LOC Precision Bruiser EXP Build

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I've been spending the past few days coming up with a mitigation for a mistake I made on this build. After I glued the middle CR to the MMAS mother tube, I did a trial fit of the fins and had trouble getting them to line up correctly. Upon further investigation, it looks like the middle CR, which has notches for the fins, was shifted/rotated slightly (maybe 1/32" or 1/16") so the notches in it don't quite line up with the notches in the bottom CR. I'm not sure how this happened, but, I think maybe the lines I used to align the middle CR were just a bit off. I put the whole MMAS assembly into the slotted body tube to confirm the mistake. Below is a picture and you can see the top CR notches not quite lining up with the slot. They look to be about 1/8" off here because any mistake made at the inner part of the circle (CR) gets amplified as you go further out in the circle.

IMG_20221204_123941796.jpg

Fortunately, I caught this before I glued the fins in place. Unfortunately, this has to be fixed as it would cause the fins to be out of alignment along the length of the rocket. That is not acceptable as it would likely cause significant spin and I'm aiming for a straight flight with no spin.

My plan to fix this is to file the notches in the middle CR so that they line up with the bottom CR and then use a few jigs/guides to ensure the fins are straight. I'm also going to confirm the lengthwise alignment using the slotted body tube. I'll put a shim in each middle CR notch to fill the gap I created when I filed them. Below are some pictures of the jigs I'm going to use. One is made from some spare 2x4 and modelled after others I've seen here on the forum and the other uses foam board and a pattern from PayloadBay at https://www.payloadbay.com/index.php?page=Tools&action=FINGUIDES. Note that the wooden jig will be held in place with some elastic wrapped around the MMAS mother tube. I've also put together two short pieces of 1x3 into a basic 90 degree angle guide and used it to mark new fin root lines on the MMAS tube.

I'm planning to start gluing fins once I've looked this over a few more times to be sure the fins will be aligned (within a few microns) in all directions.

IMG_20221206_184035275.jpgIMG_20221206_184111848.jpg
 
Yesterday I finally got around to working on this some more. I glued the first fin (finally!). I used T-88 epoxy and all of the jigs I had available to ensure it was straight. Although you can't really tell from the picture, I think it it straight and vertical. Once I have all of the fins glued I will go back and add some substantial internal fillets before the fin can goes into the body tube. Below is a picture. The lighter area in the upper notch is the shim that I added to fill the gap I created by filing the upper notch for proper alignment.

IMG_20221212_190951553.jpg


Also, I'm considering getting a K motor to use as a test for this rocket before I do the certification flight. I'm mostly concerned with the recovery side of the flight as that is when things often don't happen as expected. My L1 rocket flew successfully for the first time on the L1 cert flight, but, this is a much larger scale.
 
Here are two pictures from my Bruiser-EXP build First shows the epoxy fillets on the fin can. Maple blocks with epoxied T-nut inserts are glued to the centering rings for rail button attachments.415F3EC1-45F9-4F2E-BF35-251A7C34AC71.jpeg
A little out of order here. Using foam board for fin alignment and a band clamp to secure the fins when epoxying to the MMAS tube.

801298A5-F8E8-4933-B712-688AF177339B.jpeg
 
A bit more progress.....last night I glued on the second fin. I'm not going to post a picture of it because it looks just like the first. I also started working on the sled that I'll use for the tracker in the nose cone. I'll post a picture of that once it's done.

Tonight I stitched the second side of the Kevlar harness to the upper CR and covered the end with heat shrink so it won't fray. Here's a picture:

IMG_20221215_201622501_HDR.jpg

Also, here's a picture of the stainless steel swivel I'm planning to use between the fin can and the electronics bay. It's from Fruity Chutes and it's rated to 3000 pounds:IMG_20221215_194923311.jpg
 
Also, here's a picture of the stainless steel swivel I'm planning to use between the fin can and the electronics bay. It's from Fruity Chutes and it's rated to 3000 pounds:View attachment 551158

I only use ball bearing swivels so I've never used one like that. How well does it spin under load? Some of those kind of swivels are only designed to spin before loads are applied, which may not apply during rocket recovery.
The only non-ball bearing swivels I've tried didn't work very well. Amazon have some children's swing ball bearing swivels with 800 lbs. working loads, which should work fine if you're interested. Of course climbing swivels work very well too, but they are bigger, heavier, and a little more expensive.
 
