Madcow Super DX3 & Patriot - a build thread -

[dr wogz]

A build thread!

Featuring not one, but two rockets! The Madcow Super DX3 and the 4" Patriot. I got them both over Christmas, and figured I might as well build them both at the same time. They are, essentially, the same kit: one extra fin on one, and a longer AV bay tube on the other. All the rest is the same.

The plan: make them both dual deploy, and both share the same altimeter (use a swappable sled). I have an Eggtimer Quantum for that.. The AV bays will not have a vent band, but be secured to the upper tube with screws. Interconnection will be a single 1/4-20 threaded shaft with eye nuts, no 'U' bolts. (Both these ideas were discussed in another thread a few moths ago..) And, to have them (one at least!) ready for NYPower!

I've decided to add a third CR to the motor tube, for a bit of added structure.

One note, as I discussed in yet another thread, Madcow's use of CG and CP in therms of balancing. One kits give the CP location, which I think we all prefer, and the other give a recommended CG point..

 

[dr wogz]

I've cut new centering rings and new inner bulk plates. I have the tools, so why not!
I ended up cutting 3 CR, and 2 bulk plates if I recall.. (more a re planned for another night!)

 

[dr wogz]

Let the gluing begin!

first up, the inner bulk plates to the outer bulk plates. And the inner bulk plates to the inside of the AV bays. They are shallow enough that I fee I can get away with one fixed, one removable end.. And the nice shiny eye nuts that'll go on each end!

 

[dr wogz]

Next up, the first CR, the upper CRs glued in place.. I'm using the regular Bob Smith epoxy for the gluing task. it's wood & paper, so not too worried. Tubes are sanded for extra boinding power.

I've added the drips of epoxy to the lower nut on the eye bolts, and they are set aside to cure..

And then secured in place with the top epoxy bead added to the MMNT & CR.

 

[Tim51]

Let the gluing begin!

first up, the inner bulk plates to the outer bulk plates. And the inner bulk plates to the inside of the AV bays. They are shallow enough that I fee I can get away with one fixed, one removable end.. And the nice shiny eye nuts that'll go on each end!

Looking good - subscribed! Presumably at least one of the eye nuts will be removable to allow access to the AV bay, so what method will you use to stop it/them spinning off if the attached shock cord twists during descent?

 

[dr wogz]

One thing I've learned from using rail buttons: trying to get a screw dead center in the edge of the CR is no easy feat! So, I planned ahead this time, and I've added a small chunk of ply to the upper side to the bottom CR. This way, when I go to screw my button in place, I've got a 1/2" to aim for, not the usual 1/4"!

A bit of sanding to remove the points, to make it round, and all done! I usually glue the bottom CR in place once the fins are glued, and internal fillets added.. A mark on the back-side of this CR will help align it when the time comes.

 

[dr wogz]

Looking good - subscribed! Presumably at least one of the eye nuts will be removable to allow access to the AV bay, so what method will you use to stop it/them spinning off if the attached shock cord twists during descent?

Yes, both will be, at least at this point.. I plan to double-nut them to lock them in place.

 

[ascastil]

One thing I've learned from using rail buttons: trying to get a screw dead center in the edge of the CR is no easy feat! So, I planned ahead this time, and I've added a small chunk of ply to the upper side to the bottom CR. This way, when I go to screw my button in place, I've got a 1/2" to aim for, not the usual 1/4"!

A bit of sanding to remove the points, to make it round, and all done! I usually glue the bottom CR in place once the fins are glued, and internal fillets added.. A mark on the back-side of this CR will help align it when the time comes.

Excellent idea! Im gonna do this also on future builds.

 

[Tim51]

Yes, both will be, at least at this point.. I plan to double-nut them to lock them in place.

Good idea. I came up with a similar (albeit smaller) single all thread + 2 eye nut Av bay design, but given the size the eye nut loops were too small to take another nut. In the end I 'tethered' the loop to an anchor point with a cable tie, fresh tie for each flight. It works fine, but then the rocket's relatively light. Build thread here: <<https://www.rocketryforum.com/showthread.php?131906-Back-in-Black-2-26-quot-57mm-semi-scratch-build&highlight=57mm+2.26++Back+in+Black>>

 

[smugglervt]

Nice work Paul, I'm subscribed.

Looking forward to seeing these two down by the bay this summer.

 

[dr wogz]

And a bit more..

I've glued the center CR to the MMNts, and started sanding the fins.

Let me take a moment to thank my sponsors.. Two of my favorite local micro breweries.. (Although one isn't as small as it once was, and the other boasts it's own line of "hopped" vodka..)

