Week 6: Team Project Update

This week the team used down-selection matrices to make a final decision on the product we are going to design. After conducting feasibility calculations for the work output and time/effort required, the team figures it can design a pull-string device that will be able to charge a smartphone in a reasonable amount of time. One pull should provide around 8 Joules, taking into account inefficiencies in the drivetrain and motor. The total charge time is estimated to be around 5 hours, but the team is striving to lower this time by keeping the total system efficiency higher than 20%.

Essentially, the device will be a case that attaches to the back of an iPhone and features a pull-string handle that the user tugs on. The force of the user pulling outputs a torque to the pulley, which will transmit that torque through an optimized gear-train and to a DC electric motor (acting as a generator). The generator converts the mechanical energy to electrical, and from here the energy will be stored in a large capacitor or small buffer battery. This energy will then be output at 5V to a charge port on the phone and hence will charge the phone battery.

We delivered a solid presentation Thursday for Gate Review 2 that really emphasized the feasibility of our product. The alpha prototype was demonstrated in class that was made from cardboard and a small-tape measure to show the retracting motion. All in all, it was quite a busy yet productive week and the team is looking forward to begin designing the physical product!