1. Grab the HDPE container and cut out a circle about 2” in diameter, exact size is not important. If using a container similar to the one in the picture, put the hole in the middle of the container, we will use it again later. Put small hole in approximate middle of the HDPE circle. This hole needs to be smaller than the motor shaft so the shaft will fit tightly.
2. Put the HDPE circle on the motor shaft and apply power to the motor. Now, take a sharpie marker and lightly touch the spinning HDPE with the marker about ¾” away from the shaft middle. Now turn off the motor. This should have produced a black circle on the HDPE with the motor shaft hole being the precise middle.
3. Cut out the circle in the HDPE. And cut "fins" approximately as shown. Precision is not necessary but do not cut too close to the center hole. ¼” fins work just fine. Once fins are cut, go around the circle and bend each fin in the same direction, as the picture shows.
PRO TIP: If making your own impeller sounds like too much work then try to find a small hand fan. The kind you can get at the dollar store (see image). It usually takes 2 AA batteries, has a motor you may be able to use and a ready made impeller that fits the motor shaft securely. This way you wont have to bother with the glue on the impeller, but you will have to cut the fins down to fit your container and the motors are usually weak and under powered, which is why I am not using it. So I guess that makes this less of a pro tip and more of a noob step. Ah, whatever!
Another PRO TIP: The shape the tornado will take is directly effected by the impeller. The width of the overall tornado is directly proportional to the diameter of your impeller. IE; bigger circle of HDPE equals wider tornado. BUT a wider tornado will take more energy to get it going and won't reach the same length a similar powered motor using a smaller diameter impeller would. To summarize. Smaller diameter impeller = taller and faster moving tornado. Larger diameter impeller = wider, shorter and slower tornado.