Last year was apples, the year before what lime, and there was a year with raspberries... This year seems to be grapefruit.. Grapefruit in a beer?! I had to try, and ya know, it's actually pretty good! I'd have to say, it is a pleasant surprise! The other is the smaller of the two, from the east end of the city. "Oshlag" always come up with unique brews and are equally a pleasure to drink. Small batches, unique ingredients, superb tastes!

(and yes, it's the same glass, but washed between two nights of building...)

 

[dr wogz]

Fin sanding..

Plywood find sanding... I'd take advantage of modern day power tools, but my belt sander is broken. Looks like the power switch finally gave up. Broke into little pieces..

So, first break the edges with a plane, get the basic shape. one pass, check.. pass again, check.. I usually carve off a 45° chunk off each side, then sand & round one by one. And yes, planning ply is a pain, and can lead to a disaster pretty fast.

Do I count my strokes? Generally no.

Do I have a special technique? Somewhat. I run my ring finger (of the hand holding the sanding block) against the edge of my bench to ensure my strokes are even. I rotate along the axis of the curve to try and maintain a constant curve. I then will sand across the curve to even it out. I then flip the fin over to do the other side. Its' usually pretty even.. I do wish I was more ambidextrous, so that I can sand one side with one hand, then sand the other side with the other hand.. Somehow I feel this would make things more even..

Anyways, preliminary sanding & shaping done. A quick final sand later..

 

[smugglervt]

Paul,

I use this Dremel accessory with a router bit to do my fin edges. Not perfect but gets them down to where there is less sanding involved.



We'll have to hit one of the microbreweries in town sometime after a launch.

Have a great weekend

Jim

 

[dr wogz]

Back to the build.. (sorry, had a week-end hiatus to travel to Rutland VT, then over to Woburn MA, then back up to MTL via N. Conway NH.. The rt 100 between Waterbury & Rutland is one of my new favorite drives!)

Shock cord attachment. This time, I went with the 'Trilene' type knot recommended by PML for flat tubular nylon. I also added my usual trick of heat shrink to the knot & base, to add a bit of protection, and to help the knot stay in place. I used a short piece of 1/2" heat shrink over the knot, then a short piece of 1" heat shrink to get over the eye bolt.

Shock cords done!

 

[dr wogz]

And a little bit more of the builds..

Let's talk a bit about manufacturing. TTW fins are strong, easy, and help with structure of our bigger builds in a big way. And, will tooling, if you can have one tool for many jobs, the overall costs are lower, as the tool is amortised over more products over a shorter time frame. So, in this case, make the slots in the tubes the same, and all the tabs that go in all the same. The only issue with this, is that the lower ring is where it ends up. and with the Aeropack retainer i plan to use, the motor sticks out past the bottom of the tube. Personally, I hate this. I don't mind the motor hanging out a bit, but not a lot. And, I like when the rocket is empty / in storage, that it can stand on its own, not on a small 38mm footprint. (Too easy to knock over..) So, I've decided to 'alter' the design a bit to have the end of the fixed retainer flush with the end of the tube.

So,measure, and measure my 'glue stick' to apply epoxy at the appropriate location inside the tube. Then, insert the MMT assembly into the tube. Push it, pull it, and twirl it a bit to ensure the epoxy is [fairly] evenly distributed, and in where it needs to be. Slap on the rear CR & retainer, and (no glue!) and set aside! (and repeat for #2!)

This night's build was brought to you by Beau's brewery out of Van Kleek Hill in eastern Ontario. Good guys, great beer! This is one of the signaure 'gruit' series, and features 'Bog myrtle' for that extra bit of flavour..
https://beaus.ca/beer/bog-water/


it's also fun to say "I'm drinking Bog water!"

And they always have cool bottle caps!

 

[dr wogz]

So, with the bottom CR expected to be higher than originally designed, the tabs need to be trimmed to fit. Measuring & prepping for the 'tab modification'. I'm not removing too much off the tab, just about 3/4". And this means the but end of the tab will be glued against the lowest CR when assembled. so, it does add a bit of stiffness. I love my little machinists squares, I have a few of them, in a few different sizes!

While I was doing this, I've applied epoxy to the inside CR, and let stand to cure. so, later tonight/ tomorrow, I should be able to finish sanding my fins, and actually start gluing them in place!

 

[AfterBurners]

Subscribedop:

They both look like 38mm? Great work so far and very neat and clean ....

Never mind I looked at the pictures of the instructions.

 

[dr wogz]

OK, so after a great Saturday spent outside, and a home cooked burger to end the day, it's time to continue building..

