AMW FiberMax Der Red Max Build

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gfunk

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I'm thinking there must be a bunch of us about to embark on this AMW Black Friday sale build. There's not really a good/complete build thread that I could find, so I'll do one if there's interest.

I'm currently mulling over a few topics...


  • HED DD (main in the nosecone / drogue in the fincan) or just SD pop and drop (maybe adding a JLCR I don't yet have)
  • U-bolt vs single eye bolt on the top CR
  • Making a 3rd centering ring, possibly as a 3/8" thick birch ply stepped thrust ring. Could do 1/4" stepped black G10, but I don't have any on hand, and if it's getting painted who cares?
  • Are the nomex honeycomb fin skins really worth the trouble? I kinda wish the fins were just thicker to begin with, but can't complain about the sale price. I would only do this for strength, not for appearance.
  • Foaming the fin can
  • Trying to do everything really nice and clear coating the red/black FG/G10, or just planning to paint it from the beginning
  • Is there a favorite motor for those you already flying this kit? Maybe a J275W? or J401FJ? This is my first 54mm rocket, so hardware must be procured. CTI vs AT in this size?
  • Maybe machining a tapered aluminum nose weight to epoxy into the front of the nose with a threaded eye anchor point to counteract all my ideas above which add weight to the wrong end

Definitely planning on:


  • a bad German accent DAS IS GOOT, YAH?
  • Stickershock23 decals
  • 54mm Aeropack
  • Maiden flight at NCR's Mile High Mayhem?
 
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Subscribed. I’m building one right now, and I’d love to compare.

I wanted fat fins with rounded edges, so I built skins out of 1/8” balsa. I’m planning to laminate them with CF to give the balsa some rigidity. I’m not sure how it will work out, but I figured it’s with a shot.
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Subscribed. I’m building one right now, and I’d love to compare.

I wanted fat fins with rounded edges, so I built skins out of 1/8” balsa. I’m planning to laminate them with CF to give the balsa some rigidity. I’m not sure how it will work out, but I figured it’s with a shot.
View attachment 334021


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I'm not sure what you mean. It looks like you glued the balsa to the fg fins, so that should provide adequate rigidity. Are you worried about impacts dinging up the balsa?
 
I'm not sure what you mean. It looks like you glued the balsa to the fg fins, so that should provide adequate rigidity. Are you worried about impacts dinging up the balsa?

Exactly. The fins are plenty strong because of the FG core, but the balsa is so soft, it will surely get dinged up on landing. Plus, I'm hoping for a cool, CF look on the fins.
 
Here we go!


  • Gave all parts a soapy bath in the tub.
  • Drilled two 1/4" holes in the forward CR for a stainless U-bolt. Positioned the U-bolt carefully, checking distances to air frame and a potential long motor case. Did a dry fit and made sure I could connect a quick link.
  • Sanded the MMT until the AeroPack retainer would fit, then sanded the forward CR and MMT in preparation for epoxy bonding.
  • Cleaned with acetone and super glue tacked the forward CR in position using a V-block to ensure perpendicular alignment.
  • Will add Rocketpoxy fillets to the CR tomorrow... no plans for super long burn motors so I don't think JB Weld is needed on the CRs. Retainer will, of course, get JBW eventually.
  • Made a plywood fin alignment jig, stepped thrust ring from 3/8" BB ply, and an extra 1/4" BB ply centering ring I probably won't use.

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It’s off to a great start! I love the V-block.


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Slowly but surely!


  • Cut an 1/8" radius on the 3/8" thick birch ply thrust plate/rear CR.
  • Sanded the TTW fin slots until the fins would fit.
  • Rocketpoxy fillets on the forward CR.
  • Mounted the U-bolt with slightly modified supplied plate and nylon lock nuts.
  • Thinking I will stay with the thrust plate approach as it moves the motor back and allows for slightly longer motors. Hoping to someday squeeze an AT 54/1706 K456DM in there, but we'll see. The super long supplied coupler will have to lose a couple inches for this (or get a bit of a donut shape).
  • The V-block rides again! Carefully located and tacked a mid CR just ahead of the fin tabs. Debated if this was worth the weight, but figured it's stronger, less volume to foam, and the 1/4" birch ply ring was only 20g, G10 was 32g. If it's worth building, it's worth over-building right? Glad you like the V-block, I think it's currently worth more than my daily driver... one of the perks of access to a precision machine shop. Just wait 'til we "polish the cannonball" in the e-bay!

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Looks good. Are you concerned about moving the CG too far back with the weight of the foam and the movement of the motor aft b/c of the thrust plate?