I only use ball bearing swivels so I've never used one like that. How well does it spin under load? Some of those kind of swivels are only designed to spin before loads are applied, which may not apply during rocket recovery.
The only non-ball bearing swivels I've tried didn't work very well. Amazon have some children's swing ball bearing swivels with 800 lbs. working loads, which should work fine if you're interested. Of course climbing swivels work very well too, but they are bigger, heavier, and a little more expensive.

I will have to hang some weights off of it to try it out under load. I'm guessing/hoping it will do ok since it's from Fruity Chutes, but, it's better to test than to find out during a flight that it doesn't work.

If it doesn't work I may have to look into the climbing swivels. I also have a heavy-duty playground swivel, but, it is somewhat similar in design to the one from Fruity Chutes, so, I'm guessing it would behave in a similar manner.
 
I will have to hang some weights off of it to try it out under load. I'm guessing/hoping it will do ok since it's from Fruity Chutes, but, it's better to test than to find out during a flight that it doesn't work.

If it doesn't work I may have to look into the climbing swivels. I also have a heavy-duty playground swivel, but, it is somewhat similar in design to the one from Fruity Chutes, so, I'm guessing it would behave in a similar manner.
The playground one I linked actually has ball bearings in it so it should spin well under load.
https://www.amazon.com/dp/B08DS4Q4T...Tm90TG9nQ2xpY2s9dHJ1ZQ&th=1&tag=forumyield-20

When you put it on the fin can to keep the shock cord untwisted during drogue decent, I'm not sure there is much load on the swivels. If you remember Grapeshot, that fin can would spin very fast on the way down. I never got a twisted shock cord when using a ball bearing swivel since they spin so freely. I believe the non-ball bearing ones will twist up the shock cord until the twist in the cord overcomes the higher turning drag they have without the ball bearings.

YMMV. The only barrel swivel I tried bent the loops on both ends from deployment shock on the first flight which caused the whole thing to stop spinning freely and twist of the shock cord. I through it out and went with the #10 660 lbs. welded loop, SST, ball bearing fishing swivels after that. Except Big Bird, that got a 30K Newton climbing swivel.
 
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I tried out my swivels this afternoon with a 25 pound weight. The one I had in the picture spun, but, not as smoothly as I expected. It would get about 8-10 twists in the cord and then spin to catch up. It spun better with just a 10 pound weight. It weighs about 2 ounces.

The other swivel I tried was another barrel swivel rated to 2000 pounds. It spun very smoothly with both the 25 and 10 pound weights. It is about twice as long and weighs about 7 ounces.

Based on this, I think either would probably work, but, the larger one was definitely smoother so I'll probably go with that. I looked at the one @Handeman referenced and it looked good, but, even though it is probably overkill I was aiming for a higher load limit. My other option would be to get a climbing swivel similar to the other one @Handeman referenced using ball bearings. I see one on Amazon rated to 35kN that weighs less than 3 ounces. That also sounds good, but, is it worth the extra cost?

Also, for reference, in the past I always used ball bearing fishing swivels with welded rings. The largest was rated to 650 pounds, but, those rockets were all less than 15 pounds.

If anyone has experience with the Fruity Chutes swivels please let me know.
 
This rocket is not all that heavy. Th heaviest config I can put in mine would be 3 x Loki M1378s (I really don't recommend it though - that would rip this rocket apart) and even then, the recovery weight maxes out at around 35 pounds.

I use these 1500 Lbs swivels in my Bruiser EXPs. At about $1.50 a piece, they are cheap and have not failed me after many, many launches:

https://www.amazon.com/gp/product/B073JCL2GR
PXL_20211115_050520265.jpg
 
This rocket is not all that heavy. Th heaviest config I can put in mine would be 3 x Loki M1378s (I really don't recommend it though - that would rip this rocket apart) and even then, the recovery weight maxes out at around 35 pounds.

I use these 1500 Lbs swivels in my Bruiser EXPs. At about $1.50 a piece, they are cheap and have not failed me after many, many launches:

https://www.amazon.com/gp/product/B073JCL2GR
View attachment 551375
I'm glad they have worked for you. Those are exactly the ones that failed on the first flight when I tried them and I won't use them ever again. Ball Bearing swivels all the way for me.
 
I'm glad they have worked for you. Those are exactly the ones that failed on the first flight when I tried them and I won't use them ever again. Ball Bearing swivels all the way for me.

