Full Guide
A practical reducer selection process
A robot joint reducer should be selected as part of the complete actuation assembly. Start with the joint requirement, verify the mechanical and thermal envelope, and use supplier documentation to close the remaining sourcing questions.
If a specification is not available in the catalog or supplier documentation, treat it as missing information. Do not assume a value from a neighboring model, product family, application, or marketing description.
1. Start With the Joint Requirement
Define what the joint must do before comparing reducer families. Capture the joint axis, motion range, target output speed, continuous and peak torque, payload, external loads, duty cycle, environment, available envelope, and the motor and control interfaces.
Separate requirements from preferences. A compact package may be preferred, but torque, speed, bearing loads, thermal limits, and interface compatibility are requirements that should be confirmed before a candidate is shortlisted.
- - Define continuous and peak operating points.
- - Record the output speed range and required direction of motion.
- - Identify radial, axial, and moment loads at the output.
- - Record envelope, mass, cable routing, mounting, and environmental constraints.
2. Determine Required Output Torque
Use the joint load case to determine the required output torque. Consider payload, link mass, gravity, acceleration, friction, transmission losses, and any external force at the joint. The resulting requirement should distinguish normal continuous torque from short-duration peak torque.
Compare the requirement to the reducer's rated and peak torque values using the same units and load conditions. A peak rating is not a substitute for a continuous rating, and a family-level range is not a confirmed rating for a particular model.
| Input | Selection question |
|---|---|
| Continuous torque | Can the reducer carry the expected repeated load without exceeding its operating limits? |
| Peak torque | Can it carry acceleration, impact, or transient load events for the required duration? |
| Load case | Were gravity, acceleration, friction, and transmission losses included? |
3. Select the Reduction Ratio
The reduction ratio connects motor speed to output speed and affects torque multiplication, reflected inertia, efficiency, and controllability. Compare the motor operating range with the reducer ratio range and the target joint speed, rather than selecting the largest available ratio.
When a product lists a ratio range, confirm which ratios are available as actual models. A range on a family record may cover multiple configurations; it should not be treated as the specification of a specific model without confirmation.
| Question | Why it matters |
|---|---|
| What is the motor speed? | It sets the ratio needed to reach the required joint speed. |
| What is the output speed? | It prevents an otherwise suitable torque match from being too slow or too fast. |
| Which ratios are model-level options? | It separates confirmed configurations from a general family range. |
4. Evaluate Backlash and Positioning Requirements
Backlash affects direction reversal, low-speed positioning, repeatability, and the amount of dead travel seen by the control system. Compare backlash at the operating condition that matters for the joint, and check whether the published value applies to a model, a series, or a general family.
For applications with frequent reversals or precise force control, also ask how backlash is measured, how it changes with load, and whether preloading or assembly conditions affect the result.
5. Consider Torsional Stiffness
Torsional stiffness influences settling time, position error under load, vibration response, and the feel of a controlled joint. It is particularly relevant when the reducer, motor, output bearing, flange, and link structure form a compliant chain.
If stiffness is not published for the selected model, record it as a supplier question. Do not substitute a value from a different ratio, size, or product family.
6. Check Output Bearing Loads
Determine whether the reducer output bearing carries the robot link loads or whether a separate joint bearing supports them. Check radial load, axial load, and overturning moment requirements against the product documentation.
An integrated output bearing can simplify packaging, but it does not remove the need to verify the complete load path. Confirm the load direction, duty cycle, bearing life basis, and mounting stiffness with the supplier when those details are not available.
7. Harmonic or Planetary?
The choice between harmonic and planetary transmission depends on the complete joint requirement, not on a category label alone. Use the following as a comparison frame:
| Consideration | What to compare | What to confirm |
|---|---|---|
| Backlash | Published backlash and measurement condition | Model-level value at the selected ratio |
| Torque and speed | Continuous, peak, and output speed envelope | Duty-cycle and thermal basis |
| Packaging | Diameter, length, mass, and hollow options | Mounting and output interface drawings |
| Service life | Life rating and maintenance requirements | Load spectrum and lubrication assumptions |
8. Check Duty Cycle and Thermal Behavior
A reducer that meets a short peak event may still be unsuitable for a repeated motion profile. Describe the move, dwell, reversal, and load sequence and compare it with the supplier's thermal and life information.
Check operating temperature, cooling method, ambient conditions, lubrication, and whether the stated ratings assume a specific mounting orientation or housing. Missing thermal data should remain an open sourcing question.
9. Evaluate Size and Mass at the Joint Level
Compare the reducer's diameter, length, mass, flange pattern, hollow passage, and cable routing with the motor, encoder, bearing, brake, and joint housing. A reducer can fit as a standalone component but fail the assembled joint envelope.
Keep the package-level comparison tied to a specific model. Family dimensions and model dimensions should be kept separate when the database distinguishes them.
10. Evaluate Supplier and Sourcing Constraints
After technical fit, review the sourcing information available for each candidate: model-level documentation, drawings, quality records, customization options, production stage, and commercial terms available through a quote request.
Do not assume price, minimum order quantity, lead time, inventory, sample availability, or production capacity when those values are not published for the selected product. Use Request Quote to ask for the missing commercial information.
11. Compare Multiple Candidates Before Design Freeze
Compare candidates using the same requirement set. Keep the comparison focused on model number, ratio, torque, backlash, stiffness, load capacity, size, mass, interface, life, and the documentation needed for sourcing.
A blank comparison cell means the value is not available for that candidate. It does not mean the candidates are equivalent. Capture the missing field as a question for the quote request instead of filling it from another row.
12. Reducer Selection Checklist
| Check | Selection question |
|---|---|
| Load | Are continuous and peak torque requirements defined? |
| Ratio | Does the selected ratio produce the required output speed? |
| Accuracy | Are backlash and stiffness suitable for the control and motion requirements? |
| Bearing | Are radial, axial, and moment loads supported by the output architecture? |
| Thermal | Has the complete duty cycle and cooling condition been checked? |
| Envelope | Do diameter, length, mass, hollow passage, and interfaces fit the joint? |
| Sourcing | Are missing technical and commercial fields captured for the quote request? |
13. Find and Compare Robot Reducers
Use the Robotic Supply reducer catalog to browse available product families and model records. Select a reducer category, apply the filters supported by the available public specifications, open a product for its full technical definition, and add compatible model-level products to Compare.
When a candidate is suitable but a required field is missing, keep the value open and submit a Request Quote with the missing requirement included.