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Looks good. Are you concerned about moving the CG too far back with the weight of the foam and the movement of the motor aft b/c of the thrust plate?

Yes, definitely something I will be checking as we go! I did spend some time simming both configurations and decided the difference was minimal. If needed, nose weight and more thrust cure most of life's little problems, right?
 
I received one of these for xmas and will likely be starting it in the near future. I am interested to see how you do yours.
 
Finally some progress!

  • Rocketpoxied the mid CR on one side
  • Dry fit the fins and decided the tabs were .020" too long, so I took some material off the tabs (picture is before mod).
  • Sanded all epoxy joint areas on MMT, CRs, and air frame. Wipe clean with acetone.
  • Rocketpoxied MMT assembly into air frame, checking position carefully with my thrust ring and aeropack. Not super pretty, but functional.
  • Made electronics bay bulkheads, one G10, one aluminum. My thinking is that one side of the ebay should be RF transmissive as it will house a Missile Works T3 (and RRC3). Need to figure out sled layout that won't screw up the T3's GPS patch or the 900MHz whip antennae. 1/4-20 aluminum threaded rods won't be helping anything here either...
  • All design credit for the aluminum bulkhead goes to Chris Attebery... I just made a knock off for myself because I can and wanted to make some changes for my application. No, I won't sell you one. After making this I concluded APE's price on these is an absolute steal. Mine will get anodized before flight.
  • Ordered stainless U-bolt for the G10 bulkhead, will drill holes accordingly.

Next steps:
  • Rail button holes
  • Epoxy 3 fins, do internal fillets and foaming. Decide at that point if I'm adding nomex fin skins or just external fillets.

Interested in feedback on...

  • Mounting the booster side G10 ebay U-bolt off center to allow extra clearance on a 54/1706 motor.
  • Chopping ~1.5" off the coupler. Why is this thing so long anyway?! Figure I'll chop with a fine tooth horizontal bandsaw. This still gives 4" of engagement in the booster and just under an inch clearance on a potential 54/1706.
  • Switch/vent band with vent holes right below the nosecone? Initial research says it'll be OK.

In other news:

  • My Wildman BSS order arrived today with more rocket poxy. Just in time for weekend fin gluing.
  • Flew a similar sized short and fat 3 fin rocket (7 3/8" dia Fat Boy upscale with ~1 cal stability) on a J570W over the holiday. Awesome motor. Curious to hear comments on the fishtailing at 1:00 and 1:05. 10mph or less wind at launch.
  • [video=youtube;xn3PsK9wH6g]https://www.youtube.com/watch?v=xn3PsK9wH6g[/video]

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Rocket Poxy kit comes with this awesomeness. Every day is leg day for rocket man, apparently.

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Interested in feedback on...

Mounting the booster side G10 ebay U-bolt off center to allow extra clearance on a 54/1706 motor.
Chopping ~1.5" off the coupler. Why is this thing so long anyway?! Figure I'll chop with a fine tooth horizontal bandsaw. This still gives 4" of engagement in the booster and just under an inch clearance on a potential 54/1706.
Switch/vent band with vent holes right below the nosecone? Initial research says it'll be OK.

I don't see a problem with an off-center U-bolt unless you are going for speed or altitude. Possible the uneven weight could cause a little weathercocking, but not likely. If it is a concern, use a U-bolt on each side and a Y-harness.

No problem with shorter coupler, if you are using shear pins. As long as your electronics fit, knock it down. Just make sure you use pins to keep it from pressure-separating.

My Formula 75 with HED has the vent holes right in the switchband beneath the NC. No problems so far, but again, I am not going to max-performance.
 
Thanks Bat-mite and CPUTommy!

Some progress:

  • Got a 1/4" stainless U-bolt from Bolt Depot.
  • Drilled the G10 bulkhead to put it on center, should still have ~.75" clearance on a potential K456 motor (54/1706 case).
  • Chopped the coupler to 6.75" OAL using fine tooth blade horizontal bandsaw. This puts 1.75" in the nose, 1" for the vent band, and a 4" diameter's worth of engagement in the fin can. Plan to #2-56 shear pin the nose on, and maybe the booster...
  • Mounted 2 rail buttons.
  • Drilled a 3/32" vent hole in fin can, probably going to bump that up to 1/8" diameter for peace of mind.
  • Triple dipped fins for internal fillets on the MMT. Did these 1 at a time.
  • Internal fillets on fin-air frame with 1/4" wood dowel
  • Space heater helped cure Rocketpoxy.
  • Foamed the fin can. Bomber.
  • Think I'll skip the nomex fin skins, added small 3/16" radius fin fillets. Might bump these up to 1/4"R.
  • Ned LeDoux's new Sagebrush album has been the garage soundtrack for this build, finally got to see him again at the Grizzly Rose. Great show, sounds just like his dad.

