Marvin Martian Jr. Build

Creeping along with my half-scale build (approx.) of The St. Louis Kaboom Krewe's 10 feet tall "Space Oddity", which was launched at LDRS 38. My version will be 5 1/2 feet tall, 24 inches at the fattest body diameter, and a 48 inch fin wingspan. It should weight south of 50 pounds.

First thing I wanted to figure out was the round ball at the top of the rocket. Because I'll be using a launch rail tube for a 1515 launch rail (the 48" long tube will be epoxied to the full 48" length of the 4" dia. Blue Tube internal motor/parachute tube), the ball on top could be no larger that 4" in. diameter.

I found hollow 4" stainless steel hemispheres on the web- each with a 1/8" dia. weep hole in them. I drilled the weep hole with a 1/2" metal-cutting drill bit to accept a 1/2" dia. all-thread rod. I'll fill each half with BB's and epoxy for added weight and J-B Weld/ bolt the halves together on the all-thread rod.

I'll mate this assembly to a 2.56" dia. Blue tube (probably 13" long) also filled with BB's and epoxy. Once i cut and weigh the three 1/4" thick Baltic Birch plywood fins, I'll have a better idea of the total nose weight necessary.

I'm going to drag out this project build throughout 2020, and I'll post updates periodically. Plan is to fly it at the 2021 Midwest Blast at Three Oaks, MI.

Made some progress with the build. Had to make sure I could get it out of the basement, so I'm constructing it as a fin/motor section, an upper body/parachutes section, and a elongated nosecone section. The two bottom sections will be bolted together at the launch site.

The first pic will give a general idea of what the finished product will look like, minus the finlets. The rocket will stand six feet tall, the body will be 24" at the widest point, and the three fins each extend another 12" past the widest body diameter. The center 24" diameter plywood circle is of 1/2" Baltic birch 9 ply plywood, as are the fins. Fiberglassing of the fin/4" dia. Blue Tube body tube joints is to come, as well as the fin/fore & aft plywood circle joints. Corner braces will also be used to support the fin/plywood circle joints. The bottom of each fin leg will be a triple ply of the 1/2" plywood, and will extend several inches north of the smallest fin width.

The smaller 2.56" dia. Blue Tube will slide over a 1515 launch rod. The 4" dia. steel hemispheres filled with epoxy and BB's will top the 14" long nosecone section. So far, that component weighs in excess of 7 pounds, with the expectation of filling the 2.56" central nose cone tube with more epoxy & BB's to achieve the proper rocket CG.

1" thick foam board circles will be cut and sanded to achieve the overall shape. A fiberglass skin will be applied over the foam. One altimeter and one timer will be placed in a cavity forward of the 24" dia. central point (most likely a section of sealed body tube with sampling port holes leading through the exterior skin). Separate parachutes will bring down the nose cone section, which could weigh 20 pounds, and the rocket body section. The fin/motor section currently weighs 21 pounds. An L1520 Blue Thunder reload should push it off the launch pad nicely.

All comments/suggestions are welcome!!

Fiberglassed the fin connections to the 3.9" dia. Blue Tube, as well as to the 24" and 12" upper and lower centering rings on the fin/motor tube section (I guess I can call the rings that). I ended up using Bob Smith 20 Minute Finishing Epoxy for this fiberglassing step. I will use West Systems epoxy for fiberglassing the "sort-of-football-shaped" body. Installed steel corner braces between the fins and the upper & lower centering rings.

Now it's time to cut the 24" centering ring which will serve as the base for the 28" long parachute Blue Tube and the attached 1515 rail tube. The two 24" centering rings (and thus the lower and upper body sections) will be secured together using six 1/4" pronged T-nuts installed and spaced equally around the top 24" centering ring, as well as 1/4" bolts, washers, locking washers and nuts through to the bottom 24" centering ring. This assembly will take place in the field so that I can get this rocket out of the basement.....lol.

