Tank Tread Full Extension - LEGO Education

Tank Tread 

TETRIX ® Add-On Extensions 

Tank Tread Overview 

In this extension, a tank tread will be assembled and attached to the Ranger Bot. The Ranger Bot will be programmed to move 

forward until it detects an obstacle in its path with the ultrasonic sensor. It will then rotate 180° in place and repeat the process. 

Estimated Time: 90 minutes 

Preparation: 

• Clear the workstation. 

• Organize the TETRIX ® and 

MINDSTORMS ® sets. 

• Organize the TETRIX Tank Tread Kit 

• Charge the TETRIX and NXT 

batteries. 

Building Objectives: 

• Learn how to use elements from the 

TETRIX Tank Tread Kit (tank tread 

chain links, tank tread idler wheels, 

tank tread sprockets) 

• Learn how to incorporate 

the TETRIX tank tread into a 

MINDSTORMS with TETRIX robot 

Materials: 

• Completed Ranger Bot from 

Lesson 3 of the TETRIX Getting 

Started Guide 

• TETRIX Education Base Set (739143) 

• LEGO ® MINDSTORMS ® Education 

NXT Base Set (979797) 

• TETRIX Tank Tread Kit (736468) 

• Software (ROBOTC ® or LabVIEW 

for LEGO MINDSTORMS) installed on 

each computer 

Programming Objectives: 

• Learn to program a robot to react to 

a detected object in its path 

• Use an ultrasonic sensor to detect 

objects 

• Set threshold values to use when 

reading sensor values 

• Use While Loops and Case 

structures 

Resources: 

• Engineering Journal Worksheet 

• Tank Tread Extension Overview 

• Tank Tread Extension Building 

Guide 

• Tank Tread Extension 

Programming Guide 

• Tank Tread Extension Reference 

Guide 

• Tank Tread Extension Sample 

Program 

• Tank Tread Extension - How It 

Should Work video 

• Tank Tread Extension 3-D Model 

Best Practices: 

Be sure to review the General Best Practices Guide in the Introduction section of the TETRIX Getting Started Guide. 

Building 

• Note that the Bracket Switch Mount and On/Off Switch need to be moved from where they were placed in Lesson 2 in 

order to incorporate the tank tread. 

• The DC Drive Motors and motor mounts will need to be moved from where they were placed in Lesson 2. 

• The 3” Wheels added in Lesson 2 will be replaced with tank tread sprockets and the Omni-wheels will be replaced with 

tank tread idler wheels. 

Programming 

• Ensure that the sensors are connected to the correct ports. Consult the wiring diagram in the Lesson 3 Building Guide 

for the proper configuration. 

• Because different sensors may have different values for the same objects, the threshold value of the ultrasonic sensor 

may need to be changed and tested. 

• Note that the wait function uses milliseconds. 

• Note that for debugging purposes, the NXT Brick displays the sensor values when running the provided sample program. 

• Try to keep the code linear and well organized. This makes the code much easier to follow and debug. 

1



Tank Tread Building Guide 

Start with the build completed in Lesson 3 of the TETRIX® Getting Started Guide. 

Steps 1 - 7 and 13 involve removing elements from the model. Some of them will be reattached later. 

Parts to be Removed 

Step 1 

1x Switch Plate 

Assembly 

4x 1/2" SHCS 

4 x Kep Nut 

Tips 

• Take care to ensure wires don’t get tangled. 

• The switch plate can remain dangling and unattached at this point. 

2





Step 2 

1x Motor Assembly 

with Drive Wheel 

2x 1/2" SHCS 

2x Kep Nut 

Tips 

Make sure to disconnect the wire from the motor before removing it. 

3





Step 3 


with Drive Wheel 

2x 1/2" SHCS 

2 x Kep Nut 

Tips 

Make sure to disconnect the wire from the motor before removing it. 

4





Step 4 

2x Omni-wheel 2x Axle Hub 2x 100mm Shaft 8x 1/2" SHCS 4x Bronze Bushing 2x Shaft Collar 

Tips 

• Be sure to keep the shaft collar and bronze bushing in a safe place when removing the wheels. 

