Jujubee HP, first cannon shot

August 27th, 2006

Sorry for the terrible videography, I lost track of the rocket in the shot and decided to just watch it with the naked eye. :P

Oh man, what a fun weekend. Unfortunately the rocket motor ignition circuit wasn’t ready, so we just tested the cannon and the parachute deployment. There were some things I’ll tweak next time, but it went off absolutely beautifully. According to the altimeter it went 360 feet up (pressurized to 50 psi). Very nice. There are lots of us that got some footage and I’ll try to get some bits and pieces of it up. You’ll notice in the altitude graph below that there is a huge air pressure spike at the beginning. I suspected this would happen but this is proof: when the rocket is accelerated in the tube, the air in front of it is compressed down. This makes it necessary to use a mach delay if going only by altimeter, as I am. Maybe one day I can build an accelerometer system using a really high-g accelerometer. It’s hard to estimate velocity given only this barometric data but a quick spreadsheet suggests the top speed was about 180 feet per second. Not bad considering the cannon is pressurized to half its rated pressure.

After the launch we started blowing off our extra compressed air by shooting tennis balls out of the cannon. We got bored and decided to try firing the ram rod, a roughly 5-feet-tall, 1.5″ diameter PVC pipe out of it. It was magnificent.

I spent a lot of last month just scrambling trying to find a source of electric matches. Well… let’s just say that won’t be a problem again for a long time. :)

I got my CNC rotary table for my mill, and it works magnificently. I used it to cut the fin slots in the phenolic airframe. I ended up going with 6 fins just for the halibut, and fiberglassed them all together. That thing is as solid as a rock. It really does resemble a mace or something.

Possibly the best part of the day was after the test launch when we had all this extra compressed air that we needed to get rid of somehow. We started shooting tennis balls into the air (it really is impressive how powerful this thing is). Then we started looking around for other things to shoot out of the cannon. We couldn’t find anything interesting. Then at the same time about 3 of us realized that we could just leave our PVC “ram rod” in the cannon on top of the tennis ball and fire that out. We were all as giddy as little kids with too much Kool-Aid just thinking about it. We weren’t sure whether we should or not, but we ended up just going for it. Oh man, it was cool. I’ll try to get some video of it up, although it’s really hard to see against the overcast sky.

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Jujubee, Update

August 13th, 2006

I added some pictures and text to the Jujubee page.

I’ve been having some trouble getting my altimeter to fire my electric matches. I don’t have any low-current e-matches and I can’t buy them except at the launch without a LEUP (low explosives user permit), which I probably couldn’t even get given where I live. Anyway. Matches aside, Jujubee was all ready this weekend for a motor-free test shot out of the cannon (no rocket engine, since my ignition circuit isn’t done yet). Gotta do something about that soon. If I can just find my nichrome wire I can try and scratch something… The steel wool bridges weren’t working on the altimeter this time.

The ignition circuit has almost been completely designed. Basically the only thing holding it up is my laziness because I don’t have all the parts in my library already and I’m getting tired of making them myself. But it’s really close. Once it’s designed it should be a fairly simple matter to etch the board on my mill using pcb-gcode (which is fantastic, btw). But then I still have to design and make the wireless arming box, and THEN write the firmware for BOTH devices. Yeah. Less than 2 weeks left to do all that in my free time? I’m a bit skeptical myself.

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Jujubee, update

August 6th, 2006

Quick update on Jujubee. The new scheduled launch date is August the 26th, a Saturday. This will take place in Price, Maryland, with the Maryland Delaware Rocketry Association (www.mdra.org). I’m going to try hard to have this rocket ready for a low-power test run in the next week or two, possibly even the SoJARS launch next Saturday.

I’ve decided that launching on the small H is probably too unsafe to start with, and on such a small field the chances of losing it are just too high. Even on a G motor, RockSim is currently predicting a mile-high flight, so I’ll probably start with an F40 or something (sim is estimating about 3,000 feet — still pretty darned high for such a tiny rocket and a small field). It’s really going to be good to have a radio transceiver onboard the rocket, hopefully that’ll help me find it again. (I’m hoping I can make the ground station antenna directional by, say, recessing it inside a coffee can. Got a better idea? Let me know.)

The altimeter bay is almost done. I need to re-cut the 29mm phenolic tube to have squarer ends, machine some parts to double as electric match mount points and shock cord mount points, and install some nuts, and I think the bay is done. The couplers were machined out of PVC and look (and work) great. I love PVC, btw, it’s so great to machine. I’m really happy with this altimeter bay design. I’d like to write an article about Jujubee after the (successful) launch, possibly to submit to a magazine. At that time I will provide pictures and some more explanation.

