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2/3/11 7:05 PMNXT Robot Arm

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Fun Projects for your LEGO® MINDSTORMS® NXT!

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Robot ArmBuilding:

Program:

Building Instructions

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The two brackets built in this step are used to attach the arm motor to the turntable base. You will need toattach one bracket first, then attach the arm motor, then attach the second bracket, as shown below.



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20Four wires are needed in this step:

1. Use the shortest wire to connect the touch sensor to port 1 on the NXT.

2. Use one of the longest wires to connect the claw motor to port C on the NXT.

3. Use one of the medium-length wires to connect the turntable motor to port A on the NXT.

4. Use one of the medium-length wires to connect the arm lifting motor to port B on the NXT.



Robot Arm ProgrammingUse the program Arm Control for the Robot Arm. This program allows you to control the robot arm usingthe Left, Right, and Enter buttons on the NXT brick and the touch sensor button.

Using The Robot Arm

Pressing the orange Enter buttonon the NXT brick will toggle thecontrols between "Rotate" and"Lift" modes.

In "Rotate" mode, the gray leftand right arrow buttons on theNXT brick will rotate the arm leftand right as long as you hold thebutton down.

http://nxtprograms.com/programs/Arm_Control.rbt



In "Lift" mode, the left and rightbuttons will lift the arm up anddown as long as you hold thebutton down.

Pressing the touch sensor buttonwill make the claw switchbetween grabbing and releasing.

The turntable and lifting arm motors both use gears to"gear down" the motion (decrease speed and increaseforce). You will notice that this keeps you from beingable to turn the motors by hand.

To work around this problem, you can use the handle onthe side of the arm lifting motor to adjust the arm'sup/down position by hand when the program is notrunning. (When the program is running the NXT hasthe electric brakes on the motors and will not allowthem to be turned by hand).

This design does not include a similar lever on theturntable motor. Can you figure out a way to add one?

Challenges

Practice using the controls to pick up and move objects. Here is an example challenge. Place thered and blue balls on tire stands in different locations but both at the correct distance from the armso that the claw will reach it, as shown below. Now try to use the robot arm to swap the positionsof the two balls. What is smallest number of button presses that you think this can be done in?

Think of some mechanical improvements you might make to this design. For example:

Come up with a way to keep the wires out of the way.

Add a lever to the turntable motor (similar to the one on the lifting arm motor) so that you can



turn it by hand to adjust its position when the program is not running.

The claw is designed to be as simple as possible to keep it light weight. However, it would benice if both sides of it opened and closed. Can you come up with a simple way to do this? See the Claw Car project for one idea (that might be too heavy).

Gears are used on the turntable and lifting arm motors to reduce the speed and increase theforce. The gear ratios used are adequate, but the program still needs to used reduced powerto keep the motion from being too fast. It would be better if the gear ratios were even lower. For an expert building challenge, can you figure out a way to do this?

The Arm Control program allows you to control the arm using the buttons. Try making a program ofyour own that controls the arm automatically by itself with a pre-programmed sequence of moves. Here's a big challenge: Can you write a program that will swap the balls as shown in the challengeabove? Francesc X. Alvarez was the first to send me video proof of a working solution. Here is aYouTube video of his solution.

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Copyright © 2007-2010 by Dave Parker. All rights reserved. All project designs, images, and programs are protected by copyright. Please see the usage policy.

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