Part 3: Building the Motor Assembly

Step 15. Now we cut a hole in the Styrofoam baffle (Fig. 15). If you are using a hot knife, be sure to work in a well-ventilated area. If you don’t have a hot knife, a good utility knife or hacksaw will work too. The width and depth of the hole will affect how the Doppler effect sounds in your rotary cabinet. To ensure burly shifting tones, I cut a medium-sized hole that was both deep and high.


Fig. 15

Step 16. Now it’s time to mount the motor. On your 18"x18" piece of Baltic birch—the roof— create an “X” using a straight edge and pencil. Place the straight edge across diagonal corners, draw a line, and then repeat the process with the other two corners.

Place your motor with the mounting hardware in the middle of the “X,” and then verify it’s in the precise middle by making sure each side of the motor is equidistant from the edge. Finally, mark the mounting holes with a pencil.

Step 17. Find a drill bit that’s slightly smaller than the mounting hardware screws, drill through the marked holes from top to bottom, and then screw in the mounting hardware. Once all three screws are in, flip the roof over so the threads are facing up towards you. Put your motor on the screws and make sure each screw goes through each mounting hole. Drop a washer, nut, and lock washer (in that order) that fits your mounting hardware onto each screw (Fig. 16).


Fig. 16

Step 18. Now verify that the motor is level by placing your leveling tool on top of it as best you can. After you’ve tightened the mounting screws, check again with your leveler to make sure you didn’t bend anything out of shape.

Step 19. Now comes one of the most important steps in the entire assembly—making sure you properly mount the baffle. If the Styrofoam is not mounted exactly in the center, at higher speeds it will wobble all over the place and shake the entire cabinet. Take plenty of time and be very calculated in your approach. To find the center, use the “chord” method. There’s an excellent tutorial for this on YouTube called “How to Find the Center of a Circle” by Tomahawk DIY.

Step 20. Once you’ve found the baffle’s center point, drill the hole for the motor shaft. Find a bit that’s a few sizes smaller than the shaft, so when it comes time to mount the baffle, it’ll fit snugly. Drill into the midpoint of the Styrofoam baffle.

Step 21. Take your scrap wood and find its center. If you can, I recommend using a circular piece since that’ll help with rotary balance. If it’s a circle, find the midpoint on the piece of wood by repeating Step 19, and if it’s a square piece, find the midpoint by repeating Step 16.

Glue the wood piece to the Styrofoam (Fig. 17). Using a nail or some other rod-like object that loosely fits in the wood piece’s hole, probe around very lightly until you find the hole you drilled in the Styrofoam. Once you locate it, let the nail stay there for a short while to prevent the glue from leaking and drying in either hole. Pull the nail out after about 10 minutes and confirm there’s no glue inside the holes. Let the glue dry for 24 to 48 hours.


Fig. 17

Step 22. After your baffle has had time to dry, mount it onto your motor shaft (Fig. 18). Make sure it’s as straight as possible by using your leveling tool. Remember, the amount of clearance or space between your baffle and speaker will alter the intensity of the effect. I placed my baffle fairly close to the speaker.


Fig. 18