Reducers
The gearbox alone — strain-wave, cycloidal or planetary — that turns a fast, weak motor into the slow, strong rotation a robot joint needs.
- gearbox
- strain wave gear
- harmonic drive
- cycloidal drive
- RV reducer
- planetary gearbox
What it is
A reducer takes the fast, weak output of a motor and trades speed for torque. Arm joints need high ratios with almost no play, because backlash in a shoulder shows up as millimetres of error at the hand. Strain-wave (harmonic) gears, as in the Harmonic Drive CSF and CSG sets, manage that with zero backlash in a compact cup; cycloidal and RV reducers are stiffer and tougher but heavier; planetary gearboxes are cheaper and more efficient but have play, so they suit legs and wheels more than arm joints.
Names include gearbox, strain wave gear, harmonic drive, cycloidal drive, RV reducer and planetary gearbox. In this taxonomy it sits under Actuator beside joint modules, servos, motors and linear actuators, and the rule is that it reduces speed and multiplies torque and is sold without a motor.
Where they are used
- Arm joints — strain-wave sets and cycloidal units sit inside nearly every six-axis arm; this is how arm makers build joints.
- Custom joint modules — builders pair a reducer with a frameless motor and an encoder when stock modules do not fit.
- Research manipulators — a back-drivable joint built on a low-ratio planetary stage.
- Positioning stages and turrets — any axis that needs high torque from a small motor.
What to compare
| Attribute | Why it matters | In this catalogue |
|---|---|---|
reducer_type |
Strain wave for zero backlash, cycloidal for stiffness and shock, planetary for cost and efficiency | harmonic (1) |
gear_ratio |
Higher ratios give torque and precision; lower ratios keep the joint back-drivable | not yet in the catalogue |
rated_torque |
Continuous output torque; size the reducer on this, not on the motor | not yet in the catalogue |
peak_torque |
Momentary and collision loads; strain-wave gears are the least forgiving here | not yet in the catalogue |
mass |
Strain-wave sets are light for their torque; cycloidal units are heavy | not yet in the catalogue |
flange_standard |
Component sets need the builder's own housing; housed units bolt straight on | not yet in the catalogue |
In the catalogue
Professional / industrial: Harmonic Drive CSF / CSG Component Sets
Edge cases
- Component set (Harmonic Drive CSF/CSG: wave generator, flexspline and circular spline sold loose): a reducer; the builder adds the housing.
- Reducer with an integrated motor and driver: a joint module, not a reducer.
- Motor with a gearhead attached but no controller: listed as a motor; this category is the gearbox alone.
Related
Actuator · Joint module · Servo · Motor · Linear actuator · Articulated arm
Rule of membership
Reduces speed and multiplies torque; sold without a motor.
Category cp-2-4 in the whatrobot taxonomy.