Nerd Alert

[Bart_]

I've got to stop my habit of writing like a teen texting, abbreviating everything like a few extra key strokes are too onerous for the sake of clarity. I realised later how much I condensed that post. Sorry.

Practically speaking, it was a reminder lesson for me in needing to use good machining practises within normal limits. I get a kick out of big machinery equipped YT guys who occasionally actually bump into the limits of machine and toolpiece rigidity and cutting edge performance. Makes them less like supermen with unattainable skill when you see the common limitations kick in, albeit at a much higher level of operation.

 

[Reach]

I've got to stop my habit of writing like a teen texting, abbreviating everything like a few extra key strokes are too onerous for the sake of clarity. I realised later how much I condensed that post. Sorry.

Practically speaking, it was a reminder lesson for me in needing to use good machining practises within normal limits. I get a kick out of big machinery equipped YT guys who occasionally actually bump into the limits of machine and toolpiece rigidity and cutting edge performance. Makes them less like supermen with unattainable skill when you see the common limitations kick in, albeit at a much higher level of operation.

No worries, I sometimes condense posts as well and realize later that what I wrote made no sense at all to anybody but me. And every once in a while, even I have trouble making sense of what I wrote!

And that actually makes sense, thank you for the clarification there. I am no machinist, but my father used to be, so I understand a little bit of the basics. I haven't ever watched any videos on YouTube though of guys showing off what they can do. I just know that some of what is out there today is really impressive.

 

[Bart_]

Total cool nerd alert. For others this never happened and can't happen.

 

[Bart_]

Amp-ed sound effects built inside the guitar! Youtube served this up to me. Cool!

 

[Bart_]

Saw a yt vid interview of Fender's ceo prior to the stratocaster copy cease and desist issue and they were talking about the 75th anniversary of the telecaster. Story. In high school I got a 63 jazzmaster but wasn't happy with the neck (still, a cool guitar) so I ended up at a guitar collector's house where we wrangled a trade - I got a 67 345 stereo varitone gold hardware - beautiful, set up to shred before shredding was a thing. me + humbucker = no. Plus it was so easy to play I was losing the strength in my hand which ruins playing acoustic. I eventually traded that for a strat. But the story was the guy pulled out an actual Broadcaster which he claimed was 1947. Now with web info I think it existed in 1949.

Punchline - he would let me see him holding it, but I wasn't allowed to even touch it!

note- Fender was stopped by a drum? company from using the name broadcaster, so there was prototype, broadcasters, name-left-off "no-casters" and then telecasters in 50 or 51(?)

 

[Bart_]

Porta-Wrap Calibration

Been scratching my head on this since a thread on porty nomenclature came up. As a device the porty is a pure example of tension ratio, big rope tension side holding the log and small tension side being held by the groundie. It's ratio is determined by the wraps and bends of the rope going through it. In the nomenclature thread I noted the similar BMS Belay Spool and how I previously measured the expected exponential ratio change with number of wraps and spotted the particular to BMS constant of x3 ratio increase per additional wrap. A porty and BMS having roughly the same drum diameter one would expect roughly the same size constant for a porty. But things differ overall. The BMS has a pure tangential rope entry and exit while the porty has a 90 degree entry bend around a smaller diameter pin and also a similar 90 degree bend exiting toward the groundie. The entry and exit have some amount of "equivalent wrap" contribution that is always present. Also, the BMS is used at an overhead rig tip in lieu of a pulley while a porty is almost always used with an overhead rig tip block/pulley. So it makes sense to include the effect of the block similarly as the 90 degree bends, as a base or lowest tension ratio case. A challenge comes as to how to measure this.

