Wishful Coding

I found some lost and forgotten Lego building lessons. I think you’ll love them.

Over at Lugnet, in an old thread, someone asked for tips and tricks about studless building(using smooth beams rather than the classic Lego bricks). Someone linked him to the “LEGO TECHNIC Design School”, which sounded really good, but unfortunately, the links where dead.

I searched, and searched, but LEGO just seems to have removed them. Are they to good for this world? Finally, I found them using the Wayback Machine. Enjoy!

• Gearing 101
• TECHNIC 101
• Stability with LEGO TECHNIC

Unfortunately, a few images are missing, but it’s still interesting to read.

Diagonal Connections

One thing they teach that I have not seen “in the wild” much are all sorts of diagonal connections, like this 1:2 gear ratio and right-angle connection.

It is possible to build all integer Pythagorean triangles, although few of them are practical.

It might at first be confusing to build a triangle with sides of 3, 4 and 5 in length using beams of 4, 5 and 6 of length, but think of it like this:

What would be the length of a dot? Zero, right? So when talking about LEGO units, a beam with one hole also has a length of zero. Start counting at zero, and it’ll all make sense.

I don’t exactly remember how I made the claw in the video earlier, but I’ve made a new one for you, so you can play with it.

The claw can be mounted on the front side of the Rover from the NXT 2.0

You can use this claw with the gamepad code from my previous post, but maybe you can mount the ultrasonic sensor and program it to fetch you a drink?

Download Building Instructions

I had this pincer bot that I had not yet programmed, but using software remotes proved disappointing. With a few lines of code, I was able to use any gamepad or joystick to control the robot.

To use this code, you need to know how to execute commands on your computer. Then, do the following.

1. Install Python if you don't already have it.
2. Install PyGame for interfacing with the gamepad.
3. Install NXT-python for interfacing with the NXT.
4. Make sure your NXT and gamepad are connected and working.
5. Run

   python nxtjoy.py

   in the directory where you've downloaded the code below.

import pygame
from nxt import locator, motor
from time import sleep

# edit this to reflect your joystick axis and buttons
axis = {'x':0, 'y':1}

b = locator.find_one_brick()

left = motor.Motor(b, motor.PORT_B)
right = motor.Motor(b, motor.PORT_A)
action = motor.Motor(b, motor.PORT_C)

closed = False

def limit(nr):
    if nr > 50 or nr < -50:
        return min(127, max(-128, nr))
    else:
        return 0

def move(fwd=0, turn=0):
    lp = int((fwd - turn) * -100)
    rp = int((fwd + turn) * -100)
    left.run(limit(lp))
    right.run(limit(rp))

def pincer(button):
    global closed
    try:
        if button and not closed:
            closed = True
            action.turn(-40, 70, emulate=False)
        elif not button and closed:
            closed = False
            action.turn(30, 70, emulate=False, brake=False)
    except motor.BlockedException:
        print action.get_tacho()

pygame.init()
j = pygame.joystick.Joystick(0) # first joystick
j.init()
print 'Initialized Joystick : %s' % j.get_name()
try:
    while True:
        pygame.event.pump()
        sleep(0.1)

        # get_axis returns a value between -1 and 1
        move(j.get_axis(axis['y']), j.get_axis(axis['x']))
        pincer(j.get_button(0))

except KeyboardInterrupt:
    j.quit()