Ordered a Magnalite kit. I think I’m gonna make my own igniters using the steel wool bridge I’ve had such good luck with. (The idea is to use an extremely short length of steel wool. The resistance is really low so it pulls tons of current, but it heats up so fast that it pops instantly. I’ve had good luck using a suitably-beefy capacitor to give it some oomph, usually when fed from a 12v N-cell battery.) Dipping this in Magnalite should provide a decent way for my custom ignition circuit to fire up the rocket engine upon exiting the cannon barrel.

The last major hurdles remaining are almost all related to electronics. I need to build and mount a circuit on the rocket to detect cannon launch and ignite the rocket engine, and I need to build a control box that will send the authorization code to the rocket to enable the ignition circuit. (Safety first, kids.) It should also help me locate the rocket after it’s come back to earth. The circuit that resides inside the rocket is to contain one N-cell (it’s got to be light since it’s behind the CG!), a beefy capacitor, an accelerometer to detect launch, a radio to talk to the control box, a power MOSFET to ignite the rocket engine, and an AVR microcontroller to tie it all together and work the magic. Oh man, this is gonna be so cool.

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Jujubee HP — update

July 28th, 2006

I’m still alive! Ok, quick update… I have moved Jujubee back to the top of my priority list. I’ve completely redesigned the entire rocket, sacrificing some strength for accuracy, reliability, and performance. The design is still in progress so it’s bound to get heavier, but currently RockSim is estimating that it will go about twice as high as it estimated for the last Jujubee (it’s currently saying 7200 feet up, and 1020 feet per second, WITHOUT the cannon). Very, very impressive. I’m a bit nervous because RockSim’s model reports that the rocket is stable, but Barrowman says it’s way unstable. Fortunately this rocket is small enough that the ol’ string test is still doable.

Tonight I CNC’d the fins out of copper-clad 1/16″ fiberglass. This CNC mill is kicking butt for this type of work, and it’s fantastic for slotting the airframe accurately as well. I plan to fiberglass all the fin roots together so this thing will be just about bulletproof. Not as tough as the last rocket, but it will be much easier to set up and it’ll have much less chance of cracking upon launch. One interesting thing about the fins is that I designed them myself more or less through trial and error in RockSim. I don’t know if this is some artifact of its simulation mechanism that is incorrect, but it claims that this particular fin design is extremely efficient — very very short and stubby, all the way at the back of the rocket, but there are several of them (5, currently). I hope RockSim isn’t lying.

This rocket (and the entire system) is going to be pretty hardcore. I’ve got a radio link so I can arm the rocket remotely (after it’s been loaded into the cannon) as well as to help me find it again… I’ve got an awesome switch cover for the “Arm” button on the wireless arming circuit… a keypad for entering in the “launch codes”… It’s going to be great if I can pull it all off. Currently, the launch date is scheduled for Sunday the 27th of August. Gotta be ready!!!

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Still Alive

April 18th, 2006

So I know nobody actually reads this, but I figured some sort of update was in order. I’ve been having sleep troubles, possibly brought on by stress at work (but who knows).

I got my CNC mill (http://www.taigtools.com) and CNC steppers and controller (http://www.xylotex.com). Very very cool. I’ve been learning a lot in my class (Intro to Manufacturing). I still haven’t had the time to really make any actual robot parts yet, but that’s getting much closer. I’ve slowly been gathering more and more tools, and I’m developing a halfway decent little shop in my garage.

Gunther has been pretty much on hold. Now that I have the mill I need to try and get back on that. Now I have to see if I can find all the parts after my move.

The sliding-tile dinner table idea has developed to the point where we can actually start building and testing ideas. Slowly but surely.

I found a program called “pcb-gcode”, which runs from within Eagle. It basically takes board files and generates G-code to mill out (isolation-routing) printed circuit boards. Got 3 square feet of double-sided copper-clad board on the way. Hopefully this new tool will make me more likely to etch boards. It’ll be nice not having to deal with the chemicals, once I get everything tweaked just right.

Nothing new on rockets. I really want to try and get Jujubee / Jujucee working soon. Me and Heeten tested the pneumatic cannon on Sunday, firing tennis balls into the air. It’s a pretty impressive contraption really. We took it up to 70 psi with the help of the 12v compressor. Fantastic.

Went biking yesterday and found a tick on myself today. That was pretty exciting.

Now back to my sleeping pills.

