1. Ball Roller Coaster
It will keep two balls busy rolling down the track over and over again.  The ULTRASONIC sensor tells the NXT when to use the lift motor to lift a ball back up to the top of track, so the roller coaster operates fully automatically on its own. 

2. Technical Issue:
Use INCLINED PLANE (simple machine) to make balls rolling from top to down
ULTRASONIC to sense ball reach the lift
The ROTATIONAL to control the degree of lift motor to lift a ball back up to the top of track
That is a face in the LCD screen too, check it out 

3. 

4. 

5. 

6. 

7. 

8. 

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12. 

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14. 

15. 

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18. 

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48.  
2 X

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55.  
Use the shortest (20 cm) wire to connect the motor to port A on the NXT,
and one of the medium (35 cm) wires
to connect the ultrasonic sensor to port 4 on the NXT.
Important: Route both wires through the frame
as shown, to keep them out of the way.

56.   The track connects to the NXT/lift assembly using the two pegs
already on the NXT side.

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