Part

Gearbox

You might say: reducer, transmission

A gearbox trades motor speed for output torque. An ideal reduction N multiplies torque by N and divides speed by N; real efficiency, backlash and compliance reduce the result.

What it does

It lets a small fast motor drive a slower, higher-torque joint.

Ask

What ratio, efficiency, backlash, stiffness and backdrivability fit the joint?

Trouble

Backlash, elastic wind-up, friction, wear and shock loads appear as position error, heat or noise.

What to look for

1. Fast motor driving a slower joint
2. Output torque increased by reduction
3. Backlash or elastic wind-up

Parts

• Gear ratio: Gear ratio is motor turns per output turn.

Catalogue: Reducer

• Strain wave (harmonic drive): A strain-wave or harmonic reducer uses a wave generator, flexspline and circular spline; Harmonic Drive lists zero backlash and high torque-to-weight ratio. A reducer with a wave generator, flexspline and circular spline defines it; Harmonic Drive CSG/CSF is one example.
• Planetary: Modern Robotics shows a planetary gearhead in a brushed-DC motor assembly.
• Cycloidal: A cycloidal or RV reducer uses eccentric lobed gears and pins; Nabtesco lists a range of speed ratios for its robot-joint reducer family. A reducer with eccentric lobed gears and pins defines it; Nabtesco RV is one example.

Sources

1. Kevin M. Lynch and Frank C. Park, Modern Robotics: Mechanics, Planning, and Control, Ch. 8 §8.9An ideal gearhead (one that is 100% efficient) with a gear ratio G multiplies the torque at the output of a motor by a factor G and divides the speed by the factor G, leaving the mechanical power unchanged.
2. Harmonic Drive LLC, CSG/CSF Component Sets Reducer Catalog, pp. 3, 6–9The high-performance attributes of this gearing technology including, zero-backlash, high-torque-to-weight ratio, compact size, and excellent positional accuracy.

Use it on your project

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