Introduction: Electromechanical Insect or Flapping Oscillator
I've been following the development of robotics for about 10 years and my background is Biology and Videography. These interests have orbited my underlying passion, entomology (the study of insects). Insects are a big deal in many industries, and have been the source of a great deal of inspiration. Thankfully, biology and insects are gaining clout in robotics through biomimicry and synthetic biology. I am especially excited by the progress of insectothopters. The CIA created a flying insectothopter as early as the 1970's and insects will continue to play a large roll in influencing how problems in robotics are solved. I want to share an artistic method of building your own electromechanical insect sculpture.
One craft that has focused heavily on the properties of insects is the art of fly tying. Fly Tying is a method of creating lures for fly fishing. This craft employs a diverse palette of materials and tools, and requires careful attention to detail, while heavily relying on proper technique to complete beautiful designs.
I have not gotten too excited about 3D printing or Microcontrollers. I am making efforts to produce electromechanical creatures that use neither of these technologies. It seems that no matter what sensor or mechanical expression you want to explore, it all has to feed through a microcontroller. Lets take it back a bit and make our brain, an oscillator!
So what I propose to you is, we use fly tying tools, materials, and technique as a foundation for creating a beautiful, lightweight, unique, electromechanical insect. This BEAM-like kinetic sculpture will hopefully inspire your friends and family to appreciate insects and craftsmanship.
Step 1: Designing Your Oscillator
There are many oscillator circuits to choose from online. After
looking into a variety, I felt that the easiest and most "organic" was the Astable Multivibrator. This circuit can be created with symmetrical resistors or asymmetrical, resulting in slightly different pulse widths, depending on which "side" of the circuit your are taking your output from.
The components for this circuit I chose are:
x1 2N4403 pnp transistor
x1 2N3905 pnp transistor (mirrored pin out)
x2 330 Ω resistors
x2 22k Ω resistors
x2 4.7 μF 16V capacitors
x2 Light Dependent Resistors (LDR) in 0 - 30k Ω range
x1 2N4920 pnp transistor (handles 1 amp)
x1 8+ Ω Speaker coil
x1 Small nonmagnetic, not enclosed reed switch
I want a low RC time and small capacitors, so I chose 22k Ω resistors with 4.7 μF 16V bipolar Capacitors. This results in roughly 2 - 5 Hz oscillation frequency.
I also want the circuit to be effected by the environment, so I put light dependent resistors (LDR) in series with the 22k resistors. The switch is a small reed switch pulled from a disposable camera flash circuit. We'll use this switch as sensitive whiskers on the abdomen.
Step 2: Begin Soldering
Using those components, you'll need several tools to solder them together. We're not going to use a perfboard.
Grab two vises, one to hold your components and the other to hold your soldering iron.
Also, make sure you have wire cutters, pliers, and a model of your circuit as reference. I've prototyped a second version of the circuit to make sure I always know which parts of the components attach where.
Bend the leads of the two transistors so that the collector bends out to the side, and the base bends in towards the middle. Because the 2N4403 and the 2N3905 (pictured as BC557) have different pin outs, keep careful attention to where the base and collector are. Two of the same pnp transistors could be used, but I like the chiral quality of the mirrored pin out. After all, this is art.
Bend the capacitor leads at right angles.
Cut the leads short on the capacitors and transistor base and collectors.
Now place the transistor in your vise, and bring the solder iron towards the desired lead to solder. This frees both your hands to bring in the capacitor and solder, and attach them together.
Repeat this step so the base and collectors of each transistor attach to each capacitor.
Interesting to note, the vise can actually act as a heat sink for the transistors and the architecture of your finished solder job makes this structure surprisingly strong.
Step 3: Solder the Resistors
Bend and cut the leads of the resistors as pictured above.
Place the 330 Ω resistor in the vise and solder our capacitor transistor unit to the resistor. Follow the schematic, this resistor must attach where the collector of the transistor is.
Repeat with the second 330 Ω resistor.
Place the LDR in the vise and solder our growing circuit to it. Solder to the base of the the transistor.
Repeat with the second LDR.
Cut the long leads of the LDR towards the center.
Solder the 22k Ω resistors to the LDR leads such that the resistors are in series.
Each of the four resistors should have open leads pointing out in the center of our circuit (as pictured).
Bend the leads of these resistors towards their neighbors, cut them short, and solder all of them together. This resistor bundle is now part of our ground rail.
Step 4: Solder Wires and the Power PNP
This unit of capacitors, transistors, and resistors is our astable multivibrator oscillator. It is effectively our brain for the insect. The LDRs function as eyes and will slightly modify the frequency and pulsewidth of our oscillator. This circuit alone cannot power the speaker coil, so we'll connect it to Q3, our power transistor (BD140 or 2N4920).
Solder the positive rail wire to the emitter of Q1.
Solder the ground rail wire to the resistor bundle.
Solder a third wire to the emitter of Q2 (pictured as orange).
