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The next buttons to add to the interface were those to control the opening and closing of the grippers. To do so, I once again used the turn command provided by Fokke. However, in using this command, I got unexpected results. I had programmed the motor controlling the grippers to open and close 90 degrees. To my surprise, this caused the grippers to open too wide. To resolve this issue, I used trial and error. As it turns out, the degrees the motor controlling the gripper must turn works best at 60 degrees. With the addition of the open and close gripper buttons, the interface now provides the user with all the options they need to use the robot to grab a ball off a stand and then place the ball back on the stand. In addition, the interface can be used to perform other tasks with the robot as well.

Having the user select the amount of degrees to turn proved to be quite a challenging process. To control the degrees the robot turns, I thought it would be best to use a textbox in which the user typed in the degrees. In Fokke’s tutorial, he provided a command to turn the robot. However, when you type in the amount of degrees, for example 90 degrees, the robot does not turn that amount. Instead, the motor turns 90 degrees but the robot does not due to slipping. To overcome this issue, I had to determine the amount of degrees a motor must spin in order to turn the robot the correct amount of degrees. After much trial and error, I found that the amount of degrees the user types into the textbox has to be multiplied by about four. In addition, for each 90 degree interval, the amount of degrees the user types in the textbox has to not only be multiplied by four, but an additional amount of degrees has to be added to the number. Because of this, I had to create an if/then statement for each 90 degree interval, up to 360 degrees. During the process of figuring out how to get the robot to turn, I learned how to write an if/then statement, declare a global variable, and convert a string in to a number in C#.

Having learned how to use the motor commands provided in Fokke’s tutorial, it is time to start learning different aspects of C# and create an interface for running the robot.  To begin, I have placed four buttons on the interface that I plan to use to move the robot forward, backwards, left, and right.  In addition, I have included a brake button to stop the robot.  Working with the forwards and back commands, I have realized that the robot tends to move in a curved direction even though both motors are running at the same speed.  To overcome this issue, I have slowed the motor speed to about 50%.  Although not totally perfect, this seems to have greatly mitigated the problem.  My first attempt at turning the robot called for using the turn command and setting the motor speed to 50%.  In doing so, the user would have to hit a brake button to stop the robot after it turned the desired amount.  However, when trying this method out, I found it extremely difficult to precisely control the amount the robot turned.  Currently, I am trying to develop a way for the user to control the amount of degrees the robot must turn.  In order to accomplish this I will need to learn more about how to write a C# program.

Now that I am able to establish a Bluetooth connection with the NXT brick and I am able to get the robot to turn when I hit a button on the form, it is time to explore how to get the robot to move forward (i.e. have two motors run simultaneous while clicking only one button).  At first, I tried to use the “coast command” that Fokke included in his tutorial.  However, I was unable to get the robot to respond to this command.  Instead, I used the turn command and set the amount of degrees for the motor to turn to zero.  In the click event procedure for the forward button in my form, I included the turn command (degrees set to zero) for the two motors connected to ports B and C on the NXT.  When I ran the application and clicked the button, the robot moved forward.  I realized, however, that I had no way of stopping the robot.  I actually had to turn off the NXT brick to get it to stop.  I decided to use the “brake command” to stop the robot.  To do this, I added a new button to the form named “stop” and included the brake command for both motors in the button’s click event procedure.  Finally, following the same process I used to get the robot to move forward, I made a new button named “back” that moved the robot backwards. 

Here are some of the issues I ran into when following Bran Fokke’s tutorial and how I overcame them.

Problem 1: The “click event procedure”

As it turns out, I had not correctly written the click event procedure for the button I added to my form. Initially, I had nested two click event procedures within each other. Additionally, I had named my button something different than what Fokke had named his in his tutorial. As such, I started debugging my program. After some time, I was able to figure out how to add a click event procedure to a button in a form using C#. Again I ran the program. This time there was no errors when I executed it. Everything seemed to be perfect. Then I tried to click the button, expecting the robot to turn, on my form and nothing happened. This was a little frustrating for me because I did not know where to go to next.

Problem 2: The “AutoPoll property”

I started trying to find the error in my program by rereading Fokke’s tutorial. However, it appeared I had followed it correctly. In attempt to fix my problem, I decided to make sure each motor was assigned to the right port on the NXT brick and that I had chosen the correct COM port. Everything was set up right. I then looked at the program Fokke provided in the QuickStart.zip, which can be found in the download section on Fokke’s website, for inspiration. What I found out is that in his NXTBrick component he had set the AutoPoll property to true. So I went back to my program and set it to true also. To my excitement, I was able to click on the button in my form and the robot turned clockwise. Wow! Awesome! Great! Spectacular!

Knowing I was able to connect to the NXT brick using Bluetooth, I moved to the next tutorial provided on Bram Fokke’s website.

Working with the C# commands was quite an interesting experience for me, since this was the first time I have used C#. Although I never have used C#, I do have some experience with Visual Basic. Using this knowledge, I was able to get the basic idea of what Fokke was saying in his tutorial. Adhering closely to Fokke’s instructions, I began adding the motor commands to my program. Seemingly when everything seemed perfect, I ran my program. To my dismay, I got numerous errors when I tried to execute the program. I had hoped one of the motors on my robotic car would have moved forward (thus turning the robot), but it did not.

