Introduction: Solar Powered Battle Symet - BEAM Style

BEAM Solar Symets (a contraction from "Symmetrical Robots") were first built by Mark Tilden many years ago as a way to provide mobile plant-life to the other creatures in his Robot Jurassic Park. Being quite simple by only using one solar-engine circuit, they're quick and easy to build.

These versions use high-power Miller Solar Engine circuits, that make them spin much more madly than their pokey ancestors! If you are new to BEAM, it's a design philosophy that incorporates minimalist electronics, and often, solar power. Want more info? Check out and!

The Battle Symet borrows heavily from the original family of Symets, but these are designed to spin in a circle at much higher speeds.

Step 1: Parts You'll Need

We've made a convenient parts bundle of almost everything you'll need to build this project (not including the tools). You'll have all the mechanical and electrical components needed to start making this fun lil' robot!

Mechanical Parts

1 - High-efficiency Coreless Motor (Solarbotics part #: RPM2)
1 - Motor Mounting Clip (Solarbotics part #: MMFC)
3 - Rubber Wheels on Nylon Hubs (Solarbotics part #: RW)
2 - Paper clips

Electronic Parts
1 - 37 x 33mm Solarbotics Solar Cell (Solarbotics part #: SCC3733)
1 - 0.35F 2.5V Gold Capacitor (Solarbotics part #: CP.35F)
1 - 6.8uF Electrolytic Capacitor (Solarbotics part #: CP6.8uF)
1 - 3904 Transistor (Solarbotics part #: TR3904)
1 - 1381 Voltage Trigger (Solarbotics part #:1381C)
1 - Signal Diode 1N914 (Solarbotics part #: D1)

1 - Short length of twisted red/black wire

Tools Required
- Soldering equipment (soldering iron / solder / cleaning sponge) (HVW tech soldering tools)
- A pair of Needle-nose pliers (HVWTech part #: 43060 or 43061)
- A pair of Flush Cutters (HVWTech part #: 43040)
- Safety Glasses - VERY important when clipping and snipping! (Solarbotics part #: 5330)

Get the parts bundle here!

Step 2: Making the Frame

Let's start with the wire ring that surrounds the Battle Symet.

Unfold one leg of a paperclip, and snip off approximately 1cm. Finish unfolding the rest of the paperclip, and work it into a circle that touches the corners of the solar cell.

Step 3: Soldering the Ring to the Solarcell

The wire ring we just made will short out the solar cell if we just solder it on. We have to use some tape to cover the corner pads, preventing a short circuit from occurring.

Snip off a few squares, and cover up the power pads on the corner of the solar cell.

Solder the circle to the two corner pads that are connected by the fat green stripe, so it sits centered on the solar cell.

Step 4: Assemble the Circuit

Now it's time to solder all the electronic parts to the solar cell. Our MSE solar cells have the circuit for building a MSE right on the back, and it makes robot assembly really easy and fast!

Look on the solar cell's back, where you'll find a printed circuit board (PCB). You can see part numbers that label where to install the various components on the solar cell. Make sure the are installed exactly as shown, with the parts in the right location, and facing the right way!

Step 5: Installing the Motor Mount

Here's a clever way to mount a motor to your robot fuse clips. Pager motors are small and they fit perfectly in fuse holder.

We'll use a fuse holder (part # MMFC, included in the parts bundle) to mount our motor.

Use pliers to "squeeze" the legs of the fuse holder around the paperclip frame, so that it stays in place while you solder.

Note: Don't solder directly to the motor - this is difficult, and you can ruin the part!

Step 6: Inserting the Wheel to the Motor

This is a cool way to insert the wheel to motor shaft.

You've probably noticed that the inside hole of the rubber wheel is too large compared to the motor shaft. Take a piece of wire insulation sleeve and insert it onto the shaft, which creates a snug fit with the rubber wheel.

Step 7: Making the Wheel Holder

This is simply a rubber wheel holder, but it's only a bit more complex part to build than the paperclip ring from the beginning.

