4 x 4 with differentials (Top View)

This is a top view of the 4 x 4 with differentials. As you can see, there is a differential in between both front and back sets of wheels (including one under the Lego 9 Volt Motor), and also a single differential to split power front-to-rear. The shafts coming out of the Lego 9 Volt Motor have two universal joints because the end-to-end axle connectors create small amounts of pressure in the system, making it lose power. These universal joints allow for almost all of the power to be transmitted, even though there is no angle necessary.

The initial 8 tooth gear (on the motor shaft) is reduced 3:1 by meshing with the differential's 24 tooth, and upon coming out of the middle differential, the power is reduced 3:1 by the first gearing axle, and again 3:1 by the second gearing axle. This gives a final gear ratio of 27:1 from the motor shaft to the wheel axles.

However, if one set (front or back) of the wheels is held motionless, this gearing ratio decreases (and speed therefore increases) by a factor of two to become 13.5:1. If three out of the four wheels are held motionless, the gearing ratio becomes 6.75:1. This will make the one wheel have very little torque and lots of speed.

Notice the center construction using a 1x5 steering plate with an axle hole in the center. This holds the main two struts (front and back) together for good strength. (A trick I learned from the 8480 Space Shuttle satellite arm.) This connection is further reinforced by 1x6 (black) plates top and bottom.

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( Craig.Lampe@UTSouthwestern.edu )