3" Mac Performance Modified Zodiac

[thzero]

So since a used by 3" LOC/Madcow build (https://www.rocketryforum.com/threads/hpr-custom-build.162115/) for my Level 2 launch, and its now a trophy like my Level 1, I have some more I motors I want to burn, so I looked around for rockets to meet a certain weight goal and ended up with a 3" Mac Performance Zodiac. Treating it as a pile of parts, I plan to modify it slightly from the original for better weight distribution, attachable payload bays, replaceable fin cans, etc.

• 3" Mac Performance Zodiac
  • Uses the plastic nose cone, for now, to hit the weight limits I have in mind for the performance parameters.
• Custom 3d printed sled for electronics
  • Eggtimer Quantum altimeter
• Custom 3d printed altimeter and GPS holder
  • Featherweight GPS tracker
• Aero Pack 54 motor retainer
• OneBadHawk 3/16 Kevlar shock chords
• Bama Parachutes Aero-spherical main parachute
• TopFlioght 15" drogue parachute

Edit: Oops, not sure where I had the name 'Vixen', its really a Zodiac rocket.

 

[thzero]

First up is the fin can. So started with the fins.



Sanded with some 120 grit just to get the shine off, then sanded roughly on the root edge with some 60 grit sandpaper. The black markings are discussed in the next step.

 

[thzero]

Here is the fin can dry fitted. I'm going to try something new, for me, and setup the fins outside of the body tube first, then slide it into the body tube. This has ramification that I'll have to slit cute the fin slots back to the end of the tube (about .5") in order to slide the completed fin can in; plan for that is to use some epoxy to fill in the gaps, and then wrap a layer or two of fiberglass around the bottom .5" of the body tube.

Regarding the fin can. Because the tolerances are tight with a 54mm mount in a 3" rocket, I can't do my normal forged eyebolt - there really isn't that much room as will be apparent later. So I've elected, after much hand wringing, to use the Kevlar shock strap included with the kit.




The parts are internal fine guides that lock the fins in place. The reason for the black markings on the fins is to mark where I need to notch the fins slightly (1.25mm) so that the fin will sit flush.

 

[thzero]

So the fins have been beveled, which is great and all, however that revealed a rough texture although it is not terribly visible in the zoomed in picture. Wanted to take care of that a bit before I did any mounting.



So I mixed up some epoxy (just some System 3 with hardner #1) and applied to the edges and let cure.



Once cured, then used some 220 grit sandpaper to smooth out the surface and now its much smoother, enough that it'll work until final finishing.

 

[thzero]

Regarding the fin attachment, you can see the gap as demonstrated by the lower fin. So small cut outs are needed t



Cut outs are shown on the next two pictures. Just enough to fit over the 3d printed internal fin guides.





Now the fin sits nice and tight against the tube, ready to get epoxied in with some JBWeld.

 

[thzero]

So struggling with a few things on this build

• Building the fin can outside the tube which then requires cutting the tube for inserting the fin can
  • This is bothering as effectively the body tube's integrity has been reduced
• Lack of filets between the fin and the outside of the interior of the body tube.
  • There is some opinions that this is unnecessary and just ends up adding weight without a lot of benefits. I've not seen any precise authorative answers on it.

On the first one, the solution is of course not to build the fin can outside thus no cuts in the body tube. But how do deal with the internal filets?

