Madcow Level-2 Build

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KC3KNM

Probably Wrong
Joined
May 6, 2018
Messages
892
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1,145
Location
South Burlington, VT
After getting my L1 back in June, I've been excited to start on my L2 build. I've decided to go with the Madcow Level-2.

The motor mount is going to be a little... different. I abhor aligning fins and don't love making internal fillets. To get around this I've 3D printed an insert that the fins epoxy into. While it does add weight, it should make the entire assembly very rigid. It's been printed with CF PLA @ 10% infill. The fins will be epoxied into the slots which I think will provide a very rigid bond when everything is sandwiched together.

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I did have an issue with delamination on the lower end. The rest of the print seems to have worked out well, so I cut the problem area off, sanded square and laser cut a cap for it. As it was a 12hr print, I'd like to avoid going through that again. The issue was localized to that area as the rest of the print is rigid. I'll keep an on eye on later prints and likely bump up my hotend temp (already at 230*C, so I'm not sure that was the cause), but in the end it's more of an irritant than a real issue.

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I've laser cut some spacers to allow the entire assembly to butt up to the Aero Pack retainer as well as some doublers for the stock centering rings. I'd like to fly this on larger motors later on, so the idea is to spread out the force instead of localizing it to the stock two centering rings. I'm not a mechanical engineer, but I've done something similar with a 3D printed mount on my IRIS and that's stood up to an H550 very well with no signs of fatigue.

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I wanted to provide a point to install my rail buttons to further up as well as provide a little support for the motor tube, so I've come up with this. It's very rigid and should work well. I forgot to grab a picture after assembling it, but you can see it it glued up on the motor mount assembly photo.

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This is where I'm at now. Waiting on some epoxy to cure before giving a good sanding and installing into the body tube. I'll get a final weight of the assembly before install. I think it should provide a very solid mount, make the fins a breeze to install and hold up to some pretty large motors. We'll see how that goes.

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That is fantastic looking! One day will get a laser cutter... but just got a 3D printer and just starting to learn how to use it. But your build looks great and I like your idea. My L2 I used basswood to build dam for fin/epoxy to sit in and not run all over, it worked great, but my fin alignment was off just a tad, and the rocket has a spiral spin...
 
That is fantastic looking! One day will get a laser cutter... but just got a 3D printer and just starting to learn how to use it. But your build looks great and I like your idea. My L2 I used basswood to build dam for fin/epoxy to sit in and not run all over, it worked great, but my fin alignment was off just a tad, and the rocket has a spiral spin...
Thanks!

The laser was the best investment I've ever made. It's a K40 I bought second hand with a bunch of upgrades from light object. I've got a small mill I use mainly to cut circuit boards which is nice for CF and fiberglass sheet, but for ply you can't beat how fast and clean these things cut.

I've always been pretty poor when it comes to fin alignment. I'm great at getting them aligned properly then wandering off and coming back to a mess. I was considering 3D printing an alignment tool, but this might be a better option. We'll see if how it holds up over time.
 
While the motor mount assembly was curing, I got around to cleaning up the slots in the body tube. They were too small and a little jagged. Took a rotary tool with a grinding stone and widened them a bit. They don't need to be perfect as they'll be filled in when I make my fillets on the fins, but at least the fins fit through them now.

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Next I drilled the holes for the launch buttons. I just found the center between two fin slots, drew three dots along that line and used that to square a metal ruler to. Drilled the holes to match up with my mount.

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Finally, I glued in the motor mount assembly. I first laid down a ring of epoxy where the shock cord mount ring was going to fall. I bought a telescoping magnet tool at Walmart and cut the end off. Replaced it with a 3D printed part that fits these makeup applicators I found on Amazon. They work really well when you need to apply small amounts of epoxy and with the telescoping handle it makes it super easy to lay fillets on rings down in tubes or to apply adhesive in hard to reach places without making a mess. Coated the bottom half of the mount in epoxy and slid it into the tube. After it was aligned I cleaned up the epoxy behind the mount. Finished by adding an epoxy fillet on the top of the shock cord mount.

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How is the CG looking compared to the base model? Very innovative, BTW. I will be watching!
 
How is the CG looking compared to the base model? Very innovative, BTW. I will be watching!
Thanks! I'm sure it'll drag it back a little but likely not a significant amount, I'll get a better idea when I get to working on the AV bay later today and dry fit everything. I'm working on an adjustable ballast system for the nose as I'd like to fly it on some larger motors later on anyway, plus I'm going with redundant electronics, so it shouldn't be an issue. I forgot to weigh the motor mount assembly before installing it, but the 3D printed and light ply parts haven't added much weight, so it shouldn't be too bad on the CG.
 
I spent what time I've had today working on a fin sanding jig. The mirrored jig for the opposite side is printing now. I'm leaning towards printing new jigs with a steeper angle, but I'll make the decision after I get a chance to sand both sides and see how it goes. Regardless, the jig seems to work well and provides a square, straight bevel on the fin. The fins from factory were cut a little rough and have some dings here and there, but it appears that they should clean up well.
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Your rocket will be awesome!
I'm sorry for my ignorance, I'm starting to play with rockets, but what did you use to fill this part underneath the PVC tube?
That is a fiberglass rocket, not PVC. I believe you are pointing to the centering rings, which are also fiberglass. Fiberglass rocket pieces are all assembled with epoxy.
 