So far, so good. The cutting of the 1" foam insulation concentric circles which will make up the basic body shape will be a new experience for me. I will try an electric wire cutter, with the jig saw as the back up plan in case that doesn't work efficiently. Thinking of maybe mounting the concentric foam circles together on a spindle turned by my hammer drill so that I can sand them down to the football shape. That will be an outdoor activity when it gets warmer!

Assembled the middle section of the rocket, which is the 28" long parachutes/1515 guide rail tubes, epoxied to another 24" diameter "centering ring". Ive shown it sitting off-center on the bottom fin section of the rocket. I'll fiberglass the tubes to the centering ring for added strength.

The two 24" dia. centering rings (and thus the lower and upper body sections) will be secured together using six 1/4" pronged T-nuts installed and spaced equally around the top 24" centering ring, as well as 1/4" bolts, washers, locking washers and nuts through to the bottom 24" centering ring.

My historical rocket collection can be seen in the background- 7 feet tall Gemini-Titan, Apollo-Saturn V & ""stretched" V-2 custom builds, as well as the pyramid-shaped McDonnell Douglas "Delta Clipper".

The nose cone section, with it's 4" dia. steel hemisphere topper, will be built after I weight the finished rocket product and know how much nose weight to add to the rest of the nosecone section, which will be about 18" long total.

Built and installed the two charge wells, along with a 3/8" eye bolt and the igniter connectors at the top of the fin/motor section. Had to drill through the motor tube to fish through the igniter connector wires, so they can be channeled up to the middle section, which will contain an accelerometer altimeter and a baro altimeter. Still have to figure out how to create a removable door which will fit the curvature of the rocket for the avionics bay, but I have an idea or two.

Next step is to start cutting the 1" foam board circles which will be eventually sanded down and covered with fiberglass cloth to create the "skinny football" rocket body shape. Already calculated the differing diameter for each foam piece to achieve that end.

"Delta Heavy Lander" is in the background of the second pic. This 6 foot tall rocket will have four deployable landing legs during descent, as well as two side pod "retro rockets' which will fire an 8 second reload with black exhaust and almost no thrust, but hopefully will be eye-catching during final descent. Drogue chutes deploy from the top of the side pods. LOTS of failure possibilities with this rocket, but I think (hope) I can make it work.

Made some progress with the 1" thick foam board internal shaping pieces. Started cutting the 24" x 24" pieces by hand, but eventually figured out that using a jig saw, with a tongue depressor taped to one side of the guide, would give me the bevel I need from piece to piece. 5 layers done on the bottom section of the rocket; 15 to go until the layers will meet with the motor "bell".

I'm using the simplest of tools to make the ever-reducing circles- half of a yardstick with a screw as the pivot, and a thinner #2 screw as the scribe. Based on my calculations for the arc of the body curve, I keep drilling holes for the scribe screw closer to the pivot screw.

For these bottom section pieces, I cut a 4" hole in the center of the foam board, and cut the foam circle into three pieces to fit between the fins. 1/2" is removed from each foam piece to account for the fin thickness. The two openings in the foam board between each fin pair will allow me to connect the bottom fin/motor section with the middle parachutes section by means of six washered wingnuts. The rocket is too wide to get out of the basement in one piece.

Made some more progress cutting the concentric foam pieces which create the shape of the fin/motor section. Four more foam pieces to go, then I can create and mount the "engine bell nozzle". Laying the fiberglass cloth over the foam will then follow.

I have found that using deck screws to attach one foam piece to the next works well, as I can easily realign a piece if necessary, as opposed to epoxying them together.

The particles from cutting the foam board have been a real nuisance. And I'll have even more concentric pieces to cut for the parachutes section, but that will have to wait until after the Ohio "shelter in place" order is called off, as I have only enough board for the remaining four bottom pieces.

The 1" foam circles are finished for the lower part of the rocket. I made an "engine bell" from an old brown plastic flower pot and fiberglassed it inside for reinforcement. Tomorrow I'll epoxy a 6" to 3.9" centering ring inside it, epoxy a like-sized centering ring to the motor tube at the base of the lowest foam ring, and screw the two centering rings together to secure the "engine bell" in place. The bell will be painted with heat-resistant paint inside and out, although the actual motor nozzle will be flush with the opening of the bell, and the bell is 12" in diameter, compared to the motor's 3" diameter.

