Robotics-2010

NXT-Python Documentation

Largely a work in-progress, please add/edit as you learn the details. Note that this page is documenting the NXT-Python v1.1 release (http://code.google.com/p/nxt-python/), not the NXT_Python v0.7 release which appears to have gone dormant (note hyphen vs underscore).

nxt.locator

The function of this module is to locate NXT brick(s). Returns an nxt.bluesock.BlueSock object for robots connected by Bluetooth and a nxt.usbsock.USBSock object for robot connected by USB, and throws nxt.locator.BrickNotFoundError if none can be found.

• Status: incomplete as of 2010-02-14

• Objects
  • nxt.bluesock.BlueSock - The object returned by find_one_brick() when a brick is found on a Bluetooth connection [defined in nxt.bluesock]
  • nxt.usbsock.USBSock - The object returned by find_one_brick()when a brick is found on a USB connection [defined in nxt.usbsock]
  • nxt.brick.Brick - The object returned by the connect() method [defined in nxt.brick]

• Methods
  • connect() - Try to connect to the brick.
  • close() - Close connection to brick.
  • host - Returns the address of the brick (if connected via Bluetooth connection)
  • generator object find_bricks()
    • next() - Find the next brick in the sequence, returns the same thing as find_one_brick().
  • find_one_brick()
  • find_bricks(host=None, name=None) - Find all the bricks in the area, returns a generator object find_bricks.

• Example

import nxt.locator 
sock = nxt.locator.find_one_brick() 
brick = sock.connect()
if hasattr(brick, 'host'):
 print brick.host
else:
 print "brick.host is not defined for USB connections"
sock.close()

nxt.motor

• Port Constants
  • PORT_A
  • PORT_B
  • PORT_C
  • PORT_ALL

• Mode Constants
  • MODE_IDLE
  • MODE_MOTOR_ON
  • MODE_BRAKE
  • MODE_REGULATED

• Regulation Constants
  • REGULATION_IDLE
  • REGULATION_MOTOR_SPEED
  • REGULATION_MOTOR_SYNC

• Run State Constants
  • RUN_STATE_IDLE
  • RUN_STATE_RAMP_UP
  • RUN_STATE_RUNNING
  • RUN_STATE_RAMP_DOWN

• Objects
  • nxt.motor.Motor - The object returned by Motor(brick, port)
  • Class Methods
    • _debug_out(self, message)
    • set_output_state(self)
    • get_output_state(self)
    • reset_position(self, relative)
    • run(self, power=100, regulated=1)
    • stop(self, braking=1)
    • update(self, power, tacho_limit, braking=False, max_retries=-1)

• Methods

• Example

import nxt.locator
import nxt.motor
from time import sleep
sock = nxt.locator.find_one_brick()
brick = sock.connect()
motor_a = nxt.motor.Motor(brick, nxt.motor.PORT_A)
print "Initial Position:", motor_a.get_output_state()[7]
motor_a.update( 127, 360, True ) # Turn 360 degrees at full power and brake
motor_a.update( -127, 360 ) # Turn -360 degrees at full power and coast
sleep( 3 ) # update is non-blocking when braking is false, must wait for finish
print "Final Position:", motor_a.get_output_state()[7]
sock.close()

nxt.sensor

• Status: incomplete as of 2010-02-14

• Objects

• Methods

• Example

nxt.compass

• Status: incomplete as of 2010-02-14

• Objects
  • CompassSensor

• Methods
  • CompassSensor(bot,port)
  • get_sample() returns a value between zero and 180 depending on the heading of the sensor. There is a one-to-two ratio between degrees from due North and get_sample() values. At the moment this generally returns an error.
  • Methods to add
    • begin_calibration() tells the sensor to go into calibration mode.
    • end_calibration() tells the sensor to leave calibration mode

• Example

compass = UltrasonicSensor(bot, PORT_1) #declare the sensor plugged into port 1 "compass"
heading = compass.get_sample()*2 # get the current heading in degrees from due north

• Notes
  • The sensor gives errors and fails to register almost all of the time. The reasoning for this is under investigation.
  • Compass Sensor hardware info
  • URL to compass.py in source control (hint)

Scripts

Located in $DISTRIBUTION/scripts.

• nxt_filer
• nxt_push
• nxt_test

Setup

Ubuntu

If you are using Brad's livecd, make sure you have the latest version

1. Download Brad's installation kit and untar it anywhere you want.
2. In your editor of choice, modify the install.sh script to connect to your brick instead of Brad's. This will be within the first few lines.
3. Open a terminal, navigate to the folder with your newly untarred files and type

sudo ./install.sh

If your computer supports bluetooth, set up your connection to your robot

1. Turn on your brick.
2. Navigate through the menu to enable bluetooth
   • Ensure that your device is set to "findable"
3. Click the bluetooth symbol at the top of your computer's screen, next to the envelope.
4. Select "Set up new device"
5. Select your robot
6. You will be prompted to input a passkey into your robot
   • Use the small grey button to delete characters and the large orange button to select characters
   • Select the checkmark to submit your passkey
   • Work quickly! You have about a minute before the passkey kicks you out and makes you start over!
   • You will be notified on-screen if your passkey was successful
7. After your passkey is accepted, try running query.py

Tips

Wrap your code in a try/finally block so that you can stop the motors on control-c.

try:
  [your code here]
finally:
  [stop all your motors]