3" build - Dual Deploy and glass practice prior to L3

[Joe Bruce]

Nice work! I've considered a 3D printed AV bay, but haven't gone there yet. Plenty of good ideas on TRF, including this design! Good luck!

 

[Handeman]

I would be a little leary of a printed av-bay. The bay is also the coupler holding the two halves of the rocket together and there can be a lot of stress on that coupler. I've seen rocket fold in half from failed couplers and the way the 3D printing is done, the weak area is in the direction that would break with the rocket folding.

We had a guy 3D print a whole rocket. It only survived to about 100 ft. and then turned into confetti. Some of that was because he was doing a worst case stress test with an I1299N motor. But even so, almost every part failed, the nose cone, the BT, the av-bay, and the fin can.

 

[OverTheTop]

3D printed parts are quite capable of being used in HPR. I have flown nosecones, transitions and fins on L & M motors without problems. You have to design the parts to deal with the relevant stresses, just like any other material. 3D printing adds its own foibles, particularly the z-axis weakness, but the constraints are manageable.

Make sure you know what stresses your part will be dealing with and design appropriately.

 

[Dustin Lobner]

I would be a little leary of a printed av-bay. The bay is also the coupler holding the two halves of the rocket together and there can be a lot of stress on that coupler. I've seen rocket fold in half from failed couplers and the way the 3D printing is done, the weak area is in the direction that would break with the rocket folding.

We had a guy 3D print a whole rocket. It only survived to about 100 ft. and then turned into confetti. Some of that was because he was doing a worst case stress test with an I1299N motor. But even so, almost every part failed, the nose cone, the BT, the av-bay, and the fin can.

Yeah, don't think I'd try something like that (the I1299). The printed material I'm using for this thing I use for test fixturing all the time at work (I'm a Materials Engineer that among other things, runs a mechanical test lab). This particular material I've seen resist a repeated 500 psi load in compression without issue. At bare minimum the av bay has a piece of all thread running through it so if it does shred it'll stay together. Also - I can't describe how much solid plastic there is in this thing, lol. Most 3D prints are 3 solid layers with 30% infill...the Av Bay is 7 solid layers with 75% infill. Running a pretty high temp (240C) that has been shown to give good layer adhesion. I have 3D printed several rockets, biggest I've flown is an F-something without issue. I've flown a G80 and I140 with monolithic fin cans without issue. The J450 will be the biggest for sure.

Here's what the Av Bay looks like finished:


Internals:


Ends:


And the screws even line up, woohoo!



Hopefully works well. Should be fun.

 

[OverTheTop]

I have been known to use bike spokes for tension members in smaller rockets. They are around 2mm diameter and work really well. If you use titanium they have a breaking load of around 280kg each. Find a bike shop that makes them and they will cut them to size and roll the threads for you. The rolled threads work harden and provide better terminations. Threading using a die would result in stress raisers that would weaken the part at the thread root.

Keeping the 3D printed parts in compression gets around the problem of z-axis weakness.

 

[Handeman]

Keeping the 3D printed parts in compression gets around the problem of z-axis weakness.

I don't know much about 3D printed materials except I know they are weakest on the z-axis when they bend. I also know stiffy tubes came about because some av-bays, even though under compression with end caps and threaded rods, still allowed the rocket to fold in half under the stress of flight. Since that is the weakest part of a 3D printed part, that would be my biggest worry and what I would suspect would be the first type of failure.

 

[Dustin Lobner]

I don't know much about 3D printed materials except I know they are weakest on the z-axis when they bend. I also know stiffy tubes came about because some av-bays, even though under compression with end caps and threaded rods, still allowed the rocket to fold in half under the stress of flight. Since that is the weakest part of a 3D printed part, that would be my biggest worry and what I would suspect would be the first type of failure.

It's a concern to be sure. Biggest "getting around it" technique (other than having everything in compression) is just printing things really thick. That and I'm using a material that is very tough - it doesn't shatter. Doesn't mean it won't break eventually, but it's more robust than something that is strong but brittle.

 

[OverTheTop]

I don't know much about 3D printed materials except I know they are weakest on the z-axis when they bend.

Bending puts one side in compression and one in tension. It will fail on the tension side first usually, for a 3D printed part.

