Estimate cable-bore area, then check model, cable, motion, and connector limits before design release.
Estimate an area-based upper bound from the clear bore, cable OD, and an editable planning assumption. This does not verify fit.
Area division is only an upper-bound estimate. It does not model cable bundle packing, connectors, seals, bend radius, torsion, motion, or heat. Check the actual model drawing and cable data before design release.
This estimate is not a gearbox selection or safety approval.
The calculator starts at 40% as an illustration. It is not a universal gearbox-bore recommendation or thermal limit.
A hollow bore does not imply a universal stiffness penalty or match. Compare the selected reducer models and test conditions.
A hollow bore alone does not stop a cable winding up. Continuous rotation needs a suitable slip ring or other rotary interface.
The area allowance is the clear-bore circle area multiplied by the user-selected planning fill. The default is 40% only as an editable example; it is not a gearbox-bore standard and says nothing about heating, motion, or code compliance.
The displayed value is the floor of the area allowance divided by one cable's outside cross-sectional area. It is an area-based upper bound, not a packing solution or verified cable count.
Area = π × r²
Estimate = ⌊(π × bore_ID² / 4 × fill% / 100) / (π × cable_OD² / 4)⌋Circular packing constraints mean area alone cannot confirm that a cable bundle will fit or move reliably. Check the supplier drawing and cable data for the application.
| Feature | Hollow Shaft (Cable Through) | Solid Shaft (External Routing) |
|---|---|---|
| Cable Management | An internal route may reduce exposed cable run. Continuous rotation still needs a suitable rotary interface. | External routing may need cable support; check travel, bend radius, and torsion rating for the application. |
| Torsional Stiffness | Model-specific. Compare exact catalog values under matching test and mounting conditions. | Baseline reference. |
| System Footprint | Can route near the joint axis; confirm model OD, bore, and connector envelope against available space. | Include the cable path and its full-motion swept envelope in the machine layout. |
| Bearing Structure | Depends on reducer architecture; verify allowable moment and thrust loads for the selected model. | Bearing arrangement and load limits depend on the selected gearbox architecture. |
| Cost & Availability | Compare reducer, rotary interface, cable, and assembly costs in the complete bill of materials. | Compare reducer, cable protection/support, and service costs in the complete bill of materials. |
Nabtesco describes its RV-C hollow-shaft line as maintaining RV series accuracy, rigidity, torque, and load support. Treat that as a statement about its own designed series; do not transfer it to every hollow-shaft reducer or assume two models match.
Nabtesco RV-C product informationRobot cable torsion capability is product-specific. For example, igus publishes torsion limits and bending data for particular cable families; use the data sheet for the exact cable and motion duty.
igus CFROBOT2 cable specificationsBefore release, check clear bore after seals, connector envelope, bundle layout, cable bend and torsion ratings, thermal duty, continuous torque, moment load, and the required rotation range. The calculator checks none of those supplier ratings.
Use the RV reducer selection guide to prepare broader load, interface, precision, and RFQ inputs. For adjacent topics, see hollow-shaft cycloid reducer options, the backlash and torsional rigidity guide, or contact RV Reducer engineering. Sources reviewed October 7, 2026.
A hollow bore can provide an internal route and reduce the external cable sweep. It does not by itself prevent cable torsion or enable unlimited rotation. Set travel limits and select cable for the actual motion, or specify a suitable rotary electrical interface for continuous rotation.
No. It divides an assumed area allowance by one cable area to give an upper-bound estimate. It does not calculate bundle packing, connector passage, seals, bending, torsion, temperature, or a reducer rating. Confirm those against the selected model drawing, cable data, and duty.
There is no universal fill factor for a gearbox bore. The calculator starts with an editable 40% planning assumption, not a gearbox standard, thermal limit, or guarantee of physical fit. Confirm the cable bundle, connectors, motion, temperature, and usable bore against the specific supplier drawing.
Do not assume equivalent stiffness from the hollow-shaft feature alone. Ratings depend on the exact reducer design and size. Nabtesco describes its RV-C models as maintaining RV-series rigidity, but compare the specific catalog ratings and measurement conditions for the two candidates.
Include the target reducer or interface, clear bore after seals, cable and connector dimensions, bundle layout, axis rotation and motion profile, cable bend/torsion data, temperature and environment, reducer torque/speed/moment duty, quantity, and destination. Ask the supplier to confirm usable bore dimensions and provide a drawing.
Check the connector's largest cross section and orientation against the clear bore. If the assembled connector cannot pass, specify how the cable will be terminated during installation.
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Include target torque/speed, quantity, and delivery location.