1. Robofest 2007 NXT Programming Workshop Jan
Robofest NXT Programming Workshop Jan. 27, 2007 CJ Chung Associate Professor of Computer Science Lawrence Tech University
chung

2. Assistant
Joe Long
chung

3. Agenda Intro to NXT Construction of NXT basic model: TriBot
Intro to NXT programming Language: Move, Loop, Sensors, Wait, Display, Switches, and My Blocks
9 Class Missions (somewhat related to the Robofest Game 2007, Miner Rescue)
Programming Tips
chung

4. chung

5. Robots to be used: TriBot
Robo Center, Quick Start Vehicle or small booklet in the retail version box
Left motor: A
Right motor: C
chung

6. Alternative guide to build the TriBot (Retail Version)
Launch the software, Mindstorms NXT
Robo Center -> Vehicles Quick Start -> TriBot Go -> Driving Base
chung

7. Software Installation
Usually be positive! Yes, Yes, Yes,…
After the installation you will see the following icon on your desktop
chung

8. Exercise 0 (First NXT program): Go forward for 2 sec. and stop (1/3)
Let’s name the program first
Click on Go >> button
You’ll see a programming palette
chung

9. First NXT program: Go forward for 2 sec. and stop (2/3)
Click on Move button
Drag and drop the move block to the canvas
A C
chung

10. First NXT program: Go forward for 2 sec. and stop (3/3)
Change parameters for the Move
Port
Direction
Steering
Power
Duration
Next Action
Block
Configuration Panel
chung

11. How to run your 1st program (1/2)
chung

12. How to run your 1st program (2/2)
If “Found New Hardware” pops up, just follow the instruction
Click on “Download” button
Recommended to un-plug the cable from the bot
Press the orange button 4 times (Turn on, My files, Software files, Run your program entitled go2stop)
chung

13. How to rerun the program
Check the program name on the LCD
Press the orange button just once again
chung

14. Just watch: Go forward for 2 rotations and come back by reversing motors
chung

15. Ex 1: Go forward 720 degrees and come back by reversing motors
chung

16. NXT motors
chung

17. Embedded Rotation Sensor
Each motor has an embedded rotation sensor
360 counts per rotation
The counter can be incremented or decremented
Distance traveled for a rotation of a wheel can be calculated: Circumference = 2 x radius x π
Or diameter x phi
chung

18. Find out the distance a rotation of the wheels will travel (metric)
Method 1: Write a program to go for a rotation then measure the distance: almost 17cm
Method 2
Measure the diameter of the wheels: 5.5 cm
Calculate Circumference: diameter x π
5.5cm x π = 17.27cm
chung

19. Making Turns Turn left: Spin left: (point turn) Face left: Left wheel
Right wheel
stop
Turn left:
Spin left: (point turn)
Face left:
chung

20. Spin Right 90 degrees
chung

21. Ex 2: Go forward 1.5 rotations and come back by spinning left
Spinning 180 degrees?
chung

22. Sensors Light Touch Ultrasonic (Distance measurement)
Sound (microphone)
Rotation – embedded in the motors
Timer – Internal sensor
Received Bluetooth messages
NXT buttons
chung

23. Light Sensor Percent mode Reflected light mode: shines a red light
5% - lowest dark
100% - very bright
Reflected light mode: shines a red light
The light can be turned off – detecting ambient (surrounding light)
Live updates: See lower left corner, if your robot is connected to the computer via either USB or Bluetooth
chung

24. Light Sensor II
Press View | Select “Reflected Light” | Select input port number
On white area: 55%-65%
On black area: 43%-48%
If Live Update value is quite different from the View value, light sensor calibration was done (using menu Tools). Either use default or update firmware, to reset.
Light value is affected by the gap between the sensor and the floor
chung

25. Light Sensor Readings
Source: HighTechKids.org
chung

26. Attach a Light Sensor Facing down
Gap: around 0.5 cm -1 cm (What will be the problem if too close to the floor to solve the Miner Rescue problem?)
Port No. 1
chung

