Planetary Gearbox [September 2025]

Summary and Key Details

  • Designed an 8:1 planetary gearbox delivering 12.75 Nm continuous torque at 79.5% efficiency

  • Implemented a floating shaft support to compensate for axial tolerance stacks affecting bearing performance

  • Developed a parameterized involute spur gear generator on SOLIDWORKS for the ring, sun, and planetary gears

Specifications

  • 8:1 Planetary Gearbox with Spur Gears

  • ODrive S1 FOC with Onboard Encoder

  • Floating Bearing Shaft Support Structure

  • Continuous Torque: 12.75 Nm

  • Backdriving Torque: 0.3 Nm

  • Backlash: (To Be Measured)

  • Efficiency: 79.5%

  • Total Mass: 1.03 kg

  • Lubrication - White Lithium Grease

Photos and Videos

Close-up Video

High-Speed (Real-time Video)

Isometric View

Back View (Encoder)

Actuator Scale

Motor and Gearbox

3D Prints and Bearings

Actuator Mass

Efficiency and Torque Testing

Actuator efficiency was measured by comparing motor torque to gearbox torque. The videos shown are the test setups used. The recorded values differ from those used in the efficiency calculations, as the motor kV was tested and tuned after these videos were taken, and the tests were performed again.

Motor Torque (~70% Continuous Current)

Actuator Torque (80% Continuous Current)

Motor Testing - kV

I chose the Eaglepower 8308 Kv90 motor because its outrunner style rotor and low Kv rating gave it a high torque-per-amp specification.

However, testing with a drill and multimeter showed the actual Kv was higher than expected, resulting in lower torque at the rated continuous current.

For the next design, I may need a higher reduction ratio to meet the project’s torque requirements.

3D Printing

The build process for this gearbox involved a lot of iteration in 3D printing the parts. It took time to get the fits for all the bearings and gears just right, but the comparison video below shows how that printing time was well worth the effort.

1st Print - Binding Gears

Optimized Backlash

Next

Cycloidal Drive