Search This Blog

Tuesday, June 22, 2010

Pics from Southern Thunder

Ready to go for Level 1 cert. flight

On the pad. I couldn't get any pics of launches with my cruddy cellphone camera. However, I did get my L1!

Our prep area

Ready for L2

Let's play: "Find the L2 rocket in the 70ft trees!"  Yeah, this sucked. I paid an arborist to climb the tree and get it out. I got my L2, though! Been waiting 10 years to be able to that...

Dad's Maniac. To give perspective, he's 6'5"

Very pretty day. Very hot day.

A "P" motor. Damn that's big. (Pepsi can for scale)

Well, that's probably about it for rocket stuff this summer due to bad timing with being out-of-town. Back to other projects.

Tuesday, June 15, 2010


Finally, a post inline with the name of this blog! I've been working on a rocket for Southern Thunder 2010 for the past week or so. I plan on certifying Level 1 and 2 with it.

Note: This build log is written for people with some previous knowledge of high-power model rocketry.

This rocket is a Blackhawk R&D 3" Stinger kit. It came as a kit with pre-cut fins and tubes, which is very convenient. I cut my own fins/tubes for many of my rockets, and it can be a real pain.
The first steps were to rough up the 3" body tubes and glass them (I'm going to put a J engine in it afterall).

Fiberglassing setup. The tubes are slid on here and laid up. Note the wax paper on the floor.
Glassed tubes. 

Leftover resin formed to the shape of a cup it was in.

I used 4 oz. glass and West Systems 105/205 resin. You can see the rings I trimmed off the ends of the tubes in one of the above pics. The discoloration is where the resin soaked into the tubes differently. I then had to cut out the fin slits.

Then I soaked the ends of the tubes in superglue and sanded them to keep them from burring.

The dark ring is superglue.

The next step was to make the motor mount (the thing that holds the rocket engine). 

  Here's the forward centering ring epoxied on to the motor tube. 
Kevlar is used for the first part of the shock cord because it's fire-resistant (there's a black-powder ejection charge that fires to deploy the drogue or main chute depending on setup) and won't wear out as fast as a regular shock cord. This will be attached to a shock cord, which will be attached to the bulkhead.

While that was drying, I started working on the payload section:
Here's the bulk head epoxied in. I used some Kevlar pulp in the epoxy to strengthen it. Another common filler is short carbon fiber threads; I couldn't find our bag of them, so I just went with the Kevlar. Silica/micro-balloons are other common fillers.

Filleting the other side of the bulk head with epoxy.

Then the motor mount was shoved into the aft end of the body tube and glued with some 5-minute and filleted:

The shiny stuff inside the tube is a fillet of about 30 grams of West Systems mixed with Kevlar pulp poured in. That centering ring is a good 18 inches down the front end of the body tube, so the only way I could get the epoxy in there is to aim, pour, and hope I didn't make too big of a mess.
While that was setting, I worked on the back centering ring. I didn't glue the two aft centering rings in (so only the one forward ring got glued in) when I glued the motor mount; you'll see why in a moment. The back centering ring needs motor retention screw mounts:
Motor retention screw mounts epoxied in.

While all that was drying, I worked on the fins. They are laser cut out of 3/16" plywood- very nice by my standards. The edges needed to be tapered/sanded, so I went to the belt sander:

A rounded rear fin.

I also drilled 1/16" holes in the fins near the body tube interface.
Forward fins. The fin tabs were cut a little short, so I glued a then strip of balsa to the bottoms.

These holes will act like rivets when filled with epoxy when filleting. The next step was to glue in the forward fins.
First fin glued in.

All forward fins glued in. Note the aft centering ring: it's not glued in, just holding the motor tube centered.

After gluing the fins in, they needed to be filleted. I used West Systems/Kevlar pulp again. Some people do tip to tip fin glassing at this point. I didn't feel that it was necessary with this rocket. My view is that it is only necessary for rockets flying L motors and over, or anything going Mach.

I normally fillet the inside of the fins while doing the outside fillets, but I couldn't on the forward fins because of their displacement from the rear end of the rocket (you'll see in a moment how I did it on the aft fins). So I needed some other type of inside strengthener. Expanding foam to the rescue! 

The setup. Rocket, expanding foam, and MEK for clean up (lost the acetone).

I enlisted dad's hands for this part because foam is messy stuff. We attached some straw extensions to the foam nozzle in order to reach all the way down to the forward centering ring. Then I sprayed a bunch of the stuff in there. The stuff expanded a bit more than we thought, so I grabbed the middle centering ring and shoved it in there to stop the expansion. You can still see some of the mess after the first few rounds of clean up in the following pics:

The straw extension.

Overall, this method worked very well. The next step was gluing in the back fins and filleting them, outside and inside.

Note the inner fillets on the motor tube and body tube.

