01
Force depends on pose
The estimate uses F = T/r, where r is the perpendicular actuator moment arm at the checked pose. Linkage leverage changes through the elbow's range of motion.
Biped robot elbow roller screw screening
Biped Robot Elbow Roller Screw Sizing
Estimate elbow force from torque and linkage geometry.
Elbow force screening calculator
The example is prefilled. Results update as you edit; invalid or incomplete entries show a correction message.
Use output torque at the elbow joint, not motor shaft torque.
Enter a credible peak that already includes your event load model.
Perpendicular distance from joint axis to actuator force line at the screened pose.
Packaging constraint only; it is not used to infer screw capacity.
This screen requires S₀ ≥ 3, following the cited Thomson selection guidance. Confirm the factor with the selected manufacturer and application.
Screening boundary
Peak torque is 5.0× continuous torque. Confirm it represents the worst credible event and includes the applicable dynamic loads.
Preliminary force screen
- Continuous axial force
- 0.50 kN
- Peak axial force
- 2.5 kN
- Indicative roller-screw C₀ target
- 7.5 kN
- Peak/continuous torque ratio
- 5.00×
Peak axial force × S₀ (3).
Packaging input: 35 mm maximum outer diameter. Compare this with the complete nut, motor, bearing, and clearance envelope in the chosen assembly drawing.
This result is a force demand, not a screw selection. Check the candidate model's C₀ and dynamic rating against its catalog and the full duty cycle. This screen does not decide roller screw versus ball screw.
What the result means
The calculator converts elbow torque into an idealized axial force. It gives a starting demand for a catalog review; the robot's linkage, duty cycle, and the selected screw model determine the final design.
Illustrative elbow force calculation
With the prefilled example inputs (30 N·m continuous torque, 150 N·m peak torque, a 60 mm effective moment arm, and S₀ = 3), F = T/r gives 0.50 kN continuous force and 2.50 kN peak force. The indicative static C₀ target is 7.50 kN. These are illustrative calculations from example inputs, not measured robot performance or a product rating.
02
C₀ is a static check
The indicative C₀ target is peak axial force multiplied by S₀. It does not calculate dynamic fatigue life; use the candidate manufacturer's ratings and duty-cycle method.
03
Envelope is a constraint
The entered diameter does not predict capacity. Check the complete nut, motor, bearing, and clearance envelope against the assembly drawing.
Method and evidence boundary
This screen converts the supplied joint torque and moment arm into a force estimate. The C₀ target uses the selected static safety factor; it is not an impact amplification model.
1 · Inputs
Joint torque and effective moment arm at the checked pose.
2 · Force estimate
Idealized axial force: F = T / r.
3 · Catalog review
Check C₀, dynamic life, supports, and complete package envelope for a specific screw model.
What supports the method
- The force conversion is a static moment balance at the entered pose: joint torque divided by perpendicular actuator moment arm.
- Thomson's planetary roller screw selection guidance defines C₀ and recommends S₀ of at least 3, with higher factors for some quasi-static conditions.
- SKF and Thomson describe load rating as dependent on the specific contact geometry and design. Published material supports a general roller-screw load-capacity advantage in some designs, but not a universal multiplier for this elbow or diameter.
What remains unknown here
- Actual linkage efficiency, changing moment arm, load direction, inertia, and measured impact time history.
- Screw lead, candidate C₀ and dynamic rating, life, speed, lubrication, buckling, bearings, and support stiffness.
- Vendor-specific assembly dimensions, cost, and lead time; these need a like-for-like drawing review or RFQ.
Roller screw and ball screw: compare rated designs
Select by the same load cases and verified product data, not by a generic capacity ratio.
| Decision dimension | Roller screw candidate | Ball screw candidate | Evidence to request |
|---|---|---|---|
| Peak/static load | Compare the exact model C₀ with the screened demand and its vendor factor. | Compare the exact model C₀ using its own selection procedure. | Catalog rating and assumptions |
| Repeated duty | Verify dynamic rating and calculated life for the cycle. | Verify dynamic rating and calculated life for the same cycle. | Load spectrum, speed, and life calculation |
| Package and supports | Check nut/rotor arrangement, shaft, bearings, and clearances. | Check nut, coupling or motor arrangement, supports, and clearances. | Assembly drawing and tolerance stack |
| Backdrive and sourcing | Measure or calculate efficiency and backdrive behavior for the selected lead and preload. | Apply the same motion-control and backdrive requirements to the candidate. | Efficiency data, quote, and lead time |
Design boundaries and risk controls
Impact input risk
If the entered peak omits inertia, contact duration, or linkage effects, the force demand will be understated. Use a measured or validated dynamic load case and check the full motion range.
Rating and life risk
Meeting an indicative C₀ target alone does not verify dynamic life, buckling, speed, lubrication, bearings, or mounting. Confirm each against the selected supplier's data.
Safety and compliance risk
This mechanical calculation is not a safety assessment. ISO/TS 15066 covers collaborative industrial robot systems and excludes non-industrial robots. ISO lists the 2016 edition as current while marking it for revision; establish applicable standards for the actual system and use case.
Have a linkage drawing and load cycle? Request a model-specific engineering review against the complete actuator package.
Send an elbow drawing for reviewTraceable references
Manufacturer and standards pages reviewed October 12, 2026. They support selection definitions and boundaries; they do not provide a biped-elbow-specific product recommendation.
Biped robot elbow roller screw FAQ
What does the elbow calculator estimate?
It estimates idealized continuous and peak axial force from joint torque divided by the effective actuator moment arm. It also multiplies peak force by the selected roller-screw static safety factor to show an indicative C₀ target. It does not select a product or calculate fatigue life.
How should I choose the effective moment arm?
Use the perpendicular distance from the elbow joint axis to the actuator force line at the pose being checked. Linkage leverage changes with joint angle, so evaluate the worst-case geometry over the motion range. Do not use motor shaft torque unless it has already been converted to joint output torque.
Does the C₀ target guarantee the screw survives an impact?
No. It is a preliminary static rating target based on the peak force entered and the selected factor. The peak must include the relevant event loads, and the actual screw still needs catalog checks for dynamic rating, life, speed, buckling, lubrication, mounting, and bearings.
Does the calculator decide between a roller screw and a ball screw?
No. Both technologies must be checked against their specific manufacturer ratings and the same duty cycle. Roller screws can offer higher load ratings in some designs, but there is no universal capacity multiplier or selection result based only on joint torque and outer diameter.
What if continuous torque is zero?
A nonzero peak torque can still produce a peak force and C₀ target, but the peak-to-continuous ratio is undefined. A full duty-cycle input is still needed for fatigue and thermal analysis.
Does this screen establish robot or human-contact safety?
No. It is a mechanical force screen only. ISO/TS 15066 addresses collaborative industrial robot systems and does not apply to non-industrial robots. ISO lists the 2016 edition as current while marking it for revision, so confirm the latest applicable standards and perform a separate system risk assessment for the actual robot and deployment.
Review your elbow actuator against real catalog data
Share the torque profile, linkage drawing, package envelope, and operating cycle for a model-specific roller screw review.
Published October 12, 2026 · Updated October 12, 2026