Sorry they failed! I have had pretty good luck with them, but, clearly, they may not be the best if they aren't working for other folks.

For me, the recovery weight on the rockets I have been using them on have been about 25 pounds or less, just for context.
 
Sorry they failed! I have had pretty good luck with them, but, clearly, they may not be the best if they aren't working for other folks.

For me, the recovery weight on the rockets I have been using them on have been about 25 pounds or less, just for context.
My rockets were all below 10 lbs. I just don't know what size I had vs. what you were using. Mine could have been under sized (about 2.5" end to end). All I know is the rings were stretched out from the drogue charge, (doubt it) or from the fin can hitting the end of the shock cord after the main opened. (more likely). Either way, the stretched rings also distorted the parts that go into the barrel and caused the whole thing to stop spinning if there was even a little bit of load on the swivel.
The fact that it distorted and stopped working after one flight is why I only use the ball bearing swivels now. I never had that issue with them.
 
My rockets were all below 10 lbs. I just don't know what size I had vs. what you were using. Mine could have been under sized (about 2.5" end to end). All I know is the rings were stretched out from the drogue charge, (doubt it) or from the fin can hitting the end of the shock cord after the main opened. (more likely). Either way, the stretched rings also distorted the parts that go into the barrel and caused the whole thing to stop spinning if there was even a little bit of load on the swivel.
The fact that it distorted and stopped working after one flight is why I only use the ball bearing swivels now. I never had that issue with them.

Good to know, it may be time to replace those barrel swivels on these lighter rockets.

For big stuff, I use more robust swivels, but it isn't worth the cost savings on the < 50 pounders if the swivel fails and ruins a good rocket.
 
This rocket is not all that heavy. Th heaviest config I can put in mine would be 3 x Loki M1378s (I really don't recommend it though - that would rip this rocket apart) and even then, the recovery weight maxes out at around 35 pounds.

I use these 1500 Lbs swivels in my Bruiser EXPs. At about $1.50 a piece, they are cheap and have not failed me after many, many launches:

https://www.amazon.com/gp/product/B073JCL2GR
View attachment 551375

I'm suddenly feeling much more comfortable in my recovery system choices now.

It'll be < 6lbs pad weight on first flight.
 
I tried out my swivels this afternoon with a 25 pound weight. The one I had in the picture spun, but, not as smoothly as I expected. It would get about 8-10 twists in the cord and then spin to catch up. It spun better with just a 10 pound weight. It weighs about 2 ounces.

The other swivel I tried was another barrel swivel rated to 2000 pounds. It spun very smoothly with both the 25 and 10 pound weights. It is about twice as long and weighs about 7 ounces.

Based on this, I think either would probably work, but, the larger one was definitely smoother so I'll probably go with that. I looked at the one @Handeman referenced and it looked good, but, even though it is probably overkill I was aiming for a higher load limit. My other option would be to get a climbing swivel similar to the other one @Handeman referenced using ball bearings. I see one on Amazon rated to 35kN that weighs less than 3 ounces. That also sounds good, but, is it worth the extra cost?

Also, for reference, in the past I always used ball bearing fishing swivels with welded rings. The largest was rated to 650 pounds, but, those rockets were all less than 15 pounds.

If anyone has experience with the Fruity Chutes swivels please let me know.
This is the option I am going with for my 6" in. Wildman https://www.amazon.com/ProClimb-USR...recreation&sprefix=climbing+sw,aps,196&sr=1-7
 
Last night I glued the last fin to the MMAS mother tube. It looks just like the others, so, I won't bother with a picture.

I also glued on the other end of the tracking sled that will ride the nose cone just below the weight cartridge. The sled consists of two circles joined by a rectangle. The circles are sized to fit perfectly in the nose weight host tube. I have a tracker already built that I am going to use by zip-tying it to the sled. It is designed to fit in a 38mm MMT that I've added to a few of my other rockets, usually in the nose cone.

Below is a picture of it before I zip tie on the tracker and add the U-Bolts. The antenna will stick into the lower (empty) part of the nose weight cartridge. I can also replace the antenna with a shorter one if needed. The rectangular tray is made from 1/2" plywood.

IMG_20221219_201801575.jpg
 
Tonight, I installed the threaded insert I'm going to use for the rail buttons. I have a plywood block glued to the bottom CR and I drilled that out for the 1/4 x 20 threaded insert. For the upper one, I'm going to use a tee nut through a thin piece of plywood near the top of the tube coupler. I have 1/4 x 20 unistrut rail guides in addition to 1515 buttons that use the same screws, so, I should be able to easily switch between them.

