Upscale Big Brute

This thread will be the description of my upscale Big Brute (5.38"). This may not have the detail of the similar articles by Phil, Arl, and Nick , but I hope you find it to have some socially-redeemable value

Brief:

My first mid-powered rocket was the North Coast Big Brute (pre-Estes). I love stubby rockets and when it came time to decide how to use some of the 5.38” tubing that I won from LOC, an upscale Big Brute was the natural decision. I decided incorporate several features I’d been wanting to try, including: air starts, electronics mounted in the rocket’s fin unit, and an ejection cannon based on ¾” PVC fittings. My upscale has a central 38mm mount with two 29mm and two 24mm motor mounts.

Components:

·One LOC 5.38” tube
·One LOC 5.38” coupler, for the inner lining of the electronics bay
·One LOC 38mm MMT tube
·Two LOC 29mm MMT tubes
·Two LOC 24mm MMT tubes
·Short piece of 10.5mm tubing for the air start igniter conduit
·One LOC 5.38” LONG nose cone
·Three LOC 38mm-5.38’ centering rings, two of which were custom drilled for two 29mm and two 24mm mounts by Performance Hobbies
·Four 3/16” plywood fins, custom cut by Performance Hobbies
·One LOC ½” launch lug
·Two 1500-series Delrin rail buttons from railbuttons.com (Matt’s Railbuttons)
·One 38mm Slimline motor retainer from Giant Leap
·One ¾” PVC threaded adapter
·One ¾” PVC male plug
·Four small pieces of coat hanger wire, used to insure the PVC coupler is affixed solidly
·Misc. nuts, bolts, and washers for retention of 29 and 24mm motors
·Misc. 3/16” plywood for baffles in the electronics and ejection bays
·Audio quick connect terminal for ejection and air start igniters
·TBD switches to break connections to above
·TBD hardware for electronics and ejection hatches
·Clear plastic from a suitably sized plastic jar for electronics hatch window
·Main recovery harness, chute, and Nomex bag borrowed from other projects
·Backup nose cone harness - ¼” tubular Kevlar and one eyebolt
·TBD nose weight

Photos:

<a href="https://users.erols.com/rstaff/temp/ubb1.jpg"> Motor mount components, side view </a>
<a href="https://users.erols.com/rstaff/temp/ubb2.jpg"> Motor mount components, bottom view </a>
<a href="https://users.erols.com/rstaff/temp/ubb3.jpg"> Slimline retainer </a>
<a href="https://users.erols.com/rstaff/temp/ubb4.jpg"> Nose cone, body tube, and fins (note the original Big Brute in the upper left) </a>

Construction:

The first photos show the components of the motor mount assembly (top and bottom rings are dry-fit). As you can see, the 38mm motor mount extends to the third centering ring and the other tubes, including the 10.5mm wiring conduit only run between the lower two rings. These rings will sandwich the fin tabs of the fins. I added small bolts to the lower ring to serve as attachment points for outboard motor retention. Since I plan to use SU motors for the outboards, I probably will not use positive motor retention, but I included them in case I ever want to use reloadable motors. The Slimline retainer will be installed after the rear centering ring is installed, which will itself be installed after the rest of the motor mount, fins, and associated internal fillets. I will prepare a separate, brief review of this device.

The electronics and ejection charge bays will be between the top two rings. These bays will be 180 degrees apart. One bay will provide access to the ejection cannon and the conduit, and the other will hold the electronics. The ejection charge leads will be connected to quick connect audio connectors. All wiring will be replaceable after assembly (a design goal, all details not worked out). The hatch for the electronics bay will have a clear insert so the LEDs on my G-Wiz Deluxe will be visible. This hatch will also house mini audio jacks (TBD) to isolate the ejection and air start igniter current paths. These bays will be isolated from one another in case gasses enter through the air start port or leak from the ejection cannon. The section of 5.38” tubing will serve to support the hatch doors, and will be cut in-situ, to match the hatches.

