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Claw Striker
Building: Advanced
Program: Expert

Building Instructions


Start by building the 3-Motor Chassis.  Click the picture for building instructions.

Building Instructions




Important: You will need to rotate the black bushed long peg (inserted in step 17) so that the axle hole is upright before the part shown below will insert into it.


Plug the wire for the ultrasonic sensor into port 4 on the NXT, routing it through the chassis brace as shown to keep it out of the way.



Claw Striker Programming

The Claw_Strike program will make the Claw Striker try to automatically find a target and then strike it.

  1. Place the Claw Striker and a target big enough for it to see in the middle of a large open area on a hard smooth floor (doesn't work as well on carpet).  The target should be no more than about 2 feet (60 cm) away.

  2. Run the Claw_Strike program, then step back so the robot will not see you instead.  There are three warning beeps at the beginning of the program to give you time to back away.

  3. The Claw Striker will try to locate and strike the target as follows:

    1. Turn around in a slow pivot turn looking for the target with the ultrasonic sensor

    2. Sound a beep when the target is first seen (leading edge)

    3. Keep turning until the trailing edge of the target is found, then sound another beep.

    4. Turn back half of the angle between the leading and trailing edges to try to point straight at the center of the target.

    5. Measure the distance to the target with the ultrasonic sensor, then go forward or back up as necessary to adjust the range to 35 cm, which is the length of the claw whip.

    6. Strike with the claw whip


  • The process of finding the target and driving to it is not completely accurate, so try several different starting positions to find some that work well.  Also, some objects are seen by the ultrasonic sensor better than others.  Try experimenting with different targets. 

  • Although the 3-Motor Chassis used in this design has a pivoting castor wheel in the rear so that the chassis can turn well on carpet, the castor wheel introduces some inaccuracy into the turns and positioning.  Try replacing the castor wheel with a hard plastic wheel that can only roll forward, or perhaps just a LEGO beam for the rear of the robot to slide around on, and see if this makes it any more accurate.

  • The Claw_Strike program is an example of an "autonomous" (not remote controlled) control program.  You could also try programming the Claw Striker to respond to a remote control, using ideas similar to the Hammer Car, the Dial Remote Control, or the Claw Car with Game Controller.  You will need to modify these programs slightly to work with the Claw Striker.

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