Here, I'm cutting the fin tabs to size. A band saw really helps with this task! Take your time, have good light, and practice! Oh, and leave the line. Many people I know start by making the line then cutting on / thru the line. And they then wonder why they come up a bit short.. Leave the line! Remember which side you want to remove material! you then have a reference to see how close you've come! And pictured are the cut-offs! I have plans for them later!

Afterwards it's time to give them all a final sand before attaching them to the rocket body. Here, I'm using a bit of "shelf liner" (gotten at any dollar store) as my sanding base. It's a rubbery mesh that helps hold the piece in place when sanding. It's rubber (or at least a rubbery type material), so it has good grip on both the table and the piece being sanded. You don't need to tire yourself trying to hold the piece down.

 

[dr wogz]

OK, so How do you divide the distance between two fins to make the launch lug (button) line? Let's go back to Geometry class (or drafting class for you engineering types!) Use a compass. Open the compass out to a little larger than the presumed half-way mark. Tuck the point into the corner of one cut out and scribe a mark. Repeat on the other side. Where the two scribed marks cross, is the half-way mark! The run your line as per usual! (No measuring,folding paper, etc..

Next, fin gluing. So, I mixed up a batch of epoxy (I tend to use 30 minute BSI for wood paper applications and West Systems for fiberglass & other) and apply it to the root edge of both the tab and the fin root.. I've pre-sanded the fin slots so the fins slide it without binding or without too much force. And carefully lay them in place. I check their perpendicularity with a home made device. A line running thru a point on a circle and the center point of said circle will always be perpendicular. (more geometry or drafting class!) So, I took an extra 38mm - 29mm adapter and made two grooves at the extremes, running thru the center point. This gives me a place to put a straight line (object) to sight against to gauge my fin alignment. I originally made them for my smaller builds, and have made a permanent set from an old 18mm & 24mm spent motor casing. So, glue the fin, sight down the dowel (a piece of welding rod in the case) and voila! And yes, the aft CR is in place to hold the end of the MMNT steady. and the tape 'handles' will be sued to pull them out once all teh fins are in place.

First fins glued, next to come later!


(Sorry, no beer tonight, had way too much the few nights before!!)

 

[AfterBurners]

That is a really cool way to align the fins.

 

[MikeT]

That is a really cool way to align the fins.

Sure is. Beats my "looks about right" method.

Mike

 

[dr wogz]

OK, fins are in, glued, and set.

Time for internal & external fillets:

For the internal ones, i usually just mix up a batch of epoxy & slather it on. this is gonna be the last time this part of the rocket sees daylight, so I'm not too fussy about the look. as long as there's a bead in there!

Now, for external fillets. I've seen many ways of doing them, and many people have their own particular method. I've seen them built up in layers, heard of people using all sorts of fillers from flour to baby powder to balsa dust (I've actually tried that, wasn't too good..) and of course, microballons. For shaping the fillet, I've seen people use a dry finger, a wet finger, an alcohol wet finger, a layer of plastic 'sandwich' wrap (Saran wrap), using a wood dowel to shape, and soaking the dowel in alcohol, and even laying the wood dowel on saran wrap on the filet to get the curved fillet shape.. Many people also line the edges of the fillet with tape & paper & such, even going as far as getting some carbon paper to make the marks to mask-off them..

I've tried many of them, and this is my method. I find it works pretty well:
Mix epoxy.
Add West system filler .
Mix to a stiff "frosting" consistency. apply only enough as needed, to make the initial fill. I find a Popsicle stick about right. Then, from my collection of hotel room keys (cards), select the one with the right radius (or cut my own) and starting from the middle or top 1/3, carefully & slowly drag the card over the epoxy bead. I then wipe off any excess, and repeat lower down the fin. I'll make a few passes. The first pass is at and angle, to press the epoxy into place. I'm mindful of the build up / the amount I'm removing and making sure I don't get a huge ball of goop building up as I move the card along the fillet. At this point the fillet is fairly well shaped. I'll add a bit of epoxy/filler to any area that's low. I'll then make a 2nd pass at a steeper angle, and ensure one edge of the card is squarely against the fin. gain, making sure the build up on the card is minimal. I usually end up with a smooth transition on the fin and rarely a ridgeline where the card & BT meet. (If there is a ridge, and line, I quickly scrape it off. I'll make a 3rd and sometimes a 4th pass to ensure it's all smooth, continuous, and even along the length. Practice makes perfect! (I've done a few of theses!!)
let set. The epoxy & Filler gets all glassy smooth.

