Algunos supuestos de la paleoantropología

Figure 10-22 A typical medium-sized windshield wiper motor

to figure out which pair of wires will run the motor with the most RPM and torque, and this is done by trying all possible combinations. One pair of wires will make the output shaft run at the highest speed and without any pauses between rotations, so these are the two wires you want to connect. Also shown in Figure 10-23 is the control rod, which will connect to the wipers drive arm.

The wiper motor will need to be mounted to a sturdy platform made of wood or metal with enough room to carry whatever 12-volt battery you plan to use. The battery will also become the weight that will hold the board in place, and should be no smaller than a motorcycle or recreational battery and have a rating of 12 volts. Windshield wiper motors

are very powerful, and require a minimum of a few amps just to start turning, so a 9-volt battery is not going to cut it here. If you ended up with some of the mounting hardware still attached to the wiper motor like I did, then see if you can reduce it to the minimal size and shape needed to securely fasten your wiper motor to the board as I did in

Figure 10-24. If you look back to Figure 10-22, you can see how the original mounting hardware was cut down to what is essentially an L-shaped bracket to bolt the motor to the board. If you don’t have any mounting hardware, you will have to make your own motor bracket from some shelf-mounting hardware or a bit of angle iron by drilling holes for the motor shaft and mounting bolt holes.

With the wiper motor cleaned, tested and mounted to a sturdy platform, all you need to do is add your battery and a way to switch on the power and you will now have a mechanical motivator to move your Halloween displays. A pair of quick- connect terminals in place of an on–off switch will allow you to run a long wire from the motivator to your “control center,” so you can run multiple displays from a single location well out of view. The simple schematic shown in Figure 10-25 will allow any type of pushbutton, flip switch or automatic activator (shown next) to engage the motor, adding life to whatever it may be connected to. Polarity of the battery is not important here

Project 45—Universal Motivator

Figure 10-23 The bare wiper motor cleaned and tested

because the motor movement is reciprocating (back and forth), and will not be any different no matter which way the motor shaft is rotating.

The wire you will use should be at least as heavy as a typical AC electrical cord, since the wiper motor will draw between 5 and 20 amps depending on how much you load it down. If you try to use the thin wire you normally use for low- power projects, then you may be adding a bit of smoke to your Halloween show as the wires get hot, like toaster coils from a current overload. Figure 10-26 shows my completed motivator, including a 30-amp hour wheelchair style lead acid battery and the heavy-gage wire used to connect the motor to the power source. To start the

motivator running, the two quick connect terminals simply need to be shorted together, which is done manually via a remotely wired on–off switch, or by some automatic activator like the one presented next.

The actual movement generated by this motivator will be transferred to your display or prop by either a rod or a wire connected to the output arm of the gearbox connected to the wiper motor. This arm is typically 3 inches in length, so you will end up with a total movement of 6 inches as the arm makes one complete revolution. Six inches of movement is a lot, especially considering the amount of push or pull this unit can deliver, so your Halloween displays can be made large and heavy for maximum viewing impact. To connect a rod to the motivator, cut one end from the original wiper control arm and bolt it to whatever length of rod you need. This rod can be made from wood,

plastic, or metal like the one shown in Figure 10-27. The rod can be interchanged by simply removing the two bolts and replacing it with another rod or some other device that will deliver the movement from the wiper’s arm to your prop or display.

The bolts used to connect the rod to the wiper arm shaft should not interfere with the mounting hardware or your electronics when the motor makes a complete revolution, so test this before setting up your display. The end of the original control arm that is now connected to your steel rod will be held to the wiper’s drive arm by some type of easy-to-remove C-clamp or a cotter pin, which will prevent it from falling off as the motor rotates. Figure 10-28 shows the rod and all supporting hardware connected and ready to push and pull whatever may be connected to the other end of the steel rod. Some extra weight besides what is offered by the heavy battery may need to be added to the platform as well, especially if your target prop is

Project 45—Universal Motivator

Switch terminals Wiper motor

12 V battery

Figure 10-25 Wiring diagram for a remotely located switch

Figure 10-26 The completed universal motivator

large and heavy. The windshield wiper motor is more than capable of dragging a 50-pound weight around, so you might want to consider an even heavier

mounting platform made of steel or with enough room for several bricks for ballast.

With the universal motivator, you can add life to your Halloween displays, making huge bats that flap their wings up and down, ghosts that wave back and forth, witches that constantly stir the cauldron, or even indoor displays like my flesh- eating Jack-O-Lantern presented in Project 47. The motivator can be further expanded for fully automatic operation by inserting a relay- operated circuit in place of a manually operated switch on the motivator’s output jacks. Presented next is a very simple device that will switch on the motivator any time a sound is played, so you can sync your prop to some pre-recorded music or sound effects, making it jump to life without having to flip a switch on or off manually.