Double Bullwheel Roller Capstan Calculations 1

[amarks]

I'm looking at designing a utility transmission line pulling unit and am curious if anybody knows calculations used to determine the capstan sizing (number of wraps, bullwheel sizing, hydraulic gearmotor sizing, etc.) for a certain amount of pulling force?

See picture attached of a common setup.

 

[mfgenggear]

Op
What your asking for is very complicated. And a bunch of information is missing.

 

[amarks]

mfgenggear - Do you know of any manufacturers that design and manufacture these, that I can discuss specifics with?

Looking at pulling 22,000 feet of 3/4" diameter wire rope at 30,000 lbs max line line tension.

 

[3DDave]

Look for the capstan equation to find number of wraps. The diameter is based on the minimum bending radius allowable for what is being wrapped. The motor size is based on the power required, which is from desired tension and speed.

You will also want tension monitoring and feedback controls.

Buying a unit from a current manufacturer will be less expensive at most time scales.

 

[mfgenggear]

I saw videos of cables snaping and killing people. There is real safety issues . This is no cake walk.
Unfortunately I have no recommendation.
But recommend contacting companies who have expert engineers that have extensive design experience with
Loads, wire rope size, torque and rpm required. Procure the MIT Calc on line if to just experiment with it.

 

[BEMPE16524]

as we just recently had some discussions before, you could possibly refer to this same basic thread:

https://www.eng-tips.com/viewthread.cfm?qid=522409

it might help you somehow.

as for the number of wraps and layers, if you know the wire rope diameter, its lenght and the width of the drum and its core diameter, you can calculate the number of wraps and layers.
most important factor is the minimum bend radius of the wire rope to determine your minimum drum core diameter.

then you can expand your research from there weather you want to use electrical motor or hydraulic motor for the system.
that will involve more equations and further studies.



R.Efendy

 

[Compositepro]

A capstan is a very simple device. Don't over complicate things in your mind. The theory and mathematics can get complicated. I replied to your other post and I'm glad you are pursuing investigation of using a capstan. It is just a driven drum that pulls through surface friction. Smooth drums are the simplest, but for cables under high tension, grooves are needed to increase contact area and reduce contact pressure so that the cable does not get damaged. A second drum is needed so that you can get more than one wrap. That second drum can be driven or not. Wrapping can be a simple 180 degree contact or figure eight configuration between the drums. Stepping the cable over for each wrap can be by grooves or by just tilting the axis of the idler drum. A pinch roller is need on the low tension side to generate some initial friction and tension, and to keep the loose end from falling off the capstan. Generally three to five wraps will pull anything to the breaking point. More wraps will be more gentle on the cable and add no cost or complexity.

The diameter of the drum is determined by what is good for the cable. Larger diameter reduces the bending stress on the cable and the contact pressure. The equations for this are actually very simple to derive. The thought process of deriving equations is very important to understanding and remembering them.

Examine existing similar equipment, or pictures of equipment, very closely. This is so easy to do now with the internet.

 

[amarks]

Compositepro - I keep telling myself it shouldn't be this complicated but I keep coming back to calculus equations and their derivatives. I do think it is the way to go and I still want to dig deeper into the capstan route, however the customer is requesting that we not use the capstan, so we are back to very beefy drum, big sprockets and planetary gearboxes to operate.

That is very interesting about, any more than 5 wraps are just for preserving the cable. I figured that it would just continue to increase in the amount of pulling force for each wrap, regardless. I wonder why that is, that it just falls off after about 5 wraps?

I've recently come to find out that the bend radius is very important for sizing the drums. From what I have seen from other manufacturers in the industry, both capstan drums are driven by hydraulic planetary gearboxes.

Are there any advantages to the orientation of the capstan? I've seen some manufactures stack the drums vertically and some that have them side by side horizontally.

Thank you for your feedback and input.

 

[dvd]

amarks - I definitely admire your desire to jump into the unknown on the project(s) that you are discussing. Do you have any guidance from senior colleagues, or are you the senior colleague? A company which takes on these kinds of projects without knowing how to proceed seems destined to repeat the steps that successful competitors have had to painfully learn.

This thesis may be of interest - Multilayer Spooling of High-Performance Synthetic Fibre Ropes - Experimental investigations of rope properties and stresses in winch drums - there are multiple references listed.

Maybe you can find the author and hire that person as a consultant.

 

[Compositepro]

From experience with other materials, my "feeling" is that winding 22,000 ft. of cable at 30,000 lbs. of tension is not technically feasible. Each wrap has stored energy. The "lever arm" is the roll radius. The inner wraps at small radius must provide the pull on material winding at the larger radius due to slip between layers. The compression force of each outer wrap is additive onto the drum and the inner wraps. It seems that you will be able to make diamonds with such a machine.

 

[amarks]

DVD - thank you. No sir unfortunately it’s myself and one other engineer that is on a project for another industry. I’ve worked in companies with many engineers on a team and am fortunate to still have a lot of them for reference. Unfortunately that was in a totally different industry from what I am doing now. I’m trying not to reinvent the wheel but also improve on what is already out there and also not fall victim to everybody else failures by learning it through the school of the hard knocks. I’ll take a look at your thesis paper link thank you for your input.

Compositepro- fortunately I am not reinventing the wheel. This has been many times and there are quite a few units out there already doing this. I’m just trying to make sure I design my drum to withstand the forces. But I do agree, the forces are quite high and it does seem like you’d “be able to make diamonds” by the time you reach the center. Take a look at this unit for example

https://wagnersmith.com/wp-content/uploads/2024/01/T-1DP-1140-FT4.pdf