40" Saucer Build

[sailmike]

Thanks for the tip. This is my first time working with Kevlar. I guess I REALLY hope it comes ok.

 

[cjl]

I'm sort of mixed on my feelings about kevlar. On the one hand, it makes a tough, resilient laminate that is quite strong (though not as strong as CF). However, in doing so, it drinks epoxy like it's going out of style and it's an enormous pain to cut and sand.

(Oh, and if you do end up having to cut or sand it, you can get rid of the fuzziness by soaking the fuzzy areas in thin CA and then sanding it smooth. Make sure the area is well ventilated when doing this)

 

[kramer714]

Sanding Kevlar is usually a bad idea...

It doesn't really sand it more fuzzes up. The peel strength between the Kevlar and the foam is pretty low, you don't want to do something that gets a peel going.

If you do sand it you will need to put a new layer over the 'gap' 1/2 inch on either side of the gap should be good.

The CA trick with sanding works o.k., better for sanding edges than flat surfaces like yours. Plus, if you do go to bond another ply on top you would rather not be bonding to the CA.

Why not bury the wrinkle in one of your ribs?

It is looking great Mike, when do you plan to launch?

Mike K

 

[sailmike]

The reason I went with foam was it's flexibility. Carbon can be brittle. I was told that Kevlar is somewhat flexible, which is what I want. I didn't know that it can absorb a lot of epoxy. Thanks again for tips on working with Kevlar.

In the meantime, I've been thinking about what motor to use for the first flight. I do not know what the minimum thrust should be, so I'm thinking of going with the L1150 redline. I'm hopeful that the overall weight will be low enough to let me fly on an M750 eventually. Got to get my level 3 cert. first though.

 

[sailmike]

Sanding Kevlar is usually a bad idea...

It doesn't really sand it more fuzzes up. The peel strength between the Kevlar and the foam is pretty low, you don't want to do something that gets a peel going.

If you do sand it you will need to put a new layer over the 'gap' 1/2 inch on either side of the gap should be good.

The CA trick with sanding works o.k., better for sanding edges than flat surfaces like yours. Plus, if you do go to bond another ply on top you would rather not be bonding to the CA.

Why not bury the wrinkle in one of your ribs?

It is looking great Mike, when do you plan to launch?

Mike K

There's actually not much exposed foam around the edge, so most of the kevlar is bonding to the fiberglass. The ribs will not go far enough to cover the wrinkles, because the kevlar is only 3" wide and not much is above or below the disc.

I was originally hoping to fly August 14th at Lucerne, but I'm short on money now, so it will probably fly October 9th.

 

[sailmike]

Rocketjunkie, I noticed that your saucer on an N800 was coming down under power during part of it's flight. What was the wind like that day? Also, what's the weight of your saucer?

I ask because I've flown my 13" saucer, which weighs 9.8 ounces, twice on an I49. The first time was a perfect flight, but it was a very calm day. The second time was in a bit of a breeze and it flew into the ground under power. It was built very strong, so it suffered very little damage and was easily repaired with a little 5-minute epoxy.

 

[Rocketjunkie]

Rocketjunkie, I noticed that your saucer on an N800 was coming down under power during part of it's flight. What was the wind like that day? Also, what's the weight of your saucer?

It was breezy, about 10 mph. Also, the N800 has little thrust the last few seconds as it's a D grain. The saucer weighs about 18 lb., on pad weight is 45 lb. It always lands upwind of the pad due to severe weathercocking.

 

[sailmike]

Alright, the saucer came out with a number wrinkles in the kevlar. Most of it looks good though. I think I will just cover just about all of the wrinkles with filler rather than sand them out. There's one particularly big wrinkle, but it's on the bottom and I'm thinking of lining up one of the ribs with this one and just fill it and blend it into the rib. Mike Kramers idea. I give credit where credit is due.

 

[sailmike]

I decided to do the second half in shorter 12" increments. This turned out to be much more manageable. It looks like I got all the wrinkles out this time. Also, when doing the first half, I started a bit late in the evening and had to turn off the vacuum when it got too late so as not to bother the neighbors. The bag doesn't maintain it's vacuum as well as it did when new. This time I started much earlier so I can leave the vacuum on till the epoxy is mostly cured.

 

[sailmike]

Project is coming along slowly, but surely.