Instead of inner fillets, many people put sections of fiberglass on the inside. Again, I didn't think it was necessary on this rocket. 
Then the aft centering ring was epoxied in and filleted. 

 And that's it for the structure! Next, primering and painting. 

I sprayed two coats of heavy filler primer, then wet sanded. 

Much smoother!
 However, this primer is also really good at filling in the spots between grains in sandpaper. So I went through a lot of sandpaper:

Overall, I did three primer coats. Next came painting. I forgot to paint the tube white before laying down a coat of yellow on the gray primer, so I ended up having to do three coats of yellow...oh well.

Painting the fins black.

Painting black stripes.

Finished paint job! Not my best work, but ok. Time for decal work.

Post-clear coat. Done!

I now have a rocket that is basically ready for an H and J motor at Southern Thunder. It's missing an altimeter bay for dual deployment (necessary for the 7000ish feet high that it will go on the J), but that's a short/easy project.
It's also long enough for a smallish, e.g. I, hybrid engine, so that might happen if I get my cert flights in in time.

The pile of hybrid engine parts.

I'll post a few pics of the launch next week.

Laser Sailboat trailer holders

I've been fixing up our HobieCat 16 and its trailer for the past few weeks in preparation for a roadtrip. I thought I had just finished up the trailer when Dad randomly picks up a Laser at a yardsale for super-cheap.

We want to tow on our current boat trailer between the Hobie's hulls. So I made some adapter/holders for it.

The first step was to measure out the Hobie trailer, specifically the relative positions of the three cross-members that would have the holders bolted to them. After I had those measurements, I determined the position the Laser would have under the Hobie and made wire-profiles of the Laser's hull at the points of the cross-members.

I started with some stiff wire and laid it on the Laser's hull at the position I wanted a profile. Then I bent and rebent and rerebent (etc) until they matched the profile. The next step was to transfer these to some cardboard.

These are then transferred to some pressure-treated 2x10's and cut out. They are only half profiles because I found that it was easier to mark half and flip them over to do the other half than to have a full carboard profile; doing it this way also more-or-less guaranteed symmetry (the wire profiles were far from perfect).

My setup. The jig-saw was used to cut the curve. The circular saw was for relief cuts. Wasp spray was for wasps.
In retrospect, a jigsaw is not the right tool for this. They just aren't meant to cut anything over an inch thick. It was incredibly frustrating and slow, and I broke three blades on this project. Unfortunately, we didn't have any other tool that could cut curves. Here's the result after much sanding:

Profiles in order from left to right = aft to fore. Spacing not to scale.

Unfortunately, the wire must have bent slightly inward from handling, and they all ended up not fitting right. I had to go back with the jigsaw and widen up the curves.

The next step was to attach carpeting to protect the boat's hull. I cut up an old weather-proof rug into strips and shaped/stapled/nailed the fabric to the holders. Here's the final result:

Not bad.

The next step is to bring them to the trailer, mark/drill holes, and bolt them to the trailer. Due to weather, I haven't been able to do this.

TV harvest

CRT TV's are great sources for bunches of electronic components. We recently had one die from a lightening strike, so I thought I'd take it apart.
Our dead 27" CRT TV.
I wasn't sure what fried on it, and still don't know even after taking it apart. It would only show a single horizontal line in the middle of the screen, as if the entire picture had been compressed into that line, so maybe the vertical deflector coil went bad (it looked ok though...). The sound worked fine, despite the picture, but I thought that having a 75 pound, 6W stereo was pretty useless, so I started disassembling/breaking apart.
I read this instructable before proceeding. It was pretty useful, especially the safety stuff. The CRT acts as a capacitor and needs to be discharged. So I put the TV on my skateboard and rolled it outside:

The clip on the screwdriver shoved in the ground was part of my grounding rig. I attached the other end of the red wire to another screwdriver and shoved it under the suction-cup like thing on the top of the TV to discharge the CRT (I heard a tiny "pop").  The shiny thing in bottom center is one of the 3W speakers. You can see the circuit board (and the flyback transformer!) to the left of it. 

Close up of the CRT.
Some people salvage the CRT for stuff. I have no idea what I'd use it for, so I didn't mess with it. I was after the flyback transformer ( ;) watch for a plasma speaker future project). Here are a bunch of pics (click them to enlarge):

Close up of circuit board.

Close up of flyback transformer. Sorry about the bad picture quality- I should be getting a real camera, i.e. not a cell phone camera, sometime soon.

I always wondered what was inside of an S-video thingy. Turns out there are a lot of tiny coils.

Circuit board post-harvesting. I basically took everything that wasn't a tiny resistor, possibly fried, or generally useless.

Here are some pics of all the stuff that came out of this TV:

Transformers, crystals, relay, semiconductors, multi-watt resistors.


I don't know what these are. Some seem to be inductors of some type.

Moral of the story: Never throw out your TV, and before you go recycle it, steal all the useful components.