🔀 Dual Output Gear Bench: step-by-step build

One central input drives two unequal outputs: count each branch independently.

This original branched drive has a central 24-tooth input meshing directly with an 8-tooth fast output and a 40-tooth slow output. One input turn gives three fast-output turns and three fifths of a slow-output turn, both in the opposite direction. It is inspired by questions about small gears in Brick Experiment Channel’s load demonstration; it does not reproduce that destructive test rig or claim its load ratings.

  • Level 2 of 5 (easy)
  • About 20 minutes
  • 14 steps, 37 parts
  • Powered by: Hand-crank
  • Series: Starter Builds

What you will learn

  • Gears: Gears are wheels with teeth that push each other round.
  • Axles: An axle is a cross-shaped rod — anything on it turns together.
  • Frames: A frame is a ready-made strong rectangle.
  • Pins: Grippy or Smooth: Pins join beams together — some hold tight, some let things swing.
  • Bushes & Spacers: Bushes stop things sliding off an axle.

Build these first

  • ⚙️ Gear Friends: Three gears holding hands — spin one and they all dance. (level 1 of 5, about 8 minutes, 6 steps)

Parts you need

  • 1 × Open frame 5×11
  • 4 × Axle 3
  • 8 × Bush
  • 6 × Black pin (grippy)
  • 3 × Beam 5
  • 3 × Axle 6
  • 9 × Half bush
  • 1 × Medium gear (24 teeth)
  • 1 × Tiny gear (8 teeth)
  • 1 × Giant gear (40 teeth)

Steps

  1. Lay the 5×11 frame flat. Four corner holes hold retained feet; three pairs of side holes hold the bearing bridges.
  2. Fit a 3-module axle through this corner. While holding it, fit a full bush below as a foot and another above as a retainer. Repeat at all four corners; all feet must sit level.
  3. Fit a 3-module axle through this corner. While holding it, fit a full bush below as a foot and another above as a retainer. Repeat at all four corners; all feet must sit level.
  4. Fit a 3-module axle through this corner. While holding it, fit a full bush below as a foot and another above as a retainer. Repeat at all four corners; all feet must sit level.
  5. Fit a 3-module axle through this corner. While holding it, fit a full bush below as a foot and another above as a retainer. Repeat at all four corners; all feet must sit level.
  6. Pin the input bearing bridge across the open frame, 5 hole spacings from its front. Two separated black friction pins secure its end holes. Keep its centre round hole clear.
  7. Pin the fast bearing bridge across the open frame, 3 hole spacings from its front. Two separated black friction pins secure its end holes. Keep its centre round hole clear.
  8. Pin the slow bearing bridge across the open frame, 9 hole spacings from its front. Two separated black friction pins secure its end holes. Keep its centre round hole clear.
  9. Fit the input 6-module axle vertically through its bridge’s centre round hole. Hold it while fitting a half bush directly underneath and another directly above. These retain the shaft in both axial directions; leave it free to turn with minimal play.
  10. Slide the 24-tooth input gear onto its upper spacer and add a half bush directly above it. Its cross hole keys it to the shaft. Leave both sides clear for the two outputs that follow. Keep all three gears at the same height.
  11. Fit the fast 6-module axle vertically through its bridge’s centre round hole. Hold it while fitting a half bush directly underneath and another directly above. These retain the shaft in both axial directions; leave it free to turn with minimal play.
  12. Slide the 8-tooth fast gear onto its upper spacer and add a half bush directly above it. Its cross hole keys it to the shaft. Align the gear teeth with the neighbouring input when fitted; turn the entire shaft gently, keeping all keyed pieces together. Keep all three gears at the same height.
  13. Fit the slow 6-module axle vertically through its bridge’s centre round hole. Hold it while fitting a half bush directly underneath and another directly above. These retain the shaft in both axial directions; leave it free to turn with minimal play.
  14. Slide the 40-tooth slow gear onto its upper spacer and add a half bush directly above it. Its cross hole keys it to the shaft. Align the gear teeth with the neighbouring input when fitted; turn the entire shaft gently, keeping all keyed pieces together. Keep all three gears at the same height.

Play time

Hold the frame. Gently turn the central input; never brake an output. Stop if parts loosen. Per input turn, count 3 fast turns and 0.6 slow turn, both reversed.

Real-world inspiration

How Much LOAD Can the Smallest Lego Gear Handle? — Brick Experiment Channel — https://www.youtube.com/watch?v=YjhOGoZ-bNI