This is a simple easy to build kit like thing that you can use for different things. Enjoy and please vote! (:
Step 1: Collect Materials
You will need these things: 2 dc motors 1.5-3v, some 12v power source( I used a 12v regulator, but I really wanted to use 4 3v coin batteries), 2 relays, printed circuit board, 2 1000uF electrolytic capacitors, wire, soldering equipment, a SPST switch.
Step 2: The Schematic
This is a simple schematic. You may want to lay it out on a breadboard first just to make sure you have everything right. You have to make the same circuit twice so that you can use the dual motors( NOTE: You can use as many motors as you need, you just have to repeat the same circuit over and over).
Step 3: Soldering
Solder every thing in just like the schematic to the printed circuit board. It is pretty simple.
Step 4: Testing
According to what I got. The motors should do exactly what they did on the breadboard and should sort of change speed randomly. If you are having trouble, go to the TROUBLESHOOTING section. You can now enjoy your motor randomizer!
Step 5: TROUBLESHOOTING
If you are having trouble with this then here are some tips. If there is no expected ticking noise then that's okay, it should still work. If the motors aren't going then check your connections. You might smell something funny , that is just the motors going super fast. WARNING: if you use a 12v regulator like me, then it will get burning hot. Be careful and if I didn't fix your problem then put it in the comments.
Step 6: Extra Ideas
Here are just some ideas to put your random motors to work with. You could make a little robot. You could make a airplane out of wood and let randomly fly through the sky. You good use it for any number of things! Please vote and put ideas in the comments If you have any! ****UPDATE**** Here is a video someone requested in the comments.