Solder this third wire to the base of Q3, the power pnp transistor (2N4920).
Strip the positive rail wire about 1 1/2 inches down and solder to the emitter of Q3.
At this point, I like to take a break from soldering, and apply a liberal coat of clear nail polish to the circuit. This will help prevent shorts if the circuit is bent or squished, and will give it some weather proofing. Feel free to apply several coats.
Check to make sure you haven't shorted the circuit anywhere. Test the circuit to make sure it is still working by powering the red wire with +9V, grounding the black or brown wire, and clipping to the collector of Q3. I use a tiny 5V lamp or spare speaker. Because Q3 can only handle around 1 amp, don't over heat this transistor with too much power and too little resistance. Do your calculations (I=V/R) assuming DC current. In theory, the average current is half the DC current at rail voltage due to the pulsing effect, but this will help us leave room for error.
Step 5: Cut Out Voice Coil and Solder
Take a small cheap speaker with working voice coil and cut it out. Start by cutting around the edge of the speaker cone and make sure not to cut the tinsel wire connectors underneath.
Clip or desolder the tinsel wire connectors from the basket tabs.
Cut the mesh suspension just above the permanent magnet.
Remove the voice coil and trim away the excess paper and mesh. Make sure to leave the tinsel wire connectors as long as possible.
Tin the tips of the tinsel wire connectors and solder one to the collector of Q3.
Solder the other connector to an extension wire.
Strip the center of this new wire and solder it to the ground rail.
Step 6: Design the Wings
I printed out cranefly wing patterns onto transparency.
You can also draw the wings using pens and sharpies onto acetate.
Have fun coloring the wings and making them unique and interesting.
Place your acetate sheet onto an old magazine and press into the veins with an awl. Alternate front and back to create concave and convex creases in the acetate. This not only adds to the illusion of real insect wings, but it actually strengthens the wings too.
Cut the wings out, but leave them as a pair! Leave a little extra material in the center so our voicecoil has more material to push around.
Step 7: Tie the Wings to Monofilament
To begin tying, you'll need around 35 lb. monofilament, our vise from earlier, scissors, wings, thread, and a fly tying bobbin. *Suggested Correction: Use heavier monofilament or thin wire for these wing supports. The model pictured and built loses mechanical efficiency when the monofilament bows outward during down stroke.
Cut two pieces, five inches long and place one piece into the vise. Loosely tie the wings to the monofilament in a figure eight pattern.
Repeat with a second piece of monofilament and the other wing.
I added a little glue to the knots on each piece for added security. Make sure the glue doesn't obstruct the ability for the wings to flap. This is supposed to act like a hinge and the monofilament is our fulcrum.
Step 8: Build the Thorax and Head
Everything comes together all at once during this phase.
Take a three inch piece of 100 lb. monofilament or stiff tubing, and tie thread onto the length of it.
Take three, seven inch pieces of floral wire, and tie each in the center along the length of our body structure. These will be our legs.
Tie the back pieces of smaller monofilament from our wing unit just behind the rear legs, leaving room to readjust their length later.
Find a magnetic pin like the one pictured. This will hold our permanent neodymium magnet in place.
Tie the circuit we built onto the legs / body.
Tie the magnetic pin onto the body behind the head but in front of Q3.
Tie two small hackle feathers onto the body just behind the head so they poke out forward like antennae (this is purely aesthetic).
Bring the front pieces of smaller monofilament from the wing unit forward and tie them onto the body close to the head. Pull on each piece to make sure the wings are centered and rise above the magnet.
Cut the paper tube of the voice coil towards the center so we can slip the acetate of the wings inside of it. This whole structure should hover above the pin where our magnet will go, so when the current rushes through the coil, the magnetic force pulls the wings down and the tips of the wings flap up.
Step 9: Build the Abdomen
Tie the reed switch onto the back end of the body. This will be the tip of the abdomen, where our sensitive whiskers will be.
Solder our ground rail to one leg of the reed switch.
Solder a second short piece of wire to the other leg of the reed switch.
Curl the positive rail wire to create a large surface area for the battery.
Curl the new short piece of wire connected to the switch to touch the negative or 0V side of the battery.
Tie a small 12V battery onto the abdomen and secure the battery leads to have a solid connection. I had to add a few pieces of heavy monofilament to the abdomen to prevent the battery from flipping over to the opposite side of the abdomen as I tied it on.
Test it out! Do the wings move towards the magnet? Make sure the polarity of the magnet is correct by following the right hand rule of electromagnetic current, and using an analog compass to establish the polarity of your permanent magnet. If you built the circuit as I described, current is flowing out the collector of Q3, through the coil, and towards the ground rail or 0V side of the battery.
To finish it off, bend the floral wire legs to look as bug like as you want! Try a little glue where the legs meet the body if they are too flimsy. Enjoy!
Please let me know if you have any questions. This is definitely a finicky project. A small rubber band between the leads of the battery can help hold them in place.