You can see the PVC coupler (i.e. the ejection cannon) and U-bolt have already been installed in the upper ring. Initially, I was worried about two things: the cannon blowing back into the bay, and the cannon twisting when the ejection plug in screwed in. The first item should not be an issue because the coupler has protrusions, presumably to allow a wrench to attach. Although epoxy alone might have solved the twisting issue, the male plugs do get pretty tight and I’d hate for it to twist rather than unscrew. So, I drilled four small holes into the side of the coupler, ahead of where the make plug would seat. I also cut corresponding notches into the centering ring. Four small pieces of coat hanger wire fit into the holes and then down into the notches. I still epoxied it in, using JB Weld on one side and 30 minute Bob Smith on the other (leftovers from other jobs). That adapter isn’t moving now!

I found the LOC tubing was much easier to cut with an Exacto knife than I expected. I already cut the fin slots, and don’t foresee any problems with the hatches. Any imperfections with those cuts will be sanded out, as some slop between the hatch door and the slot is desirable. I have not figured out how I want to attach the doors. I wish I could get 8 samples of some Southco miniature compression latches!

More later…

Sounds like a really neat project. Can't wait for the next installment.

However... what, pray tell, are "Southco miniature compression latches?"

Ken,

I should have included this link. I'll also try to describe them. They are a latch used in electronic equipment. They typically attach to an access panel which is hinged on the other side. There is an arm that screws up and down a shaft on the latch. There should be a diagram with the attached link. To close the latch, you twist the knob on the panel, which causes the movable arm to swing outward (perpendicular to the edge of the panel) so that it will contact the inside face of the enclosure adjacent to the door. It also moves up the shaft, pulling the door flush with the side of the enclosure. To open the latch, you twist the other way. The arm then retracts away from the panel, and swings parallel to the edge of the panel so that it will no longer obstruct its opening.

https://www.southcoipsg.com/prd/sc_27?LangID=0

I was hoping (hint, hint) that some one on the forum is in a business that could use such things, and who could request samples with a 'straight face'.

Very interesting coffee cup rocket on the left side of the picture there.

I think you need to start a new thread and explain that one a little more too.

Excellent start Dick...can't wait to follow this one!!! That will be a big, cool rocket! Your report is great, so keep us up to date and keep those pictures comming.

Carl

No kidding... I just noticed that. What is the deal with the coffee cup rocket?

In case you haven't seen it, I started a thread on Styrofoam cup rockets in the Scratch Built Forum.

No wonder I could not find it -- I was looking in "The Coffee House" ...

Pitiful progresss report - not worthy of pics

I really have been stalled on this project. I sized and cut my hatches, but still need to sand them. I have almost decided to give up on quick connect fasteners for the hatches and just go with threaded inserts or T-nuts. Among the cool stuff I won in DesconX was a multi-pole key switch, so I'm set on that. I also want some removable unit to house the G-Wiz in a dual-battery configuration.

Grrrr, I knew I should have waited before starting this thread!

OMG Dick...

Don't feel bad about progress...sheesh...I haven't touched the MAverick in over a week. I have been procrastinating BAD on the sanding and what's really bad is, there's not a whole lot to sand. Go figure!

Just keep up the steady work...besides, you forgot to mention the five eleventy reviews you have done for EMRR, along with all the other stuff.

Carl

I just looked and it's been 3 weeks since my previous post! Things should go faster once I get past a few relatively minor details. Part of it is procrastination, but part has been other projects that seem to keep my attention more. There was a time that I thought HPR was going to take me over, but of late I've had more interest in some of the low-power kits, my easter-egg paint job, a desire to play with a Micro-Hybrid...and that's just the rocket distractions

...and did I mention the Lambda Shuttle... it will certainly beat this project too

btw...I bet Nick he'd see a flight report by Monday (and I don't plan to buid mine that quick!)

