This is my first instructable, so please bear with me. I am fifteen and I do the robotics competition FRC, Vex, and I mentor for two FLL teams. I designed this robot for 7-10 year olds beginning with the FLL competition to help them start with building and programming. Although I think this can help anyone to get into robotics. The logic to the NXT is fairly cheap,  and legos are readily available at any toy store. The programing laguage that comes with it is labveiw and it is super easy to use because it is an image based laanguage. If you want more of a challenge, you can use robotC, a text-based language, it is free for a trial period and can be purchased at $50 for a year of licencing.   This project can easily be build in ten minutes and programmed in twenty. If you need any help with programming in either language or building it, I would be happy to help!

The parts you need to build the core of the robot are:

1 - NXT Brick
2 - NXT Wires
2 - Motors
1 - 13 Long Studless Beam
2 - 6 Stud Long Axles
2 - Wheel Hubs
2 - Fat Wheels
2 - Angular Beams
2 - Double Connector Pegs
2 - Axle Extenders
2 - Big Spacers
2 - Pegs With Axle Connectors
4 - Corner Connectors

Colors don't always have to match, but its nice if they do.

Step 1: Building the Wheels

First, put the axle connector on the end of one of the axles, this piece is so that the wheel cant slip off while turning. These are useful because you can connect things to the end of them(you can also use the thin spacers that fit into a recessed space in the hubcap).  Now slip the wheel onto the hubcap and slide the axle through the wheel. On the other side, slide on a spacer so that the wheel dose not rub up against the body of the robot, this extra friction slows it down and causes inconstant runs of your robot. You will only need to make two wheels because a robot only needs three things touching the ground to be stable, the third will be a skid we build in the next step.

Step 2: Supports

Now we are going to build the supports for your robot. Take one of the angled connectors and put it at the very end of one of the angled beams. You need to make two like this. Next, you need to make the motor assembly by putting the angular connector near the output with the extra pegs facing the orange. On the same side, snap in a double peg into the pegs farthest from the output. You will need to make a second one mirrored from the other, like in the last picture.

Step 3: Completing the Basic Bot

Now you need to put the skids at the top and bottom to the NXT brick, it may take a small amount force to get them in. If you have a rechargeable battery you can just slip off the intruding beam and charge it.  Now you need to connect the motor modules so that they are in the center of the robot and slide on the wheels, if the motors are new it may be hard to slide the axles all the way through. It should be able to rock back and forth on its wheels. Now put the last beam onto angled connectors. This will help keep the motors from wiggling around. Motor wires need to be plugged into the ports labeled A,B, or C. To keep the wires from getting in the way use rubber bands and pegs to hold them close to the motors and body of the robot. 

Congratulations on your new robot!

Step 4: Ultrasonic Sensor

The Ultrasonic Sensor is able to detect an object and measure its proximity in inches or centimeters. It does this by emitting an inaudible high-frequency sound wave which bounces off a surface and returns to the sensor. Then, using the amount of time it takes for the wave to return to the sensor, the distance to the object can be figured out by a few equations the NXT does for you. It then gives you a nice value in centimeters or inches.  This allows the robot to detect object without even touching them.

Adding an ultrasonic sensor is simple and requires few parts.  If you build the sensor module as in the pictures and you will be able to add a line sensor also .The sensors need to be plugged into ports labeled 1-4. The default port for the ultrasonic sensor is 4.

Step 5: Light Sensor

Light sensors can detect the amount of ambient light so that the robot can tell if you turn on a light and cause it to run away or fight! They also are useful because they can generate light and be a signal or light up things in front of the robot for night time operation.  They also can be used to follow a black line on a white surface by sensing the difference in the amount of reflected light.

If you would like to build more robots there are great projects on nxtprograms. Also if you are 9 -14 you should check out if you have any FLL teams in your area or start one! If you are in middle or high school you should look at the Vex building system and their newest competition Sack Attack. Also you should check out Tetrix, but I prefer Vex because they have more parts that are able to be modified. This is mainly for high schoolers, but I joined it in middle school, so it can be for anyone. Its called FRC First, and it allows for almost any building materials as long as the robot dose not cost more than a few thousand dollars and the whole robot cannot weigh more than 120 pounds. A great website for robotics is Chief Delphi.

I hope that you have a great time with robotics, at least as much as me!

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