Solar Solutions, Professor Dan Mikesell: Solar Pet

 Harnessing the awesome power the sun is no easy task. However, with the ever improving efforts of physicists to improve solar energy devices, this task has become largely democratized and therefore can be utilized for purposes like our own. Thus, the assignment to create a toy “pet” that utilized solar technology was well within our abilities.

            When designing this solar pet, I wanted to create a toy that had at least four characteristics. I wanted to build a solar pet that could move from one location to another location, had geared mechanisms, included some organic component, and was aesthetically cute. In respects to the mobility and organic component, I had failed. The solar power/motor capabilities were limited, as the motors typically suffered from very, very low torque.  Because of this, the motors didn’t provide enough power to actually move anything, and therefore rendered mobility impossible. Here were some potential designs for how the motor could allow for mobility.

For the organic component, I had initially envisioned adding a small potted plant to the final product. However, as this plant would have a weight most likely greater than the abilities of the motors’ torque, I immediately eliminated it from the final design.

I also had wanted the solar pet to be cute, and have an aesthetic that was appealing and pet like. Initially, I had a few ideas for how I could make my pet cute, but in the end I improvised. Here are a few of the initial designs.

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The one way in which I can say I was relatively successful was in incorporating the geared mechanisms. The process of designing, fabricating, prototyping, and redoing these mechanisms took the most time and effort of the entire solar pet construction process. I began by thinking of ways in which I could have these low-torque motors actually make something substantial move. The solution was a geared system, which utilized a worm gear attached to the motor connected to a series of gears.

I began by designing a worm screw in tinker cad, which was simple as I could easily take an already existing worm-screw like shape and edit it to suit my cause.  I then printed the first version, a relatively wide but short worm screw, which I then attached to a sample motor for testing. Once the model was complete, I noted it’s dimensions and began to design gears on Geargenerator.com. Unfortunately, the design process and SVG files are not up to scale on the site, and therefore produce inaccurate SVG files. Attempts to 3D print the gears output by this website yielded unsuitable gears that did not mesh with the worm screw nor with each other.

The inefficacy of Geargenerator.com provided me with a challenge, as I now had to find an alternative way to design gears. The solution, as I realized, was to design the gear in Tinkercad along with the worm screw, so that I could create a gear that fit the worm screw perfectly. Using a custom gear shape within Tinkercad, I modified the object so that the gear’s teeth had lengths and widths congruent to the worm gear’s spirals. Once I had done this, I downloaded an SVG file of all the 3D models and placed this file into Adobe Illustrator. From here, I simply deleted all the other aspects of this file except for the gears, which I then converted into a laser cutter friendly format and tested.


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After several tests, I concluded that these gears would indeed work with the worm screw, and opted to first alter the worm screw to make it longer, as well as increase the number of gears the solar pet would use. In respects to the worm gear, this change ultimately allowed me to have a better ability to turn the gears. In regards to changing the gears, I decided to create three gears in total, each of which consisted of two gears attacked alongside one another. One half of this gear would be large and have a greater number of teeth, while the second gear had almost half this gear’s diameter and fewer teeth. The idea was to connect the larger gear to the worm screw, which would in turn rotate the smaller gear. This would take the low power from the motor and amplify it slightly, giving the second gear a greater torque. The second gear would then take this torque, and using the same technique, amplify the torque from the first gear and rotate the third gear. Finally, this third gear would take the already amplified torque and use this to rotate the Solar Pet’s hands.

Finally, it was time to design the first iteration’s body. I did this by taking the already conceived design from the previous gears and creating a new SVG file in Adobe illustrator. Here, I created three identical sets of gears, a box to serve as the solar pet’s body, arms, and a cylindrical holder to keep the motor in place within the confines of the pet. Once this was done, I went about cutting this SVG and with the laser cutter on 5 mm clear acrylic. In addition, I took the schematic of the miller solar engine and created a perfboard version. I then connected this circuit to the motor with corkscrew and the solar panel. Having both the circuitry and mechanism completed, I then built the first iteration.

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This first iteration was successful in some aspects, but unsuccessful in others. The first issue I encountered was that I didn’t create segment to hold the axis of the gears. Therefore I had to drill makeshift holes into the laser cut body several times to get the gears in the right configuration. But even with the gears in their exact position, I still failed to keep them from sliding around on their axis, which there were inclined to do when being rotated via worm screw. A potential remedy I tried was attaching small springs to either side of the gears in the hopes of keeping the gears in place. Unfortunately, the spring often exerted too much force, one greater than the torque to turn them, resulting in a fixed and worthless gear. By cutting the springs and making them shorter, I eased some of this force, but still exerted way too much to allow the gears to turn as desired. Moreover, I learned that the laser cut arms were too heavy for the motor or gears to rotate. In addition, I found that the first body was a little bit too thin, as the board and motor barely fit within the confines of the laser cut box. Moreover, all these troubles sent me back to the drawing board to design the next iteration.

Learning from the mistakes of the first iteration, I created a better final body by making several adjustments. First, I made the box slightly larger to accommodate every internal component. Second, I designed holes which allowed me place the gears’ axis perfectly in relation to one another, so that they could make efficient contact. And finally, I designed a stand and a face so that this solar pet could satisfy the previously mentioned aesthetic aspect.

Construction of the pet the second time around was much easier, even though issues still occurred. This time I decided to hot glue to gears in place on their axis, so that they could not move as readily and maintained their position. In addition, I decided to extend the metal axis of the third gear and bend it so that when it was outside the solar pet’s body. The resulting and protruding two metal appendages resembled arms, to which I added felt hands. These hands further added to the aesthetic quality. Unfortunately, despite my best efforts, the gears would often get stuck, preventing the arms from rotating as I had planned. In a last ditch effort to have the arms at least move a little, I decided to only utilize the first gear directly connected to the worm screw, to ensure continuous, albeit slow, motion.

The final product was a cute little “Sol Troll”, which turned arms slowly and also included glowing red eyes.

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