I also started tonight on the internal fillets. I'm using T-88 thickened just a bit with silica. I use a tongue depressor and a heat gun to smooth them out. The first set is curing. I'm debating with myself if I should make the next set a bit larger. Here's my first set:

IMG_20221220_192535621.jpg
 
Tonight, I installed the threaded insert I'm going to use for the rail buttons. I have a plywood block glued to the bottom CR and I drilled that out for the 1/4 x 20 threaded insert. For the upper one, I'm going to use a tee nut through a thin piece of plywood near the top of the tube coupler. I have 1/4 x 20 unistrut rail guides in addition to 1515 buttons that use the same screws, so, I should be able to easily switch between them.

I also started tonight on the internal fillets. I'm using T-88 thickened just a bit with silica. I use a tongue depressor and a heat gun to smooth them out. The first set is curing. I'm debating with myself if I should make the next set a bit larger. Here's my first set:

View attachment 552174
Unrelated, is stripping the glassine layer off standard practice?
 
Unrelated, is stripping the glassine layer off standard practice?
I don't strip it off...too much work. JUST SCRATCH IT UP a LITTLE with a few swipes of CORSE sandpaper. As soon as your glue/epoxy is on it. It will soak thru the scratches and bond just fine. (Fine sandpaper will not scratch deep enough 80grit works well.)
 
Unrelated, is stripping the glassine layer off standard practice?

I stripped the glassine on the MMT because that is what the instructions (and some others) recommended. I'm pretty sure that just roughing it up would also work.

As @Handeman suggested, I'm not planning to strip it on the body tubes where I'm painting.
 
Yesterday I did the second set of internal fillets. I made them a bit larger than the first set. Here's a picture:

IMG_20221223_122001451.jpg


The MMAS system includes an optional/auxiliary upper thrust ring, similar to an engine block in LP, that is glued into the MMAS mother tube just above the upper CR on the MMAS adapter. It is designed to spread the thrust load so it is not all on the lower CR/MMT glue joint. Since I'm using the Aero Pack retainer that will transfer thrust to the bottom CR, I don't need it for 75MM motors, but, I may want it for other configurations so I installed it. I spaced it about 1/8" above the upper CR on the 75MM adapter so it won't interfere. Note that this engages the MMAS adapter CR and not the actual motor, so, it doesn't limit the length of motors that can be used. It will eventually get a bit more of a fillet, but, here's a picture for now:

IMG_20221223_122018630_HDR.jpg
 
I've made a bit more progress. Last week I did the third internal fin fillet and since then I've added a bit more of a fillet to the middle CR. Here's a picture of the fillets before I added the fillet to the middle CR. Note the block with the threaded insert at the bottom for the rail guide/button mount:
IMG_20221227_202306926.jpg


Last night I glued the switch band to the coupler. The instructions for the electronics bay have you only use 1/2 of the length of the coupler so it ships with two 1/2 length coupler stiffeners and 1/2 length all-thread rods. Since I've got plenty of room for motors and recovery gear I'm going to keep it simple and modify it to use the whole length of the coupler. I'll glue the two stiffeners together (in the coupler) and get two longer lengths of all-thread rod. It will make the switch mounting a bit easier and reduce the amount of powder I'll need for the ejection charges. There was another thread recently on here about on this very same question and most folks seemed to agree this was the way to go for longer rockets.
 
In the past few days I've glued the stiffeners into the electronics bay coupler and I've also glued the mounts for the screw switches to the electronics sled. I'll post pictures of the sled once I've got it done.

I also received the motor (a single-use 75MM M1350) via UPS today (thanks @WILDMANRS). Here's a picture of the case next to a standard Big Bertha:

IMG_20230113_192419837.jpg
 
Great build. Will start mine on Thursday.
I have my Bruiser coming tomorrow. I just got the non dual deploy kit. Many years ago my friend flew his all most each time on a AT K550 with single deploy he had great flights and recovery each time.
 
I have my Bruiser coming tomorrow. I just got the non dual deploy kit. Many years ago my friend flew his all most each time on a AT K550 with single deploy he had great flights and recovery each time.
Same here. I have wanted one since I saw Mark Canepa's fly.
 
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