When I measured the BMS I had load cell on each end of the rope, tensioned the rope pulling from one end and watched/measured the rope take up its stretch and travel around the bollard, both rising and falling tension. I could see the simultaneously logged values and confirm that there always was a constant ratio and that it reversed with rope travel direction. Same procedure yielded a tension ratio of x1.2 for a pulley - ball bearing or bushing. Chanced across Peter Donzelli's research and discovered he was perplexed when his overhead rig tip block load cell didn't read x2 of the load on the end of the rope. In the SRT Base Tied Tip Forces thread I checked Pete's numbers and found out he had the same tension ratio 1.2 as I measured for the pulley. Happy day. Peter went on to further explore the block/rope friction, trying to interpret it as axle/bushing friction. Probably folly as bearings just don't develop that much friction but bending and deforming a rope does. In his further work online publication the raw data table wasn't available and I don't have the oomph to reverse calculate the data from the non-linear cylindrical bushing equivalence equations he used to process the data. However, he did illustrate two simpler measurement methods.

In Peter's initial work he tried for IIRC onset of motion, suspending a weight, looking for x2 tip force (which didn't happen). In his second work he had a suspended weight, overhead block and the load cell at the pulling end of the rope instead of at the x2 overhead tip. In both cases he tried for "right at the onset of motion". His interpretation of this was that there would only be static friction, no dynamic friction and no f = m x a inertial force effects. Without a high sample rate data logging and a second load cell in the system to check for force sum inequalities I think it's virtually impossible to nail that instant, procedurally or timing the data pick. IME it's even hard when you log the movement of the rope. However, a field method aiming for constant slow speed is do-able, where you acknowledge you're going to get an f = m x a dip when starting the log downwards and a corresponding bump when you halt the downwards motion - you've got several feet of travel at controlled constant velocity to see a steady reading on your eg Enforcer load cell. Bingo. As a bonus, the objective is actually the dynamic friction/losses scenario of during normal use.

From a useful numbers point of view, the two 90 deg and the one overhead x1.2 rig pulley will always be there, so the objective is to get that base combined system tension ratio. Then increment by 1 wrap and repeat. Add another wrap and repeat. If you can go 3 wraps and the groundie end hasn't gone too floppy you can check for the constant x-something (approx x3?) tension ratio change per wrap - and you're calibrated. As a side product you can also note how much force at the groundie's hand feels comfortable or uncomfortable (eg 10 lbs +/-?) to give a target for rigging operations.

And make a chart

One gotcha could be any excessive stretched out spiralling of the wraps on the porty messing with the bollard equation applicability. To be seen. Could be just a small deviation of x per wrap constant. And it's to a degree rope/porty combo specific. Also to be seen. Maybe it'll turn out to be a roughly universal calibration.

 

[Bart_]

Rope Bend Losses or Bushing Friction Losses

These two factors both undoubtedly contribute to losses that create the tension ratio of a rope bending a redirection path around a pulley. There is a similar dual contribution of rope bending a path around a bollard and simultaneously skidding across the surface of the bollard. In the case of a bollard it seems appropriate to just calibrate an empirical mu constant to the T1/T2 of the bollard equation. In my work, I did this at the tail end of including pulleys in my tip/bollard U-turn test jig. IIRC I called it equivalent mu. It doesn't seem critical to split the bending and skidding effects. In the latter Donzelli pulley U-turn (rigging block) work the rope U-turn losses were attributed or modelled as solely caused by by bushing friction of the pulley. In this case the bushing friction can be revisited to recconcile or understand the split between bushing friction and rope bending losses.

At first blush the bushing friction equations used by Donzelli seem convoluted. Further review reveals that the math is straight out of simplified standard engineering statics and dynamics textbook. In my old text there's a pencil note (used text less$) "don't have to know for exam" (950 page book 1 semester!). It was exactly the Donzelli example. It's an approximation construction that allows a simple algebraic solution. Here's the basics. The pulley hole is larger than the axle and when the pulley spins it drives/climbs up the slope of the axle till it reaches a contact position/angle where it slips - the friction angle of repose. This conveniently creates an off-center pivot point where all the forces balance at/about. tan(Angle of repose theta) is usually (friction force/normal force) or mu, but the physics trick of theta = sin(theta) = tan(theta) for small angles is used to remove the trig function. Thus the offset from center becomes mu x axle radius and life gets much easier.

