LOC Precision Bruiser EXP Build

kswing

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Today, I glued the fin can into the lower body tube. Prior to assembly I taped over the holes for the rail button threaded insert and the motor adapter screws so they wouldn't get clogged with epxoy.

I noticed that the lower CR was catching on the edges of the body tube, so, I used some thin pieces of mylar ( .014" thick) left over from a glider project as shims to help it to slide in. Prior to sliding the lower CR in I coated the bottom inside of the tube with epoxy so that it would create a nice fillet just above the lower CR. I also coated the body tube just above the upper CR and then added a fillet once it was all together. Once it was together I used a few spring clamps to keep the body tube against the lower CR. I'm planning to fill the slots in the body tube below the fins with the body tube pieces I removed backed by some lightweight fiberglass cloth.

Below are some pictures. Note that the ones with the spring clamps and the shims were taking during a dry fit.


The white strips are the mylar shims used to hold the body tube out while the fin can slides in.
IMG_20230116_114908140.jpg


The mark near the "AFT" writing is where I have the threaded insert for the rail button.
IMG_20230116_123734020.jpg



This shows my initial fillet at the upper CR. I plan to add more here in addition to on the bottom CR once this round dries.
IMG_20230116_152106464.jpg
 

kswing

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Tonight I worked on the electronics bay sled. For altimeters, I'm going to use a Missleworks RRC2L and an Eggtimer Quantum. Both of the altimeters have been used successfully for previous launches in other rockets.

For switches, I'm going to use 6-32 screw switches with covers/guides that I got from Missleworks. I'm planning to use a switch for the Quantum even though it will still be armed via Wi-Fi. For batteries, I'm using a pair of 2s (7.4V) 800mah lipos (one for each altimeter). The batteries are wrapped in bubble-wrap and held in place with zip ties.

I haven't done the bulkheads yet, but, for those I'm planning to use 1/2" PVC caps as my charge wells with euro style terminal blocks for the e-match connections. I will post pictures of the bulkheads once they are assembled.
I'm using JST connectors between the altimeters and the switches and the terminal blocks so that I can easily disconnect them as needed. In order to avoid improper connections, I'm color coding the wires near the JST connectors with tape. Red tape indicates power, blue tape indicates main, and yellow indicated drogue. I've planning to have 3 vent holes in the e-bay and I'm going to use two of them to access the screw switches. Below are some pictures with more details.

Here's the type of screw switch I'm using (before I add the cover/guide). Note that I've twisted and then soldered together the black wires and covered the joint with heat-shrink. The red wires are soldered to the switch on the other side.
IMG_20230117_192105547.jpg


Here are some pictures of the avionics sled. The arrows point toward the nose. I'm planning to do a bit more cable control, but, this shows the overall layout. One of the switches is mounted on the edge of the sled and the other on a pylon so that they will line up with 2 of the 3 vent holes. The piece of threaded rod has been added temporarily to be sure the zip ties didn't interfere with it. I mounted the altimeters using nylon standoffs and nylon screws. To install them, I drill the hole for the standoff threads and then tap it and then coat it with thin CA.
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kswing

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Why the bubblewrap? (I've not heard of this before - just curious)

I use the bubble wrap for a bit of cushioning and protection for the batteries. I'm not sure if it's necessary, but, it doesn't take up much space and it weighs very little. They usually come shipped in small bubble wrap bags (inside a box), so, that's what I've typically use.
 

kswing

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Last night I worked on the drogue bulkhead. I had been planning to use 1/2" PVC end caps as the charge wells, but, after running some calculations I found they might be a bit close on volume, so, I switched over to 3/4" PVC end caps. I suspect they will be a bit oversized, but, it is much easier to handle that with some extra dog barf than to figure out a way to get extra powder in if they are undersized. I've filled the gaps around the wires with hot glue so that they can easily be re-wired if necessary. I attach the terminal blocks and the PVC caps to the bulkhead by roughing them up a bit and then using 30 minute epoxy.

Here's a picture:
IMG_20230120_165230105.jpg
 

kswing

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Suggest coating the wooden bulk plate with a light coating of epoxy. Makes clean up a lot easier. West System laminating epoxy is what I use.
That is a good suggestion, thanks! I have some laminating epoxy so I will coat both of the bulkheads with it.
 

kswing

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Last night and this morning I added a bit more fillet to the bottom and top CR. I also glued back in the slots I had cut out for the fins. I thickened the epoxy a bit so that it would stay in place. Here are some pictures...
IMG_20230121_104406900.jpg

The blue tape is to protect the kevlar harness from the epoxy.
IMG_20230121_190028184_HDR.jpg
 

kswing

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Last night I setup the bulkhead for the main side. Since there's less volume in the top, I used 1/2" PVC end caps for my charge wells. I also sealed the bulkhead with laminating epoxy prior to installing the charge wells and terminal blocks.

This morning I cut out the hole for the rail button/guide mount. I'd put a block with a 1/4-20 threaded insert above the bottom CR, so, I just had to cut the body tube over top of it. I used 1/4-20 so that I can easily switch between 1515 and unistrut rail guides.

