My L2 Project

[thzero]

Keep in mind that the quick link's load rating is for pull along the long axis. I'd derate it to no more than 50% of its rated load and maybe down to 25%. If that's still OK, then no problem. That's just an eyeball; someone else might have better data.

Yeah, good points. Like I said, it was an idea. If I can find someone to weld this d-ring for me, then that would be better if going this route. Of course, i wonder if the quick link or the plastic would give out first. Too bad I don't have a spare nose cone to try it out.

 

[thzero]

Ok.. put a few layers of 3oz fiberglass (thats what I had on hand) on the parts.








Certainly a lot stiffer than it was with just the PETG filament. Think I'm going with twin forge eyebolts within the ring - 3/16 from https://www.rocketarium.com/Build/Swivels-Links/Eye-Bolt-250. Using 1/4 u-bolts otherwise.

 

[thzero]

Ok... working on the custom coupler for head-in dual deployment.

Basically as mentioned previously the LOC nose cone needs a slightly smaller circumference coupler, as such I cut open a one of the 5.5 and epoxied it inside a standard coupler. Taking a cue from John Coker's site with custom couplers, I added some fiberglass strips over the cutline - did three alternating layers. Then went ahead and just fiberglassed with a single layer the rest of the inside. Used 3 ounces cloth as that is what I had on hand. Then I cut up some mylar sheets, rolled them up and put them inside the tube and let them expand. Also from John's tutorial I used party balloons to apply some pressure to the mylar as the fiberglass cures.

When the epoxy gets to the leather stage, I'll pop the balloons and cut the ends.






Seems to work out well thus far.

 

[thzero]

Ok, not the cleanest or neatest epoxy job... but with the screws it is nice and solid. I'm going to do some adhesion sealer and do a nice layer of high temp, just well because...

 

[thzero]

Well, its "done". Not exactly the most pretty thing in the world but it should work.



Couple of notes:

• Tthis is a nice technique to add stiffness to the coupler without the extra weight and reduction of diameter from something like the LOC stiffy coupler
• The mylar helped get a nice finish, somewhat, but to me its not as easy as some folks videos make it out to be.
  • When I do this next time, I think I'll do the following additional steps:
    • Make sure to have a nice even layer of epoxy as best as you can.
      • Try to not oversaturate
    • Use release fabric on the inside.
    • Use the mylar and balloons to distribute the pressure.
  • That should help give a better finish as the release fabric should pick up excess epoxy.

 

[thzero]

Gonna have to do some adjustments for the coupler after performing some cold tests (i.e. its below freezing outside). Obviously plastic shrinks as it gets cold, so wanted to see what happens when its in the cold as many of the HPR launches in my neck of the woods are in the colder months. Just letting the nosecone settle on the coupler outdoors (with a pressure relief hole) its about .3" too long. Pushing it just becomes where it is really tight and hard to remove.

So may cut down the upper section a bit, and have another inner coupler cut and fiberglassed in.

 

[thzero]

After a lot of work getting a custom coupler built, then adjusting the diameters of the bulkhead here is the guts of the avbay that mounts my 3" avbay sled, which supports two Eggtimer Quantums or two Featherweight Ravens or a combination. Makes its easier to swap.



Mostly assembled and buttoned up. Still need to add the switch band after it gets fiberglassed, and then drill the static pressure holes. Tape is there for a tighter fit with the nose cone.

I did also apply a very thing layer of laminating epoxy to the outside of the coupler; just hardens the surface.



Forward bulkhead....



Aft bulkhead...



And yeah, I put a layer of fiberglass on both the bulkheads. Will sand a bit more, but will also be disassembling and painting in black high-temp paint.

 

[thzero]

Well after I painted it with some high-temp paint. Looks a tad messy with wiring, but that will get cleaned up a bit especially when I add in the secondary altimeter. I did add a ring that will support the Featherweight screw switches; thought that really with this size of rocket I should have a the ability to disconnect the batteries from the altimeter without needing the phones to hook into the Wifi.

As nice as I find the Eggtimer Quantum with its Wifi to be, its still a bit painful in that I need to use either two phones or I have to swap Wifi networks - the former is just easier and faster especially since I have my standard Android phone as well as the smaller iPhone I use with the Featherweight GPS tracker.

 

[thzero]

Ok... so got the other Eggtimer Quantum hooked up, and the Featherweight screw in switches wired up

 

[thzero]

Updated screencap of the build

 

[thzero]

Have some of the Fingertech switches (FingerTech Mini Power Switch | Connectors & Switches | FingerTech Robotics ), so this is an update to the ring that can support these switches. They do seem a bit more robust than the MW, Featherweight, etc. PCB based switches.



