First you will need a gear motor.
If you wish to modify a standard RC servo for your geared motor then follow this 'ible:
If you use a Parallax continuous rotation servo there is no need to modify the gears, but you will have to modify the wiring to the servo's motor.
The diagram above indicates how you will wire the motor, microswitch and battery pack to the pins on the toggle switch. This is called 'Dead-Bugging' and is a prototyping method from way back.
It's a very simple circuit but it's easy to mess up the wiring. Follow the directions carefully or purchase the Useless Printed Circuit Board from us to speed up and greatly simplify the wiring process. And a cool LEDs to the circuit too.
Wire the gear motor to the indicated pins.
A short length of wire connects opposite pins on the toggle.
Another wire connects the other outside pins on the toggle and this wire has the microswitch in-line.
The battery pack goes to the other remaining pin on the toggle.
If you find that the motor is running in the opposite direction from what is needed, simply reverse the wires going to the motor.
tydarby posted the great graphic below, showing how wire up a modified servo . The pins to use on the micro-switch are the common (C) and normally closed (NC). Nothing should be connected to the normally open (NO) pin.
Batteries: The original parts list used a 4 AA holder but you may find that 4 batteries driving the machine makes for way too fast operation. Blink, and you'll miss it.
In most cases you should be able to get away with just 2 or 3 AA batteries, making the overall action more slower, and more visible.
Keep in mind that the our kit only uses 2 AA batteries.
More on Motors:
I originally chose to use servo's because they are available almost everywhere, and are standardized, but you don't have to use one. Just about any motor should work, as long as it's geared down, and has enough torque to flip the switch.
The more salvaged parts you use, the better.
Keep in mind that another reason for using a geared motor is to prevent bounce-back from happening when the machine shuts off. Without the gearing, motor wouldn't keep the arm pressing down on the micro-switch while it's off. The machine's arm would just keep hitting the switch, turn off then on, then off, then on....
The next couple of steps show the original way I made my machine. If you're building one using the information above, then SKIP the next 4 steps and jump to step 10.