Moving the Tribot

Objective

To move the Tribot forward, backward, left and right.

Final Program

Getting Started

As in the first program launch Labview and open a Blank VI and switch to the Block Diagram window. Set up the Function palette and have the NXT Toolkit pinned on. Make sure your window looks as follows :

Figure : Getting Started

Running the Motors

Forward

Go to Addons -> NXT Toolkit -> NXT Library -> Output.

Figure : Choosing Output from NXT Library

Now, place a Sync Time on the Block Diagram to command the Tribot to move forward.

For this, do the following on the Sync Time block :

• Right click on the Time (500 ms) terminal.
• Select Create -> Constant from the dropdown menu.
• Enter a value of 3000 in the field. This is the time in milliseconsd that the motors will run.
• Right click on the Power (75) terminal.
• Select Create -> Constant from the dropdown menu.
• Enter a value of 50 in the field. This is the power (of a maximum of 100) at which the motors will operate..

This would make the Tribot move forward for three secondes with a a power of 50% and stop. The final block should look like this :

Figure : Block for moving the Tribot forward for 3 seconds at 50% power

Note : The panes that you see on the top, left and bottom of the block with the words Duration, Power and Travel Forwards 3 s are the comment panes. To insert a comment pane, just double click anywhere inside the Block Diagram window, and you will get a field into which you can type the comments.

Backward

The next block is to command the Tribot to move backwards. To do this, we do not have to do the whole process again. All we need to do is :

• Copy the first block and move it to the right of the existing block. This can be done in two ways :
  1. Click and drag a selection rectangle around the Sync Time block (including the boxes with the constants created) and go to Edit -> Copy and to paste it, go to Edit -> Paste. Move the new block to the right of the existing block.
  2. Click and drag a selection rectangle around the Sync Time block (including the boxes with the constants created) and hold Ctrl key while dragging the block to the right. Release the mouse button to place the copied block
• Right click on the Direction (T:Fwd) terminal and Create -> Constant. Change the constant to F by clicking on it.

This done, the Tribot will get back to its starting position.

Figure : Copying a block (Method 1)

Figure : Copying a block (Method 2)

Remember : In case you are not able to find the terminals properly, make sure you use Context Help to figure out what the terminals are and where they are on the block.

Left Turn and Reverse Left Turn

In this section, you will add the blocks to make the robot turn left and then do a "reverse" left turn.

This is very similar to the earlier blocks, except that, here you let the motors run for a specific distance, rather than a duration. For this, choose the Sync Distance block from the Output sub menu in the NXT Toolkit on the Functions Palette.

For the left turn

• Create a Constant on the Distance in Degrees(360) terminal and set the value to 200.
• Create a Constant on the Power terminal and set the value to 50.
• Create a Constant on the Steering terminal and set the value to -100.

For the reverse left turn

• Copy the previous block and Create a Constant on the Direction (T:Fwd) terminal and set it to F.

Once this is done, you should see these two blocks to look like this

Turning while moving

While the last two blocks make the Tribot turn abruptly, the following blocks will make the Tribot make a smoother turn, along an arc of a circle, much like a real vehicle.

The blocks for this task are the same as the ones used in the last section, except, make the following changes after making copies of the previous blocks to the right of the existing blocks.

• The value of the Constant on the Steering terminal should be -10.
• The value of the Constant on the Power terminal should be 90.
• The value of the Constant on the Distance in Degrees terminal should be 1440.

Make sure the second block of these two has the Direction (T:Fwd) terminal set to F.

Once done, it should look like this

So the program, at this stage should look like this

Connecting the blocks

Now that all the blocks are ready for our program, the next task is to let the program know the sequence in which the tasks are to be executed. For this, each block has two special terminals called the Sequence Flow In terminal and the Sequence Flow Out terminal. These two terminals provide the "direction" of the program. Use the Context Help to find out where the Sequence Flow In and Sequence Flow Out terminals are on the Sync Time and Sync Distance blocks.

To do this, click on the Sequence Flow Out terminal of the first block (note that once you take the cursor near this terminal, the cursor changes to a wire spool) and drag a wire and when you reach the Sequence Flow In terminal of the second block , click again to make the connection.

Repeat this for all the blocks until you see this :

Now, the program is complete!

Saving and Downloading to the NXT

Follow these instructions from the previous program to save the program with an appropriate name.

Download the program on to the brick in the following way.

• Open the NXT Terminal.
• Choose Compile and Download from the window, make sure that the brick is connected and switched on.Wait till the beep to confirm program download
• Disconnect the brick from the cable, place the Tribot on level floor and run the program on the NXT : My Files ->Software Files -> <your program>

The Sync Distance and Sync Time blocks are made in such a way that they control the Right Motor through Port B and Left Motor through Port C. Make sure the Tribot has motors connected in this fashion.

Challenge

The challenge is to create a program that would take a path as shown in Pg 13 of the attached file on this page below.