Madcow AGM 33 Pike 8” L3 Cert Build - "Maximum Plaid"

For my NAR L3 certification, my son and I are building an 8” Madcow AGM-33 Pike, just in time for LDRS. This is a whole lotta rocket!

We started planning a 4-6 months ago and building about a month ago, so we’re late getting the thread started. A lot of inspiration came from Robertv2’s build thread for the 8” Pike from a year ago. That was a first class build and I learned a lot from his thread.

This build is a straight up 98mm single motor, dual deploy, without anything too special, except it is BIG.

With every build, we try and learn a new technique or skill. For this build, we bought a Shapeoko3 CNC and made/modified all our own rings and bulkheads in the garage. We are also using more aluminum parts and have upgraded a lot of our components. We are only 50% done and about 7 weeks from LDRS, so we have some work to do. Hopefully, sharing some of our experience will give back a little bit of what we’ve learned from this community. Enjoy!

Here is a summary of vehicle and the planned components:

Airframe length: 141.75” (11.8 feet)
Motor Mount: 98mm
Airframe materials: G12 fiberglass .10”
Fin materials: G10 fiberglass .20”
Planned Motor: CTI M1450 (Aerotech M1939 as backup option)
Unloaded Weight (calc): 71 lbs / Loaded 90 lbs

Main Chute: Rocketman 18’ Standard Chute
Drogue Chute: Rocketman 4’ Pro-Experimental
Harness: 9/16” Kevlar tubing
Flight Altimeter/Computers: RRC3 and a Stratologger CF
Launch Lugs: PML Large Linear Rail Lugs
Motor Retainer: Aero Pack 98mm
Charge Canisters: Mac Performance (and custom ?)
Decals: Stickershock23
Tracker: BigRedBee APRS GPS
Camera: Veho MUVI micro

I'm down, good luck!

I forgot to take an obligatory unboxing photo, so this is about the closest you get. I am fortune to live down the street from Madcow, so there were no boxes. The components in the kit include the fincan (pre slotted), avionics bay, upper airframe, nosecone w/alum tip, couplers, fins, and a handful of G10 rings and bulkheads.

After a good sanding and smoothing, doing the dry fit is always my favorite part. This thing is a beast at almost 12 feet tall.

She's a beauty! I've got the 5.5" ready for my L3 launch!

So, the big lesson of this build was to learn how to CNC in the garage. My son and I have done a lot of 3D printing, so we were familiar with basic CAD design. It turns out CNC is just the opposite of 3D printing (subtractive vs. additive), so it was pretty easy to pick-up.

The CNC we settled on was a Shapeoko3, given a large build size (17”x17”), but still a “desktop” CNC. Overall, I have been very happy, but the setup/assembly was a bit of a surprise. It ships in about 1000 parts and takes 6+ hours to fully assemble and test. I did not plan on that part, but I am probably better prepared to fix it if it breaks.

I did a lot of learning and test runs, primarily using the basic software supplied with the machine to design and cut. Once I got the hang of it, I was cutting rings and parts like a boss – to .001” precision.

We ordered some more G10 fiberglass and picked up a bunch of 6063 aluminum from a local supplier. Then we started cutting more motor mount rings, bulkheads, and will ultimately make some custom charge canisters.

The avionics bay bulkheads and the nosecone coupler bulkheads we cut from .2” aluminum with a .1” inset, so they fit perfectly like a pot top – better protecting the bay from gases.

The CNC has also been great for cutting fin guides, cutting perfect holes for the motor retainer, and I am now the neighborhood sign maker.

Here is one more. The finished thrust plate with an Aero Pack motor retainer. Manually drilling all those holes straight, even on a press, would be very tough. The CNC made perfect holes on the first try.

The fin can is always the most work for me, so we went there first.

Since this build has a lot of fins and a lot of slots, we went with six internal rings to bookend each of the three fin slots. We used threaded rods to give us .01” precision on ring separation and additional ring support. We also notched the bottom of each ring and created a ½” high channel to create better fin alignment and seating on the motor tube. The inspiration for this came from Robertv2’s build, but we compromised and used rods for support and smaller fiberglass guides.