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Status

February 11th, 2006

Things are slow. Here’s the update though. I move to the new apartment in about 3 weeks. I can’t wait to set up my little shop.

Rockets are coming super-slow because me and Tim are terrible slackers. We got snowed out this weekend, or we were going to really try for our Level 2 certifications. Maybe next month. How many times am I gonna say that?

My class, CIM-101 Intro to Manufacturing, is really cool. Still no hands-on, but it’s really interesting stuff. So much to learn. There are so many amazing tools and ways to use them. The idea that you can measure something down to 1/10,000 of an inch with a hand tool is completely insane to me.

Gunther is VERY slowly coming along, but it’s coming. I picked up a really cheap 2D CAD program, QCAD. I had been doing a lot just using Cinema 4D, which is really cool for the money… but even 3D artists’ tools are really lacking for engineering purposes, it makes all the difference in the world. Anyway, I’ve been using QCAD to design the pulley and idler shaft supports for Gunther. Really great tool. They’re all laid out, I just need to get Chris to let me use his mill!! (Chris, are you listening?!) Picture: template for the steel motor retainer ring I CADed up for Tim’s rocket.

As though I needed another project idea, here are some of the new ones in the queue:

- a reloadable 29mm rocket motor casing that takes TWO commercial propellant reloads (shouldn’t have any trouble hitting Mach, I wouldn’t imagine — an I impulse on 29mm? interesting, however it ends!)
- sorbitol/KNO3 propellant (I have 4 pounds of sorbitol on the way!)
- custom water rocket launching system
- custom coaxial piston valve, used in a handheld pneumatic gun (do I need a reason?)

And the mother of all current crazy project ideas:

- the automated sliding-tile dinner table. Basically the table is divided up into 12″x12″ tiles, with at least one tile missing… and it’s motorized and computer-controlled so the table can pass you the mashed potatoes by shuffling the tiles around. Me and Heeten are still looking into how to do it inexpensively. We actually have some decent ideas.

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Progress

January 15th, 2006


So progress is coming along very slowly on Gunther, but it does continue. I’ve now completed the 6 aluminum axles that will transmit the torque from the two motors, through the pulleys, to the e-Maxx (remote-controlled monster truck) universal shafts. (Seen here with ball bearings, pulleys, and snap rings, and attached to the universal shaft.) I turned down the ends of the aircraft aluminum rods, and Chris helped me use his milling machine to cut some flats. (Man, I want a milling machine… CIM-101 should be fun, hopefully it’ll work out.) The robot’s design is such that even if all 4 belts were to simultaneously fail, each side of the robot would still have one powered drive wheel. As an aside, I LOVE retaining rings (aka snap rings). This was the first time I’ve installed them on anything of mine (using the lathe, of course), and they are a wonderful solution. Beats cotter pins!


The lathe is pretty cool. I was messing around with some spare 1/2″ solid plastic rod (PTFE?) and made a tiny little container. The press-on cap makes a nice “pop!” sound when you remove it quickly. It’s actually pretty cool… As soon as I get a new chuck key for the tailstock I want to try and make another one. The next one will have a cap that’s exactly the right size to hold one gram of 4F black powder, and a hole so it can be worn on a cord like a necklace. Perfect for dispensing ejection charges at the launch pad.

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Lathe

January 4th, 2006

Am I officially crazy yet? It’s almost 3am and I just got done unloading my new lathe. (Thanks, Chris.) Apparently it’s restored from around World War II. I won’t be turning any cannon barrels with it, but it should serve as a nice introduction to the wonderful world of machining for me. I’m planning on using it to make robot parts (shaft couplers, that sort of thing), and rocket parts (small nosecones, couplers, I may even try my hand at making reloadable rocket motor hardware), stuff like that. If only I didn’t live in a 1-bedroom apartment the size of a shoebox, I’d have some place to actually put it. (It’s currently standing up against the air conditioner. Ideal setup, eh? Hah.) Hopefully in a couple of months I’ll be moving to a bigger place with a garage or basement.

Planning on signing up for CIM-101, the Intro to Manufacturing class at Camden County College. That will be the first formal training I’ve had of any sort regarding anything related to hardware. Up until this point it’s all been just self-taught. (It works, but it sure takes a lot longer.)

Got Gunther’s pulleys and belts today, from McMaster-Carr. They look great (although I thought the pulleys had keyways in them). My motor shafts are metric and the pulleys are SAE, but I think they’ll be a perfect press fit. Very very nice.

