Motion Detecting Lego NXT mindstorm arm written in ruby

The building instructions for this arm can be found here:
http://www.nxtprograms.com/robot_arm/steps.html

I added the Ultra sensor to it, and you will notice some of the funtions in the code aren't used at all, because I plan on doing more with this.

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require "rubygems"
require "serialport"
require "nxt_comm"

$DEBUG = false

@nxt = NXTComm.new('/dev/tty.NXT-DevB-1')
def sleeper
 sleep(0.5)
end

@nxt = NXTComm.new("/dev/tty.NXT-DevB-1")


def do_motor_a
  a = Commands::Motor.new(@nxt)
  a.port = :a
  a.duration = {:rotations => 0.25}
  a.control_power = true
  a.start
  puts "Run State: #{a.run_state}"
end

def do_motor_b
  b = Commands::Motor.new(@nxt)
  b.port = :b
  b.duration = {:rotations => 0.25}
  b.control_power = true
  b.start
end

def do_motor_c
  c = Commands::Motor.new(@nxt)
  c.port = :c
  c.duration = {:rotations => 0.25}
  c.control_power = true
  c.start
  puts "Run State: #{c.run_state}"
end

def do_motorb_a
  a = Commands::Motor.new(@nxt)
  a.port = :a
  a.duration = {:rotations => 0.25}
  a.control_power = true
  a.direction = :backward
  a.start
  puts "Run State: #{a.run_state}"
end

def do_motorb_b
  b = Commands::Motor.new(@nxt)
  b.port = :b
  b.direction = :backward
  b.duration = {:rotations => 0.25}
  b.control_power = true
  b.start
end

def do_motorb_c
  c = Commands::Motor.new(@nxt)
  c.port = :c
  c.direction = :backward
  c.duration = {:rotations => 0.25}
  c.control_power = true
  c.start
  puts "Run State: #{c.run_state}"
end

def inputs_2
   s = @nxt.get_input_values(NXTComm::SENSOR_2)
   puts s[:value_raw]
   if s[:value_raw] > 1005
    @nxt.play_tone(659,500)
    do_motorb_a
    do_motorb_b
    sleep 1
    do_motor_a
    do_motor_b
    sleep 1
    end
 end
 
 def inputs_1
   sm = @nxt.get_input_values(NXTComm::SENSOR_1)
   puts sm.inspect
   sleep 1
 end
 
loop {
 inputs_2
}