• "Old school"
  • This involves pouring or using tools to spread epoxy along the junctions between fin and motor tube and fin and body tube to form filets. This can be messy and not very precise (at least for me) and with the reduce space (54mm motor mount in 76mm body tube) with long fins makes this a challenge.
  • This also has a bit more of a challenge in using the mechanical pin anchor for the Kevlar strap. Can't epoxy in the aft centering rings and fin guide, so that they can be pulled out and then slide over the tube and Kevlar strap, which could be challenging, after the filets are in place and cured.
  • Downsides here is no outside filets.
    • However this could be handled with the expanding foam by first epoxying in the fin guide, pouring foam in after all the other epoxy has cured, then using the aft centering ring as a cap.
• Foam
  • Use expanding foam only for the filets.
  • I'll have to check if my foam is still any good or I need to order more.
  • Not real keen on this to replace both sets of filets
  • This also has a bit more of a challenge in using the mechanical pin anchor for the Kevlar strap. Can't epoxy in the aft centering ring, but epoxy in the fin guide as it has holes that the foam can be poured through. Downside is that the pin for the Kevlar strap rests against the 3D printed plastic fin guide instead of the strong centering ring. The centering ring then would be modified to slide over the pin, so it becomes more of an endcap.
• Moat
  • Epoxy the fin guides, the centering rings, and Kevlar strap in place outside of the body tube.
  • Setup moat walls along each fin.
  • Install and epoxy in the fin can into the body tube; carefully checking alignment, etc. before epoxy sets and cures.
  • Then to install a fin in the fin slot, first pour epoxy along the fin root and let it settle, then slide the fin into the slot.
    • Be careful not to fill the moat up entirely otherwise spillage may happen
    • Installation of the fin will of course displace epoxy and should then settle in the gap between the fin, the motor mount and the moat wall
  • Downsides here is no outside filets.
    • However this could be handled with the expanding foam by just not epoxying in the aft centering ring, pouring foam in after all the other epoxy has cured, then using the aft centering ring as a cap.

The second issue ends up being addressed, mostly by use of expanding foam, in one of the three options for solving the first issue.

 

[thzero]

On the moat idea, two schools of thought here

• Use an epoxy that you pour in via the slot (i.e. west systems, thinned rocketpoxy, system 3 epoxy, etc). This way it can be done after the fin can is in place.
• Use JB weld set into the moats before inserting the fin can into the body tube. JB Weld has a really like set/cure time, so plenty of time to fill the three moats, setup the epoxy to secure the fin can, etc. and then slide and position the fins into the slots.

I'm leaning towards number 2.

 

[Handeman]

So struggling with a few things on this build

• Building the fin can outside the tube which then requires cutting the tube for inserting the fin can
  • This is bothering as effectively the body tube's integrity has been reduced I don't see how this is an issue since the body tube will be epoxied to the fins the whole way down. You can use a short piece of coupler to glue to the end of the BT aft of the fins.
• Lack of filets between the fin and the outside of the interior of the body tube.
  • There is some opinions that this is unnecessary and just ends up adding weight without a lot of benefits. I've not seen any precise authorative answers on it. If you have exterior fillets, how much more strength between fin and BT do you expect from and internal fillet? I don't think the extra weight is worth the little bit of extra strength provided by the internal fillet, unless your external one doesn't attach well to the BT or fin.

On the first one, the solution is of course not to build the fin can outside thus no cuts in the body tube. But how do deal with the internal filets?

