John's Rocket Blog

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Category: FrenzyBuild (page 1 of 2)

Testing ejection charges – Part 2

I tested the main deployment charge with 3 grams. (Ignore the narration stating it was 2 grams)

Now that I have my motor casing, I was able to test the apogee charge with 2 grams.

Testing ejection charges – part 1

Tested main ejection charges today. I started with 1gm pyrodex, but that was not enough to break the shear pins. Tried 2 gm pyrodex, same result. Tried 1gm 4FG BP, broke the pins but did not eject the laundry. Tried 2gm 4FG BP, had the desired result. Video

I suspect that the tightly packed parachute is the reason for needing double what the calculation asked for. I suspect that once I get the engine casing(to seal the compartment) and test  the apogee charge, that it will not need to be doubled.

The terminal blocks broke off the aluminum bulk plate.  I had originally attached them with epoxy. I also tried hot glue. I will have to drill a small hole and attach them with a screw because nothing wants to stick to them.

Altimeters

Mounted the primary and backup altimeters to a sled

Lipo batteries are protected in foam rubber and zip tied to the back side of the sled.

Including another photo of the switches on the switch band bulk plate… there are two others not visible in this photo, one for the primary and one for the backup altimeter.

Fins part 3

Mixed up epoxy with low density fairing filler….

measured out the width of the filet with the pipe that I was going to use to smooth things out

applied the epoxy

smoothed it out

and removed the tape

one small drip that would need clean up once fully cured

sanded things out nicely

first coat of primer

applied bondo to deal with a few things I did not like the looks of

Missing is a photo of the fins after the bondo was sanded off….

Onboard camera

Got a cool video camera…. a Mobius Mini Action Camera …. super nice and small

I wanted an outward facing camera this time to reduce drag. I marked out where the lens would look out from the switch band, and drilled the hole (not shown here)

One problem…. the camera has too small of a built in battery. It does, however, accept external power. So I mounted a 1 Ah lipo battery, and a booster/charger from sparkfun. The whole thing is attached to a bulk plate that I made out of modeling plywood.

The micro switch is accessible  via the vent holes. The camera turns on and starts recording automatically once the button is pressed.

The connectors are hot glued in place, so that g-forces do not cause anything to come loose.

 

 

Fins Part 2

This happened back in August of last year despite me not posting it until now.

Ugh…. disaster

Thought I’d be clever, and mix up some epoxy with chopped carbon…

load it into a syringe with an extension tube…

And try to inject it for my internal fillets

No pictures of the disaster that followed….. clogged tube, big mess….

Days/weeks later, I slowly finished the internal fillets by a pouring method without the carbon fiber.

Fins Part 1

Started by finishing up step 18 now that I have my motor retainer…

Step 18 – Mark the motor tube 6 1/8” and 1/2” from one end of the motor tube. Epoxy two of the three centering rings on each of the marks. IMPORTANT: make sure the motor tube is clean of epoxy from the centering ring that is 6 1/8” from the end for the remaining 15 or so inches of the motor tube because the fin roots will need a clean surface to attach to. At this point it is a good idea to test fit the retainer because it is much easier to sand the motor tube now rather than later.

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Step 19 – Sand the slotted main body tube for at least 1/2” around the fin slots inside and outside to rough the surface for the fin fillets. Also sand where the centering rings will attach in front of the fin slots on the inside. You can wrap sand paper around a large dowel to help sand the inside of the body tube.

No photos of this sanding process.

Step 20 – Test fit each of the fins in the fin slots and file the slots to make sure you have a snug but smooth fit. Also sand the sides of the fin tangs so the entire tang plus at least 1/2” of the exposed fin above the body tube is roughed up so epoxy will stick to the fin. You can clean any residue from the machining process using acetone. It is a good idea to number your fin pairs and slots to remember which fin fits best in what slot.

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Lots and lots of sanding. The slots in the main body tube required a little bit of work with a dremel.

Step 21 – Use a door jamb to mark half way between two fins on the slotted main body tube. This line will be used later to align the rail buttons.