I made a little progress on this project (finally!) Please refer to these three pics:

<a href="https://users.erols.com/rstaff/temp/ubb5.jpg"> Electronics bay, top view </a>
<a href="https://users.erols.com/rstaff/temp/ubb6.jpg"> Electronics bay, side view </a>
<a href="https://users.erols.com/rstaff/temp/ubb7.jpg"> Ejection bay, side view </a>

The first pic is a top view of the electronics and ejection bays. You can see the two bulkheads which will isolate the two from each other. The other two views are through the sides of the access holes. My G-Wiz is test-fit in the electronics bay and you can see the connectors for the electric matches in the ejection bay. The access holes are slighly smaller than the bay doors, and will provide a lip to support those doors.

The electric matches for both the ejection charge and air starts will be connected to the quick connect speaker connector. The wiring for this connector runs through one of the bulkheads to the ejection charge bay. One leg of each of the leads is switched via a multi-pole key switch mounted in the side of the airframe (not in the photos). From there, the leads will be attached to the connectors on the G-Wiz.

I STILL haven't decided how to attach the hatch doors. I'd really like some sort of quick-connect latches.

A comment on glue. I am using Tightbond wood glue for all the wood-wood or wood-cardboard joints. I will use West epoxy to glue this motor/electronics assembly into the rocket, mainly because it doesn't grab so fast and will give me time to position it properly. I will make epoxy fillets for the fins (in and out) and may fill the fin-can with foam.

That's it for now.

Maybe it's just me, but those links appear to be all busted up.

OOPS, should be fixed now. I KNOW I transferred the files earlier, now I just have to find out where they went!

Thanks Kermie. I experienced the same problem but thought it was me.

And thanks to you too, Dick.
Looks like the Brute is really coming together.

I have made a lot of progress, here are a few pics:

<a href="https://users.erols.com/rstaff/temp/ubb9.jpg"> It’s starting to look like a rocket! </a>
<a href="https://users.erols.com/rstaff/temp/ubb10.jpg"> Other side… </a>
<a href="https://users.erols.com/rstaff/temp/ubb11.jpg"> Ejection bay, installed </a>
<a href="https://users.erols.com/rstaff/temp/ubb12.jpg"> Electronics bay, installed </a>
<a href="https://users.erols.com/rstaff/temp/ubb8.jpg"> Hatches and key-switch </a>

Progress includes:

1. Applied thin CA to hatches and associated doors, and sanded them.
2. Filled and sanded spirals (Fill 'n Finish)
3. Wired and continuity-tested (with ohmeter) the connector and key switch.
4. Installed the motor mount/electronics bay assembly and the fins.

The key switch consists of a metal key latch (can be seen in the last pic) that is mounted to the side if the airframe with a retaining screw. The actual switch pops onto this from the rear (seen in side view of electronics bay). Because the switch itself is larger than the opening for the key assembly, this would not be easy to remove/replace. As a result, I will mount the switch assembly to the piece of tubing that was removed to form the view port in the electronics bay door (also in the last pic). A hole large enough to accommodate the switch will be cut in the airframe and the switch plate will be screwed to the airframe.

I will use threaded inserts and small hex-head bolts to hold the hatch doors on. I flip-flopped on how to attach them and decided I'd fit them into the lip formed by the coupler tube and back-fill the area behind them with epoxy putty. Hope this works!

Originally posted by rstaff3


I will use threaded inserts and hex-head nuts to hold the hatch doors on. I flip-flopped on how to attach them and decided I'd fit them into the lip formed by the coupler tube and back-fill the area behind them with epoxy putty. Hope this works!

Click to expand...

Dick, If you haven't already started the hatch holddowns, I might suggest using T-nuts behind the coupler "lip", and run pan-head screws threw the hatch door into the T-nuts. Since T-nuts have a deeper barrel than the thickness of the coupler, you can mount the T-nuts to small discs of thin plywood, and epoxy this on back side of coupler. I've used this technique on most of my aft centering rings when mounting T-nuts for motor retainer hardware.

Also of possible use, although I haven't used them personally, are the PML rivets. Several people in our group swear by them.