I'm going to try a shortcut for the skin of the rocket. I'll Five Minute Epoxy a precut triangular (more or less) piece of fiberglass cloth to the 1/2" thick edge of the top plywood circle. The piece will stretch between two of the fins. Once dry, I'll see if I can stretch the fiberglass piece to take on the curvature of the foam pieces, and epoxy the bottom of the fiberglass piece to the 6" to 3.9" centering ring at the bottom. If it all seems to fit well, I'll then simply "paint" laminating epoxy on the outside of the fiberglass sheet. I'll probably use an additional 2" wide strip of wetted fiberglass to create a seam between each fin and the rocket body's fiberglass skin.

Had enough fiberglass cloth left to cover 1/3 of the bottom part of the rocket- more on order through Ebay. I "5 Minute" epoxied the cloth to the 1/2" thick plywood circle forming the top of the section. When dry, I painted some epoxy half way down the fins where the foam pieces meet them, and held the fiberglass in place until dry. I repeated the process for the second half of the fins, as well as the lower foam pieces down to the central motor tube. I tried to keep the fiberglass cloth taut during each step.

I still have to strip off some excess cloth at top of the plywood piece, but so far, this method seems to work. Tomorrow I'll try to "paint" on a coat of laminating epoxy onto the cloth to stiffen it up. Hopefully, the tautness will hold and keep the conical shape it currently has.

Before I do that, I'll slit the fiberglass cloth covering the two openings (just below the plywood circle) where the middle rocket portion will attach to the bottom portion with washered wingnuts, and epoxy the cloth inside the openings. On fight day, I'll probably simply cover the openings with silver duct tape, unless I come up with covers which contain flashing lights or some other silliness.

I am surprised at how smooth that came out. I am used to stacking foam and cutting with a hotwire to get a smooth transition between pieces. Yet in your case each piece was cut separately and you are spanning the gaps with the cloth. What is that surface like? Is it soft/spongy in the gap areas? BTW, not a bad thing in particular, as no force/pressure will be on that area.

It's quite taut in the gap areas, because I pulled it tight as the 5 minute epoxy at the fin/foam joints dried. i only epoxied 5 to 6 inches at a time down the fins, so I could keep it all tight.

When applying the laminating epoxy, I'm going to use a "light touch" with the brush. Probably do a couple of coats.

jmmome said:

It's quite taut in the gap areas, because I pulled it tight as the 5 minute epoxy at the fin/foam joints dried. i only epoxied 5 to 6 inches at a time down the fins, so I could keep it all tight.

When applying the laminating epoxy, I'm going to use a "light touch" with the brush. Probably do a couple of coats.

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Cool.

Looks good to me!

Laid the fiberglass on the other two sections and applied laminating epoxy- everything came out taut. Planning to reinforce the bottom of each fin with 3/8" plywood on either side, cut to the same shape and about 5" tall. Wood glue, wood screws and clamps.

After a few coats of sanding sealer on the fins, it will be time to buy the silver & red paint and see what the bottom section looks like when painted. I'll spray paint the "engine bell" silver, screw it to the bottom section where I've already attached a centering ring, and the bottom section will be finished.

Curious to see how close I came to my 25 pound estimate for the bottom section.

Thought I'd start on the enclosure for the two altimeters. The horizontal and vertical plywood pieces are shaped to the contours of the 1" foam circles that will be cut eventually, after the Ohio lockdown is lifted and I can buy the foam 4' x 8' sheets. The box is about 8" x 8" at the front opening.

I most likely won't make the enclosure airtight: rather, I'll epoxy a 3" dia. body tube to the back of the door, and drill air sampling holes through the door and into the sealed body tube. I'll be using both a baro altimeter and an accelerometer altimeter, so the latter can be mounted inside the box and not in the sealed body tube.

