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Winch motor torque?


simonr
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Does anyone know roughly the stall torque of any of the common winch motors?

For a series wound motor, knowing the Horsepower of it is actually not that useful so manufacturers usually quote stall torque and max unloaded RPM.

I have back calculated using published figures for TDs winches - 9500 Lbs on the first wrap and 173:1 reduction.

That yields a figure of 8.74Nm - which feels a bit low to me! For the 12,000Lb version of a TDs, the same calculation gives 7.51Nm despite having the same motor.

It could be that the 12,000 winch actually pulls 14,000lb or that a 9500lb winch only really pulls 8200Lb - or it could be that the figures are just made up!

I have to assume that this is not the stall torque, but a torque at which the line is still moving at a certain speed.

I have an Iskra PM DC motor which quotes a stall torque of 30Nm. You would expect a similarly sized series wound motor to be higher!

I want to use a winch motor as a power source for something - but need to know the peak torque to work out how strong the shafts need to be and what reduction ratio is required.

Si

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Failing someone just knowing, could you make up a rig with an arm of known length on the end of the motor, and then a force reading taken off the end of that arm somehow upon the motor stalling, this should give you the stall torque?

Ie. if the arm was 5 feet long and you got a force of 50lbs off the end of it then it would be producing 250lbs-ft of torque.

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Si - surely the drive shaft of the TDS would tell you how strong your shafts need to be? They don't break when the winch stalls.

A conservative assumption of material properties combined with the cross section of the shaft should give you a reasonable estimate?

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Si - surely the drive shaft of the TDS would tell you how strong your shafts need to be? They don't break when the winch stalls.

A conservative assumption of material properties combined with the cross section of the shaft should give you a reasonable estimate?

I wondered about that - but there is no easy way to tell what material or heat treatment it has had. Also, is it over or under engineered and by how much?

Even the difference between 8Nm and 30Nm makes a big difference in drive component spec!

Si

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My guess that it would be chineese monkey metal with no special treatment. Yield stress of say 200N/mm2, maybe 250?

Being a volume product, I can't see it being over engineered by much, but I am only guessing.

The other thing to bear in mind is it is a hexagonal shaft so probably selected from readily available stock? IIRC it doesn't have any modifcatins at all, it is just a plain bar.

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I could just tie the back of the LR to a tree and connect my load cell between the winch and another tree to see what the actual pull is.

I was just hoping to avoid having to do it as it should be a simple question. I'm starting to wonder if it's not quoted because armed with the reduction ratio, you can calculate what the actual winch pull should be. I'm wondering how closely that relates to the published pull oif the winch?

Si

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I could just tie the back of the LR to a tree and connect my load cell between the winch and another tree to see what the actual pull is.

I was just hoping to avoid having to do it as it should be a simple question. I'm starting to wonder if it's not quoted because armed with the reduction ratio, you can calculate what the actual winch pull should be. I'm wondering how closely that relates to the published pull oif the winch?

Si

The problem with that is to know the mechanical efficiency of the winch - friction and other losses in the bearings, gears, brake, drum are significant.

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THe problem youre having is that with 173:1 ratio, the drag in the system can be quite high, combined with the rather carp design of some drum bearings I have seen, you could easily loose 50 % of torque in the system, so just finding out the pull of the winch doesn't tell you much. Did you ask david bowyer this question, caus I bet he knows things like this.

Daan

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I've actually asked each of the winch motor manufacturers (that I know of). David has been the most helpful - but I still have no answers! That's why I'm thinking there is a conspiracy of silence!

It seems nobody knows or is willing to tell. I plan to measure the motors I have this weekend if I have time and I'll publish the results!

Si

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Si,

i did a backward calc of the torque from the official figures on the warn 9500lbs winch with the 6hp xp motor. Torque figure came out at 3.48Nm!

so either the motor is appalling, or the gearing and bearings used in the construction are horrendously inefficient.

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May be interesting or not :lol:

But a couple of years ago I did some load cell tests of a few winches and motors etc and found a massive difference in efficiency between winches that were supposedly the same and even fitted with the exact same motor (actual motor from the other winch) and treble checked for repeatability and comparability!

I mean over 25% in some cases (forgive the pun)

I think you would need to test the motor directly to get any real figures!

I would make up a disc brake with the calliper connected to a load cell and calculate from there!

Hope comments are of some help.

Lara

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Thanks Chaps!

I didn't have time to do any testing over the weekend - but I'll try later in the week. Undoubtedly there is a big difference in the drag in different types of winch but I'm increasingly thinking that the headline winch pull figure is just made up!

Si

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Because most vehicle winches don't have self aligning bearings, just the state of alignment when the winch is mounted up to the bar and when the assembly deflects under load will have a significant affect on the line pull vs motor torque.

I have seen results of some poor winch installations.

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Surely this thread is a very dangerous can of worms

Why?

I had a quick look at bearings big enough to go in a TDs winch - and for 2.5" ID, 4"OD (Smallest I could find), they were a mere £275. Don't think I'll be rushing out to replace mine! I might have a look at IGUS Polymer bearings though. I've had very good results with one of their materials that self lubricates and is happy submersed in muddy water.

Si

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So Si, when is this being released? the winch to beat all winches? hydro or sparky at the flick of a switch. large drum, fast or slow, :D

Almost - but not quite!

I'm building electric grass-skis! Using Harley Davidson toothed drive belts inside out as caterpillar tracks. Load cells in each ski which are used to vary the motor speed differentially for steering. They could either be very cool - or very painful. I can see doing the splits at 30mph being less than desirable!

I've tried using a little Mag-Motor that we used for Robot Wars as well as a couple of Iskra PMDC motors - but none of them have the right sort of torque / speed characteristics.

Winch motors are a little bigger than I intended - but worth a shot as I have several. If that fails, the next step is to use a number of RC car motors in each ski. Just looking at the possibilities at the moment.

Si

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