Instructables
Picture of The Magbot pendulum
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I really like BEAM bots ( http://www.beam-wiki.org/wiki/Main_Page ) because the electronic circuits are relatively simple so you can focus on the looks of your bot.One of my favourite types is the Magbot pendulum.A stationary bot which works not unlike a electromotor.
What you need to make one is this:
-solarcell 
-3300 uF capacitor
-1000 uF capacitor
-2n3904 or 2n2222 transistor
-2n3906 transistor
-diode
-2 x 100K resistor
-LED (not necessary but it uses otherwise wasted energy so why not.....)
-coil. You can buy these at Solarbotics , http://www.solarbotics.com .Or salvage one from a videorecorder.
-magnet (neodymium magnets are great for this)

This is for the electronic circuit,what you use for the stand is up to.Make it big,make it small,make it short or make it tall(yes,I'm a poet ;)  )At this time I wasn't sure what I was going to use for a stand yet but I did know I wanted to use a wooden ball as the pendulum bob(the part on the end of a pendulum).
 
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Step 1: The electronics

First let's solder most of the electronic circuit together.The easiest way is to start with the two capacitors.Solder both negative leads together.Then take the diode and solder the positive lead to the positive lead of the 3300 uF capacitor.The negative lead (where the stripe is)goes to the positive lead of the 1000 uF capacitor.
Take the 2n3904 and 2n3906 transistor (hold the flat side towards you).Solder the right lead of the 3904 to the middle lead of the 3906.
Get the two 100 K resistors and solder them together.Solder the right lead of the 3906 transistor to one end of the resistors.
Solder the middle lead of the 3904 transistor to the the middle of the two resistors.
Now lets join the two parts of the circuit together.The left lead of the 3906 transistor goes the positive side of the diode.The left lead of the 3904 transistor goes to the negative lead of one of the capacitors.

At this time I usually put the electronic circuit to the side and start working on the base(it is easier to solder the LED,coil and solar cell on later when you decide where to place them on the stand)

Many thanks to Solarbotics(http://www.solarbotics.com )for letting me use the image of the circuit.
biolethal2 years ago
Awesome Project, saw this in make magazine. i tried to make one for my dad's birthday, but i hooked it up the wrong way around, and it blew up. I am trying to fix it right now, and it seems like it is not working. Is the LED necessary in the circuit? I'm running mine off of 15v, 200ma with 100v, 5a transistors.
Verga2 years ago
Great project!
Can this be scaled up to say 3-4 feet tall and about 18" in diameter?
Hey, great project, but I really would like a bit more explanation of how the circuit works... does it sense the arriving magnet and turn on the coil to pull it in for a moment, thereby giving it a little boost? What is the function of the sense part of the circuit? What components affect the timing and amount of the kick? I tried to go to the solorbotics site to seek these answers, to no avail... is there a page there that discusses the finer points, how about a url?
thanks
devonfletch2 years ago
Awesome, Bro! I've wanted to build a Foucault's pendulum ( http://en.wikipedia.org/wiki/Foucault_pendulum ) for years, but had no idea where to start with the drive. And it's so simple!
ynze2 years ago
Pretty! Mooi! :-)

Y.
Win Guy2 years ago
Very awesome project! I'm glad I'm following you, Brosiman.
5/5,
Win Guy