• "Old school" I've only done one fincan with foam, it was my L2 cert rocket. It had 50 flights, fell on only the drogue 2 or 3 times. Was cut loose from a 60- 70 ft. power line and flew past Mach a couple of times. It was also done with both internal fillets, tip to tip glass, and foamed interior, so why did it hold up so well? I think any one of those methods might have be the key, but I can't tell.
  • This involves pouring or using tools to spread epoxy along the junctions between fin and motor tube and fin and body tube to form filets. This can be messy and not very precise (at least for me) and with the reduce space (54mm motor mount in 76mm body tube) with long fins makes this a challenge.
  • This also has a bit more of a challenge in using the mechanical pin anchor for the Kevlar strap. Can't epoxy in the aft centering rings and fin guide, so that they can be pulled out and then slide over the tube and Kevlar strap, which could be challenging, after the filets are in place and cured.
  • Downsides here is no outside filets.
    • However this could be handled with the expanding foam by first epoxying in the fin guide, pouring foam in after all the other epoxy has cured, then using the aft centering ring as a cap.
• Foam
  • Use expanding foam only for the filets.
  • I'll have to check if my foam is still any good or I need to order more.
  • Not real keen on this to replace both sets of filets
  • This also has a bit more of a challenge in using the mechanical pin anchor for the Kevlar strap. Can't epoxy in the aft centering ring, but epoxy in the fin guide as it has holes that the foam can be poured through. Downside is that the pin for the Kevlar strap rests against the 3D printed plastic fin guide instead of the strong centering ring. The centering ring then would be modified to slide over the pin, so it becomes more of an endcap.
• Moat
  • Epoxy the fin guides, the centering rings, and Kevlar strap in place outside of the body tube.
  • Setup moat walls along each fin.
  • Install and epoxy in the fin can into the body tube; carefully checking alignment, etc. before epoxy sets and cures.
  • Then to install a fin in the fin slot, first pour epoxy along the fin root and let it settle, then slide the fin into the slot.
    • Be careful not to fill the moat up entirely otherwise spillage may happen
    • Installation of the fin will of course displace epoxy and should then settle in the gap between the fin, the motor mount and the moat wall
  • Downsides here is no outside filets.
    • However this could be handled with the expanding foam by just not epoxying in the aft centering ring, pouring foam in after all the other epoxy has cured, then using the aft centering ring as a cap.

The second issue ends up being addressed, mostly by use of expanding foam, in one of the three options for solving the first issue.

Since I've never seen anyone that has ever done any type of failure testing for various fin attachment methods and nobody I know of even swears by one method over the other based on strength rather than ease of use, I would pick the one you want to use and go with it. Don't overthink it, analysis paralysis and all that.

My personal opinion, and I could be wrong because I've never seen any analysis on this, but for TTW fins, the attachment of the fin to MMT is just to prevent the fin from bending/twisting in the BT slot and breaking the external fillet. I think just epoxy on the edge of the fin to glue it to the MMT is usually sufficient. If you have an anomaly where the fin can hits the ground hard, then if it breaks away from the MMT and cracks the fillets on the BT, it is much easier to fix then if it breaks the fin or the BT instead. In either case, if you have an non-nominal flight, you should expect to be making repairs, no matter what method you use.

Trying to build a fin can that can hold up to more than just the flight forces and normal landing forces is overbuilding IMHO.

 

[thzero]

nobody I know of even swears by one method over the other based on strength rather than ease of use, I would pick the one you want to use and go with it. Don't overthink it, analysis paralysis and all that.

yeah, probably exactly on target here.

 

[thzero]

Started setting up the lower rail guide. Using some 10/10 airfoil shaped guides from SCP Concepts. They use a #8-32 bolt, which works with the #8-32 t-nuts that I have a bunch of from previous builds. The idea is to just drill a hole for the t-nut to protrude from the airframe, then epoxy the backside to bond the nut to the body tube. The rail guide was drilled, ever so slightly, to allow it to slip over the t-nut then the #8-32 bolt is used to secure it.

 

[DRAGON64]

I am really liking this rail button attachment method. I have a similar set of rail guides for my Adventurer3 build, and I may use your method as a means of attaching mine. Thanx!

 

[thzero]

Well went ahead and started the fin can assembly process. Started applying a ring of JB Weld epoxy; ended up extending it a bit further to the right before sliding the assembly of the fin guide and centering ring.



Then I buttered underneath the shock chord strap and did the same on the other end to slide the first the fin guide, then when situated the centering ring. I'm not the neatest epoxier (is that a word?) in the world unfortunately.



Forgot to take a picture of slathering more epoxy on top of of the strap. Then wrapped it with some mylar to hold it tight while it cures.




Next time I do this, I'd not try and top coat it and apply the mylar and let it all cure. Then go back and add another layer of epoxy over the top. Takes longer, but think it'd just be cleaner.

 

[Hobie1dog]

You're building this thing like a brick outhouse.

 

[thzero]

Got some more work done, while sick, on this build.