A similar ring could be updated using the SMT approach, which is to use a sliding switch that then uses a screw to actuate the switch.

 

[thzero]

The body tube on the skewer ready to get its fiberglass layer.



Basically followed the John Coker method (http://www.jcrocket.com/tube-wrapping.shtml) as far as the use of the coupler tubes, mylar and plumbing tape.

Still debating whether I'll go with the Soller sock I have, or if I use some of the 6 oz fiberglass cloth I've gotten in the mean time - its going to have a more consistent finish I think as you don't have to stretch it. Last time I did this (https://www.rocketryforum.com/threads/hpr-custom-build.162115), I did use a Soller sock and the Soller shrink wrap but no release fabric.

This time if either way I go (socket or cloth) I think I'm going with a wrap of release fabric on top of the fiberglass/epoxy and then use the shrink wrap for compression. Also probably only going to use a single layer of fiberglass.

 

[thzero]

So... this went, ok. It was pretty straight forward, but not the best results were achieved but there is there is lessons learned.

So here is the tube mounted on the rotisserie that I use



Measured and cut out a piece of fiberglass. This was a 6 ounce cloth, but it had much tighter weave that what I'd get with the Soller sock. So instead of using the sock for now, I decided to just try the fiberglass. This is different fiberglass cloth that I've used with my other projects, which is only a 4 ounce cloth and not nearly as tight of weave.



First was to wet the entire tube. I wanted to wet as I went, but I didn't really see an option. But here was the first lesson learned. The cardboard tubing is very thirsty. Make sure that the tube is fully wetted.



Started applying the cloth. Used the mark I had put on the tube as the starting point and placed the edge of the cloth along the line. Then I used dabbing of the brush to get the cloth and tube wetted together. Then brush strokes towards me to keep the cloth tightened and remove any bubbles.



I had gotten it all wetted out; and not really well as I had splotches that I'm attributing to not wetting the tube fully, and/or not pausing to make sure the tube was wetted if I found a spot. Then I applied a layer of the fabric release.

Sealed it up with the Soller shrink wrap. But that was frankly a mess as the wrap is just way too big for the 5.5" tube. Also I did not leave enough overlap on the ends; you need a couple of inches for sure. So I fixed some of the issues, and used some mylar to wrap it.



This is how it came out. For the purposes which I did it for (incl. learning) I think its fine. I'll sand it out, and then address any options.




After sanding... few blemishes to work on.




So overall, I think I can live with it for the purposes of what I was trying to achieve. Some lessons learned, which is good, so can do better next time.

 

[David Schwantz]

Are you planning on flying with the plastic wing nuts?

 

[thzero]

Are you planning on flying with the plastic wing nuts?

Dunno yet... probably not, as weight isn't that important. Just had these on hand for some other uses, and they do have a locking washer, and aren't exposed, etc. so in this case I've used in the in mockups I don't think they are that big of issue.

Outside the ebay where things are exposed to the ejection charges? Just using dual nuts, unless anyone has any other good idea.s

 

[thzero]

Decided sanding more can wait... wanted to see if the fins fit and this thing actually works. So printed out the drill guide and taped it in place.





Have checked it over and thought everything lined up. So went ahead and carefully did the drilling.

Thanks didn't quite line up. One row was slightly off horizontally, vertically everything was great. Had to do a bit of reaming with a diamond bit to get everything straightened out.





Got all the fins screwed in and bam...



Kinda looks like a real rocket.

 

[bobbyg23]

Decided sanding more can wait... wanted to see if the fins fit and this thing actually works. So printed out the drill guide and taped it in place.

View attachment 500982

View attachment 500983

Have checked it over and thought everything lined up. So went ahead and carefully did the drilling.

Thanks didn't quite line up. One row was slightly off horizontally, vertically everything was great. Had to do a bit of reaming with a diamond bit to get everything straightened out.

View attachment 500984



Got all the fins screwed in and bam...

View attachment 500987

Kinda looks like a real rocket.

That is so cool.

 

[thzero]

Decided I didn't think 2 bolts to hold the thrust plate in was sufficient, so decided to add another set for 4. Then decided to add another 4 mostly cosmic reasons.



Looks better now.

 

[OzHybrid]

Decided I didn't think 2 bolts to hold the thrust plate in was sufficient, so decided to add another set for 4. Then decided to add another 4 mostly cosmic reasons.

View attachment 501854

Looks better now.