After I cut and install the foam layers, I'll lay a piece of Saran Wrap over maybe a 10" x 10" section that has the same profile, lay fiberglass cloth over it, and then use laminating epoxy. After it's dried, I'll remove, cut the stiff fiberglass to the dimensions of the door, and cut some shaped balsa internal struts to act as support on the door's surface as I epoxy the shaped fiberglass to the door. I'll drill the sampling port holes, and use small aluminum tubing to run from the fiberglass surface of the door (flush with the surface) and into the attached body tube holding the baro altimeter. I did something similar with my McDonnell Douglas "Delta Clipper' several years ago.

I'll make sure that the door is flush with the rest of the body, so the airflow isn't disturbed enough to screw up the baro altimeter. Even so, I'm using a Raven altimeter as my security blanket.

Started again on the foam circles for the middle section of the rocket. Installed nine 1" thick circles which now completely surround the wooden enclosure for the two altimeters. 9" done and 18" to go in order to reach the top of the motor/parachutes tube.

As I get closer to the top of the tube, I plan to switch to 1/2" foam board in order to match the severity of the curve better from the 24" to the 6" diameter.

It was interesting to find that the 1" foam board wasn't exactly 1" thick. The top pf the wooden altimeter enclosure was exactly 8" tall, but 8 pieces of foam left the stack of foam 1/8" shy of the top of the enclosure. It was an easy fix with some balsa wood spacers, but unexpected nonetheless.

I've switched to 1/2" thick foam board pieces, since the body curvature is becoming more severe. There is another 6 1/2" to go until I can put the 1/2" plywood 6" dia. centering ring on the top of the tubes. Then, further construction on the 17" long nosecone section will resume, after determining the CG of the rocket body so that I know how much more additional mass to add to the nosecone.

As a recap, the rocket will be six feet tall, the body is two feet wide at its widest point, and the fins make the rocket four feet wide. It should weigh about 50 pounds, with maybe 15 of those pounds being in the nosecone section. A 75mm L1520 Blue Thunder reload should push it off the 1515 rail pad nicely. And as my wife keeps asking me: yes, I've built the rocket in three detachable sections so that I can get each through the basement door.

I thought this pic would give a better gauge as to the scale of the rocket. The 14" tall nosecone still needs to be constructed, which will make the rocket about 6 feet tall. After weighing the bottom and middle portion of the rocket, the final weight will be closer to 60 pounds.

Lots more work to do in preparation for its maiden (final?) launch at the Michiana Rocketry Mayhem in Oct/Nov of this year.

The hatch cover for the electronics bay was a flat 3/8" piece of plywood. Because I'm using a baro altimeter as one of the two altimeters, I needed to match the contour of the rocket body. I glued some pieces of balsa wood to the plywood to exceed the thickness of the rounded body. I then used a palm sander to bring the contour of the hatch to match the body contour. I had attached the hatch to the body and put duct tape over the rocket body, so as not to mess up the body with the sander.

I'll epoxy a flberglass piece over the hatch, and eventually drill sampling ports through the hatch and into the altimeter bay body tube, which will be epoxied to be back of the hatch. It seemed like too much of a hassle to make the entire opening behind the hatch cover airtight.

I just started on the fiberglassing of the upper body, which is shaped kind of like a beehive. Silver and red quarts of paint have been purchased.

I affixed the fiberglass cloth to the upper body portion. I first affixed a portion to the back one-quarter of the body by 5 Minute Epoxying to the top centering ring of the body, and then pulled the cloth taut after applying 5 Minute Epoxy to the bottom 24" diameter plywood ring. No laminating epoxy yet.

I then wrapped a piece of fiberglass cloth around the rest of the body overlapping the first piece by about 2" on either side. I used the same epoxying technique top and bottom. I also put epoxy on the electronics hatch opening, which is a 3/8" plywood box attached to the foam rings and the 24" dia plywood base. The electronics hatch will not be airtight.

I'll now apply West Systems laminating epoxy to the entire upper body portion. I'll cut out the fiberglass covering the electronics hatch opening when the epoxy is cured. I'll also apply laminating epoxy and fiberglass cloth over the contoured hatch cover recently completed.

