MAXA Robotics 2011 NXT 2-Motor Car Adapted from Physics by Design, Second Edition, by Barbara Bratzel, College House Enterprises, 2007
TASK DESCRIPTION • The objective of this task is to build a simple NXT two-motor car, which will be used in several projects throughout our study of NXT robotics. • To pass off this task, you may practice it as much as you need to, but will be required to pass it off within 15 minutes whenever you are ready. • The basic instructions are shown on the next few slides…practice this process until you have mastered it!
NXT – top and side view First lets look at the brick itself. Here is a view of the top of the brick, which has the display window and several control buttons. On the side are several holes used to connect beams.
NXT – front view The front of the brick has one USB port on the left side, used to connect to a computer. The A, B, and C ports next to it are OUTPUT ports used to provide power to motors.
NXT – back view The back of the NXT has four INPUT ports, 1, 2, 3 and 4, used to connect to various sensors…touch, sound, light, etc.
NXT – underneath view Six AA batteries go in the under side compartment, as you can see. Unlike the RCX, when replacing the batteries, you can completely remove all six, and then put in fresh batteries. With the RCX, you have to replace each battery one at a time, or risk losing the firmware, which takes about five minutes to download each time it is lost.
NXT – battery pack It is also possible to use a special rechargeable Lithium battery in this underneath compartment, as you can see. However, when the battery pack is used, the brick is taller as you can see below. This must be taken into consideration later on in this task.
Step 1 Let’s build it! First you need two 2X3X6 curved beams, with a black connector and a combination connector (round/crossed) for each beam. Connect them as shown.
Step 2 Now get two NXT motors and connect the two beams.
Step 3 On each side of the brick, in the set of holes towards the front, insert two black connectors.
Step 4 Connect the two beams/motor assemblies to the front end of the brick. Notice carefully that the two views here are not exactly the same. Can you spot the difference? Look very carefully!
Step 4 Did you spot it? You should have noticed two significant differences. The bottom brick is taller than the top brick because it has the battery pack. Because of this, the bottom brick connects one hole higher on the two beams than on the top brick. This was the adjustment alluded to earlier in the lesson.
Step 5 Now it is time to reinforce our construction with braces on the front and the bottom. First find a 9-hole beam and four black connectors, connect them as shown in the top picture, then attach the beam to the front of the two motors as shown in the lower picture.
Step 6 To reinforce the bottom, find a size 8 axle and four spacers, and connect them as shown in the pictures.
Step 7 Time for the wheels! Find two medium size, wide track wheels and two size 6 axles and connect them together as shown. Pay careful attention to which side of the wheel is the inside or outside. Then connect them to the motors as shown in the picture.
All finished! You now have a simple, NXT 2-motor car which will be used for several programming projects. As long as the car runs on a smooth hard surface, it is OK for it to skid on the bottom of the motors. It is also possible to add a special skid plate if necessary, but that is not required in this task.
Time to practice! Practice this construction until you have mastered it and can accomplish it in 15 minutes or less. When you are ready, tell a mentor and you can pass it off. Good luck!