Picture of Solar-Powered Robot

A while back I made dozens of robots which were in large part inspired by BEAM Robotics. For those unfamiliar, BEAM is basically a special method of robot building with an emphasis on biology, electronics, aesthetics, and mechanics (hence the acronym BEAM). One thing that sets BEAM apart from other approaches to robotics is its insistence on using radiant energy (predominantly solar power) and its tendency towards reuse and minimalism. While I heavily borrowed from the BEAM ethos and aesthetics, the robots that I built were not quite the same (they were all battery powered for starters).

Since BEAM robotics was such a large source of inspiration, I always wanted to try my hand at building a solar robot. However, rather than simply building another BEAM robot, I decided to incorporate solar into my own style of robot building. Instead of having it be powered entirely off the sun, I decided to incorporate rechargeable batteries. This means that at any given time the motors can be running off either the batteries or solar panel, depending on which can provide the most power. The solar panel is also recharging the batteries when the sun hits it. This allows the bot to run off of the sun, but not be entirely reliant upon it to move.

I think my approach merges the two styles nicely, and is a fun and simple experiment in robot building.
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Step 1: Materials

Picture of Materials
You will need:

(x1) Solar panel (Radioshack #277-052)
(x2) Standard servos (Radioshack #273-766)
(x3) 1N5817 schottky diodes - NTE578 equivalent (Radioshack #55052253)
(x1) 9V battery snap (Radioshack #270-324)
(x8) AA rechargeable batteries (Radioshack #23-760)
(x1) 8 x AA Battery holder (Radioshack #270-387)
(x12) Wire-tie mounts (Radioshack #278-441)
(x1) Ruler (12" - 18")
(x2) Wall mount adhesive hooks
(x1) Misc. zip ties
(x1) Shrink tube

Step 2: Modify the Servo

Open up the servo case by removing the four screws from the bottom.

Desolder the circuit board inside and attach a red and black wire to each of the motor terminals.

Finally, crack open the gear box and find the gear with a little plastic tab on it that prevents continuous rotation. Simply cut the tab off the gear.

For a more in-depth guide to this, check out my other instructable on modifying a servo for continuous rotation.

Step 3: Drill

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Drill a 1/4" hole in the center of the ruler, about 5/8" from one of the shorter edges.

Drill a second hole about 2-3/8" from the same edge.

Step 4: Bend

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Using a table vise or two metal bars clamped to the edge of the table, make a 90 degree bend in the ruler at 6" from the edge that the holes were drilled.

Make a second 90 degree bend at 9" so that the ruler roughly forms a 'U'-shape.

Step 5: Attach

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Zip tie the servos to the ruler using the two 1/4" holes such that the servos sit back-to-back.

Step 6: Zip Tie Mounts

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Place two side-by-side pairs of zip tie mounts on the back of the solar panel. It is important that the channels of each pair are basically aligned.

Step 7: More Mounts

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Attach two more pairs of zip tie mounts to the ruler on the inside of the 'U'-shape that is opposite the servos.

Step 8: Connect

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Using the zip tie channel mounts, connect the solar panel to the ruler.

Step 9: Insert Batteries

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Insert batteries into the battery holder.

Step 10: Diodes

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Solder two diodes together such that the cathodes are connected (the side of the diode with the stripe).

Step 11: Build the Circuit

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The circuit for this bot is based on a simple solar charging circuit by David Cook. The circuit has two schottky diodes connected cathode-to-cathode with one diode connected to the solar panel and one to the batteries. This setup allows either the batteries or the solar panel to be providing power to the motors, depending on which can provide the most current.

Since the batteries are also rechargeable, there is a third schottky diode connected from the solar panel directly to the battery back. This allows electricity to flow to the batteries and recharge.

To wire it up, first connect a red wire from one of the servos and a black wire from the opposite servo to the center point of the cathode connection.

Next connect the red wire from the battery snap to the anode of one of the schottky diodes. Connect the red wire from the solar panel to the anode of the other diode.

Once that is done with, solder the anode of a third diode to the red wire connected to the solar panel, and the cathode to the red wire from the battery snap.

Using shrink tube or electrical tape, insulate the wiring to prevent it from shorting.

Step 12: More Wiring

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Solder together all of the black ground wires and the remaining free red wire from the servos.

This should leave you with two bundles of soldered connections; one for power and one for ground. Insulate both connections with shrink tube or electrical tape.

Step 13: Even More Zip Tie Mounts

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Attach two pairs of zip tie mounts to what is essentially the underside of the 'U'-shape.

Step 14: Attach Batteries

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Zip tie the batteries to the inside of the 'U'-shape such that they are held firmly in place.

Step 15: Trim

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Trim the actual hook-part off of adhesive wall-mountable plastic hooks.

Step 16: Affix

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Stick the modified wall mountable hooks to each of the respective servo horns (the thing that looks kind of like a gear).

Step 17: Plug In

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Connect the battery snap to the battery pack and the robot is now fully operational.
M.C. Langer6 months ago



Jacky P1 year ago
You could add a photocell and make it only turn on when it has light as well.
Jacky P1 year ago
I got a more powerful solar panel for about $9 online (us)

I like the use of the ruler for the structure.

great job

I do not have very much access to sunlight at all. Would this lamp


work as an alternative? If not, what would you suggest?

DieCastoms1 year ago

Ok, I'm confused (yes I admit it). From my understandings of diodes, you are wasting two of them ...


SP 2====> | <====3 Batt.

Ok, I understand that 2 prevents battery power from feeding back into the solar panels, and that 1 allows solar power into the battery pack. Don't one and 3 completely cancel each other out? 3 prevents solar power from reaching the batteries, yet 1 allows it, but 1 allows power to go in the direction that 3 prevents??

If the only thing you are protecting is battery power into the solar panels, than diode 2 is the only one accomplishing anything.


randofo (author)  DieCastoms1 year ago

Check out the explanation halfway down this page:


I have been studying this project and come to the conclusion I do not know enough about servos. I am also confuse by the diode circuit. The link to the Shack catalog listing gives me an other question. Why that motor and not the continuous bidirectional motor for the same price? It would require no modification. Was it a size or current problem?

looks like a small switch could be installed between the motors and the power.


ynze1 year ago

Great little beambot! The solar panel seems expensive though (US$ 20). Is a 1.5 Watt panel really needed?

jaff5211 year ago
great idea. 3 doides is a good way, but does it really work?
Great little BEAM robot. Really love the use of the 3 diodes - never thought of using them that way!