Biped Robot Arm Actuator Screw Sizing
Screen peak thrust, stroke, and lead against published actuator examples. Then identify the load, motion, and supplier data still needed before selecting an arm actuator.
Published September 25, 2026 · Last reviewed October 4, 2026 · Prepared by the Inverted Roller Screw applications team.
Arm Screw Range Screen
Compare your inputs with one manufacturer’s published linear-actuator examples. This is a reference check, not a screw selection.
Maximum force at the screw during the motion cycle. The HJL examples publish 0.6–8 kN maximum thrust.
Published HJL examples list up to 96 mm, with the limit varying by model.
HJL examples list 2, 3.5, 5, or 6.5 mm; lead alone does not establish backdrive behavior.
Enter the RMS value from the load cycle. No continuous rating is published in the referenced summary.
Added to the inquiry summary; joint type does not change this reference-range screen.
Enter axial force at the screw, not joint torque. For a simple linkage, force is approximately joint torque divided by the perpendicular moment arm; use the worst case across the full motion and include push and pull loads.
Reference Check
Inputs do not exceed the published maxima and the lead is listed; model fit is not confirmed.
- Peak axial force does not exceed the highest published HJL example (8 kN); this does not confirm a model or duty-cycle fit.
- Stroke does not exceed the longest published HJL example (96 mm); the maximum stroke differs by model.
- The 5 mm lead appears in the published HJL example options; verify which model and rating combination supports it.
- No continuous RMS load rating is published in the referenced summary, so compare the force-time profile with the selected model’s continuous and thermal limits.
This screen does not calculate a minimum screw diameter, dynamic capacity, service life, or safety rating. Those require the full load and speed cycle, geometry, support conditions, and selected supplier data.
Request Engineering ReviewArm Actuator Architecture & Published Reference Data
A linear screw actuator can drive an arm joint through a linkage, but joint torque does not directly specify screw load. For a simple linkage, actuator force is joint torque divided by the perpendicular moment arm; evaluate the changing geometry across the complete range of motion.
| Published module example | Max thrust | Max speed | Max stroke | Lead options | Mass |
|---|---|---|---|---|---|
| Techrobots HJL08 | 0.6 kN | 300 mm/s | 38 mm | 3.5 mm | 0.5 kg |
| Techrobots HJL12 | 4 kN | 120 / 300 mm/s | 72 mm | 2 / 5 mm | 1.3 kg |
| Techrobots HJL15 | 8 kN | 120 / 400 mm/s | 96 mm | 2 / 6.5 mm | 2.8 kg |
Published Hybrid Arm Configuration
Techrobots describes a seven-axis humanoid arm that combines linear and rotary actuators: MJB20T on axes 1–3, HJL12 on axis 4, MJB14T on axis 5, and HJL08 on axes 6–7. The supplier reports a 10 kg single-arm mass and at least 5 kg payload. This example supports evaluating a mixed architecture by joint; it does not establish that every arm axis should use a screw actuator.
Supplier-published configuration; not independently measured or validated by Inverted Roller Screw. Review the source configuration.
One Possible Rotating-Nut Layout
Illustrative only: this drawing shows a fixed stator, rotating nut, and translating screw shaft. Integrated motor, bearing, and support arrangements vary; confirm them against the selected supplier’s assembly drawing.
Key Decision Drivers
If: A linear actuator drives a rotating arm joint
Then: Convert the joint torque target into actuator force using the effective perpendicular moment arm, then evaluate it across the full range of motion.
Why: For a simple linkage, joint torque is actuator force multiplied by its perpendicular distance to the pivot. That distance changes with linkage geometry and joint angle.
If: Backdrivability or physical interaction is required
Then: Request assembled-actuator backdrive data and define the force-sensing and safety strategy.
Why: Backdrive behavior depends on the complete transmission, friction, motor, and controls; lead is only one design input.
If: Considering an inverted screw layout
Then: Check rotating-part choice, shaft support, stroke, motor integration, and service access against the package drawing.
Why: Inverted screws can use a rotating nut with a translating shaft, but integrated motor and bearing layouts vary by supplier.
If: Stroke is long or the actuator is compression-loaded
Then: Have the supplier check buckling, critical speed, and support conditions.