 

[Dustin Lobner]

Tried starting the fincan/motor mount print this morning before work but discovered a pretty bad bed leveling error. ...when printing small things in the middle of the bed, leveling issues aren't as big of issues. When printing something that takes basically the whole 300x300 bed, leveling is critical. So, releveled the bed and just hit the go button on a print that the computer is calling a 109 hour print...guessing it'll be closer to a full week. Also need to print the tailcone/motor retainer, so this is going to be a close one.

 

[Dustin Lobner]

Some first layer porn if that's your kindof thing...

Edit - the lighter area about 4:30 on the rings is reflection from my work light, there's good plastic there.

 

[Dustin Lobner]

Now have the issue that the ematches I bought from Apogee are "moving in the USPS system", aka been sitting 2 hours south of me in Chicago for the last week and I really don't know when they're going to be here. And I need to do ground testing before Memorial Day weekend. Debating ordering some from Wildman and paying the $18 for shipping via UPS so I actually get them. Ug.

Print is coming along well. 10% done after 12 hours...not sure how it counts that, number of gcode lines, number of layers? Either way, not too bad.

 

[Dustin Lobner]

Starting to get fins appearing amongst the support material, woohoo! It's 100% infill right now, will go to less that that pretty soon, pretty sure I set that changeover layer somewhere just above where the rail lugs mount and it's just about there. 23 hours after start, reading 19% done...still on track.

2nd Eggtimer Quantum just arrived, so I guess I know what I'm doing tonight. (-:

 

[Dustin Lobner]

Pretty much all of my supplies have arrived. Went from 0 ematches to 110 in about an hour, lol. Doing deployment testing either Sunday or Tuesday, depending on how life goes and if I can get those brass things epoxied in easily tomorrow. 2nd Quantum is done and boots up, so looking good there. The print is continuing...48 hours in and showing 37% done, so 6 days is looking about right.

 

[Dustin Lobner]

Print is hanging on, just saw that all of the support has peeled off the base...that's fun. That wasn't holding it down to the plate obviously (the center part that's touching is), but still kinda distressing. One of the things on the 1-3 year plan is the build a bigger printer, one that's completely enclosed so I can run the whole chamber warm and this doesn't happen.

 

[wsume99]

Following along here. You've posted lots of good information. Over the winter I printed a fincan for a 38mm OD rocket with a 29mm MMT. It also has a printed nosecone. Only been able to get one flight in so far. I plan to ramp from 29mm hobbyline motors up thru H. I constructed it so that I can replace the fincan and try different designs as I learn.

From what I have learned so far I'd have zero concerns about the strength of your fincan. If it were me I'd reduce the infill. You have tapered fins so geometry is on your side for flutter. I'd bet you could easily go under 50% infill.

I suspect the same for your coupler as well. Wouldn't be too difficult to print some test coupons and get some material strength data. Then you'd be able to design to your anticipated max flight loads.

I really commend the OP for sharing his build. I hope this thread and the handful of others like it will begin to show how all the naysayers are/were wrong about the sufficiency of 3D printed parts.

 

[Dustin Lobner]

Following along here. You've posted lots of good information. Over the winter I printed a fincan for a 38mm OD rocket with a 29mm MMT. It also has a printed nosecone. Only been able to get one flight in so far. I plan to ramp from 29mm hobbyline motors up thru H. I constructed it so that I can replace the fincan and try different designs as I learn.

From what I have learned so far I'd have zero concerns about the strength of your fincan. If it were me I'd reduce the infill. You have tapered fins so geometry is on your side for flutter. I'd bet you could easily go under 50% infill.

I suspect the same for your coupler as well. Wouldn't be too difficult to print some test coupons and get some material strength data. Then you'd be able to design to your anticipated max flight loads.

I really commend the OP for sharing his build. I hope this thread and the handful of others like it will begin to show how all the naysayers are/were wrong about the sufficiency of 3D printed parts.

I've flown up to an I140 so far with zero issues. Half a dozen flights on a G80-sized motor with 100% awesome results.

As far as material data, I'm a Materials Engineer and run a mechanical test lab, so I could certainly get the data, and get it scientifically correct. The biggest issue I have is being able to estimate flight loads...what good is the data if you don't have a model to apply it to. What could be done is to instrument a flight...put some strain gauges on it and try and get some info that way. Don't know how well that would work...will kick it around.