5





Step 5 

1x Servo Controller 2x 3/8" BHCS 2x Kep Nut 

Tips 

• The 5/64” hex key will need to be used to remove the Servo Controller 

• Make sure to disconnect the wire that connects the Servo Controller to the DC Motor Controller 

6





Step 6 

4x 3-Module Connector Peg 

with Friction 

Tips 

• Set the pegs aside in a safe place. They will be re-added later. 

7





Step 7 

1x NXT Mount 

Assembly 

Tips 

• Do not disassemble the LEGO ® elements that are used as the mount. 

• Set aside the whole assembly, as it will be re-added later. 

8




Parts Needed 

Step 8 

1x Switch Plate 

Assembly 

4x 1/2" SHCS 

4 x Kep Nut 

Tips 

• It may be necessary to rearrange some wires or unwire and then rewire the switch to move the plate to the rear of 

the robot. 

9




Parts Needed 

Step 9 

2x 32 mm Channel 4x 1/2" SHCS 4x Kep Nut 

Tips 

• Make sure to put one channel on the very end and the other in the middle of the other two channels. 

10




Parts Needed 

Step 10 

2x 32 mm Channel 4x 1/2" SHCS 4x Kep Nut 

Tips 

• Make sure that the channels on both sides of the robot are aligned. 

11




Parts Needed 

Step 11 

6x Idler Wheel 6x 100mm Shaft 24x Bronze Bushing 12x Shaft Collar 6x 3/8" Axle Spacer 

Tips 

• Add an idler wheel, as shown above and then repeat for the remaining five channels. 

12




Step 12 

Tips 

• Tighten the set screw to couple the shaft collar with the axle, keeping everything in place. 

13





Step 13 

2x 3" Wheel 

8x 1/2" SHCS 

Tips 

• Remove the four screws and set them aside to be used in the next step. 

• Remove the wheel from the motor, but do not remove the motor hub. 

• Repeat for the other motor that was removed. 

14




Parts Needed 

Step 14 

2x Tank Tread 

Sprocket 

8x 1/2" SHCS 

Tips 

• After adding the sprocket, use the four screws that were set aside in Step 13 to fasten the sprocket to the motor hub. 

• Repeat for the other motor. 

15




Parts Needed 

Step 15 

2x 1.5" SHCS 


with Sprocket 

Tips 

• Note that the motor assembly is NOT to be mounted directly above the middle idler wheel. 

• Be sure to use the longer 1.5" screws to reach all the way through the channel. 

16




Parts Needed 

Step 16 

2x 1.5" SHCS 


with Sprocket 

Tips 

• Note that the motor assembly is NOT to be mounted directly above the middle idler wheel. 

• Be sure to use the longer 1.5" screws to reach all the way through the channel. 

17




Parts Needed 

Step 17 

1x Servo Controller 2x 3/8" BHCS 2x Kep Nut 

Tips 

• Be sure to use the smaller 3/8" screws. 

• Align the servo controller in the same orientation as the DC motor controller. 

• Daisy chain the two controllers. 

18




Parts Needed 

Step 18 

1x NXT Mount 

Assembly 

Tips 

• Slide the NXT Brick and its mount into place. 

• Note that it is now facing the opposite direction from how it initially was. 

19




Parts Needed 

Step 19 

4x 3-Module Connector Peg 

with Friction 

Tips 

• Use the four pegs that were set aside in Step 6. 

20




Note: This step is optional. If the rubber traction elements are not available, continue without them. 

Parts Needed 

Step 20 

148x Tank Tread Chain Link 

148x Rubber Traction Element 

Tips 

• Inserting the rubber elements will add additional traction to the treads. 

21




Parts Needed 

Step 21 

148x Tank Tread Chain Link 148x Rubber Traction Element 

(Optional) 

Tips 

• Use 74 links per side to assemble the two treads. 

22




Step 22 

Tips 

• Loosen one of the motor mount screws in order to rotate the motor within the hub. 

• This will allow the treads to slide on. 

23




Step 23 

Tips 

• Carefully slide the treads onto the set of idler wheels and the tank sprocket that is connected to the DC motor. 