Why: Allowable load and speed depend on the screw dimensions, unsupported length, end supports, and operating conditions.
Evidence & Limitations
Checked October 4, 2026
Application: Publishes three inverted planetary roller-screw modules: HJL08 (600 N, 38 mm stroke, 3.5 mm lead), HJL12 (4,000 N, 72 mm, 2 or 5 mm lead), and HJL15 (8,000 N, 96 mm, 2 or 6.5 mm lead). Published maximum speeds are 300 mm/s, 120/300 mm/s, and 120/400 mm/s respectively.
Constraint: These are one supplier’s integrated actuator specifications, not universal screw ratings. The page does not provide continuous RMS load or life data for these examples; model-specific limits and duty cycle must be confirmed with the supplier.
Published November 11, 2025; checked October 4, 2026
Application: The supplier describes a seven-axis arm combining HJL linear modules on axes 4, 6, and 7 with rotary modules on the other axes; it reports a 10 kg single-arm mass and at least 5 kg payload.
Constraint: This is a supplier-published configuration and specification, not an independent test or a performance guarantee for another arm.
Checked October 4, 2026
Application: Describes one common inverted arrangement as a rotating nut with a fixed or translating shaft.
Constraint: This is a general supplier description, not the drawing for the HJL modules or a guarantee of a particular motor/stator layout. Verify the actual assembly with the selected supplier.
Tool Boundaries
Understand what this screening tool can and cannot do.
Use this screen for
A first-pass comparison of peak axial force, stroke, and lead against one manufacturer’s published HJL module examples. Enter force at the screw, not joint torque.
Do not use it for
Choosing a screw diameter, dynamic load rating, service life, or safe human-contact setting. This needs the full load and motion cycle, screw geometry, end supports, temperature, lubrication, and supplier ratings.
Common Integration Risks
Failure modes that should be addressed before prototype freeze.
Thermal Overload (Holding Current)
Trigger: Sustained force or high duty cycle without a verified motor, drive, and screw thermal rating.
Mitigation: Provide the force-speed-duty profile and ambient conditions; verify continuous ratings and any holding-brake behavior with the supplier.
Shock Impact & Backlash
Trigger: Impact loads or reversals that exceed the selected assembly’s peak rating or create unacceptable lost motion.
Mitigation: Specify peak load, reversal count, allowable backlash, and shock spectrum; check the supplier’s rated limits and preload tradeoffs.
Distal Mass Accumulation
Trigger: Mounting heavy linear actuators far from the shoulder.
Mitigation: Compare complete installed mass and center of gravity for rotary, linkage-driven linear, and remote-actuation options before freezing the arm layout.
Frequently Asked Questions
Why use an inverted roller screw for biped robot arm actuators?
An inverted roller screw can support a rotating-nut, translating-shaft arrangement that may help integrate a linear actuator into a compact joint. Packaging depends on the motor, bearings, shaft support, stroke, and linkage; the architecture is not automatically shorter or lighter in every design.
How do arm actuator requirements differ from leg actuators?
The load case depends on the task and linkage. Arm sizing still needs peak and continuous loads, speed, duty cycle, range of motion, and the actuator moment arm; do not assume a lower force or a particular backdrivability target just because the joint is in an arm.
Is backdrivability important for arm joints?
It can matter for force control and physical interaction, but screw lead alone does not establish backdrivability or make an arm safe for human contact. Ask the supplier for measured backdrive force, friction, motor cogging, reduction, sensing, and control details for the assembled actuator.
Should I use a ball screw instead of a roller screw for a robot arm?
Compare actual catalog ratings, duty cycle, shock loads, speed, life, lubrication, and package for the candidate assemblies. A roller screw is not automatically the better choice, and a screw actuator still needs a linkage to create joint torque.
What is the recommended lead for an arm actuator screw?
There is no universal lead recommendation. Lead affects travel per revolution and the force-to-torque relationship, while friction, motor, transmission, sensing, and control also affect backdrive behavior. Size it against the required speed, force, and measured actuator limits.
Does this calculator replace a complete dynamic simulation?
No. It only compares selected inputs with published product maxima and lead options. Final sizing needs the complete force and speed profile, linkage geometry, support conditions, thermal limits, bearing life, and the selected assembly datasheet.
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