Make a Solar Powered Bug Robot




These robots might be small and somewhat simple minded, but their easy construction, unique locomotion, and quirky personality make them great as a first time robotics project. In this project we will be creating a simple bug-like robot that will store light energy until it has enough power to move itself with a vibration motor. This simple robotics project can be done in a few hours and it is an excellent introduction to the concepts of electronics and soldering.

Step 1: Collect Your Supplies

Below are all of the supplies needed for this project as well as links to buy them. Most of the items you can find on amazon however some of the components are best purchased from Mouser or DigiKey.

Update: It has been brought to my attention that the voltage trigger that I linked to above has become obsolete. But have no fear! I have found what I believe to be a suitable substitute in the DS1233A Voltage Trigger. Unfortunately the legs of this component are different from the TC54 so you'll have to keep that in mind throughout the project.

Left leg of the TC54 ===> Middle leg of the DS1233A

Middle leg of the TC54 ===> Right leg of the DS1233A

Right leg of the TC54 ===> Left leg of the DS1233A

Step 2: Prepare Your Components

The first part of the Solar Bug Robot that we are going to construct is the "solar engine." This is the part of the robot that checks the capacitor to see if it is charged enough. When it is, it dumps all of that power to the motor for a short spurt of movement. To build the Solar Engine first we are going to need to prepare our components. I believe that the easiest way for me to show you this is by referencing the pictures above but I will also write out instructions to narrate what I'm doing.

NOTE: For the sake of consistency when I refer to the "left" and "right" legs of the components I am talking about them being oriented with the flat side facing me and the legs pointing down (as shown in most of the pictures.)

First bend the left leg of the 2N3904 to the left and down and the right leg to the right and towards you leaving the middle leg pointing straight down. Now the 2N3906 and the TC54 Voltage Regulator will be bent the same way, with the left and right legs bent outward and down and the middle leg pointing toward you.

Step 3: Connect the 2N3904 to the 2N3906

Time to pull out that soldering iron and and get to work putting this thing together. First place the 2N3904 adjacent to the 2N3906 then solder the middle leg of the 2N3904 to the right leg of the 2N3906.

Next, take the 2.2k resistor and solder it between the right leg of the 2N3904 and the middle leg of the 2N3906. At this point you can use the wire cutters to snip the excess lead from the resistor.

Step 4: Attach the Voltage Trigger

Now let's throw the voltage trigger into the mix. Solder the left leg of the voltage trigger to the middle leg of the 2N3904 and solder the left leg of the 2N3904 to the right leg of the voltage trigger. At this point your solar engine should look like the first picture above.

Now cut a piece of 22AWG wire about an inch long and solder it between the middle leg of the voltage trigger and the left leg of the 2N3906. Now your solar engine is complete!

Step 5: Attach the Solar Engine to the Capacitor

Note: Now that we have completed the "brains" of the bot its time to give it a place to store its energy. In this project we will be using an electrolytic capacitor to store electricity. This type of capacitor is what we call polar, this means that it only works in one direction. To figure out which lead is which, look for a stripe printed on the side of the capacitor. This is the negative lead, therefore, the other one is positive. This will be important to this step.

Use a dab of hot glue to attach the solar engine to the capacitor with the negative leg closest to the voltage trigger. Be sure to place it somewhere where the legs of the capacitor will reach.

Now bend the negative leg of the capacitor back and solder it to the right leg of the voltage trigger. Also bend the positive leg of the capacitor into place and solder it to the left leg of the 2N3906.

Step 6: Attach the Motor

Now lets attach the motor! First decide where you want to place the motor, I decided to put the motor coming out the back like a stinger. This requires some planning because the wires on my motor are a bit short. I used the leftover legs that I snipped off of the resistor to extend the motor wires a bit so it would reach the back of my robot.

solder one of the motor wires to the right leg of the 2N3904 and the other wire to the positive end of the capacitor. it doesn't matter which wire goes where, flipping the wires will just flip the direction of rotation of the motor.

Next use a dab of hot glue to secure the motor in place. Be sure that the counterweight is able to rotate freely or your robot won't be able to move.

Step 7: Solar Power!!

We are in the home stretch! Now its time to attach the solar panels. First, if there aren't wires soldered to the panels now is the time to do so. I recommend using two different colors of the 22AWG wire so you can easily identify the positive and negative legs of the solar panel.

Note: In this tutorial I am using two solar panels, however if you only have one that'll work too. The more panels you have, the faster the capacitor will charge and the more the motor will pulse. So, if you want your bot to move more add more panels.