• Make sure the sprocket gets firmly interlocked with the tank tread. 

• It may be required to rotate the mounted motor to provide more slack. 

24




Step 24 

Tips 

• This step introduces more tension in the treads and will prevent the treads from slipping off. 

• After this is done, be sure to tighten the motor mount screw to prevent the motor from slipping in its hub. 

25




Final View 

26



Tank Tread Programming Guide (LabVIEW for LEGO ® MINDSTORMS ® ) 

Introduction: 

In this guide, the Ranger Bot with Tank Tread will be programmed to move forward until it detects an object within 30 cm. 

It will then rotate 180º in place and repeat the process. This guide is for use with the LabVIEW for LEGO ® MINDSTORMS ® 

programming language. 

Review: 

• To review the basic principles of connecting to the NXT Brick and configuring LabVIEW for LEGO MINDSTORMS for use with 

various sensors and motors, review the Programming Guides and Tutorial Videos from Lessons 2 and 3 in the TETRIX ® Getting 

Started Guide. 

• To review the basic principles of programming in LabVIEW for LEGO MINDSTORMS, review the Programming Guides and 

Tutorial Videos from the Line Follower Programming Extension in the TETRIX Getting Started Guide. 

• These materials contain detailed information about how to use the Schematic Editor and how to create the structures, 

functions, constants, and wires that are presented in this guide. 

• This program makes use of the Screen Update SubVI, provided on the TETRIX ® Getting Started Guide Resource page. This 

function uses the NXT to display custom text as well as light and ultrasonic sensor readings. 

• Use these steps to add the function to the program: 

a. Within the block diagram, right-click to bring up the Functions palette and choose Select a VI. 

b. Then navigate to where the Screen Update SubVI is saved. 

Note: If the Screen Update SubVI has not been saved on the computer in a specific location already, download it from the 

TETRIX Getting Started Guide by navigating to the Resources tab and selecting the Screen Update SubVI Program 

(LabVIEW for LEGO MINDSTORMS) button. 

c. Once the Screen Update SubVI has been located, open it and place it on the block diagram. 

Getting Started: 

1. Create a new Ranger robot project and name it Tank Tread. 

2. Check the Schematic Editor to make sure all the motors and sensors match the robot’s hardware setup. 

3. Create a new VI. 

4. Create a While Loop that will encase the code. 

5. Check if there is an object within 30 cm, and output sensor values to the screen. 

a. Use the Screen Update SubVI to read the ultrasonic sensor and automatically output sensor values. 

b. Use a Less? function to compare the sonar value (X terminal) with a constant value of 30 (Y terminal). 

27




6. Use a Case structure to execute code depending on the result of the comparison. 

a. Create a Case structure inside the While Loop and wire the output of the Less? function into the Case selector. 

7. If the robot detects an object within 30 cm, it will output a message to the screen, and then rotate 180-degrees. 

a. First, drag a Screen Update SubVI into the True case of the Case structure. 

b. Create 2 string constants for the “Line 5 Text” and “Line 6 Text” terminals. 

c. The first constant should say “Object Detected!” and the second one should say “Turning…”. 

d. Next, place a Move Motors function in the Case structure. 

e. Create a motors constant and re-wire it so that it is outside of the Case structure. 

f. Expand the constant and select “Left Wheel” and “Right Wheel”, respectively. 

g. Now, wire a constant of 30 into the power terminal for the left wheel and a constant of -30 into the power terminal for 

the right wheel. 

h. Finally, add a Wait For Time (msec) function and add a constant of 1700 (this turn duration may vary for each robot). 

i. Be sure to wire all NXT terminals in sequence. 

8. If no object is detected, the robot simply drives forward and a message is output to the screen. 

a. First, use the Screen Update SubVI to output a string of “No Object Detected” on line 5. 

b. Next, use a Move Motors function and wire it up to the motors constant. 

c. Now, create a constant of 15 and wire it into both power terminals. 

d. Finally, wire up the NXT wires. 

28




9. Finally, the program must stop if one of the NXT buttons is pressed. 

a. Drag a Read NXT Buttons function into the While Loop. 

b. Wire the Boolean value from the “Yes/No” terminal into the conditional terminal. 

