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Robofest 2007 NXT

Programming Workshop

Jan. 27, 2007

CJ ChungAssociate Professor of Computer Science

Lawrence Tech UniversityCHUNG@LTU.eduwww.Robofest.net

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Assistant

• Joe Long

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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

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Robots to be used: TriBot

• Robo Center, Quick Start Vehicle or small booklet in the retail version box

• Left motor: A• Right motor: C

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Alternative guide to build the TriBot (Retail Version)• Launch the software, Mindstorms NXT • Robo Center -> Vehicles Quick Start -> TriBot

Go -> Driving Base

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Software Installation

• Usually be positive! Yes, Yes, Yes,…• After the installation you will see

the following icon on your desktop

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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

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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

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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

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How to run your 1st program (1/2)

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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)

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How to rerun the program

• Check the program name on the LCD

• Press the orange button just once again

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

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

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NXT motors

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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

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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

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Making Turns

• Turn left:

• Spin left: (point turn)

• Face left:Left wheel

Left wheel

Right wheel

Right wheel

Left wheel Right wheel

stop

stop

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Spin Right 90 degrees

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Ex 2: Go forward 1.5 rotations and come back by spinning left

• Spinning 180 degrees?

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

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Light Sensor• Percent mode

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

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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

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Light Sensor Readings

Source: HighTechKids.org

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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

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Ex 3. Stop at Edge of the table

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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.

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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

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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

Lightsensor

Lightsensor

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Stop when it sees the black line on the Miner Rescue field

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Ex 4. Stop when it sees the 2nd black line on the Miner Rescue field

What is wrong?

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How about stopping at the 4th line?• Loop (Repeat)

Block

Count = 4

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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)

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Attach a Touch Sensor

• Port No. 2

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Ex. 5 Loop until a touch sensor is pressed

Display seconds until touch sensor is pressed.

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Line following - Zigzag methods

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Ex 6. Follow the black line until a touch sensor is pressed

SwitchFor Robofest field, the power should be less than 40

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Ex 7. Follow the line until it detects the foil

• Need more power to climb• Use rotation sensor to locate the

robot

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

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How to improve line following?• Three way branch• …• Use two light sensors

• http://home.earthlink.net/~xaos69/NXT/Line_Follower/Line_Follower.html

• http://www.teamhassenplug.org/NXT/ - Steve H’s line following block

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

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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

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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

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How to reuse the MyBlock

• Select it from the Custom Tab

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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 100.4 inches, 8.4ft)• Precision of +/- 3cm (1.2 inches)• Press View | Select Ultrasonic cm |

Select input port number

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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

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Can you guess what the following program is behaving?

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The same program – event driven

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Not covered advanced topics

• Variables

• Multiple tasks & Synchronization of multiple tasks

• …

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NXT Programming Tips

• “Out of Memory” problem 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

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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)

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Please go through Getting Started and Software Overview after this workshop

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Where to get additional Lego blocks?

• http://www.bricklink.com/• eBay for Legos