Mai re (Dastak).
Tumse Kahoon (I could sing this)
Monday, January 28, 2008
Monday, January 21, 2008
Doorbell
Redid a project from my childhood, which didn't work too well.
Unfortunately, this one didn't either, but it did sorta work.
Basic idea is to make a primitive "oscillator" with an electromagnet: make and break contact using the armature as a switch. Cannibalized the primary windings of an old 12V power supply transform for the electromagnet, and had Shashank do the winding. Turned out to be the only thing he ended up doing, even though this (and the Gauss rifle) were projects I undertook to have him do things other than to play video games. Sigh.
A piece of hardboard ("masonite" in this country, I believe) served as a mounting board for the project. I started out with the idea of making contact posts with little screws and two nuts on top, but ended up not doing that -- the circuit is too simple.
Used the steel reinforcing strip from an old windshield wiper as the armature. Thought that was a master-stroke of ingenuity, but it turned out to be devilishly tricky to make good contact to it, and to achieve just the right flexibility.
Couldn't find a bell (this was a problem in my childhood version, too), so it ended up buzzing anemically, and then only after much coaxing and aluminum foil. Nice L dI/dt sparks, though!
Gauss Rifle
Saw this on the web somewhere (do a search for "Gauss Rifle" -- I couldn't be bothered), and made my own. Got 1/2" x 1/2" x 1/2" neodymium magnets from K&J Magnetics and 1/2" diameter steel balls from Boca Bearings, and then a two-foot section 1"x1" poplar from OSH.
CK showed me how to use a router to cut the groove (and let me borrow the router as well), and I let the kids lend a hand with it. The noise, power and imminent threat of maiming and dismemberment makes routers quite irresistible to some boys (perhaps girls as well, but none that I know).
Did an evenly-spaced ten-stage one first, which worked fine, but was disappointingly slow. I was hoping for something that would embed balls in the drywall. The second five-stage one worked better, and the one in the picture is a "progressive" one (the distances between the magnets is largest near the "muzzle". Jim claims that progressive is no better than uniform: I've yet to prove him wrong.
It's a fun device nevertheless, regardless of the fact that there's no danger to life or limb.
CK showed me how to use a router to cut the groove (and let me borrow the router as well), and I let the kids lend a hand with it. The noise, power and imminent threat of maiming and dismemberment makes routers quite irresistible to some boys (perhaps girls as well, but none that I know).
Did an evenly-spaced ten-stage one first, which worked fine, but was disappointingly slow. I was hoping for something that would embed balls in the drywall. The second five-stage one worked better, and the one in the picture is a "progressive" one (the distances between the magnets is largest near the "muzzle". Jim claims that progressive is no better than uniform: I've yet to prove him wrong.
It's a fun device nevertheless, regardless of the fact that there's no danger to life or limb.
Sunday, January 20, 2008
Wednesday, December 26, 2007
Ideas for a shuttle launcher
According to the all-knowing web, a nail gun uses one of (count 'em!) four mechanisms:
- A spring
- A solenoid
- Compressed air
- Combustion (wow!)
A shuttle weighs about 5 g, and has a maximum initial velocity of 300 km/h, which is about 83 m/s.
E0 = 0.5 * m * v^2 = 0.5 * 0.005 * 83 * 83 = 17 J
How much does a nail weigh? Let's say we have a 5 cm nail, about 2 mm in diameter:
V = pi * 0.001 ^2 * 0.05 = 1.6 e-7
If it's iron, that works out to a mass of 1.2 g, and:
E0 = 0.5 * 0.0012 * 470 * 470 = 136 J
That's almost 10x the energy release I need, so perhaps even a solenoid will do the trick (which is not quite at the top of the heap as far as nail guns are concerned).
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