Step 2: Motor and Bottom Roller
To create the bottom roller, cut a narrow strip of polyvinyl chloride electrical tape and wrap it around the motor's shaft. The best way to get the tape to wrap around the shaft is by pinching the tape to the shaft and rolling it between your thumb and index finger. You also want to crown the roller (make it thicker in the middle) by pulling your index finger slightly to the right for a couple turns then pushing back to the left for a couple more turns repeatedly as you roll on the tape. A crowned roller will keep the rubber band from slipping off the roller. Add a bit of super glue to the end of the tape strip to prevent it from unrolling, also add a little super glue to the edge of the roller to bind all the layers of tape together. I tried making rollers out of Teflon tape and silicone rubber, both of which are lower on the triboelectric series, but a roller made from electrical tape was easiest to work with. I did not know what material the generic black electrical tape I had was made from, so to be positive the bottom roller was vinyl electrical tape I used blue 3M 35, but 33+ should work well too.