Here are some pictures:
IMG_20230122_095220381.jpg IMG_20230122_101102541.jpg
 

kswing

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Yesterday I glued the lower coupler into the middle body tube. I'd already glued the stiffener into the coupler. Once I've done the fin fillets I'll glue the other half of the lower coupler into the fin can tube to join the two lower tubes.

Tonight I started on the external fin fillets. I'm using RocketPoxy here instead of the T-88. I mix it for about 5 minutes, then let it set and thicken for 20-30 minutes, then smooth it in place with a tongue depressor. I taped off the fin and body tube to reduce the potential for mess. The RocketPoxy I had on hand was one month past the expiration on the container, so, prior to doing this I mixed a batch to verify that it would cure properly. It cured well without any residual stickiness, so, I'm considering it good.

Here's a picture:

IMG_20230123_202057998.jpg
 

kswing

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A few days ago I drilled the vent holes in the switch band. Based on the calculations, for 3 holes they should have been 11/32" each. I didn't have an 11/32" drill bit, so, I went slightly larger with 3/8" (12/32"). After drilling I cleaned up the edges and coated them with thin CA so they aren't fuzzy.

Last night and today I did the other two sets of external fin fillets. Overall I think they're ok, but, they may need a bit of sanding at the edges. Here's a picture of one from a different angle:

IMG_20230125_152647404.jpg
 

kswing

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Yesterday I finished assembling the electronics bay. I've attached the all-thread to the lower bulkhead using fender washers and nuts and I coat the end of the threads with epoxy so they won't shake loose. The upper bulkhead will be held on with wing nuts and fender washers. I use other nuts along the all-thread to keep the sled at the proper height. I had to adjust the position of one of the screw switches a bit, but, now they both line up with vent holes. Here are some pictures:

IMG_20230128_165318134.jpg IMG_20230128_170004718.jpg


I also did some calculations based on actual weights, and it looks like I might have to re-think my parachute a bit. My current final descent rate using the 96" LOC parachute comes out to about 23 ft/sec which is a bit high but would probably be ok. I haven't yet found information on what the actual Cd (Coefficient of Drag) of the LOC parachute is, so, I'm using .75 which is the default. If the parachute actually has a better Cd or if I think the rocket is strong enough I can probably stick with the current chute. The parachute is urethane coated calendared nylon (almost non-porous), so, it is probably better than the default.

If I decide to make the descent rate bit slower, I'm considering either having a separate smaller parachute for the nose cone with the two parts connected via a long cord, or, buying some bulk nylon fabric and stitching a new, bigger parachute. @Handeman did the separate parachute thing for his L3 and it seemed to work well.
 

kswing

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The past few days I've filled the spiral grooves on the body tubes. I probably could have skipped this step since it is a big rocket, but, I thought it might make it look a bit better. I used slightly thinned Elmer's Carpenter's Wood Filler (CWF) and applied it into the spirals with my fingers. Once it dries I sand most of it off. Here's a picture of the fin can with a piano bench for scale:

IMG_20230130_200248412.jpg


Tonight, I connected the tracker to its sled. I put together a new tracking transmitter for this rocket so that I wouldn't have to switch it out. I'm using a slightly smaller antenna this time, but, it still has plenty of range when I test it driving around the neighborhood. It is my own design and it uses a GPS signal transmitted down via LoRa radio (in the 900Mhz band), so, it should be good for a few miles line-of-sight. I bought the components from Adafruit and wrote some software to make it all work together. Send me a message if you'd like more information about it. I'm holding it onto the sled with zip ties and I have a thin piece of balsa under the electronics to protect the connections. I don't have a switch for the power. The battery has plenty of capacity to power it for a few hours, so, I plan to just plug it in prior to assembling the rocket at launch. This will slide into the nose weight mother tube and the antenna will stick into some of the extra room in the weight cartridge. Here's a picture:

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kswing

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I was out on travel this week, but, I have been working on this on and off.

I glued some thin copper into the body tube to act as a backing for the shear pins. I'm planning for three 4-40 shear pins for the nose and just one 2-56 for the fin can. I'll use plastic rivets to keep the upper body tube attached to the e-bay.

I started stitching a deployment bag out of Nomex cloth and Kevlar thread. It won't be as pretty as those you can purchase, but, it will cost much less and should work just as well.

I also started painting. I've painted the NC and parts of the body tubes. I'm planning to have a dark green nose cone and fins with white everywhere else. I may also do a green/white roll pattern just below the nose cone.

I decided I'm going to use a separate parachute for the nose cone that will also act as the pilot for the deployment bag I'm using for the main. This will reduce my descent rate a bit. I will size the extra parachute to bring the NC down just a bit slower than everything else. To keep everything together, I'll connect the main to the deployment bag with about 100' of either 250lb kevlar cord or possibly dacron line. I got this idea from @Handeman.

Today, I worked a bit on a 54mm adapter for the MMAS. I need this because think I'm going to do a test flight with a K1100 or K1103. I had some extra 54mm MMT around and I'm cutting the centering rings and thrust plate out of 1/4" ply using my drill press and an adjustable hole saw.