I also added three small holes on each ring for pressure ports, since each fin, essentially has a sealed chamber around it’s base.

Before we put together the internal fin can assembly we tested each ring pair with a small rig through the length of the fin can. There was some sanding of the inside of the fin can and of the rings, but ultimately we got them all to fit like a glove.

We did a final dry fit test of the motor mount tube and all the fins using a few fin guides to make sure the alignment was good. Then did an initial epoxy of the motor tube assembly to lock the alignment. Fins, heavy epoxy, bulkhead, and thrust plate will go in this weekend.

BTW -- the PML launch lug is also pictured. We've used these on previous rockets. This is the larger 1515 lug and we created an aluminum back plate with threaded holes to retain it (along with epoxy).

Excellent. Find Robert V2's thread from a couple years ago for additional ideas for this rocket.

Great looking build!

Why all the threaded rod?

DAllen said:

Great looking build!

Why all the threaded rod?

Click to expand...

Originally, I planned to used the three small (#8-32 .16") threaded rods just to get perfect ring alignment, but then I realized how much strength and stability they provide to the overall design, so I decided to leave them in. The rods provide ring alignment to .001" and ensured a perfect fit of the entire assembly on the first try. The vertical support means that every ring, as well as the bulkhead and thrust plate, are supported by every other ring in the assembly. Probably overkill, but it only adds about a pound of weight and it gives the engineering support for a much larger motor in the future (six grain N or O).

can't wait to see it fly.

We did a full sanding of the fins using 220 then 400. We mounted each pair and let them set 24 hours before rotating to the next pair (we were in no hurry). We filled the alignment trough with copious epoxy and then shot the fillets using a Loctite epoxy gun (love it!) and E-20HP epoxy. We also coated the top part of the rings fore and aft of each fin, before inserting. We used a fin alignment guide, but it wasn’t really necessary, since our tolerances were so tight on the motor mount tube. After a thorough drying and sanding of the fillets, we moved on to the thrust plate.

We dry fit the thrust plate a few times to ensure a perfect fit, and then it was inserted on top of good helping of JB Weld. It also has three lock nuts that connect into the motor mount ring harness. We taped off the aluminum plate and then put a .05” layer of JB Weld epoxy around the inside exposed tubing to better protect the fin can tube from ignition heat.

The nose cone on this kit comes with an aluminum tip and a coupler for connection to the upper airframe. Before we did anything, we made two aluminum bulkheads for the coupler with a .1” inlay, so they fit like a pot top.

I believe in a little extra reinforcement for the nose cone and the coupler, in the case of a hard landing, high gee flight, or an accidental synchronized double bang ejection at apogee. For the extra reinforcement I used a .25” threaded rod epoxied into the very tip of the nose and then bolted into the forward bulkhead of the coupler. To set this rod we first tightened down the aluminum tip screw, sanded the inside tip, poured in about six ounces of epoxy and then dropped the rod in with a few bolts/washes on the end for traction. Large quantities of epoxy tend to heat up, so we set the tip of the nose in ice water, while the epoxy set.

The coupler was assembled by attaching support rods to the forward coupler, epoxying the forward bulkhead to the coupler, and then epoxying it into the nose cone as far down as possible. Once it was set we bolted down the center rod and attached the aft bulkhead. Ultimately, we’ll create an electronics plate to go inside the nose cone bay for a tracker, but that can save for later. Note the vents on the forward bulkhead to depressurize the nose during ascent. When the airframe is assembled the coupler and bay will have a vent port to the outside.

Man, that thing is a tank! (in a good way)

Nice work. Now, let's see that Tesla

The AvBay bulkheads are fairly straight forward. The only thing that is truly unique is the blast covers for my terminals, to keep the terminal screws pristine clean after a load of FFFF goes off at each end.

