HAHAHA. Who would do that?!
Oh you are so silly. I now unveil to you the true purpose of our solar experimentation.
MADDIE THE SOLAR MADAGASCAR COCKROACH!
You may scream now.
These little darling Gromphadorhina portentosa cost less than a bug sandwich and 15 minutes to make. Inspired by the bristlebots of yesteryear, this is a solar-powered variety that you can make from scratch with raw photovoltaic silicon mounted directly onto the body of the beast. All told, we've made about 77,504 autonomous Madagascar cockroaches that feast on two things. Photons and your fears.
We will unleash our precious soon, in a Disneyland and Maker Faire near you. They will hiss and entertain your kitten until the sun extinguishes itself billions of years from now. A well placed umbrella is your only hope!
Oh how I hate umbrellas.
This instructable is part of the Solar Pocket Factory series -- a growing list of solar hacks that you can find here:
If you're a cleantech hacker and want to chat with others like you in garages and workshops around the world, check out the Solar Pocket Factory Forum.
And now, back to making a robot cockroach race car. Kenshin, you are our only hope.
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Step 1: What You Need
- A playing card (although a piece of cardstock, cut piece of acrylic, scrap PCB, or really any flat material thinner than 2mm should work), available here
- Double-stick tape: any will work, but my favorite for all sorts of projects is called Window Tape by Duck
- A couple strips of adhesive copper tape: a must for everyone's solar toolbox. Readily available at art supply shops or on Ebay
- A piece of acrylic or PET sheet smaller than your playing card: I am using a 70mm x 60mm piece of acrylic.
- Five solettes*, like these from a random Ebay seller
- A pager motor that vibrates when supplied with 0.5VDC- 2VDC, like these
- Clear 5-minute epoxy that is designed to withstand temperatures of at least 90C (or 194F). I've found the VersaChem 46409 works particularly well
- Hot glue and a hot glue gun
- Teflon sheet (optional)
Shameless plug: I've listed some sources for the above materials, but if you're lazy and/or want to support the future of all that is good and pure, we've got most of the above materials available here too: http://solarpocketfactory.com/collections/solar-panels
Step 2: Add the Copper Tape to the Playing Card
You'll need two pieces of copper tape, to pickup the two poles of the solar panel you are assembling. Cut, peel, and stick. Rub it down with the back of your fingernail for that retro gloss finish.
Since we will be making a 2VDC panel (with one solette as a dummy conductor) and this requires 5 solettes, I spaced my copper tape by about 45mm (or 1.75") along the length of the card, with the copper tape coming in at around 25mm wide (or 1").
>>Note that the copper tape conducts best along the surface without the adhesive. It doesn't conduct reliably through the tape thickness.
Step 3: Lay Down Your Double-sided Tape
Flank your copper tape with some double-sided tape. Just make sure not to overlap the double-sided tape with the copper tape, since that can cause a reduction in power of your completed solar panel.
Step 4: Shingle Your Solettes With a Whistle and a Tap
This is the step where the solettes get combined together in series.
In previous Solar Pocket Factory instructables I've shown a couple techniques involving superglue or conductive paste or soldering. For the Photonic Madagascar Cockroach you don't need any of that, and you'll be doing something far simpler. Basically, you need to overlap each solette in a shingling pattern, without any adhesive or solder joints. Pressure along is what will complete the solar circuit.
This pretty pretty sunset infographic is compliments of a guy who drinks sunshine for breakfast and craps out pure light by dinnertime.
Each solette, or any chunk of mono or polycrystalline PV silicon for that matter, outputs around 0.5 - 0.6VDC, which is not enough voltage to do very many useful things. So, we need to combine enough of these solettes together in series so that their voltage outputs add up.
In order to make the pager motor spin and create the vibration necessary to propel the robot cockroach we need to supply around 2VDC to the motor's input wires. This means we will need 4 solettes in series (or, 2.0Vopen). The solettes I recommend using are 13mm x 52mm in size and each will output Im (or, the max current at the maximum power point of the cells - about max power point here: http://en.wikipedia.org/wiki/Maximum_power_point_tracking) of around 150-200 mA per solette, far more than is necessary to make the pager motor spin at full velocity even on a cloudy day. So, since we are combining the solettes in series, the voltages add up, but the current does not. Or, to put it another way, 4 of our solettes in series will output 2.0VDC and 150mA-200mA on a nice day and about 1/3 that on a cloudy day.
Back to the solettes: The (+) output is the grey underbelly of the first solette in your shingled stack. The (-) output of the series connected shingled lineup can be accessed either at the bus bar or white silver ink runners on the blue top surface of the final solette in your stack, or by using a "false" solette that doesn't produce electricity but just serves to bring do the top surface connections to a solette underbelly. This is the easiest and cleanest approach and it's what I show in these photos, and is worth the sacrificial solette in my estimation, just for the simplicity it provides. So, ignore what I wrote in the paragraph above -- you need 5 solettes if you are using one as a basic conductor.
