Bart said: "Still waiting for someone to calibrate a porty for tension ratio vs wraps. Its exponential."
I have developed my own rule of thumb for porta-wrap friction. Maybe it will be helpful to someone.
It obviously has to make many (too many) assumptions. But I still find it useful.
Here are my "rule of thumb" weight ranges for different wraps: [See PortaWrap Load Ranges. JPG]
View attachment 92166
This calls "One Wrap" when the rope comes in the porty at the top, goes under the porty once, then around the post on the top to the groundsman.
This assumes a Coefficient of Friction of 0.25 for nylon rope on aluminum porta-wrap. Ropes can vary a lot, higher and lower than this amount.
Reading the chart - If I estimate the load will be 125#, then 1.5 wraps might work, but groundsman would have to have a very light touch on the rope or the load won't run at all. For 125# 1 wrap would work much better, meaning it's easy to let run and easy to stop the load and hold it.
For those who want more precise measurements, here are the actual percentages, then how I fudged them to make them memorable.
View attachment 92167
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Not inventor but accepted as lead capstan formula/root work to what i show :
The Mechanics of Friction in Rope Rescue by Stephen W. Attaway, Ph.D. for the International Technical Rescue Symposium (ITRS 99)
>>full kudos and many thinks for doorways opened.
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Very sorry, seem to have somehow lost a quantum of work on this.
Remaining in the wake of the loss persists common table of accepted engineering CoF of mated surfaces such as common as .gov reference and at :
engineeringtoolbox.com of assumed linear faces;
then my own adjunct of radial conversion, for the CoFs, in spreadsheet(link) (that crying lost the 14x expanded version of...)
>>'my' conversion of linear to radial CoF, is simply radial cof of mated materials= linear cof of mated materials X pi
>>as i model properly from capstan formula : Euler's number, raised to the power of:
CoF(common linear) x PI(i see as radial conversion) x 'strokes'( compounding applications i think) ;
>>strokes i mean as to, and then fro as to make a cycle, as cam shaft, so 180 degrees = 1stroke, 360 as a full cycle very logically.
Can make addition slide rule with 2 sheets of notebook paper w/numbered lines, 2+2 lines shows 4.
>>to make multiply would space by organic logarithms/not evenly to extrude answer, cuz adding logs multiplies
>>Euler's number is log of 1ish
Formula then says to me very logically take this organic log of 1
>>and compound to the power of radial CoF of mated surfaces x Strokes to find brake force gift as a pattern.
Euler's number:2.71828 is so relevant, is a special key e on many calculators
>>it is used to calc compounds of interest, population growth and disease spread biologies, probability/statistics, engineer, thermodynamics, as well as these physics etc. as a very defining key to truly organic progressions, even for our mychors. So seen as a deep, key, organic constant to how things work/not a one off type, semi-questionable, how far is this true; but purposeful usage here.
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To this model, we take the pattern from Euler's number above xTension
where input of xTension is just at what point you start the same pattern from for the Euler's part
>>for same bell curve progression given by the Euler's number part, starting with xTension is all.
>>we watch the macho xTension hand of magician, as other Euler hand ninjas the throttle control from there.
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'lighter pic' at an assumed .25 linear CoF between nylon/aluminum with these numbers
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don't mean to be redundant, but here is another remaining piece of the loss,
focussing out to show how much change just a small bit of CoF increase can reverberate thru compounding very exponentially as things go leaving the lesser CoF shrinking in the rear view mirror :
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All this distance/force stuff in the end is geometry of a dimension of full potential vs it's dimension of non(e) as limiting extremes of pure potential or non(e) as logical, organic, universal patterned limits.
>>and the range of hybrid inheritances from each parental extreme at a given position
>>applied to a linear force line imposer perspective or linear support receiver perspective of cosine benchmark alignment as full dimension and crossing at 90 the non(e) dimension influence to a given position.
Cos:sine value pair gives us the percentage of inheritance from each extreme purebred parental extreme to present position.
>>this universal organic goes WAY further than tangible/viewable length examples, into force, light, electric etc. all same rate of change from full hero expression of potential to the non(e) of flat zero expression of potential. Seeing in length is most tangible viewport, to this pattern in everything.
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Most things force wise may only capitalize from here on cos/alignment for support
>>and sine/cross alignment for leverage in standard linear rigids to a specific point.
Radial Rope Friction puts that math on friggin steroids as can capitalize on cos+sin both at once(to mostly greater sum than cos/sine individually or initially.......) and then apply that crazy expanded math over not a point but a range(that then can stay virtually in the same position); totally different class animal.
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But material CoFs vary per if clean/dirty/wet X rope material X aluminum/steel porty type variances. Natural Manilla was MUCH GREATER mating CoF.
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We can see these cos:sine things visually in distance to l-earn by making more tangible
>>but apply to force as well , with same model, as unachieved, unrequited distance potential aligned confronted by equal/opposite or funneled denser into smaller space by crossing force of leverage
>>but in either instance(aligned or crossing dimensions of consideration) force is a reciprocal of distance traded
>>so same formulas work
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Very intuitively in linear CoFs, distance matters,
counter-intuitively in flexible rope radial friction, greater radial distance only matters
>> for softer arc curve to baby rope more properly
>>spread out heat from frictions
>>tighter/denser per inch choke of smaller diameter on host(type distance), if rope still in flexible range/host not too small
As long as rope seats well to round capstan, distance has nothing to do with friction !!
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ya know i ken go on fer hours on this....