29



Tank Tread Programming Guide (ROBOTC ® ) 

Introduction: 

In this guide, the Ranger Bot with Tank Tread will be programmed to move forward until it detects an object in its path. It will 

then rotate 180º in place and repeat the process. This guide is for use with the ROBOTC ® programming language. 

Getting Started: 

1. To start the program, type the Main Task function, followed by an opening brace. 

task main() 

{ 

2. Declare four integer variables as seen in the code below. Set them to values shown. Beside each variable, there are two 

slashes (//) followed by what that variable is representing. These mark a comment. Notice that comments appear in green 

when code is typed into ROBOTC. 

Note: A comment is not part of the code that the NXT Brick will execute, but it helps the programmer by allowing the 

addition of notes to describe what has been done. 

int dValue = 15; 

int tValue = 30; 

int threshold = 30; 

int sonarValue; 

// Forward drive motor power 

// Turning motor power 

// Ultrasonic sensor threshold value 

// Ultrasonic sensor reading 

3. Add a While Loop to make the contained code repeatedly execute without pressing any of the buttons on the NXT Brick. 

while(nNxtButtonPressed == kNoButton) 

{ 

4. Add a conditional statement that checks if the ultrasonic sensor reading is greater than or equal to the threshold variable. 

In this case, set both motors’ power to the dValue variable. This will make the robot move forward in a straight line. 

if(SensorValue(SonarSensor) >= threshold) 

{ 

motor[motorD]= dValue; 

motor[motorE]= dValue; 

5. Update the display using the NXT write to screen command to show the current ultrasonic sensor value, as well as a message 

that reads “No object detected.” Also add a closing brace to the statement. 

The NXT write to screen command requires three pieces of information, called parameters, in order to write both text and a 

variable to the screen: 

i. The line number. 

ii. The text (in quotations) which includes a display variable caller. 

Note: In this case, %d is the display variable caller. In the place of %d, an integer variable is displayed on the screen. 

iii. The variable name. 

30




This information is inside the brackets beside the command, separated by commas. 

sonarValue = SensorValue(SonarSensor); 

nxtDisplayTextLine(2, "Sonar Value: %d", sonarValue); 

nxtDisplayCenteredTextLine(4, "No object"); 

nxtDisplayCenteredTextLine(5, "detected."); 

} 

6. If the statement above is not True, meaning the sensor reading is below the threshold value, the robot should rotate. Add an 

else to the Case structure and set both motors’ power to the tValue variable. One of these must be set to negative for the 

robot to turn. 

else 

{ 

motor[motorD]= tValue; 

motor[motorE]= (tValue*-1); 

7. Update the display to read “Object detected! Turning…” 

nxtDisplayCenteredTextLine(4, "Object detected!"); 

nxtDisplayCenteredTextLine(5, "Turning..."); 

8. Add a Wait command, allowing the robot to turn for 1700 ms. This value can be changed when the program is tested to 

make the robot turn exactly 180°. Also, add a closing brace to the else statement. 

wait1Msec(1700); 

} 

9. Add a closing brace to end the infinite While Loop in Step 3. 

} 

10. Add a closing brace to end the program. 

} 

31




Completed Code: 

task main() 

{ 

int dValue = 15; 

int tValue = 30; 

int threshold = 30; 

int sonarValue; 

// Forward drive motor power 

// Turning motor power 

// Ultrasonic sensor threshold value 

// Ultrasonic sensor reading 

while(nNxtButtonPressed == kNoButton) 

{ 

if(SensorValue(SonarSensor) >= threshold) 

{ 

motor[motorD]= dValue; 

motor[motorE]= dValue; 

// Run while NXT buttons not pressed 

// If the ultrasonic sensor value is greater than 

or equal to the threshold, set motor power 

to dValue 

} 

sonarValue = SensorValue(SonarSensor); 

nxtDisplayTextLine(2, "Sonar Value: %d", sonarValue); 

nxtDisplayCenteredTextLine(4, "No object"); 

nxtDisplayCenteredTextLine(5, "detected."); 

else 

{ 

motor[motorD]= tValue; 

motor[motorE]= (tValue*-1); 

// Update sonarValue variable with current 

sensor value 

// If the value is less than the threshold, 

turn the robot 

nxtDisplayCenteredTextLine(4, "Object detected!"); 

nxtDisplayCenteredTextLine(5, "Turning..."); 

wait1Msec(1700); 

} 

} 

} 

// Turning duration 

32



Tank Tread Reference Guide 

Expectations 

Technology: 

• Develop an understanding of the core concepts of 

technology. 

