This type of motor can be used affixed to all kinds of objects, which will cause them to vibrate and move freely about. This is a quick and dirty way to get a Simple Bot to move about, but not exactly the most elegant.
Vibrating motors can be found inside cell phones, pagers, gaming controllers, and personal massagers.
In absence of those, you can easily build your own vibrating motor by attaching any off centered weight to any motor shaft. They can also be created by breaking in half balanced components already attached to motor shafts.
Follows are some simple examples.
Step 1: Find one
Simply take apart the gaming controller and free the motors. They should be ready to use.
Step 2: Unbalanced fan
Step 3: Add Eraser
Another simple way to make a vibrating motor is to stick a pencil eraser (or cork) onto the shaft of any standard reversible DC motor.