Doing the kevlar in 12" increments works great and got no wrinkles as you can see in the photo. Just takes longer and probably adds slightly more weight.

Also worked on the rib template. There's lots of trimming and checking the fit.

 

[sailmike]

Finally got the kevlar done. Second half of saucer has no wrinkles in the kevlar, so doing it in increments works great. Overall weight of disc is approximately 4 pounds. That's heavier than I'd like. I'm thinking of trimming off some of the unnecessary foam leaving a 5 or 6 inch wide ring on the underside around the rim.

In the meantime, I've started on the electronics. It takes a long time to solder 88 LED's!

 

[sailmike]

Got the circuit board mostly completed. The chaser kit is from All Electronics and comes with 10 LED's. I replaced each of the LED's with a switching transistor. The transistors are N-channel mosfets. Two strings of LED's, each with a current limiting resistor, will be wired to each transistor. The strings will be wired in parallel. The current will range from 40 mA to 70mA when the batteries are fresh. Also, the kit comes with a 4.7 uF capacitor. I replaced this with a 1 uF capacitor because I want a faster flashing speed.

 

[bandman444]

Have you picked a pattern for the LED's?

88...8 groups of 11?

top or bottom..or both:confused2:

Looks good

 

[sailmike]

No pattern. I like random flashing or the appearance of randomness. The chaser has 10 outputs and there will be 2 strings at each output for a total of 20 strings. I bought the LED's from Superbright LED's in five colors. They don't all require the same voltage so some strings will have 5 LED's and some will have 4 depending on the voltage. All the LED's will be on top.

There is a kit available that uses up to 625 LED's and can be programmed to flash in countless patterns. This would be too expensive and complicated to do in a saucer however. LED's cost about 50 cents each depending on the type and that would have cost 312 bucks. Of course you could save money by getting all the LED's in the same color. I just chose the simpler method. This would have been super cool though.

Well, I trimmed off the unneeded foam and that shaved about a pound. This was more than I expected. The scale I used was a very old and rusted one though!

 

[sailmike]

Here's a photo of the trimmed saucer. I put a layer of thickened epoxy on the exposed foam rather than glass. That area doesn't need much strength.

 

[kramer714]

Mike,

It really is looking good! You might want to use a strip of boat tape on the fillets from the ribs to the cone. mix up a little flox and/or micro with your epoxy smooth out the fillet and let it tack off, the a strip of 1" wide boat tape in the seam gives nice strength and durability, plus comes out looking nice.

One thing I have told people that have asked me for help with composites is to make a 'pathfinder' of each technique they want to try. I would bond up a flat 'T' to work up your technique before doing the saucer.

October would be great, I have been promoting the Roctober launch to Scouts and youth groups, I'm sure the kids (and this old guy) would like to see that on fly at night!

Payton (the kid) And I are going up for the Roctober weekend.

Mike K

 

[sailmike]

The rib to cone joint doesn't need to be strong. It's the rib to central body tube joint that needs to be strong. I'm currently planning on glassing this joint. I just haven't decided on how wide to make the fiberglass strips. It'll be similar to glassing the fins on a regular rocket.

My first flight will be a day flight. This will be my first time using a parachute with a saucer. I'm not sure if I will fly it that night. It depends on how much dough I have available!

Mike

 

[sailmike]

Made a little jig to help find the curve of the disc for the ribs. Worked great. So I finally got the rib template cut out. I decided not to use the 1/8" plywood I have and use it for fins on a future rocket. I thought the wood was too nice to use as a template. My hot knife is too short to cut all the way through with the template on there. Thinking of making another jig to help cut the ribs out or just cut part way with the hot knife and then cut the rest of the way with a hand saw. Might get an irregular cut if I use the latter method.

Twelve lines of LED's are done and got 8 more to go.

 

[sailmike]

Got 8 ribs cut out. Seems I worried needlessly. I just needed a bit of practice to get good cuts and no saw was necessary. Next step is to sand them a bit and then glass them. I've got an idea on how to vacuum bag them. Just hope it works.

 

[sailmike]

Taped some 60 grit sandpaper to some leftover 7.5" body tube to sand the curve into the side of the rib that meets the body tube. I don't know if you can see that curve in the photo. The black lines were to help sand it so I know where to sand. So now the ribs are all sanded and ready for fiberglass. Also, got all the LED strings done.

