As part of user testing exercises, I gave a kit to two different guys, both from very different backgrounds. The main goal of these testing was to see what other people would make with the kit, I wanted to see what routine motion meant for others. This first user test prototype was made by Frank Lefnesky. Frank is a 32 year old male who has no experience with electronics or any design background. He enjoys different outdoor sports and activities like biking, skateboarding, and camping. When I gave a kit to Frank he was very excited about the idea. He assemble the kit by following the instructions and took the kit home. A week later he came back with a pimped out skateboard that lights up an LED strip that he put in the front of the board.

I took the pinwheel appart, attached a medium gear to the back of the hub and a small gear to my dynamo generator. Ran the wires from the generator through the EHC and to a set of AA rechargeable batteries, and done!

Initially  I tried using it with a 3.7V Lipo battery but that only charged up until 3.45V, it seems like we are not generating enough power to fully charge a 3.7V battery, this should be fixed with a bigger gear behind the pinwheel hub. I started making A LOT of gears to see what would better fit the kit which are now out for production at the laser cutter center at school. This first batch is being made out of wood, once I decide which are the best gears, I will make them out of a more durable material, below the sketch of the gears being made now.

So, I made a new frisbee which goes more along the lines of what I am thinking the final product will look like. I want it to be transparent and pretty simple, if it was to have an enclosure to protect the PCB and the rest of the electronics thats should be transparent as well. I am shying away from making an enclosure right now, because I want the easiness of how making one of these is, to come across in the design.

I’ve also started to think about how to apply KinetiKit to a pinwheel and make a cellphone charger with it, kinda like this

KinetiKit is  an open-source, self-contained adaptable and embeddable kit for harvesting small amounts of renewable energy to power batteries and mobile devices.  KinetiKit includes several examples how it can be leveraged to harvest kinetic energy in very small scale, unique, and affordable contexts showing how generating power can be achieved in fun, game play, physical exercise, and low-impact installation contexts.

Joe Saavedra, once again came through and helped with this, transferring, remaking the entire circuit on Eagle Cad. A more robust, flexible software for PCBs. I am very happy with the final product, so exciting!!! On March 15 the PCB was sent out for production.

This chip starts working with an input of 0.7V which is really low, but it only becomes efficient when the input source hits 1.3V. This is both good and bad, mainly bad. When the super capacitor in the circuit reaches 0.7V, the Max1675 starts working at its maximun capacity pulling energy trying to boost the voltage to whatever we have set it to, in this case 4.2V.  So why is this bad? While the circuit starts at 0.7V it will only output the desired voltage (4.2V) when we have 1.3V in the super capacitor. Anything that we collect before that is energy that the MAX1675 is pulling but is being wasted. Its like putting water in a bucket with a hole in it, unless you are putting A LOT of water in it at once, it will never get full.

According to the datasheet there are a couple of things that can be done to try to go around this, like lowering the 1.3V input that it is asking for, to somewhere around 0.95V. This could make a difference, this is what I will try next.

First an image of the original sketch and then the first prototype

When I went out to test this I had two big questions, will the frisbee fly with all the hacking that was done to it? Will it charge the batteries? Here is a video of the first test.

The answer is: the frisbee flies, the batteries don’t charge but why???

Once I got this working, meaning that it was giving me the output voltage I wanted (4.20V to charge a 3.7V lipo battery). I started making a much smaller circuit that I could fit into my objects.

This circuit was widely modified from the original one that I found on Design Ideas, simply because it wasn’t doing what I needed it to do. This circuit is outputting 4.2V when I use  the mini handcrank generator from the previous post as an input source. Energy harvesters systems store small amounts of energy over long periods of time. For this, an energy storage subsystem is required. In this case a super capacitor is used (0.47F, 2.5V in the schematic). Here we store small amounts of energy until the super capacitor is full, then the collected energy is boosted with a dc/dc-voltage-converter (MAX1675 in the schematic) providing a higher, steady voltage, which is then stored in the rechargeable battery. In this iteration I added a few resistors to adjust the output voltage to 4.2V, and added a shottky diode at the output to prevent the energy from flowing back into the circuit wich causes the battery to discharge.

The next steps is to test in one of the objects, the frisbee. Snapshot of the original schematic below.