I used a basic terminal block (Amazon https://amzn.com/B0053WRTQ8 ) and mounted them with two screws through the bulkhead into PCB stand-off spacers (https://amzn.com/B018FR4DGG ). Then I cut some 1.5” PVC in half to form a protective dome. The sides and front are filled in with cutouts made from welding felt. The dome attaches into the two threaded spacers. Hopefully, 3-4g of FFFF does not blow the thing clean off. It is pretty solid, so hopefully it does the job of protecting the terminals.

The charge wells are from Mac Performance. Everything on the bulkheads is mounted using copious JB Weld and/or Epoxy to form an airtight seal. Especially, on the AFT end (drogue side). I’ve had a few premature mains deploy due to bad seals, so I am intent on making sure the AFT end is more than airtight.

For my charges, I found a perfect size plastic tube that fits snug in the Mac Performance charge wells. Here: https://amzn.com/B00N3YEXDK I cut the threaded top off, add my FFFF, and then insert a small piece of foam rubber and a dab of epoxy. The match will run through the foam. These can hold a lot of FFFF (>5g) or just a little (1g) in an easy to insert form.

For my wiring to the terminals, I am using high temperature silicon wire. Resistant to 200 degrees Celsius. I am not sure how much that matters, but hopefully it lasts longer under the stress of the heat. Link here: https://amzn.com/B00EZH3IOY

The AvBay is setup with four threaded rods between the two custom aluminum bulkheads. The plan is to seal the AFT end, so all the maintenance should be possible by removing the forward bulkhead only. Inside, I’ve also got a G10 fiberglass spacer.

To make sure everything was easily accessible from the forward end, I created a sled that goes in and out on a ring. It is anchored to the ring at 90 degrees using an aluminum corner and the ring mounts in with four anchor nuts/washers. The other end of the sled feeds into a slot with foam rubber creating a tight fit.

On the sled I’ve got a Stratologger on one side and an RC33 on the other. Given the 8” airframe, there is room for days inside this thing to play around.

For the batteries, I used a fully enclosed battery case. I modified this case by removing the switch (direct solder) and adding mount holes for bolting it down to the sled. Link: https://amzn.com/B00K86F1O6

Next on the list is mounting the switches, camera mount, external LEDs, buzzers, etc. into the avionics bay.

That's cool. Nice work and all, but what about that Tesla? P90D?

Looking through the upper airframe and a little something for Corzero...

We got the Avionics Bay finished up over the last week. This included mounting of the switches, launch lug, external LED/beeper, camera and vent holes.

I am using a StratoLogger CF (primary) and a RRC3 (backup). I checked with the manufacture and both only use a capacitor for brown-out (not firing), so my L3CC said it was ok to only use 2 switches – for battery cut-off. The switches I am using are simple key switches. I considered flush-mount flathead screwdriver switches, but I couldn’t find any I liked. I am also going to be with a group of Boy Scouts at LDRS and thought it better to stay with key switches for now.

For the camera, I am using a tiny Veho Muvi camera (https://amzn.com/B0037P5CAI ). I’ve used these before on other rockets and they work great. I used a 3D printer to create a custom mount, so the camera slides in from the outside and fits very snug.

The pressure vents were sized using David Shultz’s method and formulas. For this AvBay I needed four (4) ½” holes.

Since the Stratologger is new, we did a launch simulation test with our electronic matches to make sure they fire and fire under expected conditions. For this test we used a sealed Tupperware container and drilled a port for a vacuum line and for two eMatches to ignite outside the box.

We drew a vacuum to maximum pressure, turned the vacuum off, watched the drogue match fire, then the main match fired after a few seconds of pressure loss in the box. Overall, a successful test.

Note: We are using MagFire matches from RocketFlite dipped in a mix of pyrogen/magnesium.

There is nothing too special about the airframe, but for this rocket we used LumaDyne inserts as “removable rivets”. In the past I’ve used nylon screw rivets, but they tend to break and be less reliable. These LumaDyne aluminum inserts look great and work very well at anchoring one end of the airframe. We had to buy slightly longer screws, given the width of our airframe, but the inserts rock.