And as far as the last comment goes, thank you for your kind words...I'll declare victory when it's at 200 feet coming down on a fully inflated main chute and all the pieces are intact. (-:


Good progress being made today. I got 40 Quickburst ematches dipped to suppliment the 30 I bought from Wildman...good to go on the recovery activation front.

I got the brass strips put in (at least how I think they're supposed to go). I put 4 in on the main and 2 on the drogue side. Hoping to get deployment testing done tomorrow at a friend's place. Need to knock epoxy down and get the 2-56 holes drilled and tapped. I did trigger one of Wildman's ematches with a 9V just to see what happens, it was pretty startling how loud it was.


Got the rail lugs put on the top of the motor mount, I love how they look with the standoff kindof "growing" out the side of the part. Put 1010 and 1515's on...when asked what size rail guides I have, I can reply "yes", lol.



One of the stipulations for Mini Midwest Power is everyone has to wear facemasks, my mother made me a couple with a P51 on it...awesome. I'm ready for Mini MWP...or to rob a bank, lol. (and duh, the last part was in jest...never know these days how seriously people take these things).

 

[Dustin Lobner]

Fin can / MMT is coming along nicely. 60% and counting.


Got those brass pieces in, have the drogue side looking good...friction fit with 2 2-56 nylon screws. For the main side, one of the brass pieces isn't as tucked in as nicely as it could be, so I'm having trouble getting the nose cone smoothly in. Sanding the OD of the nose cone to take off some OD on it using this apparatus:


Hoping to get to ground testing at a friend's tomorrow. Made up a bunch of charges...two different charge holders at 1.5, 1.6, and 1.75 grams of FFFFg, qty 2 in each config.

Here's what the charge holder looks like with an igniter in it:


With BP and then taped off:


Box of test charges ready to go:


Good day of progress, starting to get nervous about next saturday already, lol.

 

[Nytrunner]

Just a word on the charge building: You've placed the match under the blackpowder. Despite taping over the charge, this can result in inconplete combustion as the flane front and pressure wave displaces the powder in front of the match.

In future charges, consider placing the match on top of the powder, then taping over.

 

[Dustin Lobner]

Just a word on the charge building: You've placed the match under the blackpowder. Despite taping over the charge, this can result in inconplete combustion as the flane front and pressure wave displaces the powder in front of the match.

In future charges, consider placing the match on top of the powder, then taping over.

Some of them are like that, some the match is above, tried it both ways.

Biggest concern is that we're getting 2.5" of rain today, does the power stay on till the end of the print??? Aaah....

 

[wsume99]

Regarding ematch placement, couldn't you vary the height of the head by feeding more or less charge wire into the well before applying hot glue?

 

[Dustin Lobner]

Regarding ematch placement, couldn't you vary the height of the head by feeding more or less charge wire into the well before applying hot glue?

That's exactly what I did, lol. The picture I showed was probably the deepest one I had.

Learned I can close up the wire hole some, it was big enough that I could insert the ematch through the bottom.

Also discovered that if I need to go over 1.75g, I need to make it taller.

 

[wsume99]

That's exactly what I did, lol. The picture I showed was probably the deepest one I had.

Learned I can close up the wire hole some, it was big enough that I could insert the ematch through the bottom.

Also discovered that if I need to go over 1.75g, I need to make it taller.

This is big advantage of 3D printing, you can iterate the design as you learn. If you do the end result is a part that is perfectly suited for your application. At least that's been my experience.

Fingers crossed that you don't have any power interruptions today and your print finishes without issue.

 

[Dustin Lobner]

This is big advantage of 3D printing, you can iterate the design as you learn. If you do the end result is a part that is perfectly suited for your application. At least that's been my experience.

Fingers crossed that you don't have any power interruptions today and your print finishes without issue.

True story. It's great for initial runs but crap for volume production.

Where I work, I turned our 3D printer farm loose on making faceshields for healthcare workers for Covid stuff. Had 250 after a few weeks. The rest of the company was still getting organized. Then, in the span of a week, they cranked out something like 40k faceshields on CNC laser cutters. 3D printers are great for initial runs, prototyping, etc but if you want things in bulk, there are better ways.