Still waiting for my AllElectronics order. I’m making a doohickey for one of Chris’ battlebots — the idea is to have two big beefy motors that can each drive the weapon disc, and I’ll make a circuit that will use the weapon’s RPMs to determine whether to run one or both motors. (Both motors to get it up to speed, and one motor to keep it going while saving power.) Planning on using a hall effect sensor and an AVR to monitor the spinning wheel and work the magic. Some dirt-crazy-cheap 70-amp relays will kick the motors on and off (gotta love surplus). I’d hate to be on the business end of that.

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Vacuform Rig

December 31st, 2005

Well I finished the vacuform table. The materials, all purchased from your local hardware store: hardboard, pegboard, wooden slats, wood glue, vinyl foam weatherseal, some screw hooks, duct tape (of course), some wooden dowel, and metal clips (of the office supply variety). Tools used: hacksaw, miter box, drill press.

I got the store to cut the big pieces of board into more manageable chunks, which I then attacked with my hacksaw. (Yes… a hacksaw. I never said it was pretty. I live in a 1-bedroom apartment, what can I say.) I made three similar frames out of the wood and wood glue, big enough that a one-foot-square sheet of plastic can be used as the thermoplastic (which becomes the mold). One of the frames was made with a gap in one corner, which is where I would later attach the vacuum cleaner.

I wood-glued a stack of solid hardboard (like pegboard but with no holes in it), one of the wooden frames (as a spacer of sorts), and a sheet of pegboard on top. This leaves a gap between the hardboard on bottom and the pegboard on top, which allows the air to flow through the holes in the pegboard when the vacuum is turned on. (I also glued some wood scraps as support spacers underneath the pegboard to prevent it from buckling under the vacuum and weight of the part.) Then, a simple border of weatherstripping makes the seal, and duct tape connects it to the nozzle of the vacuum cleaner. I then drilled out a couple of holes and glued in some lengths of dowel. This helps to steady your hands and ensure that you align your frames correctly (it’s easy to mess up that melted plastic!).

For the molding frame, I simply clip the two remaining wooden frames together with a sheet of thermoplastic in between (I’ve been using styrene from the hobby shop — thinner stuff takes on more details, thicker stuff will smooth over nicely and is stronger). Holes were drilled in the top frames to match the bottom frames (they were drilled at the same time actually, and then widened to make an easy fit).

After testing the vacuform frame once, I noticed that the thickness of the weatherstripping and the bottom half of the molding frame were separating the plastic from the pegboard, and this was causing a fair amount of slack to be taken up needlessly around the edges. I then added a smaller piece of pegboard on top, and that should give me a little more slack to use to capture a deeper mold.

The final touch was to screw in three metal screw hooks. This way I can hang the molding frame in the oven underneath one of the racks, and watch through the door. When I see the thermoplastic sagging sufficiently under its weight, I whip it out of the oven, turn on the vacuum cleaner, and lower the molding frame.

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Gunther – rough first concept design

December 11th, 2005




Still haven’t gotten either of the RC trucks that I won off eBay, so I can’t do too much low-level designing, but I’ve been chugging along anyway. Built the guts of a hot-wire foam cutter this weekend. My floor is covered in little scraps of foam now, that thing is so cool and so much fun to play with. Built most of a small (9″ square) vacuform table, too. Should come in handy (not to mention looking a little nicer than my original pizza box version) [some results from pizza box experiments].

Image: work-in-progress, a design for Gunther. (For reference, the wheels are about 5.75″ diameter, and the robot is about 18″ wide.) Lots of things are missing (the tires have no wheels, there are no drive belts or shafts yet, etc), mostly because I’m still waiting for parts to come so I can measure them. This is what I’d love for Gunther to resemble, though. Learned a little about painting camouflage today from this place, this picture uses the “snow – temperate with open terrain” color scheme.

I feel like such a little kid. This is *exactly* the sort of stuff that I always dreamed about doing when I was little.

Now I’m entertaining the idea of enlarging, say, two of the rails on the multi-rail rocket pod, to be big enough to support a minimum diameter 29mm rocket. That way at least two of the rockets could potentially be high-power (a small H, like the one I got for Jujucee). That may be too large for such a small robot, but it’s fun to think about.

UPDATE 12-20-05: I got the first truck, and the second should arrive shortly. I think I’ll definitely have to put stiffer springs on the suspension, and even then it’ll probably be on the heavy side. Still waiting for the composite board (a 1/4″ sandwich of fiberglass laminate around a nomex honeycomb core — this is officially The Stuff), which I’ll be using for the baseplates. They did bill me yesterday, so with some luck it won’t be much longer.

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