8" dia short ROC on the cheap

I just couldn't pass up the Loki Research sale so I picked up a 76mm 3600 deal, quick run of the numbers and its about a hundred dollars off. I’m getting the L-930 white. Only I have one small problem I don’t own a 76mm rocket so its time to fix that.

As the title suggests I'm building a 8” dia short rocket and so far I'm only into it about $19 in materials. The most expensive part so far has been the ply for the fins and the centering rings, the tube is just a 8” sonotube I got from Lows, it was about $7.50 for a 48” piece. It’s pretty stiff and should make a nice air-frame. The motor mount is a 76mm, just a 3’ packing tube that I pulled out of the garbage at work, all the 3 “ tubes that I have found so far will work for a 76mm motor mount, some are a little loose but I have yet to run into one that was too small.

The 5 x 5 x ¼” Baltic birch ply I bought from a local lumber yard for $27 a sheet, by the time I’m done with the rocket I will have used roughly 1/3 of it. So it’s around $9 in wood, and I have a few dollars in some hardware, U-bolts and T-nuts.

I’m sure the nose cone will eventually be the most expensive part, I haven’t quite decided what to make it out of or how. I have access to a lathe; its just getting there and doing it. Right now the plan is turning a form out of Poplar, Basswood or Alder which ever I can get that’s cheapest and then do a fiberglass layup, I’m figuring $12 in glass and epoxy and around $25 in wood, I will be able to use the form more than once.

This isn't going to be a very in-depth build mostly because I can never remember to take pictures. As you can see I have already cut out the fins and two of the centering rings and coated the tube inside and out with epoxy. One of the things about a Sonotube is you have to peel the inside layer out, as it is impregnated with a wax and will repel glue, that was a major pain. What I couldn't peel out I had to sand out, and it was fun getting epoxy all the way up to my arm pit and that’s with starting with the middle and working my way out. More than likely put one more coat of epoxy on the outside once I get it all assembled.

This is just the rough draft Open Rocket file I will fine tune the weights and sizes as I get closer to the finish line.


TA



View attachment bigfat.ork

You can do the nose cone that way, but an alternative is to cut the nose cone undersized and then coat the foam core with glass layers. For my L1, I just used some resin for a coating, but for L3, you'll probably need a few layers of glass.

The plan is to cut it under size, the wood turning is just a form then I was going to pop it out or make a mold. Last time I used foam form it melted from the heat of the epoxy curing, although it wasn't really epoxy it was a polyurethane resin that cures at a much higher temperature. Humm... I will have to look into foam a bit further, thanks.


TA

Well I might not get this done for our next launch but I am making progress, got the centering rings glued on and all the mounting hardware. I have some High density styrofoam a friend gave me that I'm going to turn my nose cone out of. Not sure if I will use it as a mold or just lay the glass on top and core some of the center out to accommodate the AV bay, leaning towards the latter. Plus I need to get 20 oz or so of weight to the tip of the cone.


So far its working out that I will need at least a 96" parachute to get below 21 ft per, that's going to cost me. My plan is a single separation redundant DD, using the Archtype cable cutter, only hang up is finding a Nomex blanket to contain a 96" chute. Might have to get a custom one made, of course I haven't spent a lot of time looking for one yet.

Anyone ever bought stuff from this web site? www.rocketwoman.com


TA

About a year ago she helped me with some 4" tubes "and stuff" at much better pricing than anywhere else. Rude of me to not remember her name but she's very helpful and has a lot of odds and ends to dig through. As far as chutes go her pricing is decent too !! I'm excited to see how your build goes...Im working on an 8" bird myself !! Good luck !!

Gordon

The fin slots are cut did some of it on my table saw that was fun! Going to use my new 3" cut off grinder from Harbor Freight next time.



TA

ZeroG said:

About a year ago she helped me with some 4" tubes "and stuff" at much better pricing than anywhere else. Rude of me to not remember her name but she's very helpful and has a lot of odds and ends to dig through. As far as chutes go her pricing is decent too !!

Click to expand...

OMG that's Jodi Michaelson, Ky's recently-divorced wife. Looks like she got the toll free number, old fax number, and the remainder of the kit business. You can buy those chutes with confidence, since they're what RM sells too!

Yep that's her !! Check out her experimental pro and ballistic chutes in 8'. Great prices !!

Glued up a big chunk of styrofoam, and epoxied a wood plate on the top and bottom with a dowel running through the middle of it. I don't have a lathe yet so I hooked it up to my drill press, it wasn't to hard to get it centered, I just turned it down to a manageable speed and went at it with a wood rasp.

I cut the top plate off and glued a piece of foam on and then shaped out the tip by hand. It looks pretty uniform and symmetrical. Now for some 6 oz fiberglass and epoxy.


TA

Nice! What'd you use to glue up the foam?

Just 3M spray contact adhesive it is mellow enough it doesn't melt the foam and just a lite shot on both sides hold great.

Plus it doesn't create a hard seam that wont mill out, I just finished it off with a 80 grit sandpaper belt I had and it turned out quite nice.

The drill press worked out surprisingly well, so far i'm only a few dollars into this nosecone and just a few hours.


TA

The fins are in, I cut a 2 inch piece of tube and doubled up the base and gave it all a nice coat of epoxy. Filled in the bottom of the fin slots and now its time to do the fillets. The rocket BTW is being supported by my wonderful multi use Rockwell Jaw Stand, no hunching over a build table for this fat guy.

Also I fiber glassed the nose cone over the weekend, its four layers of 6oz glass, bought some cheap vacuum bags form Harbor Freight and sucked the air out.

I just laid the glass right on the foam, I figure I wont be building many rockets of this size so no real need for a mold. I guess the nose cone isn't going to be the most expensive part after all, I'm maybe 20 bucks in glass and epoxy and the foam was free YAY! :clap: I like free!



TA

So freaking cool looking.

It is looking great. As a quick question, am I seeing correct in that you laid strips of glass horizontally wrapping around the cone?

1tree said:

It is looking great. As a quick question, am I seeing correct in that you laid strips of glass horizontally wrapping around the cone?

Click to expand...

Those are the lines of the foam that you see, they were 2 inch blocks.

TA

This has been fun to watch. I've been toying with the idea of a "build on the cheap" rocket, and this is inspiring me.

Well I got my motor a few weeks ago (gratuitous beauty shot). Also started on the coupler, gave it a nice coat of epoxy and cut it right down the middle with my table saw. It took a few small passes to get it sized right, I also cut a small one inch ring off that will bridge the cut and help strength it up.


TA

What's the coupler for? NC shoulder?

The coupler is for the nose cone shoulder, it sets an inch inside the nose cone and butts up to a four inch ring of the tube.


TA

Looking Great so far!! Greatg job on the nose cone carving/shaping.

Looks great, super job on the NC!

Did some more work on the rocket this week finished the AV plate and got the shoulder glued in. The wire harness plate is from another rocket so it is interchangeable and is how the AV sled is attached.




I normally try to make everything tool-less but it's sometimes just not the best route, so the AV plate will have to be screwed on. There is just enough room that I can get my arm inside the AV bay and fix or add weight if need be.

Here is a dry fit it should hold together.





TA