Once the fiberglass excess is cut away top and bottom, that will petty much finish the major construction of the rocket body. The nosecone with the 4" dia. stainless steel ball mass object on top (about 7 pounds) will now need to be constructed. I'm going to try using concentric foam rings to taper from the 6" top of the rocket body to the 2.56" dia body tube that connects to the stainless steel ball on top.

I'm ending the build of Marvin martian Jr. I'm awaiting the 4" steel sphere which will top the nosecone. For now, a softball rests in its place. The nosecone will be painted red.

Final specs of the rocket will be about 65 pounds at launch, with an L1520 Blue Thunder motor lifting it up the 1515 rail. The rocket is almost six feet tall, is two feet at its fattest body diameter, and the fins make it four feet wide. A Raven and a Perfectflite altimeter will be mounted in the non-airtight electronics hatch. The Perfectfilte will be in it's own airtight body tube mounted to the back of the hatch, with sampling ports drilled through both. Two Top Flight Recovery 120" thin mill chutes will bring the rocket down slowly enough to keep the 1/2" fins from snapping at impact (hopefully). The fins are reinforced at the bottom to give more strength.

I plan to launch Marvin at the October Michiana Rocketry launch in Three Oaks, MI.

Finally finished construction & painting of the eight pound nosecone. Also completed and installed the removable 9V battery holders for the two altimeters- Raven and Perfectfilte.

I've decided to put both altimeters in the sealed 3" dia. body tube compartment, which will be epoxied to the back of the electronics hatch door. Sampling port holes will be drilled through the door and into the body tube.

A block of screw terminal connectors will be mounted to the back of the door to allow for all the necessary connections. Two Shurter switches still need to be installed in the door. After that, the remaining tasks will be to install the 3.9" dia thrust plate and the Aero Pack motor retainer. I'll also get around to making the 3.9" dia. piston and kevlar shock cord assembly eventually.

looking good!

Finally decided on the best way to create the airtight housing for the two Stratologger CF altimeters. Epoxied a four inch length of a 3" dia. Blue Tube to the back of the electronics hatch. Drilled holes through it to feed the wires from the two Shurter switches, as well as the 9V power wires & the Apogee charge wires. Used the small white terminal blocks for the attachment of the wires in the rocket. Nothing very fancy, but should do the job.

Drilled right-sized sampling port holes through the front of the electronics hatch and into the airtight housing. Made sure that they were as free of burrs on the hatch surface as possible, and that the the holes were clean all the way through. Used a Dremel inside the housing to sand down the burrs created when the bit popped through the housing.

I'll use some silver electrical tape on at least the top joint of the hatch/body to create as smooth a transition for the air reaching the sampling ports as possible. Ordered some art from Stickershock23 to put on the fins. Received the L1520 Blue Thunder 75mm reload from Balsa Machining. A second 120" thin mill parachute with upgraded shroud lines from TFR, as well as two six feet long bridles, have already shipped. Working on the piston / 2000# Kevlar braided shock cord.

Can't wait until the Oct./Nov. Michigan Mayhem event with Michiana Rocketry!

Super cool build, looking forward to launch pictures/videos

Well- the weather in November scared me away, but the weather for this upcoming weekend at Mayhem looks pretty promising. Saturday afternoon is my preference, with Sunday as the fall-back day, just in case.

Good thing I ground-tested the recovery charge in November, because the 3grams of ffff (which should have been more than enough) didn't quite push out the main chute. Very heavy nosecone was the culprit. I upped the bp ante and all deployed well.

Fingers crossed that moving the fins forward so that they emerge from the fattest part of the body shape will allow the fins to do their job.

jmmome said:

Fingers crossed that moving the fins forward so that they emerge from the fattest part of the body shape will allow the fins to do their job.


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You could always hire a local crane and do a swing test

It didn't fly at Mayhem 2021, but did fly at Mid Ohio Tripoli April 2021 launch. Just noticed that I didn't post a link to the video:

Unfortunately missed Mayhem 2022 because we're in FL for a month............hopefully will have an unusual rocket or two for a Nov. Three Oaks launch.