Limited Slip Gear Differential

I went to the new exploratorium in San Francisco where I saw a working model of the limited slip differential system used in cars.  I'm still learning about it, but I think the gearing mechanism is used to allow one wheel to move faster than the other to prevent skidding on a turn.  Basically, when one wheel has friction and slows down, the other wheel speeds up to compensate for the lack of energy.  Differentials are important because on a turn, when the outer wheel travels more distance then the inner one.  If they both rotate the same amount of times, then the outer wheel will be dragged, ruining the tire.
Here is my firs differential:

More lego guns- and now a working one!

After ordering some new pieces, I made a new lego gun.  This one holds eight bullets and fires them all within a few seconds.  It just uses the basic lego "rocket launchers" that fire when the trigger is pressed.  Because of the circular rotating design, all of the triggers are pressed after a complete circle.  Unfortunately, in this video, the shots are staggered because the triggers weren't pulled all the way.  It's not perfect, but its an improvement from my earlier designs.

My Excavator

I haven't posted in a while, but here is a video of my fully built excavator with my custom additions.  I added two motors to power the treads, a motor to shift between arm functions, and I made the whole thing remote control.  Also, when the arm moves, lights on it turn on to illuminate the way (sorry, they aren't easy to see here).  It's super fun to drive.  Here is the video of it just moving a roll of wrapping paper: