Does satisfying cable bend radius prove a yaw cable loop can tolerate torsion?

The short answer

No. Bend radius describes curvature, while torsion describes twisting along the cable. A cable can satisfy its bend-radius requirement and still exceed its permitted twist or cyclic duty. A wind-yaw cable loop needs evidence for both motions in its actual installed geometry.

Distinguish the two deformation demands

A bend curves the cable centreline. Torsion rotates its cross-sections relative to one another along the length. The conductor lay, shielding and construction affect how a cable tolerates those demands. A general flexible-cable label does not establish torsional suitability. The manufacturer should identify whether the rating concerns occasional installation movement, repeated bending or repeated twisting under specified conditions.

Use the length that actually twists

For a simplified hypothetical uniform distribution, one full turn across 2 m corresponds to 180 degrees per metre. The same turn across 1 m gives 360 degrees per metre. This does not establish a permissible twist: clamps, friction and routing can localize deformation rather than distribute it uniformly. The cable maker’s limits and the designed free length are therefore required together.

Request motion-specific cable evidence

Ask for minimum dynamic bend radius, permitted torsion per length, cycle/temperature conditions and the routing/support arrangement that those ratings assume. Igus explains cable-specific bending constraints; torsional capability needs the selected cable’s own evidence. MARSTON cable construction and yaw travel are unconfirmed. Do not infer unlimited rotation from a generous loop or add turns to test flexibility. The decision is whether the actual cable and free length accommodate the combined bending/twisting envelope defined for the equipment. A cable bundle needs assessment as an installed arrangement, including clamps and neighboring cables. One cable’s standalone torsion capability does not establish how twisting is distributed through a restrained multi-cable yaw loop.