I have a final exam coming up this Thursday, so I'm putting aside this project till then.

 

[sailmike]

I've decided to sand down the wrinkles in the kevlar and then put 3" wide strips of 2 oz FG over that. You should be able to see the results in the pictures below. I'm not sure what to do about this at this point and could use some tips here. So, does anyone have tips for me here? The kevlar is far thicker than the FG and there is a seam where the kevlar meets the FG. Should I worry about the kevlar delaminating here? I'm thinking of covering the seam and wrinkles with thickened epoxy only and no FG. What do you guys think?

Thanks for your help,
Mike

 

[sailmike]

Finally started glassing the ribs. I've cut out a rib shape out of some scrap 2" thick foam. This cut out was made slightly larger than the rib. The FG, peel ply, and breather were all applied and then the whole thing put inside the bag. The bag was sealed and as the vacuum was being pulled, the rib was pushed down into the cut out so that the bag wouldn't put wrinkles in the FG where I don't want it. I'll know how well this idea works in a couple hours.

 

[sailmike]

The method of bagging described above worked perfectly. There's still a couple small wrinkles at the curved section, but I expected this and will leave them be. You should be able to see in the photo that the corner came out clean and sharp. I only have one cut out so I can only do one side at a time. That's 16 times for 8 ribs. Also, I'm only glassing the exposed sides. The other edges will be glued with thickened epoxy to the central body tube and disc.

 

[sailmike]

Rats! Ran out of peel ply and breather. I made sure to order more than I needed this time. I have enough on hand now to finish 3 ribs. The photo shows the first of three. They weigh about 3.45 oz each. So, 8 X 3.45 ounces plus 11 for the central body tube and 21 for the 75mm MMT plus about 3 pounds for the disc plus the epoxy gives me a total weight of approximately 7 pounds. I expect it will weigh little bit more than that, but I'm happy with that weight.

I decided to make the curved part more beafy to absorb impacts with the ground better.

 

[sailmike]

Sorry I haven't updated this thread in so long. My project has been on the back burner since the fall semester started at the end of August. At least I was able to get all the ribs glassed and trimmed. I hope to get back to it sometime in the middle of December. My final exams are around the 2nd week of December.

Electrical engineering isn't an easy major!

Mike

 

[sailmike]

I'm finally done with the spring semester and now back to work on my saucer. I won't be able to fly it for a while because nearly all of my money is going to tuition for the fall semester, but I hope to get out in August maybe. We'll see.

I've got the disc painted a florescent green. I've changed my mind about putting the lights in a pattern. The five different colored lights are going to be in concentric rings. Also got five of the ribs glued to the 7.5" body tube.

Once the lights are done, I'm going to test them to be sure they work as they are supposed to. I'd like to get a video of the lights in action and post that here, but I don't know if videos from iPad can be posted here or if people without an iPad can view it. Anybody know?

 

[jeffgeraci]

I just found your thread; great project. What did you use to "vacuum bag" the disc? I just attempted my first fiberglassing project, and I never knew you could vacuum bag fiberglass- Doesn't the bag stick to the resin? I bet I could've saved hours doing it like this!

 

[sailmike]

Vacuum bagging doesn't save time, if anything, it can take more time. It does help in reducing weight by optimizing the resin to fiberglass/carbon ratio. Basic items needed are an air compressor, tubing, plastic bag, peel ply, and breather cloth. If you want to know more about it, check out CompositeRockets group over at Yahoo.com.

 

[sailmike]

Got all the ribs glued on and all the LED's done. Still need to wire them to the circuit board. Feels like the overall weight when done will be between 10 and 15 pounds mostly because of the epoxy. I hope I'm wrong and it's lighter than that. Still wonder if I could have done with 6 ribs instead of eight to save weight. The wiring looks a mess right now and I think I'm going to shorten them to clean it up. That should shave a little bit of weight.

Some photos:

 

[sailmike]

Got the e-bay and parachute bay done. You can see in the photo I decided not to go with tubes. This way gives me more space. I'll have to make the e-bay heavier than the parachute bay, because the parachute will weigh around 21 ounces and the altimeter and battery weigh far less than that and the saucer needs to be balanced to fly right.