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Sunday, November 25, 2007

Building A BEAM Symet

The symet for some reason always tends to be a three fold rotation symmetrical robot, but I like to push the envelop a little. The Quaret, hence its name, is a four fold rotation symmetrical robot. It's very small, very active, and a lot of fun to watch. So enough chit chat lets find some parts!

List of parts
(most are available at DigiKey)
-1 x cassette tape player motor (or equivalent)
-1 x Solar panel (i use the Panasonic sunceram 37x33mm)
-Coil of heavy gauge wire (copper is good, but anything will work!)
-1 x 2.2k resistor
-1 x CMOS 1381J (The letter denotes the voltage it is triggered at, try some higher or lower voltage ones if you want!)
-1 x 2N3904 NPN transistor
-1 x 2N3906 PNP transistor
-4 x 1000uF capacitors (these can be substituted for any rating wanted, just remember, the more capacitance the longer charge)
-small diameter heat shrink (for motor actuator)
-4 x small washers (you'll see)
-plenty of electrical tape!

Now go find those parts!!

Now that you have the parts

So you finally got all of the parts, good! It's a lot easier to build this bot when you have all those parts lying right in front of you, trust me!

Lets build our chassis

Gather together your tape player motor, your large value caps, and some heavy gauge wire. To build you chassis you'll need to glue you caps onto the sides of the motor, just remember we need to put those caps in a parallel circuit. You should either glue the caps with all the positive ends facing out, or with all the negative ends facing out (see illustration).

Once you have all of those caps on there, you need to solder the post together (see illustration). The outside post probably won't reach each other, so get that wire out. Make the wire into a small ring just big enough to fit around the posts, solder it into the ring. Then take and solder all those posts onto the ring (see illustration). The last step is to solder the inner post together, these should reach each other but if they don't, use the wire again.

(click for bigger pic)

On to the SE

Lets define what exactly a solar engine is

Solar Engine - a circuit used to drive a motor which requires several tens of milliamps, with a solar panel that produces only a few milliamps.

See the illustration for the freeformed layout of the 1381J SE. Pretty simple. If you've been involved with BEAM before, this circuit should seem quite familiar! Keep in mind when you make this circuit that you want to have plenty of lead to solder to, but not to much that its a burden.


(click for bigger pic)

You have the SE and the chassis lying next to each other, right? From here on out its a piece of cake. First thing to do is to solder you positive and negative leads to the rings on the caps, once you have that take you motor (some motor might have wire leads, some have solder tabs, use precaution either way, even the best screw up motors!) and hook it up according to the drawing of the SE, that middle lead goes to the negative and then you can hook up the other end to the positive (you can reverse that so the motor positive goes to the middle lead, but I just happened to draw it that way). Those leads should be stiff enough to hold up that solar cell, but if they aren't, you can use glue or anything to hold it down, just make sure it works first!

Finishing touches

(click for bigger pic)

It works, but doesn't move to well, eh? This is where the heat shrink and washers come in. first off, take some heat shrink and put it on that motor shaft, chances are that it will slip off right away. To rectify that put on another layer. From there you can add as many layers as you see fit, just remember, to get that nice rounded finish, cut the inner most ones shorter than the outer ones so they shrink inward to round off the edges. Now your Quaret works, but goes in little circles. It's time to talk about symet behavior.

Symets exhibit random behavior depending on their surroundings and the available light. The key to making a symet interesting to watch lies in the angle it leans at. If your symet leans at a 20 degree or more angle, chance are that its hard to tip and it just makes little circles. If you symet leans at a 18 degree or less angle it will travel almost in a straight line. If its too small an angle, it will tip ever trigger. So here's the down low on getting it to travel straight. The symet should trigger and the edge its leaning on should cause it to turn, but if you decrease the leaning angle, the motor shaft is more perpendicular to the ground causing it to torque the symet the opposite direction of the turn, making it travel straight!

The washer can be glued to the bottoms of the caps (see picture) to rectify angle. use hot glue here, this way, if want to move them to adjust angle, take a heat shrink gun (or equivalent, a.k.a. something hot) and melt the glue so you can move the washer.

One more finishing touch is to add electrical tape around the edges of the solar panel, it help to protect you solar panel from nicks and cuts. Just remember, A for aesthetics, keep it pretty!

How does it work?

By now your Quaret should be up and running, work well? I hope so, cause i was pleased with mine. Now its your turn to experiment, Symets are so simple you can easily come up with your own plans. Hope you no longer refer to them as the brainless 'bots, because a good symet can even display problem solving abilities, as well as brute strength.


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