To compact the math:
mu is bushing coeff of friction
r is axle radius
R is radius out at center of rope pulling downwards
T2 >T1, T2 and T1 are the two rope end tensions like used in the bollard equation
c = r/R for later normalisation of the result
A = T2/T1 tension ratio

torque from bushing friction = (T1+T2)x r x mu
net torque by two rope ends = T2x(R-r x mu) - T1x(R+r x mu)

these two are equal at the angle of repose
T2x(R-r x mu) - T1x(R+r x mu) = (T1+T2)x r x mu

I'll skip steps that suck to type, but divide both sides by T1 to use A:
A(R - r x mu) = r x mu + A x r x mu + R + r x mu

A = (R + 2 x r x mu) / (R - 2 x r x mu)

Now some numbers.
W47 big blue roll gliss pulley 1.97" groove diameter 1.2 equivalent mu 0.06
3/8" dia axle solid bronze bushing
1.97/2=.485" 11.7 mm dia rope = 0.46", .46/2=.23", 0.985"+0.23" = 1.215" R
3/8" dia/2=0.187" r

bronze (lubricated) bushings on steel have eg min mu 0.05 and eg max mu 0.15

saving the pain of typing out the substitution A was 1.03 and 1.1, measured definitley 1.2 same as Donzelli got. So there's more loss than the bushing can explain. On probabilities I'd say the bushing material was in the mid range so bushing A is about 1.07 a little under 50% of the measured drag. It confirms an expectation that the rope bending contributes the other roughly 50%. This is the first time I've ever seen a quantitative split out of the two effects.

One step further.
W44 Petzl Partner 1.06" groove dia 1.18 ball bearing
example lily-bearing.com friction torque = 0.5x0.0015 x radial load (N) x bearing bore (mm)
eg T1=T2 = 100 lbs 3/8" I.D. works out to 0.05625 in x lbs bearing friction torque
At 100 lbs T with about 0.75" R that's about 0.06 lbs difference between T1 and T2
So A would be 100.06 lbs/ 100 lbs = basicly 1.0 wheras the measured A was 1.18
Note the pulley diameter was about 1" vs about 2" in W47
NTN info said bearing friction torque "is less than 1/100 of a sliding bearing"
So the rope bending is a real thing besides bushing friction in a pulley.

Sorry Peter, with best of intentions.



In discussion, smaller axles reduce your bushing drag torque but reach surface contact psi material limits sooner, as well as bring the shear strength of the axle into play as a limit. An example of the limit of this effect is the knife edge pivot/bushing of a doctor's or similar scale. In my 1964 machinery's handbook they even mention radiusing the knife edge with a whetstone! At the opposite Google served up a paper mathematically integrating up the contact friction torque contributions based on parabolic contact distribution near the conceptual repose point. Yeah, more real but not at this time. Empirical wins the day for now as mfr mu was based on repose model.

 

[Muggs]

@Bart_ I realized another factor with pulley efficiency many years ago when setting up a climber zipline, and that is, small diameter sheaves are unable to rotate freely at high speed without "jittering". I set up a zipline at a golf course during our apprenticeship training. The rope ran from a little maple at the top of a hill, down to a big willow at the bottom. I tried different pulleys on the zipline, with myself as the load. The small pulleys just couldn't go down the line smoothly without skittering and jittering, which really slowed things down. It wasn't until I tried an old 3" pulley that it actually performed the way I needed. Here's the video of that setup, which is actually the very first tree video that I ever posted online. Apologies for the terrible video quality, this was the first digital camera I ever owned, truly a piece of junk:

It seems to me that speed of rotation relative to the sheave diameter is another crucial factor in determining pulley efficiency. In other words, a good pulley might be able to rotate just fine at low speeds and thus would measure out as highly "efficient", but take that rope movement up to high speed and the situation changes dramatically. Thoughts?

