I'm in a use case where the outer surface is a gear driven by a motor (that's the easy part) and the inner surface meshes with a metallic (iron) rope. When the part rotates, I want the motor and everything to climb the rope the same way a nut moves in a bolt. The part and the rope share the same cylindrical axis.

I want the part to be as simple as possible, no assembly required. I also need the part to be as general as possible. Let's say the pitch of the rope is p mm and the angle is theta degrees.


If there's any more details required, I'm happy to elaborate. I've brainstormed for a few hours and I'm coming up blank. Best I can do is doing a 3D negative of the rope surface. In theory it will climb but in practice, it will be unreliable and easily wear out

  • $\begingroup$ Loop the rope once around the pulley. $\endgroup$
    – Solar Mike
    Mar 14, 2022 at 11:17
  • 1
    $\begingroup$ I think the problem is that a "rope" is not a machined part with guaranteed uniform structure. You seem to be heading towards a screw drive, replacing your "rope" with a threaded rod. $\endgroup$ Mar 14, 2022 at 12:27
  • $\begingroup$ See if ski-lifts offer any ideas but I suspect that any attempt to do what you are proposing will chew up the rope due to changes in helical pitch with load. $\endgroup$
    – Transistor
    Mar 14, 2022 at 12:28
  • $\begingroup$ As soon as the cable bends it would seize inside the nut followed by any manner of failure such as winding and tangling itself up, the cable shredding, or the nut stripping. Thread percentage for filament bundles is also too low. $\endgroup$
    – DKNguyen
    Mar 14, 2022 at 13:47
  • $\begingroup$ think of bulldozer treads instead of wheels $\endgroup$
    – jsotola
    Mar 14, 2022 at 18:53

1 Answer 1


I believe this answer is mostly applicable to your question, although the "assembly" would be ninety degrees rotated. I've recently learned of a system known as Synchromesh Drive Systems which involves a straight wire wrapped with a helical wire, making up the drive cable, and a matching pulley.

synchromesh drive pulleys

synchromesh drive cable.

Photos from linked site. There is also a video showing this type of drive system being used in a 3D printer.

One could use this system for climbing if the cable was fixed securely and the motor was part of a traveler, designed to maintain cable contact, perhaps with tensioning pulleys on the inbound and outbound sides of the drive pulley.

If one considers the typical wire rope, the alignment amounts to a very steep pitch, making the mechanical aspect quite challenging. A wire rope with a smaller pitch akin to a screw is going to be more like a spring than a rope. Combining a conventional wire rope with a "spring wound rope" begins to approximate the Synchromesh Drive System.

  • $\begingroup$ That just seems like a different take on timing belts, chains and sprockets, except that the pulley/sprocket can engage from any approach. $\endgroup$
    – DKNguyen
    Mar 14, 2022 at 18:50
  • $\begingroup$ In the case of 3D printing, I suspect one advantage is lighter weight, no stretch (belts), less inertia. There's also an unfounded aspect that (in laser cutters) that the typical Gates belt causes "flutter" as the air is pushed out from the teeth during operation. This type of drive would eliminate that. $\endgroup$
    – fred_dot_u
    Mar 14, 2022 at 20:10

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