Use your soldering iron to connect the negative wire of the solar panel to the negative leg of the capacitor. Then, do the same on the other side by connecting the positive end of the panel to positive leg of the capacitor.

Step 8: Make It Look Pretty

At this point your Solar Bug-Bot is almost done! The final step now is just cosmetic.

Cut off two lengths of the jewelry wire about three to four inches long. Use some needle nose pliers to bend either end of both pieces of wire into little feet. Now bend both lengths of wire into an "M" shape and hot glue them to the bottom of your bot. These will act as the legs of your robot.

And with that your Solar Bug-Bot is complete! Now all you have to do is take them out in the sun and watch them go!

Step 9: How Does It Work?

When the bot enters sunlight the solar panels will begin to charge the capacitor. As it charges the voltage across the capacitor will increase until it eventually surpasses the voltage triggers "tipping point." At this point the voltage trigger will apply voltage to the base of the 2N3904. Now because the 2N3904 is an NPN transistor it acts like a switch, when a current is applied to the base it allows current to flow from one side to the other. This "switch" will activate the motor. The 2N3906, on the other hand, is a PNP transistor. This means it allows current to flow when the base connected to ground. When the 2N3904 is tripped it trips the 2N3906 and completely bypasses the voltage trigger allowing all of the electricity to flow into the motor until the capacitor is empty and ready to be refilled.



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    13 Discussions


    Question 1 year ago

    Hello, that's a very nice idea that showcases the potential of the small solar cells.

    Would it be possible/practical to use this technique to power a microcontroller doing some sensor work? I am not very knowledgeable about capacitors and power, so let's say:
    I have a 3300uF/10V cap and Attiny85, which should eat about 1mA at 5V. I use the solar cell to charge the cap up to 5V, then turn on the micro until I reach 3V. According to some cap calculator, that is 16.5mC (energy stored at 5V) - 9.9mC(energy at 3V) = 6.6mC usable energy, and that should be 6.6 seconds runtime at 1mA, is that correct? Of course the micro by itself won't do anything useful, so we need to use additional energy to do something else, like log data to flash, run some motors/actuators/something, or ideally transmit data by some radio or wire. Don't know about the power consumption of radio (LoRa or anything), would that be possible?


    1 year ago

    Slight problem with this design. The TC54VC in a TO92 package is obsolete. Neither DigiKey, Mouser, Alibaba, Bangood, Ebay nor Amazon have any stock of the 2.7V threshold version. You can still get it in SOT23 package, and there are a few TO92 around with different thresholds. Maybe consider redesigning it with a 2 transistor schmitt trigger?

    1 reply

    Reply 1 year ago

    Oh man, you're totally right. I purchased the parts months ago and I guess they have since become outdated. I will revise the parts section with some alternatives ASAP. And I might consider making a tutorial using the Schmitt trigger in the future.


    1 year ago

    I was looking to build something very similar. Thanks for posting this!

    How long does it take for the capacitor to discharge? If I read the how it works correctly, it will sit idle until the capacitor is fully charged, the run until the capacitor has been completely discharged.

    I was hoping to make something even smaller with a much smaller capacitor and wanted to know if it would even work. I am looking for a 15-30 second run time for my requirement.

    1 reply

    Reply 1 year ago

    Unfortunately this circuit is more in the realm of a 0.5 second burst every second in direct sun light. The circuit actually doesn't fully charge the capacitor, it only charges it to around 3v before dumping it. You could use a different voltage trigger that would allow the cap to charge more and a resistor in series with the motor so it doesn't dump the power so quickly. Otherwise you might want to consider a small battery instead of a capacitor.

    I would be interested to see what you come up with, good luck!

    I agree with ShamWerks regarding 'Beam Robotics'. Very similar concept...nice. You've explained how it works really well, better than I've read in my Beam Robotics book. Nice Instructable Logan. I may have a try at this one.

    1 reply

    1 year ago


    This to me, is in the realm of "BEAM Robotics", look it up! :)


    1 year ago

    so you mean

    "First bend the left leg of the 2N3904 to the LEFT and down and ..."


    "First bend the left leg of the 2N3904 to the right and down and...." ???

    1 reply

    Reply 1 year ago

    Ah youre right! My bad haha! Ill fix that right away...


    1 year ago

    Nice gadget, well and simply explained.


    1 year ago

    Fun idea! Those are cute little bots :)