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Step 22 – Test fit the motor tube assembly inside the slotted main body tube to ensure a smooth fit. The two centering rings should go in first. When you are satisfied with the fit, spread epoxy on the inside of the body tube above the fin slots and slide the motor tube in until the centering rings clear the forward fin slot. Make sure any fillet on the forward centering ring is clear of the slot also so the fin root can seat against the motor tube. The aft end of the motor tube should be recessed about 1/2” inside the aft end of the body tube. IMPORTANT: do not use epoxy on the 3rd centering ring yet. Insert the 3rd centering ring temporarily inside the aft end of the rocket to make sure the aft end of the motor tube remains centered while the epoxy sets.

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Testing, sanding, testing, sanding, and finally epoxy them into place.

Step 23 – With the 3rd centering ring temporarily still in place, tack each of the fins in place using CA on the root edge of the fin. Start with the aft fins first because the forward fins overlap the aft fins. Make sure each fin seats properly to the motor tube before applying CA. Readjust your slot if needed. IMPORTANT: make sure you do not accidentally glue the 3rd centering ring in place. Clamp a scrap of wood to the fin pair to make sure they stay in alignment with each other. Remove the aft 3rd centering ring after the glue sets

I printed a fin alignment guide from PayloadBay.com and cut it out of some thin plywood.

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I used JB Weld to tack the aft fins in place and let it sit undisturbed overnight.

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Next, I tacked the forward fins in place, using angle irons and clamps to ensure perfect alignment.

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Motor Tube Part 1

Step 17 – Sand the outside of the motor tube to rough up the surface for the epoxy to stick to.

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Step 18 – Mark the motor tube 6 1/8” and 1/2” from one end of the motor tube. Epoxy two of the three centering rings on each of the marks. IMPORTANT: make sure the motor tube is clean of epoxy from the centering ring that is 6 1/8” from the end for the remaining 15 or so inches of the motor tube because the fin roots will need a clean surface to attach to. At this point it is a good idea to test fit the retainer because it is much easier to sand the motor tube now rather than later.

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I had not yet purchased the retainer, so I had to stop here.

 

Payload Bay Part 3

Step 16 – Measure 2” from the aft end of the payload tube on each of the lines (the opposite end you did the shear pins earlier). This is where you will drill the rivet pin holes. IMPORTANT: when you seat the altimeter bay inside the payload tube, make sure your altimeter vent holes are not lined up with the rivet lines – turbulence from the rivets can disrupt the airflow over the altimeter vent holes. With the altimeter bay seated properly, drill a single 5/32” hole at one of your 2” marks. IMPORTANT: insert a rivet into this hole before you rotate the tube for the other 2 holes. Last make an alignment mark on the altimeter bay and payload tube so you can remember the orientation since the spacing of the rivets may not be even. Make sure you transfer this mark when you paint the rocket.

I’ve not had the best of luck with plastic rivets in the past. So I decided to go with a stainless steel screw and weld nut. I measured and drilled…

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Placed a few drops of thickened epoxy onto the weld nuts, and some vaseline on the screw to protect the threads…

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And then secured the parts together. I applied thickened epoxy all over the weld nuts.

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I also drilled and tapped for shear pins on the av bay to main body tube joint.

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Payload Bay Part 2

Step 10 – Measure 2” from one end of the payload tube on each of the lines. This is where you will drill the shear pin holes. With the nose cone seated properly, drill a single 5/64” hole at one of your 2” marks. IMPORTANT: insert a 2-256 nylon screw into this hole before you rotate the tube for the other 2 holes. Last make an alignment mark on the nose cone and payload tube so you can remember the orientation since the spacing of the shear pins may not be even. Make sure you transfer this mark when you paint the rocket.

My drill and tap set arrived today, so I went back and completed this step.

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I was originally hoping to counter sink slightly in order to make the head of the screw more flush, but the fiberglass walls are so thin, I am probably going to let it sit proud.

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