Here's a picture of the copper reinforcement (I haven't drilled for the shear pin yet):
IMG_20230212_130048789.jpg


Here's a picture of the deployment bag. It still needs another elastic band to hold the shroud lines and straps/cords to connect it to the pilot and the main.
IMG_20230212_190000644.jpg
 

kswing

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The past few days I've been finishing up a few things on this rocket. Today I drilled the holes for the shear pins. I had reinforced the tube with thin copper and as I drilled through one of the copper disks came loose. I could re-glue it, but, the tube where it was is coated with epoxy, so, I think that will work almost as well as the copper disk.

Yesterday and today I worked on the recovery harness. I'm using 5/8" tubular nylon (TN) that came with the kit. It is rated to 2200 pounds. On the drogue side, I have a loop of Kevlar that ends just above the fin can and will have a swivel attached. Between the swivel and the e-bay will be 25 feet of the TN, so, the total length on the drogue side will be about 30 feet.

On the main side, I've shortened the TN down to about 15 feet and sewn a loop in the cut end with Kevlar thread in a sewing awl. This length will be from the e-bay to the main chute. The nose cone will have a separate parachute, so, I will also have a short length of TN (about 2 feet) that goes from the nose cone to its parachute since the attachment point on the nose will be at the shoulder. Here's a picture of the loop I sewed in the TN:

IMG_20230217_201245299.jpg


I'm hoping to start testing my deployment charges this weekend. I'll probably use a temporary harness to connect the NC during testing so it doesn't fly all the way across the yard. I'm going to start with the smallest charge that I think might work and go up from there. I also have somewhat new neighbors, so, I'm going to give them a heads up before I start making loud noises.

I also still need to paint the fins and put another coat on some of the body tube, but, that shouldn't interfere with charge testing.
 

kswing

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In addition to making a nose weight cartdridge and gluing together a 54mm MMAS adapter, yesterday and today I worked a bit more on painting this rocket. Last night I taped off as needed for a roll pattern at the top of the body tube and this morning I painted it. Prior to painting the darker color (hunter green) I painted a bit of the base color so that if any seeped through it would be in the base color (white). I let this base coat dry for about 45 minutes before painting the green. I've never painted a roll pattern before, but, overall I think it turned out ok. There are minor mistakes in a few places, but, I think it will mostly pass the 5 foot test. Here are some pictures:

Body tube taped off:
IMG_20230218_191041725.jpg


After pulling the tape:
IMG_20230219_114521267.jpg
 

crossfire

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In addition to making a nose weight cartdridge and gluing together a 54mm MMAS adapter, yesterday and today I worked a bit more on painting this rocket. Last night I taped off as needed for a roll pattern at the top of the body tube and this morning I painted it. Prior to painting the darker color (hunter green) I painted a bit of the base color so that if any seeped through it would be in the base color (white). I let this base coat dry for about 45 minutes before painting the green. I've never painted a roll pattern before, but, overall I think it turned out ok. There are minor mistakes in a few places, but, I think it will mostly pass the 5 foot test. Here are some pictures:

Body tube taped off:
View attachment 564282


After pulling the tape:
View attachment 564283
Looks nice
 

kswing

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Launch this coming weekend?
I think it is almost ready to launch, but, I won't have a motor ready for it this weekend. My current plan is to do a shakedown flight on a 54/1706 K1103 probably at the first BattlePark launch in March. It sims out to just over 2K which should be high enough to verify my recovery system.
 

kswing

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Today I started testing deployment charges on the drogue side. To plug where the motor would be, I put a circular piece of poster board across the top of the motor tube. I'm triggering the test via Wifi using the Eggtimer Quantum. I used the online calculators to estimate how much powder to use, but, they warn you that they will overestimate for larger body tubes.

I started with 5g and I think that might work. The pieces separated fairly well, but, it also blew the poster board apart. It should have even better separation with the motor tube fully plugged.

I will probably run another test on it in a few days with 4.5g (and a better plug for the motor tube) to see if that is enough. My wife says I shouldn't do too many each day as it may scare the neighbors. I may also try a test on the main side later today as that will use much less powder.

Here's a video:
View attachment VID_20230220_110212757.mp4
 

pathtouch

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Today I started testing deployment charges on the drogue side. To plug where the motor would be, I put a circular piece of poster board across the top of the motor tube. I'm triggering the test via Wifi using the Eggtimer Quantum. I used the online calculators to estimate how much powder to use, but, they warn you that they will overestimate for larger body tubes.

I started with 5g and I think that might work. The pieces separated fairly well, but, it also blew the poster board apart. It should have even better separation with the motor tube fully plugged.

I will probably run another test on it in a few days with 4.5g (and a better plug for the motor tube) to see if that is enough. My wife says I shouldn't do too many each day as it may scare the neighbors. I may also try a test on the main side later today as that will use much less powder.

Here's a video:
View attachment 564504
Haha yea can confirm I did 3 grams in a 7.5ā€ Doorknob and the camera doesnā€™t do justice
to how loud they are. I usually end up getting at least one of the neighbors dogs barking even though we all have 2acre min lots.
 
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