 

[Bart_]

As a kid we were building upside down "slider chopper" trikes, bicycle trailers and such. It was cheap junk, no bearings, all bushings. Unmaintained junk that we happily cut up. We didn't even know what lubrication was. So sometimes at speed a wheel would break into a squeel or howl, maybe a chatter and we just went "oh well" did nothing or thought nothing about it and moved on to the next thing. Later we learned about lubrication and specifically saw the crazy whipping around the stub axle in a rapid cyclic motion while hardly rotating - lube it and it went away. The next observation was stick-slip motion where a wheel or lever or whatever would "bind" (static friction), spring deflect the whatever mechanical structure until the force built up enough to cause slip/motion, jumping a tiny bit to unload the built up spring deflection force and then at that position start a rinse/repeat. Once I learned this I freaked out my mom driver training practising by being super light on the brake pedal stopped in drive in an automatic - just lift your foot pressure and you could trigger the brake drums/shoes/assy's into stick slip that sounded like a cross between grinding and vibration while creeping slowly forward "Don't wreck the car!!". I only did it a few times knowing it was harmless to torment her Point being once you recognise this you can spot lots of situations where spring or proportional element plus stick/slip motion = judder. Eg creaking door hinge. A zip line pulley on a short tether can build up off vertical angle till the pulley moves on the line, maybe overshoots the steady tilt angle, stops, you catch up tilt the tether jumps again rinse repeat. Even the pulley body can be viewed as a super short rigid tether doing the same thing.

So that part is about system dynamics, overshooting, oscillation etc. A key part of that is damping caused by simple friction or lubricated friction. Too much friction results in chatter like a near seized bolt coming out. "screeeek" Too little friction results in underdamped like a swinging spar log chunk getting bupkus damping from air resistance (ever notice how a leafy top can nearly not swing past it's first drop to hanging?).

It gets more interesting with "bearing" friction. Look up the Rybeck (sp?) curve. mu vs load-speed-viscosity combo. Has metal to metal contact, partial lube film and then full lube float like your crank main bearings. When you're talking about actual bearing friction performance you can substitute mu for efficiency so you don't bring in confusion about square laws, quantities of energy or power rates - instead, just forces.

"Rybeck" makes me think of Gary Busey playing a high school football coach character

edit - it's coach Stribeck, my bad

 

[Bart_]

I knew I saw it somewhere. I finally relocated Coach Stribeck's presentation of his graph. Warning, for some this never happened and can't happen (knowledge).

About 5 minutes in this guy explains coach Stribeck's mu vs x-axis graph.

Arborist pulleys are pretty much at the left edge of the Stribeck curve. Doh. But bushing's peak load capability vs roller bearings wins the day. As to speed effects, higher mu makes more friction-force work, and how fast you do it is power, and power in vs heat sent out makes temperature - I figure only plastic bushinged pulleys would ever need to be worried about in arborist activities.

 

[Bart_]

Shop Trick to Get Out Stubborn Carb Mainjet/Emulsion Tube

First thing is sacrifice a medium flat blade screwdriver by grinding the width flare off so it fits down the threaded hole pretty close to snug. Grind the blade sharp and square. This is because the jet slot is missing it's center material and the slot is shallow and the brass is soft - if you ruin the brass slot the carb is scrap.

Normally using such a dedicated screwdriver by hand does the trick. But this one was really stuck. Clamp the carb level (vertical hole) and line it up precisely on center with the jet/hole. Get a tiny double-ended 1/4" ratchet drive and adapt it it via 1/4" socket to hold a fresh flat screwdriver bit on one side and a teeny socket on the other end. Chuck the teeny socket end in your drill chuck to 1) hold it axially exactly aligned on center 2) use the quill to provide "keep it in the screw head slot" force, while precisely applying torque via the ratchet - you can modulate both to apply torque right to the limit without skipping the flat blade and ruining the slot.

Took me 1/2 hour of patience but that's better than having to buy a new carb.

Threads turned out to be 5/16-24 so I chased the bore with a tap to get rid of the binding.

edit - I also chased diameter protrusions deformations in the brass thread when I noticed per 1/2 turn binding variation as it screwed in past the casting's side fuel inlet holes. For binding testing I screwed it in backwards so I could grip the emulsion tube if it got stuck.

