Kinetic Energy Converter Project

I have a 3 year old cat named WiFi (pronounced Wee Fee) who seems to have an endless supply of energy. He loves to play, so I was motivated to help him harness his own muscle power in order to keep himself entertained. My idea was to create a device that would be attached to a cat toy on a string. When WiFi pulls the toy, a generator is turned, storing electricity in a capacitor and potential energy in a constant force spring. When he lets go of the toy, the string retracts, being pulled by the constant force spring, and even more electricity is stored in the capacitor.

The complete retraction of the toy flips a switch that activates a small fan attached to a 555 timer circuit. Using the electricity in the capacitor, the fan periodically blows onto the hanging cat toy, moving it, and motivating WiFi to start the process over again.


I started with an initial test using a tape measure. A standard tape measure has a constant force spring inside of it, and the 25 foot length was perfect for the open layout of my apartment.


Wifi seemed to be interested enough for me to continue work on this route. I hacked the tape measure and attached a spindle and pulley to it. Once mounted, I placed a small DC motor alongside, mounting that with a piece of hardware I had in my junk box.




The most time-consuming part of the fabrication was fine-tuning the motor and pulley so the belt would ride true and not slip off. There were lots of tiny adjustments of position, and I had to shim the motor into exactly the right place.


Once done, I knew that this could produce a viable amount of electricity, so I set to work on the circuitry. Since the motor would be spinning in both directions, I started with a bridge rectifier, this then went into the capacitor stage, followed by a 5V voltage regulator. After this was the 555 timer circuit. The 555 is a real nifty IC that I had never used before. Now that I know how it works I'm sure I'll implement it in future projects.


All components of the circuitry appeared to work except for the capacitor stage. I was told part of the problem was that I wired the capacitor in series rather than parallel, which turns the capacitor into a DC blocker. However, it still did not seem to work properly when I tried wiring it in parallel. This is something I'm going to have to continue to troubleshoot. This video shows the circuit working properly, but with a 9v battery in place of a capacitor

This photo shows the circuit with a capacitor wired in series.

This photo shows the circuit with what I believed was a proper parallel wiring.


If this gets worked out, I'd like to make a 2nd prototype using the spool from an auto-retracting AC power cord. The robust design and internal constant force spring makes this superior to the tape measure, not to mention the lack of sharp metal edges that the tape measure poses as a danger to both felines and humans.