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# Capstan Drums need Help

11/11/2006 3:10 AM

Hi

We have built a machine using a capstan drum and we are having problems.

Not having looked correctly at the way capstan drums work we machined the drum surface flat and the rope keeps riding up onto the shoulder because it has to displace the previous wrap as the rope winds on.

There was initially 4 wraps, we have reduced this to 2 and increased the slack side tension, this has made it work but really need to go to at least 3 wraps.

The rope is essentually continuous, and travels 35 each way (up and down) max speed 2m/s

The drum mean dia is 525mm, rope 28mm T1 max is 167 kN.

Is there any design rules for the shape/profile of the capstan?

It would appear that if we put a radius into the drum rather than flat it should assist the inner wraps to move to the centre and reduce the side load required to displace it!

Best regards

Burgs

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Join Date: Mar 2006
Posts: 11
#1

### Re: Capstan Drums need Help

11/11/2006 12:22 PM

Hi Burgs

The drum with a radius is usually called friction drum which has the advantage of maintaining constantly the same positioning of the rope (for large radius). It has the disadvantage of the rope wearing.

The large capstan drums have an appropriate length for the corresponding length of the wraped rope. The capstan drum it can be made with a helical path on the face of the drum in order for it to work corectly. The pitch of the helix depends on the diameter of the rope. Below are listed some diameters and their corresponding pitches:

rope diameter (mm) ------pitch(mm)

24 -------------------------27

27--------------------------31

29--------------------------33

31--------------------------35

Usually the pitch=(rope diameter mm +1)/2.

For more wraps probably you will need a driver to reverse the wraping direction of the rope.

lgeo

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#2

### Re: Capstan Drums need Help

11/11/2006 1:56 PM

I think your problem is either the size of your spools related to the thickness of the material being spooled, or the traveler is the problem when reversing direction and causing the pile up on the interior spools sides.

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Join Date: Nov 2006
Location: Austrlia
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#3

### Re: Capstan Drums need Help

11/13/2006 3:42 AM

Thanks for the replies

A helix will not work in our case as we end up needing a drum 1200mm wide to accomodate the movement of the rope across the drum as it winds in and out, we do not have the room or ways to control the resulting fleet angle as well. We have fitted a set of rollers to guide the rope off the drum this has the effect of reducing the side loads as the rope leaves the drum, much the same as you do using a simple capstan with light rope by hand.

We have looked at a double drum which would have worked but the complications and size restrictions headed us this way first

We will do a test run tomorrow and see what happens.

Best Regards

Burgs

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Join Date: Oct 2006
Posts: 61
#4

### Re: Capstan Drums need Help

11/14/2006 9:15 AM

if i remember correctly there is standard for capstan drum, you can try ISO6482 and have a look at the profile. you are right that the curve up at the end of the drum actually made the rope slip across the witdh of the drum. you may consider modify your current design by making a cone and welded at the drum face and flange. I think you are using wire rope by the look of the strength and drum diameter, you may want to use the term "traction winch" and look up in the www. hope this help

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Join Date: Nov 2006
Location: Austrlia
Posts: 2
#5

### Re: Capstan Drums need Help

11/17/2006 12:10 AM

Hi

We have remachined the drum with a concave curve instead of flat profile and now the rope is behaving ok. The machine has now left the factory and we will assemble on site over the weekend and start commissioning test Monday. I will have a look at the ISO6482 Standard, thanks again

Best Regards

Burgs

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Join Date: Oct 2008
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#6

### Re: Capstan Drums need Help

10/07/2008 5:02 PM

Hi, I am presently having the same problem than you. We designed a machine that is moving itseft with a capstan. The cable is fixed and the capstan is on the moving machine. We curently have a flat drum, and we are having the same problem than you.

I know that we msut use a concave shape, but I don't know what is the slope of this shape. Could you gine me an idea?

Cheers

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