The image for this process shows each step, from top to bottom.

1. Unbend the large curve of he paper clip.
2. Cut off the smaller curve.
3. Bend in a foot at each end - this is simply two right-angles. Make sure the tip is long enough you can stick the rubber wheel on (~1cm or 0.4")
4. Mentally divide the long, straight length into quarters. Bend the two outside segments out by about 45degrees (should be ~ 1cm or 0.4" at the bend). Think three dimensionally!

Step 8: Solder the Wheel Holder to the Frame

Take your new body axle,  and solder it to the frame as shown. We're trying to make a nice triangular rolling base for your Battle Symet.

If the axle doesn't look quite right, get another and try again - paperclips are cheap!

Step 9: Making a Protective Shield

Find another paperclip, and unfold it so you can make a matching arc to cap off and protect the wheels.

We'll be using this to also retain the wheels on the axle.

Step 10: Your Robot Is Finish

You're ready to test. Put your bot under some light (sunlight works best, or a bright incandescent lamp works well too), and watch it spin!

Don't forget to make another one to battle with!

Have fun!

Note: If you start adding more weight, the motor may have trouble making the entire robot spin.


Michael_Bell made it! (author)2012-05-02

Personally, I used a pencil head for the eraser :)

lharvey619 made it! (author)2011-12-23

while trying to do this myself, with parts I have at hand, I am finding that the wire insulation I have available are too loose in the above fitting, too big to fit in the wheel, or too small to fit over the motor shaft.

So, simple question: what guage wire is that sleeving salvaged from?

lharvey619 made it! (author)2011-12-23

I have been playing around with these 3733 solar cells for a while now, and think I found a better way to use them with a 1381c solar engine.

See, the 1381c is set to trigger at 2.6Vdc or so.. but the 3733 cell is a 6 volt cell! This means that the top 3v are never used, as the solar engine oscillates between 1vdc an 2.6vdc (typically), so really all you need is a 3v solar cell.

What great about the 3733 6v cell is that, as you notice on the front, it is 2 cells strung together... meaning each half is a 3v cell!

The 3733 is rated at (looking it up)6.7V, and 15ma, so, that means each half is 3.35v, and 7.5 ma. more or less. I bring this up because if you do the following mod to the chip, it will be a 3v cell, with TWICE the amperage supply! This means that a supercap should charge up faster.

The modification you need to do is pretty simple to explain even without pictures embedded. Look at the picture above of the back of the board. Along the right side is the long strip that connects the two cells together. If you scrape away at the strip somewhere in the middle, you can break that circuit by scraping away at it until the thin copper strip underneath is gone (you dont have to do the whole strip, just break its connection completely)

Then, make an X with two wires, connecting each opposite corner together. and thats it! you now have 2 cells in parallel instead of series, and now it is acting like 2 cells teaming up.

One problem that I have noticed with doing this though is this mod hampers low light operation... as a 3v cell in low light is a .7v cell... whereas a 6 volt cell in low light is still roughly around the 2.6v needed for the solar engine to still work.

Solarbotics made it! (author)2010-02-22

Ah! I see I can attach images to the reply. Here's the schematic (remember, no R1 needed - just a wire connection is fine!)

Solarbotics made it! (author)2010-02-22

The solar engine is a very well documented circuit. I'll add a version to the end of the instructable. Keep in mind that the R1 resistor is no longer required.

matstermind made it! (author)2010-02-09

could you add a schematic for the circuit?

salahaddam made it! (author)salahaddam2010-02-19

 This one is assembled on a Solarbotics Solar Panel, with the PCB already on the back. The components are just soldered onto it.

 If you're looking for a BEAM Solar Engine schematic, Google it.
 This is a 1381 based circuit. Also checkout FLED Solar Engine.

 I prefer to freeform my robots.

 I have Solar Robots and Solar Robot Kits available.
 Also cheap Solar Cells and Efficient Motors.



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