Instruction Guide: Introduction to Gear Trains

Submitted by Randy Steele on 30 May, 2011 - 11:51

Build the following crank-and-wheel assembly with an NXT kit:

  • See Photo 1_2
    • Use medium length axle for first and last gears, non-friction peg for center gear
    • Attach any wheel to one axle, and crank (handle connector peg) to other axle
  • Have students turn handle/crank and observe wheel
  • Switch location of crank and wheel and repeat observation

Discuss with students how this relates to their experiences with bicycle gears (size of front and rear gears when going uphill vs downhill)

  • When going downhill student pedals (cranks) on large gear with small gear on wheel (maximizing speed)
  • When going uphill student pedals (cranks) on small gear with large gear on wheel (maximizing torque/power)
  • We will revisit the speed vs torque tradeoff later in the future Getting in Gear lesson

Have students set the wheel on a table and turn the crank 3 times in both configurations:

  • Ask students what determines how far the assembly moves:
    • Number of rotations of the wheel
    • The circumference of the wheel
      • This is foreshadowing for the future How Far lesson
  • Note in the "downhill" configuration how much further the assemble travels
    • Greater distance = greater speed (in the same period of time)
  • This can also be looked at from an energy conversion perspective:
    • Rider inputs energy by pedaling:
      • In one case, the energy converts into more kinetic energy (speed)
      • In the other, the energy converts into lifting the bike/rider up the hill (increasing potential energy)