Re: [taigtools] Drill Chuck Arbor
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> You just HAVE to tell us about 2-stage water rockets!!!! I want oneHey, altogether too happy to get other people into this hobby. ;)
> already. MJ
This is going to be a little long, so if you're not interested in water
rockets, feel free to skip it.
My first introduction to water rockets was one of those little water
rocket toys with the red and white rocket and a hand pump. You fill it
about half way with water, pump it up 'till it won't pump any more, and
release. Whee! Up it goes.
A friend of mine bought about five of them, and we lost them all the same
night. Gosh, that was fun. A week later I'd forgotten all about it.
Not so my friend. He wanted to see if he could build some out of 2-liter
soda bottles, and went looking around on the web. Turns out there are
people building these things all over the world, and not just out of
2-liter bottles. He started building them, and never quite managed to
stop. About two or three months after we'd played with the rocket toys,
he invited me out to see a launch. He had a long skinny rocket made out
of some kind of plastic tube sitting on a launcher made out of PVC pipe.
He pumped the rocket up with a tire pump, pulled the release string, and
BANG! It just about disappeared from view.
I was hooked...
There seem to be two camps of people who do water rockets. One is the
school-sponsored event people. Here in the United States the official
organization is the Science Olympiad, who publishes the rules and regs
under which they're built. For the most part the rules are to promote
good sportsmanship and safety (like not having anything metal in contact
with the pressure vessel.) Science Olympiad events tend to focus
primarily on hang time, that being something that's relatively easy to
measure. As a result people focus on parachutes, parachute deployment
systems, etc. They're limited to 60psi launch pressures, so building high
pressure vessels isn't their thing.
The other camp is the unlimited group. No rules, no regs, just don't kill
yourself or get hurt. Until recently there was really only one event
here: max altitude. One of the masters in the craft is a guy named Bruce
Berggren. He holds the current record of 1060 feet above ground level. He
did it with a two-stage rocket. The bottom stage was made out of 3 liter
bottles that had been spliced together to form a pressure vessel with
about a 7 liter capacity. The top stage was made out of a 4 foot long
fluorescent light tube cover (the kind that are used on shop lights to
contain broken glass in case the tube gets hit).
Bruce subsequently tried to break his own record with an even larger
rocket that had four booster motors, each with a 7 liter capacity, and an
8 foot tall fluorescent tube cover sustainer rocket as a second stage.
Problems on the launch pad pretty much shredded the rocket, and he vowed
never to build one that complicated again.
Here's where it gets fun...
Of the people I've talked to who are making water rockets, only two have
any kind of background in machining. They both own lathes, and have used
them extensively in their rocket designs. In an odd sort of way, there's
almost an attitude of, "If you have to apply that much technology to it,
you're doing something wrong." I don't believe it for a second.
After explaining that the lathe I'm using costs only a couple hundred
dollars, people at least relaxed a little. But I haven't seen anyone else
go out and get one yet. I'm giving them some time.
With a lathe, though, I've been able to make some stuff that no one else
has tried yet:
Custom nozzles - Water likes to have as straight a nozzle as possible.
Air, on the other hand, wants one shaped more like what you expect a
rocket nozzle to look like: a double cone. Let's just say I'm glad I got
a compound slide when I bought my Taig. I haven't been able to
successfully test the custom nozzles I cut (I wound up blowing the back
off my test rocket), but if this gives me more altitude, my compound slide
will be getting a serious workout.
Hose fittings - There's some advantage to be had from having multiple
"motors" on the booster stage of a two-stage rocket. The problem is, the
staging coupler relies on knowing when the pressure in the booster stage
drops to atmospheric pressure. The only way we've been able to get around
that is to have the booster "motors" share pressure. Voila, hose
fittings. (Bruce's record-setting rocket only had a single booster
motor, so no pressure sharing was involved. That rocket's successor
relied on having each booster motor let go of the sustainer independently,
so no pressure sharing was required.)
Staging couplers - Bruce Berggren came up with a design for a staging
coupler that's tough to beat. He also designed it in such a way that you
don't need any special tools other than a drill. Even so, I tweaked the
design on my lathe and managed to shave off some weight. You don't
strictly need a lathe for this, but it helps.
Launcher parts - Most launchers are made from PVC. It's cheap, it's
locally available, and the tools for working it are easy to use. But
bring a lathe into the equation, and you have one other advantage on your
side: PVC is almost trivial to machine. Cutting big chunks of aluminum
or steel on my lathe makes me worry about chatter. Cutting big chunks of
PVC is a snap. I have yet to get any chatter, even on sizable chunks.
The one catch with PVC is that it's very very flexible and will jump out
of the chuck jaws. Jigs and fixtures that might be optional on an equally
sized metal part are a requirement with PVC.
I think the most exciting thing about making water rockets on small shop
tools is that so few people are doing it, there is almost endless
unexplored territory to go after.
Which is where the second (potential) event comes from. A couple of
people have made water rocket powered cars, but most of these have been
pretty clumsy looking affairs. (The one exception is a guy in Japan who
has made some FANTASTIC water rocket cars. But no one remembers his
e-mail address, so we can't find out how well they work!)
I started making one. It's not done yet, but it's getting there. Using a
slightly tweaked water rocket simulator, its got a projected top speed of
180MPH. I don't believe that for a moment, so I figure 120-150 is a safer
bet. But I want to make one that will top 200.
If other people get interested in land speed record attempts for water
rocket powered cars, the unlimited camp has two events to compete in.
Gotta love it.
In case you're interested in getting into water rockets, here are the two
links I use the most:
Bruce Berggren's Water Rocket Garage -
Clifford Heath's Water Rocket Page -
Bruce has some of the best drawings online, including a full set for the
rocket he used to set the altitude record. He's also got one of the most
complete simulators available for download.
Clifford has an online simulator that uses the same math as Bruce's
explicit single-stage simulation, as well as the most complete set of
water rocket links I've seen. He's also the guy who maintains the water
rocket mailing list.
Hope you get interested in building these things. They're addictive!