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How to Make a Mini Tornado Siren

For generations, the tell tale, alternating high and low pitched wail of a tornado siren or air raid siren has warned residents of impending danger from storms or enemy aircraft. These loud devices, often on top of telephone poles or tall buildings, create a sound that travels for miles. Air is drawn into the cone by a rapidly spinning rotor and expelled through holes that are alternately covered and uncovered to produce the siren sound recognized by most people.

Things You'll Need

9V constant electric motor (3300 rpm)
Two 1.5 inch mounting screws
6-inch-by-6-inch square of plywood
4-inch diameter 1/2 inch thick stainless steel circle
3 inch diameter 1/2 inch thick 4 inch tall stainless steel collar
2.8-inch diameter rotor
Large traffic cone
Permanent marker
Clear silicone gel
Gator clips
9V battery

Instructions

- 1
  Mount the 9V motor to the piece of plywood using the two 1 1/2 inch mounting screws through the holes in the sides of the motor. The shaft part of the motor should be facing upward.
- 2
  Place the traffic cone narrow side up on a solid surface. Lower the steel collar over the traffic cone until it fits snugly. Use a permanent marker and draw a line around the top and bottom of the collar on the traffic cone. Set the cone aside and remove the collar.
- 3
  Measure one inch from the edges of the stainless steel circle and draw a 3-inch diameter circle in the center. Use two C-clamps to secure the circle to a solid surface. Cut the 3-inch diameter circle out using a 3-inch diameter circle saw bit.
- 4
  Center this 4-inch stainless steel circle over the motor. Set the 3-inch diameter collar in the center of the circle. Place the rotor on the shaft of the motor and check to see if it spins freely.
- 5
  Take a marker and a piece of cardboard. Place the cardboard on the rotor and trace one of the open chambers on the cardboard. Note that the rotor is made up of two levels. The top of the rotor has six chambers that are open and six that are closed. The bottom level of the rotor has four chambers that are open and four that are closed. The open chambers allow the air to flow out of the siren to generate the noise.
- 6
  Cut out the shape on the cardboard and use it as a template. Remove the collar from the assembly and trace the template piece onto the outside of the collar. Draw six evenly spaced templates on the top of the collar and four on the bottom. Cutting round metal takes special tools you may not have. Call a machinist shop to see if they can cut the marked template pieces from the collar.
- 7
  Set the collar down over the rotor when the cuts have been made and seat it firmly against the inside edges of the hole in the 4 inch steel circle.
- 8
  Cut the base of the traffic cone off. Cut around the lower mark you made earlier on the traffic cone.
- 9
  Invert the cone so the wide side is up and place it over the top of the collar. Use clear silicone gel to secure it in place.
- 10
  Attach the red (positive) and black (negative) gator clips to the power supply on the motor. Attach the other end of each gator clip to the positive and negative terminals on the 9V battery. Turn on your new mini-tornado siren.

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