For the opposing ends, we are using three 4-40 nylon shear screws. These are rated at 38 pounds of force each, so we have about 115 pounds of hold on each end. We calculated the max drag separation to be around 81 pounds of force, so three pins on each end should be good.

Once we had everything lined up, we also tested the launch lug alignment. We are using the PML Large Linear Rail Lugs that ride on a 1515 aluminum rail. We used a piece of 1515 rail to make sure we had good alignment and glide.

We also ported the airframe in a dozen places with ¼” ports, to prevent pressure build-up, premature separation, and airframe stress. Each cavity has at a minimum of three ports.

We setup the rigging and did some ground testing today. For the rigging, we have our main in a 24” compartment in the forward airframe and a drogue in a 12” compartment at the top of the fin can.

For the drogue, we are using a Rocketman 4’ Pro-Experimental. We have 45 feet of 7/16 tubular Kevlar, rated at 5300 lbs, from OneBadHawk, and 5 feet connecting the drogue back to the AvBay and upper airframe.

For the main, we are using a Rocketman 18’ Standard Chute. My son was running around with it and almost took off, before ending up in a tree. It is big. The main is connected with 20 feet of 7/16 kevlar tubing and 5 feet connecting the main to the nosecone. 1700 lb quick links hold everything together.

We also have two Giant Leap “Fire Balls” to prevent airframe zippering wear and tear. I’ve used these on other rockets and I really like how they protect the edges of the airframe during hard whiplash.

Ground Testing is always exciting. I am sure there are better methods and locations for ground testing, but for us it is in our back “yard” next to the pool. We anchor down the fin can with 100 pounds of weight and then eject the forward section and nose under separate tests.

BP Calculation: For this rocket we used Vern’s Rocketry Formulas for PV = NRT.
https://www.vernk.net/EjectionChargeSizing.htm
The drogue compartment calculated to about 1.8g of FFFF and the main compartment to 4.3g of FFFF. We went with 2g and 4.5g respectfully for the ground test. We were targeting 350 lbs of force for both ends. The shear screws separate at 115 pounds (combined).

Our first attempt to fire on the ground was a bust. Oddly, neither match would fire with a 9V battery, but they both had continuity. After a closer look, I figured out that the 50 feet of CAT5 wire I was using as a firing wire, had 8 ohms of resistance. A quick swap of the wire and we were back down to 1.2 ohms on each match. This was not material, as it is only used for ground testing. Everything else in the rocket was sound.

Both ground tests were successful. For drogue separation we got a solid two feet break with the laundry delivered. For the main, we got a nose cone about 5 feet off the deck, but our laundry wasn’t fully ejected. I’m sure in the air the loose nosecone would have pulled everything out, but I’ll up the charge slightly just to make sure.

We shot slo mo video of both tests and I was amazed to see the size of the fireball that lights up inside the airframe, since the unpainted rocket is pretty translucent.

Speaking of paint… I think it is time to start prepping.




Slo Mo Fireball Capture:

We checked out the avBay bulkheads after the ground test. The powder tubes and the custom terminal covers worked perfect. The tubes were inserted into the charge wells and had a small foam top with a few drops of epoxy to hold them in. The tubes did not melt. They came right out of the charge wells after 4.5g of FFFF.

The terminal covers also did good. No BP residue on the terminals and no cracks after 4.5g of BP. See pic. All good.

Tease! Build is coming along nicely. Any ideas for paint?

We're going metallic silver with the Stickershock Pike AGM decals. I'd chrome dip the thing if I could. I've never found chrome paint that is quite as good as the real deal. So, metallic silver will have to do.

We've got a full garage converted into a sealed off painting station with plastic sheeting. My neighbor asks, "you got some kind of Breaking Bad thing going on in there?" "No, I'm just painting a giant Pike missile." "Oh, that's good!"