So far power is good. I was worried that I wouldn't get to fly at Mini MWP if the power goes out, but I do have an I280DM I could fly Airmail with (see elsewhere in the thread for a link) and the J450DM was originally purchased for my L2 rocket...so, feeling less twitchy about it, I'll get to fly regardless.

 

[wsume99]

True story. It's great for initial runs but crap for volume production.

Where I work, I turned our 3D printer farm loose on making faceshields for healthcare workers for Covid stuff. Had 250 after a few weeks. The rest of the company was still getting organized. Then, in the span of a week, they cranked out something like 40k faceshields on CNC laser cutters. 3D printers are great for initial runs, prototyping, etc but if you want things in bulk, there are better ways.

So true. I used to work in high volume manufacturing and it's amazing what a purpose built machine can do. Where I work now there are a lot of senior managers who think 3D printers are some kind of magical solution to all our problems. 3D printing is well suited for low volume and one off type parts OR something that has very complex geometry and cannot be made through traditional means. Unless I really crank up my output of rockets it fits into both of those categories for my personal use. I find it very helpful for producing jigs and fixtures to make assembly of rockets much easier.

 

[Dustin Lobner]

So true. I used to work in high volume manufacturing and it's amazing what a purpose built machine can do. Where I work now there are a lot of senior managers who think 3D printers are some kind of magical solution to all our problems. 3D printing is well suited for low volume and one off type parts OR something that has very complex geometry and cannot be made through traditional means. Unless I really crank up my output of rockets it fits into both of those categories for my personal use. I find it very helpful for producing jigs and fixtures to make assembly of rockets much easier.

As a Materials Engineer, I'm basically the lead process engineer for my company, and I'll second all of that. I really want a good metal printer for making prototypes and whatnot...not for actual production though.

Like the background to this thread states, this is basically practice for starting my L3 build. A lot of the focus has been on the 3D printed stuff, because it's freaking awesome, but I otherwise on this project learned a ton about glassing tubes, will hopefully have good results on dual deploy, etc. The only thing I'm going to 3D print on the L3 project is basically sleds on the avionics bay, probably the charge holders, and then jigs and fixturing like you mention.

72% and climbing.

 

[Dustin Lobner]

Knock on every wooden surface available, the power is still on and we have the appearance of the leading edges of the fins!



Using the overly simple maths of about 20%/day and it being at 77% currently, should be done late tomorrow night or early Tuesday morning. Hang in there bed adhesion and power!

Looks like ground testing is going to happen on Wednesday. Weather for Mini MWP is supposed to be partly cloudy and 83° w/ 9mph winds. Sounds pretty dang perfect, hopefully it holds! ...when I was in college 15 or whatever years ago, I took basically Weather 100 as a "interest that isn't a hard Engineering class" and one of the best quotes from that was "Any weather forecast over 48 hours out is nothing but witchcraft and lies". In recent years as I've been watching it feels like they've been getting better, but the point remains.

 

[Dustin Lobner]

Fincan finished safely ahead of schedule! Getting it cleaned up and then will post pics. Should also be the first time I can get a close to correct dry weight on this thing.

Gotta print the tailcone/motor retainer yet too.

 

[Dustin Lobner]

Got a pretty significant seam on one side and the bed isn't quite level anymore, so something shifted during the print. Nothing terrible though, part is completely usable and it fit pretty much to perfection over the double glassed tube. Looking good, really happy with how this turned out.

...it definitely could be better, lol, but I think I'm about at the limits of what a 2 year old CR-10 can do.

And WOW is plastic dense. This thing is gonna need a J just to clear the tower.

 

[Dustin Lobner]

Motor fit is basically perfection, it won't slide in via gravity but a finger's worth of weight and it slides smoothly in. For the last one, AirMail, the motor was a bit tight and I had to sand the inside of the mount for it to fit. What a difference 0.6mm on the diameter makes, lol.

 

[Dustin Lobner]

Tailcone/motor retainer is done and is fantastic. All the structural parts are done, going to start a reprint of the Av Bay that had that crappy grey printing on it. If it works and I get a better quality blue one, awesome...if not, the grey one is flight worthy, so that's good too.