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Pulling Strings


New member
Can anyone tell me how to model the cables in a bloc and tackle assembly?You know; flexible components that wind around cylinders and respond to changing configurations of the assembly.

As an example, here is a model of a robot worm to test a linkage concept for mechanical replication of reptation.

Also, I would appreciate it if some of you were to venture an estimate on how many man hours it normally requires to build this model and do the animation when you actually know what you are doing. Just to get an idea if we are near the ball park.



hey thats cool:)

it looks like i am going to have to play with flexible components.

want to share your model so we can see how it was done?

or email :)


New member
Sure thing. No problem sharing the model.

Yes problem getting under the 500K upload limitation. I'll see if I can finnagle something. If not just send me your email address.

I must state however that for the threading mechanism I cheated outrageously. That's why I'm asking for help in understanding the way it is supposed to be done properly.


New member
I'm not sure if Pro/E can do belts like that. According to PTC's Suggested Technique for Modeling Gears in Mechanism Design Extension:

"Pulleys with flexible belts are not available in MDX, MDO or Pro/MECHANICA Motion. Instead, a gear connection will be used to transfer the motion from one pulley to the other without any intermediate component to transfer the motion. "

and: "Since belts can not be modeled as continuous systems, a gear pair will successfully define the relative motion between the pulleys. "

I don't know if that helps you any or if I'm totally wrong but I'd thought I'd add it to the discussion. With any luck since you've come this far with the model you'll be able to laugh at me and tell me it can be done. I'm intrigued by what you've come up with so far.


New member
No I'm not laughing. And yes that answers my question. It can't be done.

So I'll have to be content with the workaround you saw on the post. I don't mind sharing the model, but I can't post it becauseit weighs 2Mega and there's a 500k limit for uploads. So I'll send it individually to those who ask, if they'll just send me a handle. I can be reached at [email protected]

The cheat could be made to work for belt and pulley assemblies. You would have to calculate the point of tangency of the belts with the pulleys and use that as a parameter. Note that in my case the string is not resting properly against the sides of the grommets. It could be done if there were a reason to deploy all that trig.