4 Wheeled Lego Chassis

The basic idea with this 4 wheeled chassis is to use one motor to drive the back wheels for forward and backward motion; a second motor is used to steer the front wheels through a rack-and-pinion system; and a touch sensor is used to determine when the wheels are pointing forward.

Feel free to make changes to this design, but if you want it to work with the RCXEngine and RCXSteering components in MindRover then you should keep these points in mind:

  • The steering motor and touch sensor have to work together for the RCXSteering component to be able to simulate it.

  • The ports on the physical RCX and the MindRover steering component must correspond.

  • The RCXEngine component is used to drive the vehicle forward and backward.
STEP 1: Combine 2 12x1 bricks (11 side holes); 1 8x1 brick (7 side holes); 6 2x1 bricks (1 side hole); and 6 joiner axles as shown.
STEP 2: Add 2 10x1 bricks and 2 2x2 bricks as shown.
STEP 3: Add 3 6x1 flat bricks; 3 8x1 flat bricks; and 2 2x1 bricks to form the grid configuration.
STEP 4: On the bottom of this assembly, add 4 4x2 flat bricks; 2 3x2 flat bricks; and 1 8x2 flat brick as shown.
STEP 4a: 2 more 6x2 flat bricks.
STEP 4b: Set the RCX motor into the well that was just created. Add a 24 tooth gear with protruding teeth to the motor shaft.
STEP 5: Add 2 10x1 (9 side holes); 4 joiner axles; 1 24 tooth gear (flat teeth); 1 12 length axle rod; 2 grey positioners (to keep the rod from sliding).
Here are some other views of the assembly so far.
STEP 6: This is the worm gear assembly for the steering motor. It includes a 24 tooth gear (flat teeth); a worm gear; 2 connecting pins; 1 8 length axle rod (going out of the back of the assembly in this picture); 1 6 length axle rod (going into the worm gear housing); 1 small hub connector for the right side of worm gear axle to connect a rubber band to; and 2 positioners on both sides of the worm gear axle to keep it from sliding.
STEP 7: Fit all the worm gear components together as shown.
STEP 8: Attach the worm gear assembly to the base by fitting the two protruding connecting pins into two side holes of the rear cross bar. See the picture with STEP 12 as well.
STEP 9: The rack-and-pinion assembly starts with 1 4x1 flat brick; 1 4x1 brick (with 3 side holes); 1 8x1 flat brick; 1 10x1 flat brick with a hole at both ends; 2 angle axle connectors; 2 4 length axles; and 4 positioners on either side of the axles to keep them in place.
  STEP 10: Next add a 10 length flat gear with 2 joiners to the angle axle connectors.
STEP 11: Add 2 wheels and positioners.
STEP 12: Attach the rack-and-pinion assembly to the axle from the worm gear assembly.
STEP 13: Add the steering motor; 1 4x1 brick (with 3 side holes); and 1 4x1 flat brick as shown.
STEP 14: Add a belt wheel to the motor and a rubber band between this wheel and the small wheel on the worm gear assembly.
STEP 15: A 6x4 flat brick and a 4x1 flat smooth brick will be used under the flat gear of the rack-and-pinion for support.
STEP 16: Position the rack-and-pinion support piece on the bottom of the vehicle. Later on when you are trying to line up the wheels and the touch sensor cam you should remove this piece so you can adjust the straightness of the wheels.
STEP 17: This is the touch sensor assembly: 1 3x2 touch sensor; 2 2x1 bricks (with 1 side hole); 1 4 length axle; and 1 4x2 flat brick. This picture also shows the wire brick that will evenuatlly connect to port 2 of the RCX.
STEP 18: Add 1 6x2 flat brick; 2 4x2 flat bricks to the top of the touch sensor assembly.
STEP 19: Attach the touch sensor assembly to the front motor.
STEP 20: Add an offset cam to the worm gear axle such that it can activate the touch sensor when the front wheels turn.

To position the cam so that the touch sensor is pushed in when the wheels are pointing straight ahead, remove the rack-and-pinion support plate underneath the flat gear.

Next rotate the motor wheel until the cam is pointed straight up and is activating the touch sensor. Gently pull down the flat gear under the chassis so it disconnects from the driving gear just above it.

Straighten the wheels and then re-attach the flat gear support plate to hold the flat gear in place against the drive gear with the wheels straight and the touch sensor button is pushed in.

STEP 21: Add the RCX such that the infrared is pointing towards the back of the vehicle (with no obstructions so you can download new code). Also add a 6x4 flat brick to join the RCX to the worm gear and touch sensor assemblies.

Add a wire connection from the touch sensor to port 2 of the RCX. Add a wire from the steering motor (in the front) to port B of the RCX. Add a wire from the drive motor (in the rear) to port A of the RCX.

These are the default settings. If you change your motor and sensor connections, be sure to change their default settings in MindRover.