• Develop and produce a product or system using a 

design process. 

• Develop an understanding of the engineering 

design process. 

Science: 

• Implement a proposed solution. 

Mathematics: 

• Understand measurable attributes of objects and the 

units, systems, and processes of measurement. 

Engineering: 

• Redesign what has been created. 

• Test and evaluate. 

Classroom Organization and Setup 

1. Set up a projector with a computer to show the Tank Tread Extension - How It Should Work video. 

2. Provide a copy of the Engineering Journal worksheet for each student. 

3. Ensure that the NXT Brick and TETRIX ® batteries have been adequately charged. Consult page 55 of the Lesson 2: 

Ranger Bot Movement Reference Guide for more detailed information. 

4. Obtain various objects to use as obstacles for the robot. The ultrasonic sensor detects objects with a flat surface much 

more effectively than those with a curved surface, so obstacles with flat surfaces are recommended. A wall can also be 

used as an obstacle for this activity. 

Lesson Progression 

1. Review the tasks and concepts from Lessons 1-3 of the TETRIX Getting Started Guide. 

2. Watch the Tank Tread Extension - How It Should Work video. 

3. Follow the Tank Tread Extension Building Guide to create the Tank robot. 

4. Download the Tank Tread sample program or create the program by following the Tank Tread Programming Guide. 

Note: For more information about how to do this, watch the Program Deployment video or consult the Program Deployment 

Programming Guide from Lesson 3. 

5. Follow the Tank Tread Programming Guide to have the robot move forward until it detects an object, at which point it turns 

around and repeats the process until a button on the NXT is pressed. 

6. Test the program and compare it to the way the robot behaved in the How It Should Work video. 

Frequently Asked Questions 

Q: Is it possible to view the sensor values while debugging programs? 

A: The sensor values can be viewed on the screen of the NXT Brick. The sensor values can also be viewed in LabVIEW for 

LEGO ® MINDSTORMS ® or ROBOTC ® if the robot is connected to the computer. 

Q: Why is a False Boolean constant not used as the stop condition for the main loop? 

A: By using the Read NXT Buttons function, we can safely stop the robot from executing the code and properly shut down the 

motors by pressing a button on the NXT Brick. 

Q: Why does the robot turn too close to or too far from the obstacle? 

A: The threshold value for the ultrasonic sensor may need to be adjusted in order for the robot to turn at the desired distance 

form an object. Different sensors and robots may require slightly different values for the threshold. 

33



Tank Tread Reference Guide 

Innovation and Inspiration 

Suggestion #1: “How does the tank tread affect how the robot turns?” 

• Measure and record the robot’s turning radius with the tank tread and with wheels. Do several tests with the motor power 

set to different values. 

• Discuss the differences and determine reasons for these differences. 

Suggestion #2: “How does the location of the motors affect the axis around which the robot turns?” 

• Try shifting the position of the motors on the robots. 

• Discuss how this affects the centre axis of the turn. 

• Discuss the differences between the turning axes in the tank tread robot vs the Ranger bot. 

Suggestion #3: “Towing challenge” 

• Stage a competition to pull different weights with the robot. 

• Try pulling weights on different surfaces. 

• If the rubber inserts are available for the tread, try pulling weights with or without the inserts. 

• Investigate ways to modify the weights to allow them to be pulled more easily. What happens if the weights are placed on 

a piece of paper and the piece of paper is firmly attached to the back of a robot? 

• Discuss which configuration allowed the robot to pull more weight. Why is this? 

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Tank Tread Full Extension - LEGO Education

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