Build Instructions

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• 1

  Build the Frame

  The frame needs to be:

  • Tall enough for a meaningful drop (we used 1.80 m total height)
  • Rigid enough to handle the mass without vibration
  • Perfectly vertical — any tilt causes the mass to swing

  Build a rectangular tower using wooden beams. Use bolts, not nails — you need structural rigidity. The mass will be pulling on the top of the frame during descent, so the joints need to hold.

  CRITICAL DIMENSION: Not all of your frame height is usable. The top section holds the transmission, and the bottom needs clearance. Our effective drop was 1.39 m out of 1.80 m — that's 41 cm of dead space. Minimize this. Every centimeter of height is gravitational potential energy you're leaving on the table.

  If you have access to the FreeCAD files from our GitHub, the frame_structure.FCStd file has the exact dimensions we used.

• 2

  Install the Chain Drive

  This is the heart of the mechanical system.

  Mount the large sprocket on the descent axle (where the mass pulls). Mount the small sprocket on the motor axle. Connect them with the chain.

  The gear ratio matters enormously. We started with 1:5 — it wasn't enough. The motor needs higher RPM to generate useful voltage, and a falling mass moves slowly. The jump to 1:9 was the single most impactful design change we made.

  To verify your ratio: rotate the large sprocket one full turn by hand. Count how many times the small sprocket spins. It should be approximately 9.

  Chain tension is important. Too loose and it skips teeth. Too tight and you add friction. Chain friction accounted for about 10% of our energy losses — replacing chains with timing belts is our top recommended improvement.

• 3

  Mount the Hub Motor and Magnetic Brake

  The hub motor is what converts rotation into electricity. We used a 36V multi-pole hub motor — the kind used in electric bicycles. The multi-pole design is critical because it generates meaningful voltage even at low RPM. A standard DC motor wouldn't work here.

  The magnetic brake is what makes this system controllable. Without it, gravity accelerates the mass and the motor spins too fast, producing voltage spikes that damage electronics.

  Position neodymium magnets near the motor's rotating element. The magnets create eddy currents that oppose the rotation — braking without physical contact. Adjust the distance between magnets and rotor to control braking force:

  • Closer = more braking = slower descent
  • Farther = less braking = faster descent

  TARGET: The mass should descend smoothly in approximately 9-10 seconds. If it drops in 3 seconds, add braking. If it barely moves, reduce braking.

  The fact that our angular velocity stabilized at 15.65 kg (varying only 0.01 rad/s) proves this braking system works. It's the result we're most proud of.

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