Looks great. A big flat end will create a good vacuum behind it. This will suck the hot exhaust gasses against the back. That whole flat back area can get hot enough to blister paint. Make sure it's up to the hot challenge. If the bolts are for cosmetic reasons, make sure the washers a centred and the hex position is consistent. Tsk, tsk....
Love the drill jig. I remember a few years ago when I proposed using 3D printing to produce a drill jig and was shot down in flames......Way too complicated.....
Norm

 

[OverTheTop]

If you are using the pan-head equivalent of capscrews you can do without the washers. Capscrews in particular, and some other screws, are designed to be used without washers.

This is my 1/2 scale Nike Smoke.

 

[OzHybrid]

If you are using the pan-head equivalent of capscrews you can do without the washers. Capscrews in particular, and some other screws, are designed to be used without washers.
View attachment 501859
This is my 1/2 scale Nike Smoke.

Button head hex headed screws have a bad habit of rounding out at the hex due to the shallow hex depth. Make sure you use your best allen keys( not the ball headed angle drives or a battery drill) to put them in. You'll only get one shot at them.....

 

[thzero]

..

Looks great. A big flat end will create a good vacuum behind it. This will suck the hot exhaust gasses against the back. That whole flat back area can get hot enough to blister paint. Make sure it's up to the hot challenge. If the bolts are for cosmetic reasons, make sure the washers a centred and the hex position is consistent. Tsk, tsk....

Thanks! Yeah, its engine spray paint, so think should be ok there (claim is 2000F). Well "cosmetic" in that it looks cooler with 8 bolts rather than 2!

Love the drill jig. I remember a few years ago when I proposed using 3D printing to produce a drill jig and was shot down in flames......Way too complicated.....

3D printed drill rigs are great... until you did something incorrect in the model, the math, or the 3d printer goes out of alignment.

If you are using the pan-head equivalent of capscrews you can do without the washers. Capscrews in particular, and some other screws, are designed to be used without washers.

Got a link to mcmaster or bolt depot, etc. on what spec you are thinking of as example? I did quick search for capscrews and got a bunch of answers.

Button head hex headed screws have a bad habit of rounding out at the hex due to the shallow hex depth. Make sure you use your best allen keys( not the ball headed angle drives or a battery drill) to put them in. You'll only get one shot at them.....

Yeah, I typically per socket head bolts for just that reason. But didn't have any 8-32 socket head bolts handy.

 

[thzero]

Very nice looking... I like it...

Have a cheap CNC router to put together that might be able to do, eventually with enough practice, something like that (well at least with wood).

View attachment 501859

 

[OzHybrid]

Looks great. A big flat end will create a good vacuum behind it. This will suck the hot exhaust gasses against the back. That whole flat back area can get hot enough to blister paint. Make sure it's up to the hot challenge. If the bolts are for cosmetic reasons, make sure the washers a centred and the hex position is consistent. Tsk, tsk....
Love the drill jig. I remember a few years ago when I proposed using 3D printing to produce a drill jig and was shot down in flames......Way too complicated.....
Norm

Post M900 flight and cleaning. Heat pock marking of the paint. It’ll get warm there.

 

[thzero]

Post M900 flight and cleaning. Heat pock marking of the paint. It’ll get warm there.

Ouch! Glad I'm only dealing with an I to start with!

 

[OzHybrid]

Ouch! Glad I'm only dealing with an I to start with!

Did have nearly 14 seconds of motor burn to do that. Good luck with the flight. Looks like you're pretty sorted.

 

[thzero]

Not many photos right now, but made some more progress

• Drilled holes for the static ports in the ring. I ended up going with 6 5/32 (well Missileworks and Off We Go arrived at 5/32, VerK algo arrived at 3/16). Mostly because I needed two ports for the twin "remove before flight" flags on 180 degrees on the opposite sides, and couldn't odd # seemed weird. I did offset them by about 5mm from center line (flags are that way anyways, so just continued the pattern)
• Drilled three holes and tapped them in the nose cone, .75" up from the edge, for the shear pins. I'm still pondering a metal backing plate even though the custom coupler has two layers of fiberglass on the inside as well as been dosed in epoxy from an outside surface perspective. I used 3mm nylon screws as I have a ton of them - 4-40 major diameter is just shy of 3mm. Used them without issue on my 3".

 

[thzero]

Stack without nose cone...



Stack with nose cone...



Thinking about doing shear pins for the booster too now.

 

[OzHybrid]

There is a minimum distance behind the nosecone for a static vent. Not sure what it is without looking it up. I'll leave that to you. The nosecone creates a wake vacuum immediately behind it.
Norm

 

[OzHybrid]

from Verns page "They should also be well away from the nosecone joint or any other transitions in the body diameter since these can cause turbulence and either increased or decreased pressure regions.