↔️ Twin-Length Timing Bench: step-by-step build

Compare a short and a long freely swinging arm, and measure their full cycles.

A longer arm has more gravity leverage, but also more rotational inertia. This original timing comparison carries separate end-pivoted five-hole and seven-hole beams on one retained support axle. Release them gently from the same small angle and measure complete out-and-back cycles. Inspired by Dawid Marasek’s pendulum-wave display, not a replica of its suspended wheel bobs or a clock.

  • Level 2 of 5 (easy)
  • About 20 minutes
  • 11 steps, 24 parts
  • Powered by: Gravity
  • Series: Starter Builds

What you will learn

  • Pendulum: A hanging weight swings back toward its lowest point.
  • Centre of Gravity: Keep the heavy stuff low and in the middle and your model won't tip.
  • Torque vs Speed: Slower gears are stronger gears.
  • Axles: An axle is a cross-shaped rod — anything on it turns together.
  • Bushes & Spacers: Bushes stop things sliding off an axle.
  • Frames: A frame is a ready-made strong rectangle.
  • Pins: Grippy or Smooth: Pins join beams together — some hold tight, some let things swing.

Build these first

  • Tiny Roller🚗 Tiny Roller: Your very first rolling car — only 13 pieces! (level 1 of 5, about 5 minutes, 6 steps)

Parts you need

  • 1 × Open frame 5×7
  • 4 × Blue long pin
  • 4 × Split pin block
  • 4 × Red axle-pin
  • 2 × Beam 11
  • 1 × Axle 12
  • 6 × Half bush
  • 1 × Beam 5
  • 1 × Beam 7

Steps

  1. Lay the 5×7 frame flat on a level table. Its two short ends will carry separate rigid posts.
  2. Insert two blue long pins upward through the second and fourth holes of the back short end. Fit two split pin blocks one above the other onto the same pins.
  3. Put a red axle pin in each back block’s centre cross hole, pointing backward. Two fixing points stop the post tipping.
  4. Stand an 11-hole beam at the back. Fit its second and third holes onto the back pair of red axle pins.
  5. Pass a 12-module axle through the back post’s ninth hole, eight hole spacings above its bottom hole. Fit one half bush immediately outside the back post. Slide another to the middle, against the back face of the future yellow beam.
  6. Slide the end round hole of a yellow 5-hole beam onto the axle, hanging downward one module behind the centre. Add a half bush against its front face. Leave the beam free to rock; the bushes grip the axle, not the beam.
  7. Fit a half bush one quarter module in front of the centre. Slide a red 7-hole beam onto the axle by its end round hole, one module in front of the centre, then cap its front face with another half bush. This longer arm has the same kind of end pivot. Both beams must rock independently. Neither arm is keyed to the axle; check that the bushes retain without pinching.
  8. Now add the front block pair: two blue long pins upward through the second and fourth holes, then two split pin blocks stacked on them. Adding these after the pendulum keeps its insertion path open.
  9. Fit two red axle pins pointing forward in the front blocks’ centre cross holes.
  10. Fit the front 11-hole post onto its two red axle pins while guiding the long axle through its ninth hole. The two posts are eight modules apart, supporting both ends of the pivot axle.
  11. Add a final half bush just outside the front post. The outside half bushes retain the axle in both directions; the four middle spacers retain the two swinging beams. Check every block and pin is firmly seated.

Play time

Hold the stationary frame level. Gently displace each arm at most 15 degrees, without touching its neighbour, then release without pushing. Time several complete out-and-back cycles from the same-side extreme; record how many cycles actually finish before friction stops it. Repeat three times with the same release angle and viewing side. Stop for rubbing, loose caps or moving supports. Do not hold the moving arms in alignment. No motor or added bob is part of this guide. We have not physically tested this model.

Credited demonstrations and component sources