Lee,

I've used the method you've proposed for motor retention and for holding an altimeter bay into a rocket (review of that alt bay is on EMRR). The inserts could also work this way (ie with a wood backing). In fact, I bought the inserts expecting to use wood backing. However, for better or worse, I decided to try the method I outlined. I wouldn't try this for either of the other applications though.

The reason I chose this approach is that I wanted to drill the holes and install the connectors after the motor mount/electonic bay assembly was permanently mounted in the rocket. Using the epoxy putty should hold pretty well, and it will be easier than trying to glue inserts or T-nuts in place in the limited space available.

Still, thanks for pointing out a potentially better method. (I say potentially since I'm optimistic that this will work out OK) Had I mentioned this before I glued in the unit, I might very well have changed my mind.

Also, I am not at all familiar with the PML devices, I'll look into them for future reference!

For some reason when you mentioned threaded inserts and hex head nuts, I thought you meant threaded rod sticking out, and fastening the nuts on the outside. Will be interested in your assessment of the epoxy putty. I haven't used any, but plan to get some.

The PML rivets are neat. They snap in, and are removed by prying up with small screwdriver blade or knife edge. They've been on my list of "Parts To Buy" for some time now.

ACK! Do I say what I mean or mean what I say?????? I meant hex-head bolts! Will edit my post!

Those rivets look cool. They are now on my list too. Without some reinforcement, I don't know how well they would work in cardboard (not listed in the recommended uses). In my application, they will be near the edge and if it takes too much force to set them the cardboard might just deform over time. Still it could be reinforced/hardened. Hmmmmm (sound of gears turning).

Originally posted by rstaff3

Those rivets look cool. They are now on my list too. Without some reinforcement, I don't know how well they would work in cardboard (not listed in the recommended uses). In my application, they will be near the edge and if it takes too much force to set them the cardboard might just deform over time. Still it could be reinforced/hardened. Hmmmmm (sound of gears turning).

Click to expand...

Good point -- I hadn't thought about the bending and flexing due to the cutout in the coupler. OK, we'll be interested in knowing if that epoxy putty works well. It looks pretty tough. In the instructions for my Apogee Saturn 1B, it shows how to use the putty to build up the long, "pointy" areas of the resin fins. One of the eight of mine is missing, and at first, I thought I'd have to return it for replacement. I guess this is typical, since the instructions include this step. It looks too fragile, but after getting roughly formed, it is sanded to shape and I was amazed that the "add-on" stuck to the rest of the fin.

Here is my 2 cents on the matter...

The threaded inserts and hex head bolts should work fine. And the plastic rivets wouls probably have been fine too, with a little reinforcement.

I was debating which to use in attaching my alt. bay to the fore airframe and eventually chose to use...BOTH...actually...I used 6 of each and so I doubt it is coming free. The threaded inserts worked great in PML phenolic tubing (I don't know about LOC). In fact, the wood backing strips broke off but the threaded inserts stayed in. They don't even need the backing strips because they are going through three layers of PML phenolic couple tubing and there is a little JB Weld on the inside to keep them from rotating.

As far as the quality of the PML rivets...they are great. You can get them from McMaster-Carr cheaper and in bulk too. They hold NC's great in PML Phenolic, Quantum tube or LOC tubing. A friend uses just two of them to hold his electronics bay in his 2.5" diameter PML kit w/ Phenolic tubing w/o any reinforcement. Be careful how thick the pieces you are trying to hold are though. Anything more than a piece of QT and Phenolic combined is too much.

Dave

Here are the two latest photos:
<a href="https://users.erols.com/rstaff/temp/ubb13.jpg"> Hatch door and key switch plate</a>
<a href="https://users.erols.com/rstaff/temp/ubb14.jpg"> bottom with rear CR installed </a>

As I mentioned last time, I was going to use both threaded inserts and small socket head cap screws (I was calling them hex-head for some unknown reason) to hold the hatch doors on. However, after I drilled the holes and test fit the doors, they seemed to be attached soundly with only the screws. So, I treated the holes with thin CA, re-drilled them because of swelling, and reinserted them. I think they will be fine and if they loosen over time, I can add the threaded inserts.