27. Ex 3. Stop at Edge of the table
chung

28. Comments Use balloon text tool Add the following information
Author, when
Who made changes, when
How to use
Functions
Block descriptions
Assumptions: 1 - light
Expected results
Known bugs
Rooms to improve
Etc.
chung

29. Measure Light Sensor Values on the Miner Rescue field
White:
Black:
Foil:
Outside Edge:
Crack (gap) between home base and ramp:
Approaching down ramp
Approaching up ramp
stopAtBlackLine.rbt
chung

30. The gap between the Light sensor and the floor!!!
Both Reflected and Ambient light values are affected by the distance between the sensor and the floor!
The light sensor value is in inverse proportion to the gap
Light
sensor
Light
sensor
chung

31. Stop when it sees the black line on the Miner Rescue field
chung

32. Ex 4. Stop when it sees the 2nd black line on the Miner Rescue field
Need to skip the black line
0.1 rotation is OK
What is wrong?
chung

33. How about stopping at the 4th line?
Loop (Repeat) Block
Count = 4
chung

34. Touch Sensor Press View | Select Touch | Select input port number
If released (not pressed): 0
If pressed: 1
Is it sensitive? – it seems not
NXT-G can handle “Bumped” - (pressed and released) or (released and pressed)
chung

35. Attach a Touch Sensor
Port No. 2
chung

36. Ex. 5 Loop until a touch sensor is pressed
File name: DisplaySec
No event; Same as do while
Display seconds until touch sensor is pressed.
chung

37. Line following - Zigzag methods
chung

38. Ex 6. Follow the black line until a touch sensor is pressed
For Robofest field, the power
should be less than 40
Switch
chung

39. Ex 7. Follow the line until it detects the foil
Need more power to climb
Use rotation sensor to locate the robot
chung

40. Ex 8. Follow the line until it climbs back to the home base
chung

41. How to improve line following?
Three way branch …
Use two light sensors
- Steve H’s line following block
chung

42. Ex 9. Follow the line until it climbs back to the home base – Use My Blocks
chung

43. My Blocks Wrap a procedure into a package
To do the same thing from different places; to reuse code; to make code non-redundant
To divide a large task into smaller meaningful modules (provide structure)
To hide complex details
chung

44. How to create MyBlocks Start with working code
Highlight blocks to include
Click the “Create My Block” button
Name the MyBlock
Describe the MyBlock
Build icon(s)
MyBlock replaces the selected Blocks
chung

45. How to reuse the MyBlock
Select it from the Custom Tab
chung

46. Ultrasonic Sensor
Uses the same scientific principle as bats: it measures distance by caluclating the time it takes for a sound to hit an object and return – just like measuring an echo.
Measures in centimeters and in inches
0 to 255 cm (or 0 to inches, 8.4ft)
Precision of +/- 3cm (1.2 inches)
Press View | Select Ultrasonic cm | Select input port number
chung

47. Ultrasonic Sensor II
Large-sized objects with hard surfaces return the best readings
Objects made of soft fabric or that are curved (like a ball) or are very thin can be difficult for the sensor to detect
Note that two or more Ultrasonic sensors operating in the same room may interfere with each other’s reading
Connect an ultrasonic sensor to port no. 4
chung

48. Can you guess what the following program is behaving?
utraTst2.rbt
Data driven
chung

49. The same program – event driven
chung

50. Not covered advanced topics
Variables
Multiple tasks & Synchronization of multiple tasks …
chung

51. NXT Programming Tips “Out of Memory” problem Debugging
Do not use sound file
Do not display graphics
Minimize number of programs on NXT
Delete unnecessary programs
Debugging
Gradually, not all at once
Display
Tone
chung

52. Tips for Robofest 2007 Game Line following is required?
Ultrasonic sensor – No. 3 ball
May be light sensor for No. 4 ball in the tunnel
NXT conversion cable: you can use your existing RCX sensors and motors with the NXT brick! (3 cables for $10)
chung

53. Please go through Getting Started and Software Overview after this workshop
chung

54. Where to get additional Lego blocks?
eBay for Legos
chung