Balancing Device - Construction Manual

Device Description

The device consists of a frame and a Lego motor balanced on a single axle with two wheels. At each end of the frame is a Lego sensor that faces towards the ground. Each sensor measures its distance from the ground based on the reflection of a built in LED. The closer the sensor is to the ground, the more light it senses, the higher the value it reports. By examining the values of both sensors, the device can determine if it is tilting in one direction or another and rolls in the direction that will correct that tilt.

Self-Balancing Device

Parts List

To build the balancing device you will need the following parts which can be found in your Lego kit:

  • 4x - 256mm cable
  • 2x - sensors
  • 1x - basic motor (1420 RPM)
  • 1x - 4 point beam
  • 4x - 6 point beams
  • 4x - 16 point beams
  • 4x - 6 point axles
  • 1x - 12 point axle
  • 3x - 2x6 plates
  • 8x - full size bushings
  • 1x - 24 point gear
  • 1x - 8 point gear
  • 2x - tires/hubs
Lego Pieces

Building the Device

Follow these instructions to build your balancing device. Keep in mind that the device should be physically symmetric about the axle of the motor so that it can balance.

The Frame

  1. Attach two 12 point beams to the motor so they extend evenly on both sides. Note: the rightmost beam is not flush with the back of the motor. 1
  2. Flip the device over. attach two more 12 point beams directly above the first two beams. Attach one 4 point beam as shown. 2
  3. Attach one 2x6 plate evenly over the 12 point and 4 point beams. 3
  4. Attach one end of a 256mm cable to the two metal contacts on the motor. Attach the other end to the center of the 2x6 plate as shown. 4

The Sensor & Mounting Block

  1. Start with a 2x6 plate. 5
  2. Attach two 6 point beams. 6
  3. Attach a sensor. 7
  4. Build another sensor mounting block, repeat steps 5-7. 8

Mounting the Sensors

    1. Place one sensor between the beams at the end of the frame so all the holes align. Insert one 6 point axle through the bottom holes of the frame and sensor mounting block. Secure the axle with two full size bushings. 9a
    2. Attach the sensor cable to the 2x6 plate next to the motor cable. 9b
  1. Insert one 6 point axle through the top holes of the frame and sensor mounting block. Secure the axle with two half sized bushings. 10a 10b
  2. Attach the other sensor. repeat steps 9-10. Verify that your device looks like the picture below. 11

Attach the Wheels

  1. Flip the device over.
    1. Attach the 8 point gear to the motor.
    2. Insert the 12 point axle into the center holes of the top two beams. Attach the 24 point gear to the axle, make sure it engages the 8 point gear.
    12a 12b
  2. Attach a wheel to either side of the 12 point axle. Make sure the wheels are not tight against the frame such that they cause resistance. Also make sure the wheels are not so far apart that the gears can become disengaged. 13

The Finished Device

Flip the device over. Make sure your device looks like the one pictured below.

final1 final2 final4

Connecting to the Breakout Box

Now, use the other three 256mm cables to connect the motor and sensors to the breakout box. NOTE: you will want to keep the cables parallel to the axle, and give the cables a bit of slack. This is to make sure the wires don't affect the balance of the device.