Your rocket will be awesome!
I'm sorry for my ignorance, I'm starting to play with rockets, but what did you use to fill this part underneath the PVC tube?
That is a fiberglass rocket, not PVC. I believe you are pointing to the centering rings, which are also fiberglass. Fiberglass rocket pieces are all assembled with epoxy.
Yup, the rear ring is fiberglass, but is doubled up with a .125” piece of ply.

Right!?

My phone always wants to focus on the larger surface down the span
This was with a camera, even then it was difficult! I cropped the image as the lenses I have aren’t well suited for macro shooting, which didn’t help my cause.


I’m in Chicago for work for a couple weeks, so I’ll get back on the build when I return.
 
You should come up to our launch at the Richard Bong Rec Area in WI not a far drive from Chicago. Its this weekend a 2 dayer
 
I’m in Chicago for work for a couple weeks, so I’ll get back on the build when I return.

What Gary said! If you can head to Bong Recreation Area in Kansasville, WI, make a day of it. 15 bucks per day for out of state plates, bring lunch and water, straight up 94.
 
You should come up to our launch at the Richard Bong Rec Area in WI not a far drive from Chicago. Its this weekend a 2 dayer
What Gary said! If you can head to Bong Recreation Area in Kansasville, WI, make a day of it. 15 bucks per day for out of state plates, bring lunch and water, straight up 94.

I’d love to, but I’m not sure it’s in the cards for this weekend.

I’ll be back here for more training in mid to late September, any launches then?
 
And, can you believe it, there’s a craft hard cider place and distillery a mile from the launch pads.

There will be apples in September.
 
Yes TWA and WOOSH both have 2 day launches in Sept.

Sounds good!

And, can you believe it, there’s a craft hard cider place and distillery a mile from the launch pads.

There will be apples in September.

I’ve never had actual cider, just what’s in the beer section at the grocery store. I’ll definitely have to stop in. From your site it looks great!
 
Not much accomplished this weekend. I'm going to try to get a little more done today, but I've gotta pack for a trip to Michigan this week. It'll be a slow go for a little due to work, but at least that gives me some time to think through the process!

Edit: Added STL files. This is designed for the 6" GP sanding bar and uses #6 screws. The cutout for the sanding bar is over sized so you can slide it to different positions to make better use of your sandpaper.
 

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I swear I haven’t given up on the build! I’ve been home maybe 7 or 8 days over the last month and a half.

The good news is that I’ve got some delrin on order, so when I do get home (the 21st), I’ll be able to start on the ballast system I plan to build into the nose cone. I’ve also got some components coming to build my DD system. I’m shooting to launch in October... let’s hope that works out.
 
One of the main reasons I wanted to design a 3D printed fin can was to allow me to square the fins with some ease. Allowing the fins to slide into a slot gives me the ability to measure and shim each fin before I epoxy them into the slot.

While probably not conventional, this method seems to work well. I'm just using a surface plate, dial indicator with sliding base and some V-blocks to square the fins. After getting my V-blocks setup, I checked the squareness of the body tube to the surface plate. After some adjustments and shimming I got to good to about five tenths over a 3" segment. The tubes themselves aren't perfectly round, nor are they perfectly straight, so I'm going for an average. Even so, that's a lot closer than I thought I'd get.

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Once I know the tube is square to the plate, I can square the fins to that same level. While the photos show the fin square to within a tenth or so, it's more likely square to around .001" over it's width. Even so, that's only going to have us off about .02*. There's a lot of things that can add up or subtract to how far we show we're off. The fins themselves are pretty flat, but if the deviations line up in the right way through the chain, it's likely we'll end up thinking we're closer than we are. Still, this seems preferable to the TLAR method. :D

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I've still got some more sanding and squaring to do, but I figured I'd make a quick post on how I'm going about squaring the fins.

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Tolerance stacking. Odds say there's a fair chance chance of minor manufacturing glitches offsetting each other. In the real world it doesn't always work out that way. That's why even with "identical" samples, one is always better than the rest.
 
Tolerance stacking. Odds say there's a fair chance chance of minor manufacturing glitches offsetting each other. In the real world it doesn't always work out that way. That's why even with "identical" samples, one is always better than the rest.
That’s the term I was looking for, I couldn’t think of it at the time!

Yeah, I’ve come across some weird stuff. Plus, it’s hard to keep from influencing measurements. As a human it can be rough not to tweak the calipers to match the measurement you’re going for, consciously or not. :D
 
Spent the morning beefing up the table for this guy. Pretty excited to turn some parts for this project. After I get it setup and play a little, I’m hoping to get back to the Level-2 build.

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Here's a rendering on the next idea. I've only got 2" brass stock on hand, so I'll be making weights out of that. The aluminum tip is threaded as well as the base. The base will be attached to the shoulder of the nose cone, probably 4 screws. It's not going to see much tug, due to the threaded rod being screwed into the tip, which will be epoxied in. The weights themselves will just be brass pucks with a 1/4-20 thread tapped into them. Locked in place along the rod with two nuts. I've got a section of aluminum threaded rod, as well as some aluminum stock to turn the tip with. The base will be .25" delrin.

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It's been a while since I've even looked at my L2 build. I'll have a bit more time coming up to get back on it... and a new machine to make some parts with. :D

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