler on the seams on the nose cone. If the rain stops long enough today, I'm going to get this one into primer. Then it will be time to figure out a paint scheme.

Here are some assembled pics.

DB_59.jpgDB_60.jpgDB_61.jpgDB_62.jpg
 
Did you run a simulation on this? Really cool Design / Build.

... kind of like an Honest John / Der Red Max Dwarf.
 
Did you run a simulation on this? Really cool Design / Build.

... kind of like an Honest John / Der Red Max Dwarf.

I have although I'm not sure how accurately OR simulates rockets with larger nose cones.

The PSII nose cones are heavy so no nose weight was needed. After weighing all the parts and punching those into OR, my CG should be about 13.5in from the tip giving me a stability of 1.13 with an
E12 motor on board. Odds are this will be a D motor flyer most of the time so the lighter motor put stability at 1.22.

I just clear coated the lower section this morning so I'll have updated Pics this afternoon. This one should be wrapped up this week.
 
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