Cut out some strips for creating the dam/mounts for epoxy.



The used some CA to attach them to the motor mount; the printed fin guides came in handy. Then made sure to scratch up the motor mount surface.



And then to be able to apply epoxy in the moat areas, I created a small tool. Nothing but a syringe with some tape around it to give it a tight fit for the straw to slide onto it.



Straw is flexible enough to fit into the fin slot of the body tube. I used Rocketpoxy for this step.



And after the process we have a mostly completed set of fins. Still need to do the outer filets and JB Weld the motor retainer onto the motor tube. The later is waiting until I decide whether to foam the can or not.



All total, the JB Weld for the fin guides and the shock chord strap, as well as the internal epoxy for the fins added 1.67oz to the rear end. Not totally unexpected and had plenty of allowance for the shift.

Of course downside is more to come a bit with the motor retention attachment, as well as the external filets.

 

[thzero]

Next up was to start getting the avbay situated. I'm using the same electronics bay that is from my 3" LOC rocket I used for my Level 2. Same bay was also used in my scaled down 5.5" warlock, and the same bay is planned to be used in by Level 3 (bit debatable on this one, I may try a new design, we'll see).



Runs two Eggtimer Quantum altimeters each with their own 2S Venom 300MaH LiPo (unfortunately having hard time finding these again). Uses JST RCY connectors (I always end up referencing https://www.mattmillman.com/info/crimpconnectors/common-jst-connector-types/) that have have color shrink tube used to color code them so that its easy to tell what connects together. Also there are two push pin flags that are used to close 4 OMRON SS-5GL switches - one switch cuts the power off to each of the 4 ejection charge leads.

Used a 3d printed guide to know where my static port holes are for the altimeter, as well as the holes for the push pin flags.



Then epoxied it together with some Rocketpoxy.

 

[thzero]

Next up is to work on the bolts and connectors to mount the lower recovery bay to the fin can's exposed coupler. Does this add weight? Yes. Is it necessary? No. But its now sorta my "style".

Again using a 3d printed drill guide, I drilled the holes for the bolts. Since I'm using #8-32 hardware I used a 5/32" drill bit for the bolt in the body tube, then a 13/64" for the fin can coupler where the self-clinching nut (Amazon sourced) will go. Previously I've used t-nuts which have worked well, but that requires a lot of grinding, etc. to get them flush. Had seen the self-clinching nuts mentioned by others, and since this isn't carboard (nor is it it fiberglass) I thought I'd give it a go.




Did a quick test on scrap tubing...



Seems to come out ok and pretty tight. I just used a long #8-32 bolt and some washers to slowly pull it together and into the material. When I do the set on the rocket, I think I'll use some JB Weld also.

 

[thzero]

As I forgot to mention, I'll note it here. For the 3D CAD designs for the various components (including my e-bay) I've used OnShape to model all the designs, and then for printing purposes currently I'm using a Bambu Labs X1 Carbon which I really like. I'm using Overture PETG for anything going on the rocket, although I have some eSun PETG I'd like to try too, and then using eSun PLA or PLA+ for parts such as the drill guides, etc. that are not part of the actual rocket. So for the X1 has printed all three with good success.

 

[thzero]

Previously I've used t-nuts which have worked well, but that requires a lot of grinding, etc. to get them flush. Had seen the self-clinching nuts mentioned by others, and since this isn't carboard (nor is it it fiberglass) I thought I'd give it a go.

Yeah, big nope. Maybe better on the fiberglass? But one with just some light testing of screws popped off and had me going about gingerly cutting the head off the bolt to get it out.

Back to the use of t-nuts.

 

[blackwing94]

Thank you for trying out the self-clinching nuts on MAC body tube. You saved me from doing the same experiment.

 

[Banzai88]

Thank you for trying out the self-clinching nuts on MAC body tube. You saved me from doing the same experiment.

Many of us have been doing it for quite some time with no problems.

