Nuts and Volts - September 2015

3/4” wide slot in the center — left to right — all the way through the cardboard, leaving only a 1/4” of cardboard on the left and right sides.

This is where the book gets its locomotion.

Drill the eye socket with a 13/16” drill bit. I used a Forstner bit. The placement of this hole is critical so that the eye mechanism doesn’t rub on the 600 RPM motor mount. After a lot of trial and error, I determined the best placement is in the upper left corner of the cover, 1-1/4” from the top, and 1” from the spine (where it bends). Refer to Figure 3.

Drill the plastic eye with a 1/16” drill bit close to the mold mark all the way through to the other side. I drill each hole separately (since the eye is hollow) to make sure they are perfectly aligned. Turn it 90 degrees and drill close to the end of the ‘stem’ as shown in Figure 4. Place the two inch piano wire through the first holes creating a hinge point. Place the eye in the hole and tape the wires on both sides with filament tape so the eye can look left to right. Take the FF-030 motor and carefully (gel) super glue it adjacent to the eye so that it does not interfere with the 600 RPM motor. Be careful that the super glue doesn’t enter the motor, or you will have a paperweight and need to buy a new one. Tie a surgeon’s knot with the thread (I used Fireline — strong stuff!) onto the end of the motor shaft and put a tiny spot of gel type super glue to keep it from slipping. Tie the other end of the thread to the end of the eye stem. Attach a weak spring as shown to pull the eye back after the motor has de-energized. This is a lot of commotion to get the eye to move — but it’s worth it. Color the eye if you want and hook the motor up for a test. Fiddle with it, restring, fiddle — done (Figure 5).

Drill the center of the aluminum bar all the way through with a 3 mm drill bit. Then, turn it 90 degrees and drill a setscrew hole (#43 drill bit) for the 4-40 setscrew. Tap the setscrew hole and mount the bar on the 600 RPM motor. You now have a “propeller.” On each end of the propeller, put some Sugru or Oogoo for traction. Once dry, mount the motor so that the propeller is central in the slot. I used a 3D printer to make the plastic motor mount (the file is at the article link), but wood or cardboard will also work. Just make sure it is secure and doesn’t interfere with the eye.

After populating the PCB and attaching all the external parts (Figure 6), place the PCB inside the box to the lower left as far as possible. Use foam tape to hold it in the box. The LM317 regulator is to output the voltage your sound module needs. Only two resistors are required to get the proper voltage. The schematic is set up for 2. 9 volts. See the LM317 datasheet for the proper resistors if

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■ FIGURE 6. Populated and wired PCB.

Qty Description

1 L293D dual H-bridge motor driver; Adafruit #807

1 FF-030 motor; All Electronics CAT#DCM-433

1 600 RPM 12V gear motor; Deal Extreme #323578

1 7805 T220 5V regulator; Mouser 595-UA7805CKCT 1 LM317 T220 regulator; Mouser 511-LM317T

2 470 μF 16V electrolytic capacitor

8 1N4148 diode or similar; Mouser 583-1N4148-T

1 100 ohm 1/4W resistor

1 1K 1/4W resistor

1 1.2K 1/4W resistor

1 9V battery clip

1 Small SPST slide switch

1 Sound module (see text)

2" 1/16" piano wire Fiberglass tape 1/2"

6" Strong thread

1 Weak spring

1 Aluminum bar 1/4" square, 2-1/4" long

1 Small book box, made by Punch Studio #10808, 4-1/2" x 6-1/2" x 1-1/2"; or try Michaels, Joanne Fabrics, or book stores (could not find these online!)