- Aug 11, 2009
VIDEO: Limited slip differential Lego style
Lego open differential - click image above for Lego LSD video
After spending enough time searching YouTube to make us reconsider our personal path in life, we're slowly coming to the conclusion that there just aren't other old-timey awesome vids like the one on the differential. Which, while a pity, isn't the end of the world. It's not even the end of videos. Case in point: today we learn how you tackle the issue of slip when playing with Legos.
First, let's a define our terms. A differential is a set of gears that allows drive wheels to turn independently of each other. Otherwise you'd snap an axle going around a turn on dry pavement. Slip is what happens when one wheel loses power (via the differential) and the other lose traction. Put another way, with an open diff if one tire is touching pavement while the other is on ice or in mud, the car won't go anywhere. Why? Because the differential allows 100% of the torque to be transmitted to the wheel that can spin freely, i.e. the wheel with slip. What you need then, is a way to limit the slip.
Now, in a real, non-Danish plastic brick-mobile, the solution proposed by the video wouldn't work so hot. For one thing, it would be very heavy and bulky. On real cars however, there's no one best solution -- or least no one can agree on a best solution. And really depending on the application -- road racing, suburban commuting, Baja 1000 -- one size doesn't fit all.
Dominant types include clutch-type (where clutches on the half-shafts compress based on torque input -- a spinning wheel would cause the clutch to engage, binding it to the non spinning wheel and transfering torque), geared (where after a predetermined torque split is achieved -- say 75 to the other -- worm gears spin both drive shafts), viscous (increased heat from increased torque makes special oil have more friction, thereby tying the wheels together) and electronic (