For your first solette, make sure it has part of the white bus bar underneath the solette in contact with the copper tape. I used a full bus bar solette in this example. And just overlap the bus bar under the solette with coppertape by at least 2mm to ensure a good stable connection, and the two strips of double-sided tape you laid down will hold it in place. Blue side up facing the sun.
Now, overlap your second solette by 2mm with the first solette you placed. Again, at least some of the white conductive bus bar under your second solette needs to be in contact with the white bus bar on the top of your first solette to ensure good conduction. (this isn't actually strictly true for shingled panels....but more on that in a future instructable). Repeat this shingling for solettes #3 and #4. The fifth and last solette you place will need a full bus bar on its underside, to make sure the top of solette #4 gets electrically connected with the copper tape on what will be the (-) side of your panel. This last solette is really just acting as a conductor, and a piece of aluminum foil or folded copper tape would work as well -- but using this "false" solette gives me the most reliable results and I highly recommend it.
Step 5: Encapsulate and Cover
To protect your soon-to-be photon-driven little shop of horrors, a dab of 5-minute epoxy with a sheet of acrylic will do the job. Epoxy is generally not the best choice for making microsolar panels, since it yellows in the sun as a result of UV degradation. But, acrylic blocks out UV, so this 1-2 combo punch can make cheap, long lasting panels.
Or, so the theory goes. I actually haven't tested this type of panel for more than a few days. Let me know whether this theory matches reality or not!
Just mix up the epoxy -- about 2mL will do just fine, since it will get spread out in the next sub-step.
Blob the epoxy over your solettes. Add the acrylic topsheet (I used 1mm thick acrylic, but thinner or thick acrylic works fine too). The acrylic sheet should just cover your solettes with several mm of border, leaving around 20mm of uncovered card on either side, as pictured. I am using a 70mm x 60mm piece of acrylic.
And then put 10-20 lbs of mass on this card-solettes-epoxy-acrylic sandwich. I've been using about 15 lbs reliably (which translates to about 2 psi of pressure on the panel). Also, you should use something non-stick separating your compression weight from the panel, lest your bug get squashed irreversibly forevermore. I used a sheet of teflon myself.
Let the sandwich cure for about 10 minutes, then remove the weight and voila! Your panel should now put out around 2.5Vopen and 150mA - 200mA Isc in full sunlight. Even a bit less current from the panel will work fine for powering up the pager motor full tilt, since the motors only consume tens of mA at 2VDC.
Step 6: Glue the Pager Motor on the Back of Your Playing Card Panel
There are a couple main varieties of pager motors out there. The most popular has an asymmetric mass on the end which causes a vibration of around a few hundred hertz when the mass is rotated. Another less popular variety is a fully contained disk. More than you ever wanted to know about pager motors is available here (along with some well spec'd models for high performance Madagascar racing roaches)
If you're using the asymmetric mass variety, center the mass in the center-ish of the back of your playing card. Add a dab of hot melt glue and then mount the pager motor's body on the hot melt, taking care not to get any hot melt on the rotating mass. If even a dribble of hot melt gets onto the mass, your roach will likely be bellyside up before you're out of the gate. So take care at this stage with the glue.
Step 7: Solder the Pager Motor to the Copper Back Contacts
Copper tape is wonderful to solder onto. Since kids like to grab real and robotic insects, I used lead-free solder and just got my soldering iron to 350C and the joints are a dream.
I found it generally doesn't matter which wire goes to which piece of copper tape, (+) or (-). Maybe it does for some motors. If it does, then just match your red wire on the pager motor to the piece of copper tape under the very first solette you placed, since that will be the (+) of your panel.
Step 8: Fold Your Legs
This is the last and most crucial step!
Choose which side of the card will be the head of the critter. Then fold those two corners just like you'd dogear a page in a book. Those dogears need to be at least 1cm along their sides so that when you card is rest on a surface the spinning pager motor spins free.
Now dog ear the trailing rear of the card.
When the pager motor spins, the entire card and panel assembly will vibrate. The goal of these legs or dogears of the corners of the card is to redirect that vibration in one direction. Notice in the photo how the front two legs are pointing in the same direction as the trailing legs. That's key to making your roach a racer rather that a paranoid insect quivering in the corner at prom.
And that's it!
Step 9: Pocket Prize #1: Escape From Madagascar!
Oh, and a standing offer (hey folks at Instructables the company -- let me know if my challenge here isn't ok).
Pocket Prize #1: SOLAR ROACHES ON THE HIGH SEAS
The first person or group to make a solar powered vibrationally propelled robot insect that can move more or less in one direction for 10 meters in under 1 minute on or under water will get a free Solar Pocket Phone Charge Kit. Just post your video or step-by-step instructable and send a link to firstname.lastname@example.org or post the link in our forum to claim your prize.
Go on. Be a hero! FREEEEEEEEEEDDDDDDDDDDOOOOOOOOOOOMMMMMMMMMMMMMMMMMMMM!!!!!!!!!!!!