The addition of a tiny drop of epoxy, as most of us also use with fiberglass, prevents all issues.

As always, YMMV.

 

[thzero]

Many of us have been doing it for quite some time with no problems.

The addition of a tiny drop of epoxy, as most of us also use with fiberglass, prevents all issues.

As always, YMMV.

As I noted, it may work better with fiberglass but these are not fiberglass tubes. Composite? Yes, but fiberglass they are not. For these tubes, at least the ones I tried did not work to my satisfaction even when using JB Weld

I may try again with actual fiberglass tubes. We'll see, but that is not on this build.

 

[Banzai88]

As I noted, it may work better with fiberglass but these are not fiberglass tubes. Composite? Yes, but fiberglass they are not. For these tubes, at least the ones I tried did not work to my satisfaction even when using JB Weld

I may try again with actual fiberglass tubes. We'll see, but that is not on this build.

Your rocket, your build, but I assure you that PEM nuts work just fine in MAC phenolic, properly spec'd and seated. It's getting it properly pulled in that can be tricky.

The addition of a little blob of epoxy (fiberglass or phenolic) is usually out of an abundance of caution and the propensity to over build

 

[thzero]

Your rocket, your build, but I assure you that PEM nuts work just fine in MAC phenolic, properly spec'd and seated.
More than a few of us have done it repeatedly.

The addition of a little blob of epoxy (fiberglass or phenolic) is usually out of an abundance of caution and the propensity to over build

I'm not using the self-clinching nuts on this build now. They did not work properly; whether that be they just did not work with the MAC tubing, or the Amazon sourced self-clenching (never said PEM which is a specific company), not sure. But they did not work, period, so they are not being used on this build.

If you have a specific PEM nut specification (and link on their website) for the PEM self-clinching nuts you have used successfully, that would be good information.

 

[Banzai88]

I'm not using the self-clinching nuts on this build now. They did not work properly; whether that be they just did not work with the MAC tubing, or the Amazon sourced self-clenching (never said PEM which is a specific company), not sure. But they did not work, period, so they are not being used on this build.

If you have a specific PEM nut specification (and link on their website) for the PEM self-clinching nuts you have used successfully, that would be good information.

I get mine from McMaster Carr, and use #2s on 4 inch and below tubes.

I think rfjustin has a cheat sheet posted somewhere with part numbers, but they're not hard to find. Self clinching/PEM, whatever you want to call them, same thing, same usage, same installation instructions and methods generic or name brand, although quality may vary.

 

[thzero]

Prepping the t-nuts; measured the depth then used a dremel tool to cut them down to approx. right depth. Then put some green tape over the bolt hole on the back to keep the epoxy out.



Not best photo, but basically these are epoxied in with some JB KwikWeld and then covered in just BSI 15 minute epoxy for smoother finish to keep anything from hanging up on them.



After installation from the outside. Carefully do any grinding to make sure that the nuts are flush.

 

[thzero]

Then working on the attachment point for the upper main parachute harness. Took a fiberglass bulkhead and turned it down so it in fit nicely in the body tube. First step is to drill a hole for a bolt that it used in the turn down process.



Then using the electric drill, add the bolt/bulkhead as if you were any drill bit. Using an abrasive (used 80 grit) wrapped around popsicle stick, turn/sand until desired size is reached. Wear protective gear including face mask.



Then used a hole cutter to cut a hole big enough to allow the quick link to fit through.



Pieces ready to go together. First will be to attach the t-nuts to the bulkhead and then the forged eye bolt to the smaller bulkhead. It was also turned down to be a bit smaller than inside diameter of the coupler using the same method as above.



Here is the drill guide that was used to drill the holes. Hindsight I should have done the three bolt holes before using the hole drill, that way I could have had the three pieces (guide, small bulkhead, large bulkhead) all assembled together and centered through the forged eyebolt. As it was I had to carefully measure and make sure that the smaller bulkhead was centered on the ring prior to drilling.



