Place one LEGO Technic 14-tooth bevel gear onto the small spindle on the inside of a LEGO Technic differential mounting. Make sure that the gear sits flush with the differential and that the bevel is angled facing the interior of the differential. If it faces the other way, it will not lock well with the next ones you fit.
A differential gear overcomes the problem of a vehicle cornering effectively by allowing the inside wheel and outside wheel to turn at different rates. In rear-wheel driven cars the differential converts rotational motion from the shaft to rotational motion in the axles. Shock absorbers keep the ride smooth and allow the wheels to move up and down while turning. There are different types of LEGO shock absorber assemblies, but all use small springs to make them work.
- LEGO Technic differential 73071
- 3 LEGO Technic 14-tooth bevel gears 4143
- 2 LEGO Technic axles 3708
- 4 LEGO Technic shock absorber assemblies 2909c01
- 4 LEGO Technic bushes 3713
- 4 LEGO Technic axle pins 3749
- 2 LEGO Technic bricks 1-by-12-inches with holes 3895
Push one LEGO Technic axle sideways into the differential through one of the holes on the side. Just push it through a little way. The differential has a large outer gear on one side, and it is easier to start from this end. The axle can be of any reasonable length to suit the size of your model vehicle. Place a 14-tooth bevel gear on the inside of the differential such that the beveled teeth interconnect with the one that is already mounted at 90 degrees. Now push the axle into the gear to fix it in place. Turn the axle; both gears should rotate.
Push a second LEGO Technic axle into the other side of the differential. As before, mount a 14-tooth bevel gear on the inside of the differential to meet the incoming axle. The three internal gears of the differential should connect in a U-shape. The differential will allow the axles to turn independently from one another, but they will turn together when the differential itself is rotated. You can fit wheels to the axles later, if you like, once the shocks have been built.
Set the differential in front of you so that the axles extend left and right. Slide a LEGO Technic shock absorber assembly onto the right-hand axle so it is flush with the differential. Ensure that you use the end that allows the axle to turn freely. Fix the shock absorber in place by sliding a LEGO Technic bush down the axle. Now push a second shock absorber down the right axle and fix this against the first bush by sliding a second bush down the axle.
Make a mirror image of the right axle on the left one. You should end up with two shocks and two bushings on either side of the differential. You now need to fix the shocks to the chassis of your model vehicle. To do this, fit a LEGO Technic axle pin to each of the four shock absorber assemblies at the other end from those attached to the axle. For the two shocks closest to the differential the axle pins should point away from the differential. For the furthest shocks they should point toward it.
Point the two shocks on the right-hand side upward so they make two approximate sides of an equilateral triangle. Place a long LEGO Technic brick between them to make the third side of triangle. The brick must have holes and can extend either side of the triangle, but it must be one-unit-wide only. Work the axle pins into the holes in the side of the brick to fix the shocks to it. Use a similarly sized brick to make a mirror image of the shocks on the left-hand side.
Connect the two LEGO Technic bricks together with any LEGO parts that fix them together easily. Most bricks are good for this purpose. You now have a differential gear mounted to a chassis with independent shocks, left and right. Complete your model by adding wheels and a structure to the rest of the vehicle.
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