Lifting and holding capacity?

[GGOSS]

Hi guys,

I'm electrical, not mechanical so please excuse me if my question seems a little basic I am looking for advice/guidance on how to calculate maximum lifting and maximum holding capacities (preferably in kg) for a drum style winch with the following details.

Drum diameter - 250mm
Drum shaft diameter - 20mm
Drum speed - 80RPM
Gearbox - approx 70:1 right angle worm box
Motor power 500W 12V DC

Any help would be greatly appreciated.

Thanks & regards,

 

[desertfox]

Hi GGoss

Workout the max torque that can be exerted by the motor on the drum, then divide the radius of the drum into that torque figure to get the load exerted at the edge of the drum.
Bear in mind as the cable wraps round the drum, the tension in the cable might stay the same but this increases the torque on the drum and thus, the motor as to work harder to continue to wind.
Thats just a starting point, why not contact a winch manufacturer or obtain a catalogue.

desertfox

 

[GGOSS]

Thank you desertfox,

I am actually comparing a couple of winches and have found the manufacturers published data on max lift and max hold to be very different even though the products appear very similar eg same motor and gearbox. Also, as neither are prepared to give me a straight answer, I was hoping with the assistance from people like yourself on eng-tips I could perform my own calcs and make a more informed decision. But I do not have a formula or set of formulae to work with. Are you able to assist with that?

Max lift, I would imagine would be calculated with minimal wraps on the drum shaft. I would imagine gearbox size eg 40, 45, 50 etc would influence holding power but do not know for sure. As you can see, i'm flying blind at the moment.

 

[asimpson]

That's pretty fast for a big motor. Over 5000 RPM. And over 6 M/min on winch.

Would need to know motor torque at 5600 RPM. Depends on motor. Should be in data sheet.

 

[GGOSS]

Unfortunately no data sheet for the motor asimpson. Can we assume a value for the sake of the exersize. Then maybe I can repeat the calcs once the motor torque details are known.

 

[desertfox]

max torque at motor 0.85Nm through the g/box 59.5Nm at drum

 

[desertfox]

I calculated the torque from the information you posted ie power=2*pi*N*T/60. So by transposing the formula to find the running torque of the motor, having found this figure I then multiplied that by the gear ratio in your original post.

desertfox

 

[unclesyd]

In the US a manufacturer of any lifting device is required to have a full disclosure of the full capacity of the machine and if required availability to see the raw data. In most cases this has to be verified by proof testing.
I don't have the exact available.

I believe that most European countries have very similar requirements.

 

[Cockroach]

Wow, this is one of my favorite engineering questions, wireline rope drum. Be very careful with this one, she's a beast! I crushed about twelve designs before getting it right, almost gave up on it.

You need to determine the wireline load or tension in the windings! This is the trick. You can get that noting horsepower equals the torque times RPM divided by 5252; torque is in "ft lbf" and obviously RPM is in rev per minute. You know the motor horsepower so can easily determine the torque.

This is the trick. In the first layer of windings, assuming you lay the wireline uniform and neatly without gaps, the compression on the core of the drum is simply the hoop stress. In other words, you can determine the pressure exerted by the first layer of windings noting torque and distance from the drum axis to the centre line of the first layer wrapping.

Maintaining the line tensile load, you begin the second layer wrapping. But your moment arm just changed by the diameter of the wire rope being layed. So the second layer does not have the same pressure laid to the core and first layer of windings. You should find that the compressive strength applied to the drum jumps significantly. This phenonema occurs for each successive winding of wire laid upon the layers below.

The required radial compressive strength is the sum of all pressures determined per layer. Also, there is a side load imparted to the flanges of the drum which induces a moment to the core. This is amazing considering each successive wrap of wireline is actually cradled by the layer below. Once you have that estimate, you are pretty much in control of the dynamics of the drum, less thermal expansion of the system, which can be significant.

Look at it like this. Take an elastic and start wrapping it around your finger. Finger turns blue right? That is the core pressure exerted by the elastic tension as it is being wrapped. If you can stand it, try to wrap a second layer. You will feel the pressure on your finger go through the roof! Imagine what the drum is going through using wire rope!

I do recall several excellent references from the industry. I need to pull some files and get the actual model I used to solve this one, but I recall it was a major struggle for me over a two year period. It's not about the money lost in failed designs, it's about my stubborn attitude never to give up. Some of the industry drum guys may be of help, but depending on your application, they are actually of little help. Wire rope industry reference is much better, sometimes limited. There is a welding reference from Lincoln that discusses this problem in detail, that is what I researched years after my experience.

Yup, fun times!

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[Cockroach]

This is a decent beginning on the subject of wireline drum design. Lots on the web, never had that in my day, LOL!

Kenneth J Hueston, PEng
Principal
Sturni-Hueston Engineering Inc
Edmonton, Alberta Canada

 

[GregLocock]

Had a quick scan through it, couldn't see any discussion of two rather important properties. First, build up of hoop stress with number of layers. We measured this and for one particular cable found that the 7th layer and more added nothing to the hoop stress in the drum. The ratio of the radial to the axial stiffness of the cable is important here.

The other rather more exciting property that is important is the coefficient of friction. If it is low the the cable can remain tensioned even if it is on the bottom layer. If it is high then the layers lock together, giving the effect in the first para.

Cheers

Greg Locock


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