The t-nuts mounted.



Showing the pieces assembled.



The attachment ring will be mounted on top of the coupler, and then coupler will be epoxied into the payload bay. The bottom of the coupler slides into the recovery bay for the main parachute.

 

[bobbyg23]

Holy cow. Can't wait to see the final weight on this beast!

 

[mpitfield]

I'm not using the self-clinching nuts on this build now. They did not work properly; whether that be they just did not work with the MAC tubing, or the Amazon sourced self-clenching (never said PEM which is a specific company), not sure. But they did not work, period, so they are not being used on this build.

If you have a specific PEM nut specification (and link on their website) for the PEM self-clinching nuts you have used successfully, that would be good information.

Excellent build and attention to detail; I appreciate it.

Not to beat a dead horse; however, if you're ever interested in revisiting the self-clinching (PEM) nuts discussion on a future build, just let me know. I have used them exclusively on many rockets for years. Your level of success will depend on the type of nuts you purchase. I use the NJ Broaching style, and you want to ensure the shank length is long enough to go as far into the airframe without sticking out the other side. Based on what I use, the shank length in your posted picture needs to be longer.

Installation technique is also essential. I drill a hole, just undersized the knurl diameter, then using a q-tip, I put a fine bead of structural epoxy around the knurled base of the shank and use a machine screw with a nut and washer to pull and secure the nut from the outside until cured. Field maintenance is straightforward. When they fail, and they will with enough use, all you need are the following:

• A machine screw/washer/spare nuts
• A q-tip.
• A piece of sandpaper.
• A safety razor or suitable knife to scrape the old epoxy and some epoxy in your kit.

The bottom three items are things I would have in my field kit, so the only net addition for me is a small machine screw with a washer and a few spare nuts screwed on.

 

[thzero]

Excellent build and attention to detail; I appreciate it.

Not to beat a dead horse; however, if you're ever interested in revisiting the self-clinching (PEM) nuts discussion on a future build, just let me know. I have used them exclusively on many rockets for years. Your level of success will depend on the type of nuts you purchase. I use the NJ Broaching style, and you want to ensure the shank length is long enough to go as far into the airframe without sticking out the other side. Based on what I use, the shank length in your posted picture needs to be longer.

Installation technique is also essential. I drill a hole, just undersized the knurl diameter, then using a q-tip, I put a fine bead of structural epoxy around the knurled base of the shank and use a machine screw with a nut and washer to pull and secure the nut from the outside until cured. Field maintenance is straightforward. When they fail, and they will with enough use, all you need are the following:

• A machine screw/washer/spare nuts
• A q-tip.
• A piece of sandpaper.
• A safety razor or suitable knife to scrape the old epoxy and some epoxy in your kit.

The bottom three items are things I would have in my field kit, so the only net addition for me is a small machine screw with a washer and a few spare nuts screwed on.

Thanks, that's helpful!

 

[thzero]

Onto the avbay stepped bulkheads. Need to drill some holes for the ebay, as it has different spacing than the pre-drilled holes, and then some holes as attachment posts for the 3D printed ejection charge cannisters.

Of course another drill guide..



And after the use of the drill. The unused holes sit underneath the ejection charge cannisters, so they'll be covered however I will be doing just some Bob Smith 15 minute epoxy to fill in the holes.



Test fit with the electronics bay, looking good thus far.



And then to see if it all fits together.



Yup, looks great!

Not much left to do here. Fill in the unused holes with epoxy, probably paint the tops of the stepped bulkheads and then thread on the forged eye bolts. Otherwise just need the drill bit and tap for the m2.5 bolts to come in - I'm using 2.5mm nylon as I can get a bunch of them cheap, whereas I struggle to find #2-56 or even m2 bolts.

Oh and of course print some 3D cannisters out of PETG.

Other than that? Think its pretty much done except take some final weights, compare with the OpenRocket sim that has been kept up-to-date and run a few sims with any adjustments.