Once cured, you can see that sanding is minimal. I use a rolled up small piece of sand paper, and use the side of my index finger to get into the curve of the fillet. there a re a few (very few!) low spots, and I don't think I'll need to add any filler once sanded.

And that's it!

(oh, and I use a standard note pad for epoxy mixing, and get cups from the local burger joint for mixing fillet epoxy!)

 

[dr wogz]

With the fillets done, its time to add the last CR!

Apply epoxy, and press into place. A lot of pressing!! Align the marks for eh extra backing for the rial button with the rail button line, and stand upright to set. Both done, both done for the night!

 

[dr wogz]

Now, I was talking about fillets before and finishing. Here, I'm going thru the motions of sanding them down. You can see a before & after. Not much effort as the filler is the sand-able kind. And a small rolled up piece (fold over itself twice, then rolled), and somewhat used fit the bill. As mentioned I use the side of the my index finger to get into the fillet curve. Long smooth strokes to ensure it lays flat along the length of teh fillet.

And there we go. A final sand with a fine sanding pad (sponge) and I'm just about ready for paint!

 

[dr wogz]

AV bays is next. I"ll have an Eggtimer Quantum in here, and will need a battery too. I'm still debating on the mounting method for the altimeter & such, but for now, to get the bay joined to the upper tube portion. I had originally planned to blind nuts and screws.

I was going to use 4 screws, but feel I can get away with 3. I've marked the tubes as required both inside & outside where the blocks are to be glued. I've sanded down the backside of the block I cut from the fins. I've glued them in place with CA. Then, with help of the trusty drill press, I've drilled three holes in each tube / AV bay assembly. I decided to tap the wood blocks. No need for the blind nuts, this is a hardwood ply I"m tapping into. A shot of CA on the tapped threads (and then chased later once dry) will ensure tight 6-32 threads. I stole some S/S truss head screws for this assembly. truss heads have a wide face, and a low profile. Perfect for good grip & minimal air resistance. A bit of CA on the outer BT hole, and we're good to go!

Now, to get some 1/4-20 rod and start really thinking of how to mount the altimeter!

I have an idea of how I'll be painting the DX-3. The Patriot I'm still debating.. Now, if only the weather will cooperate to allow me the temp & RH (and low wind) to paint!


Off to dinner with the family!

(And yes, there has been some beer, but nothing really spectacular to write about. I had a scotch one night too..)

 

[dr wogz]

I'd like to take an moment to talk abut the building environment. i have a shop , a hobby room that I build in. as you can see, I do have another love, Lego.

And I do like a beer when I build. I don't have 14 at a time, usually just one over the length of the build. And, when I build I need a bit of auditory stimulation too. I have a DVD player, and sometimes watch a movie. The fin fillets got me watching 'Animal House'. The rest of the build has been music. My tastes vary, but this one has been a lot of early British Punk: Toy Dolls, Sham 69, Clash, etc.. I also have a fondness for the Rolling Stores (pre "Tattoo You", when Keith was smacked out, they played their best!) and Frank Zappa.. The wife doesn't understand Frank, but I do.

 

[tHoagland]

I'd like to take an moment to talk abut the building environment. i have a shop , a hobby room that I build in. as you can see, I do have another love, Lego.

I share my space with my children and it looks a lot like yours.

 

[SeanW78]

Fin sanding..

Plywood find sanding... I'd take advantage of modern day power tools, but my belt sander is broken. Looks like the power switch finally gave up. Broke into little pieces..

So, first break the edges with a plane, get the basic shape. one pass, check.. pass again, check.. I usually carve off a 45° chunk off each side, then sand & round one by one. And yes, planning ply is a pain, and can lead to a disaster pretty fast.

Do I count my strokes? Generally no.

Do I have a special technique? Somewhat. I run my ring finger (of the hand holding the sanding block) against the edge of my bench to ensure my strokes are even. I rotate along the axis of the curve to try and maintain a constant curve. I then will sand across the curve to even it out. I then flip the fin over to do the other side. Its' usually pretty even.. I do wish I was more ambidextrous, so that I can sand one side with one hand, then sand the other side with the other hand.. Somehow I feel this would make things more even..

Anyways, preliminary sanding & shaping done. A quick final sand later..

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View attachment 317926

I have a decent collection of handplanes. Sanding is for suckers if you've got the right tool!

 

[PatD]

Frank Zappa.. The wife doesn't understand Frank, but I do.

Goin to Montana soon. Gonna be a dental floss tychoon!

 

[Sluggo]

We can jam in Joe's garage.....