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It's been more fun to work on my MAC Black Fly 3" upscale lately, but the Fibermax is plodding along.


  • Drilled and tapped three #2-56 shear pins for both apogee and main event separations.
  • Anodized AV bay bulkheads.
  • 3/8" tubular kevlar harnesses from MAC appear bombproof!
  • Made a G10 bracket and baltic birch ply sleds for T3 GPS and RRC3 altimeter. Dry fit looks OK, time to wire it up! Screw switches are 120º apart for access thru vent band holes.
  • Bought some motors and hardware from Sirius. Anything bigger than AT 54/852 is out of stock, everywhere?

Next up...
  • Epoxy in a NC eye bolt anchor point
  • Ground test ejection charges at midnight :wink: This will require some creative rocket holding to not load the fins with the ejection forces.
  • JB Weld the aeropack
  • Order spherachtues. 72" main to not break these bendy fins?
  • Probably a naked test flight in March?

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I love the sled and the bulk plate! This thing is going to be beautiful inside and out.


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First post from iPhone app... bear with me...


Plan to glue this aluminum anchor in the nose cone, unless someone stops me! It's got grooves to help hold rocketpoxy. Loctite blue on threads.

Aeropack is on with JB Weld.

Avionics are wired up and ground tested. T3 seems to preliminarily work OK even with an aluminum bulkhead and threaded rods. I walked a half mile away with bad line of site (houses) and still had signal. Can you buy threaded fiberglass rod in 1/4”? Ebay is upside down for pics, flight orientation puts the other end up, G10 bulkhead facing down.

Ebay is a heavy pig... good thing this is a low and slow fun flier.

Starting to look like a rocket! Maybe some ground ejection charges testing this weekend.


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After adding external fillets I was concerned about how floppy the big fins are. I ran some fin flutter analyses and concluded I better beef them up for the motors I hope to fly in this rocket. So, I milled off most of my fillets, sanded the fins with a DA sander, and added the AMW honeycomb skins.

Chris H's documentation of this process is great, so I won't go into detail. I used US Composites 635 Thin Epoxy with the Sloooooow 2:1 hardner. I could do one fin set every 24 hours. I didn't use clamps or foam cauls, but instead sandwiched my fin stacks between 2 granite surface plates covered with parchment paper. I added a couple hundred pounds of weight and let gravity do its thing.

I filled the voids in the edges with Rocket Poxy and sanded that smooth using 2 boards clamped on the fin to ensure I sanded perpendicular to the fin. I think this is going to work OK, though I have few spots to fill. I'm thinking I will leave the edges pretty square, maybe just break the edge on the corners with a tiny chamfer.

I've added preliminary 1/2" diameter fin fillets, and will pull bigger fillets over these.

The fin skins transform this rocket, totally worth it. They feel like nothing when you handle them, but they add remarkable stiffness. I ended up with exactly 0.250" thick fins.

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The fin skins transform this rocket, totally worth it. They feel like nothing when you handle them, but they add remarkable stiffness. I ended up with exactly 0.250" thick fins.

I like the look of the honeycomb. Are you considering leaving it that way?
 
Thanks, y'all!

Ground testing complete.

I made a V-block 2x4 to hold the booster for testing and not load the fins.

I ended up with 1.2gr for the NC main, this is packed in an integral charge cup in the forward HED ebay bulkhead. I know some people do NC charges in the very tip of the nose cone. That makes sense, but this seems to work ok...
1.0g: https://youtu.be/v8WogMOg-SU
1.2g: https://youtu.be/rO1rVY7CKic

Apogee event is 1.5gr, which gets all the laundry out without loading the shock cord. This is in a nitrilie glove tip, CJ style.
1.3g: https://youtu.be/yRdT6cS1oqM
1.5g: https://youtu.be/3nakh5CyxcM


Both separations shear three #2-56 nylon screws.


On to finishing!


I'd like to leave the honeycomb visible, but there are enough imperfections here and there I think I need to Bondo GSP and paint to have a finished looking rocket. That and my birch ply thrust ring looks out of place.

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Rockets in Iowa - I approve! (former Iowan here). Building one of these gems myself (and it's 2.6 brother), with an NC sled instead of full HED, and the coupler bulkhead offset to the top end to allow maximum possible motor case length. Now I gotta get a v-block, great idea there. Thanks for posting the details.
 
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