Using Chandima’s  tutorial on “Installing NXT# components in Visual Studio 2005,” I was able to place the necessary components in the toolbox to get started with Bram Fokke’s beginning tutorial on using Bluetooth to connect to the NXT brick. 

Once the components were correctly added to the toolbox, I was able to use the commands provided in Fokke’s tutorial to establish a connection with the NXT brick.  This is a major stepping stone in this project, as we finally have a method that allows us to routinely connect to the NXT brick using Bluetooth.

 

Wow, we have come a long way since the beginning of this project.

 

This is an ongoing series of screencasts on how to use Bram Fokke’s NXT# components to control the NXT over Bluetooth. This will be just a test to see if the computer can connect to the NXT over Bluetooth. I’m following the instructions provided on Bram’s site to create a simple C# application that connects to the NXT. Each step outlined below has a corresponding screencast, and I will keep adding to it. Note that I’m a complete novice to C# and have just ordered Learning C# by Jesse Liberty and Brian MacDonald. So, if I’m taking the long route on any of these steps, please post a comment and I’ll fix it.

1. Pairing the NXT as a slave via Bluetooth in Windows XP.
2. Installing NXT# components into Visual Studio 2005.
3. Creating a new application that connects to the NXT.

I was able to reestablish the Bluetooth connection on three different occasions. Only twice it did not connect. Hopefully the success can continue. One thing I learned is that occasionally you must just shut off the NXT brick and then try and reestablish the Bluetooth connection.

Managed to get iCommand working on MacOSX Tiger 10.4.10 (running on an Intel iMac) after a few hours. I followed the instructions in the README.txt file in iCommand-0.6 folder. The brief, but accurate instructions on how to compile the sample programs using the Eclipse IDE also came in handy. Tony Buser’s instructions on pairing the NXT over a serial port as a slave is a useful reference as well. The iCommand README has instructions for Windows, Linux and MacOSX with several alternative options for each. I’m listing the options that worked for me (mostly a copy-and-paste from the README).

1. Download iCommand (version 0.6 as of this writing) and Unzip the contents into a directory (Desktop is fine).
2. Copy icommand.jar to the Java extensions directory /Library/Java/Extensions/.
3. Download RXTX java binaries for source/Mac OS X and Unzip [rxtx-2.1-7r2.zip (Final) as of this writing].
4. Copy files RXTXComm.jar and rxtxSerial.jnilib (inside the rxtx-2.1-7r2/MACOSX_IDE/ForPackageMaker/install/Library/Java/Extensions folder) to the Java extensions directory /Library/Java/Extensions/.
5. Create the /var/lock directory with the command sudo mkdir /var/lock using he Terminal application (I didn’t find it necessary to create /var/spool/uucp directory and add yourself to the uucp group as indicated in the README).
6. Make /var/lock world writable with the command sudo chmod 777 /var/lock from the Terminal.
7. Pair your NXT and your computer using the Bluetooth setup assistant following Tony Buser’s instructions.
8. Edit the icommand.properties file ( inside icommand-0.6/dist folder), uncomment the line specifying the serial port and set it to the serial port name from step 7. You can edit the file using TextEdit and the port specification would normally be nxtcomm=/dev/tty.NXT-DevB-1 . If you have changed the name of your NXT the port would be something like /dev/tty.YOURBOTNAME-DevB-1 .
9. Copy the icommand.properties file into your home directory (/Users/YourUserName directory).
10. Download and Install Eclipse Classic for Mac OS X (Europa build 3.3.1 as of this writing).
11. Start Eclipse and create a new Java project (File > New > Java Project and give it a name – I called mine robotest). Click on the Finish button when done (see screenshot).
12. Import the icommand sample programs into your project. Expand on your project folder in the Package Explorer and select the src folder. Now choose Import… from the File menu (see screenshot). Expand the General folder and select Filesystem for the Import Source in the resulting dialog box (see screenshot) and click on the Next button. Then select the samples folder inside icommand-0.6 folder in the resulting dialog box by clicking on the Browse… button. Make sure the checkbox next to the samples folder is checked and click on the Finish button (see screenshot) .
13. Open the RadioControl.java file that is inside the default package in your Eclipse project (see screenshot).
14. Make a simple 2-wheeled robot (or hook motors to port A and B).
15. Make sure the NXT is on and Bluetooth is turned on in the NXT.
16. Compile and run the RadioControl.java program (Shift-Command-F11). The RadioControl application window will open a window (this is a blank window with no UI). The computer will connect to the NXT (bluetooth indicator on NXT will turn into a diamond). Use the arrow keys to move forward, back and turn.

If you get an gnu.io.PortInUseException error it usually means that your application terminated prematurely and the lock file didn’t get cleared. You have to manually delete it before it will work again from Terminal. Go to the /var/lock folder and delete the lock file using sudo rm lockFilename . The lockFilename is something like LK.003.009.014 .

If you have problems connecting to the NXT; delete the NXT device in Bluetooth preferences and pair it again as described in step 7. I find that the computer connects to theNXTalmost instantaneously and command response is near instantaneous as well. This is a very viable way of remotely controlling an NXT.