I also drilled and cut holes in for the key switch mounting plate. You can see this dry-fit in the first photo. It was going to be further over, but I found it would interfere with the rail buttons. Well, actually the rail itself.

Originally, I was going to use epoxy fillets inside the fin can area. Instead, I ended up adding dowels glued in with wood glue. The thick outside fillets, however, are epoxy. Somehow I messed up slightly on about half of the outer fillets and had to fill them with a mix of epoxy filler and Fill ‘n Finish. Nah...I'm not going into it, let's just say I had a brain fart...or two.

It's actually pretty close to being ready for primer. I still have to finish sanding and filling before I move on. I also need to get it all together and check its stability. Those long LOC 5.5" cones are fairly heavy so I don't think I will need a huge amount of nose weight. Well...with a J350 and a coupla 29mm motors....I'll see.

Later....

You're doing a fine job.
Perhaps you would allow me to send copies of my "Adjustable Nose Weight System"?

Cool...I have since found out I need to add about a pound of nose weight for a J350 (+ a couple of small 29mm motors), and less for a I357 (also + 29mm's). I forget what format you said the plans were in but I'd like to take a look-see!

. . . look-see is can-do from this end. Files are many, in dxf. and MS Word. Too much for TRF site. Will send hardcopies (via USPS) pronto. Copies of Copies will be sent via e-mail address for immediate edification in same formats as previously mentioned.

Thanks for the interest.

I don't mean to make anyone highlight a "brain fart..or two", but if you've made any sort of a mistake whatsoever, I'm liable to duplicate it. Is there any chance I could talk you into at least emailing me what not to do so I don't duplicate the mistake?

Alright, alright, alright....it's probably better anyway...I obviously am not 'all that' working with epoxy and could use pointers too.

First, this was my first time using West epoxy for what I consider really big fillets (the puddle was ~3/4" - 1 " across, in that range). I used 105 resin, 205 hardner and the the 'tape around the end' method to TRY to contain/dam the puddle. I have used that method many times with no issues. Most of my problems came from the runny nature of this epoxy vs. Bob Smith.

First set of fillets. I suspected the epoxy should be thickened. Used 404 hardner. Still, my setup wasn't parallel to gravity and the puddle meandered to the front of the fin (problem #1). Not too bad, but more than I was happy with. (Rats! where is my little level when I need it?) Also, the filler left a rough finish that demanded an epoxy filler top coat later (problem #2).

Second set of fillets. No hardner. Lots of tape around each end of the fins. Extra on the backside to contain leakage. Wasn't enough. Watched it for long enough to convince myself that it wasn't leaking and left. Bad idea, minor runs down the side/back of the rocket. At least this was relatively easy to remove when not fully set. Lost a little tube surface here and there - fixed by more filler later. Also found an interesting phenomona. Maybe I just never noticed this when I used West for smaller fillets(?). This stuff wicks up the tape buffer on BOTH ends, leaving a large peak on each end of the fillet.

feeble attempt at AASCI art:

(deleted- looked bad once posted, too early to fiddle with)

Fillet #3. Even more tape (pulled long pieces across the dam to try to keep pressure on the end of the fin where it met the BT), new location outside to try to get the epoxy to set faster. Ack! Not level again, wicking, leakage. It did set faster though.

Fillet #4. Still more tape, re-leveled. Very minor leak on one spot, still wicked.

Finishing consisted of grinding down and shaping the ends of the peaks where it wicked. Sanding the ends where the fillets thicketened. Filling the fillet area with epoxy filler. Sanding....

Now I'm using some Fill'nFinish for a bit of minor touch-up, and still am sanding.

This response is definately rated PG - pretty gross

Thanks for the info. When I do move over to West Systems, it'll probably save me a lot of heartache! Sounds like it was painful all the way around.