 

[Bart_]

On The Topic of Rope Technique Practical Limitations

This post is inspired by the post showing IIRC 10:1 actual block and tackle performance no matter how many extra pulleys you throw at it. In this post I recall the technique where, with your arm or with an extension stick, you whip sideways onto the end of a rope that has been set aloft over a crotch or branch, so a single wave hump/shape travels up the rope, temporarily jumping the rope off the tip or lessening it's grip at the tip so either 1) a throw weight can descend by some increment per whip, or 2) by angling the whip you can make the rope typically jump a bit sideways too to get it more inboard closer to the spar to lessen the cantilever load on the branch.

When you get this technique to work you feel like a smarter, in the know, tips and tricks climber. When it refuses to work it just generally degenerates into low morale, disappointment and questioning.

So today I pose the question, can somebody come up with the analysis of presumably what max height branch the technique fails at? What I remember was on a very high branch, no matter how hard I whipped it the rope wouldn't jump at the branch. First thought, well the rope is too heavy. But it's not that simple - you can't use whip technique on a throw line because it's too light. So rope weight i necessary to carry the wave shape. Then you could say you just need a heavier throw weight to pull it over the branch - but that also holds it tighter to the top of the branch, doesn't it? To make this analysis realistic we'll have to assign some friction+bending losses to the rope going over the branch top half bark and a tension ratio of 1.3 would be pretty reasonable middle ground.

I have vague recollection of mass per unit length and elasticity (or not) and of course tension being in some physics equation for wave speed and shape. But in our case the rope tension goes from near zero where you hold the rope to max, maybe rope weight (plus tension effect from wave energy?) at the branch where we want it to jump. There's also the dynamic consideration of to get a jump, the (mass of the) whip leg of the rope has to lift ie accelerate/move upwards so it's not just overcoming the weight of the rope leg. Also if in contact, any ratios of tension within 1/1.3 to (reversed) 1.3/1 the rope won't slide as the fiction will hold it still. Greater ratios will slide, maintaining the ratio (measuring this is where the ratio came from!). And the contact force/weight is directly affected by the throw weight and the weight/length of it's rope leg. Also the throw bag side has to f = m x a itself downwards during the whip wave's release action at the branch contact. Also if the whip action just makes the bag rise up towards the branch that's a fail! (I've seen that happen!)

So my brain isn't likely to solve this. Maybe you or some (Professor) you know could. I friendly throw out the gauntlet.

Half marks (technically still a passing grade) if it is solved empirically by field experiment. Bonus marks if an analytical solution is verified.

 

[Matias]

On The Topic of Rope Technique Practical Limitations

This post is inspired by the post showing IIRC 10:1 actual block and tackle performance no matter how many extra pulleys you throw at it. In this post I recall the technique where, with your arm or with an extension stick, you whip sideways onto the end of a rope that has been set aloft over a crotch or branch, so a single wave hump/shape travels up the rope, temporarily jumping the rope off the tip or lessening it's grip at the tip so either 1) a throw weight can descend by some increment per whip, or 2) by angling the whip you can make the rope typically jump a bit sideways too to get it more inboard closer to the spar to lessen the cantilever load on the branch.

When you get this technique to work you feel like a smarter, in the know, tips and tricks climber. When it refuses to work it just generally degenerates into low morale, disappointment and questioning.

So today I pose the question, can somebody come up with the analysis of presumably what max height branch the technique fails at? What I remember was on a very high branch, no matter how hard I whipped it the rope wouldn't jump at the branch. First thought, well the rope is too heavy. But it's not that simple - you can't use whip technique on a throw line because it's too light. So rope weight i necessary to carry the wave shape. Then you could say you just need a heavier throw weight to pull it over the branch - but that also holds it tighter to the top of the branch, doesn't it? To make this analysis realistic we'll have to assign some friction+bending losses to the rope going over the branch top half bark and a tension ratio of 1.3 would be pretty reasonable middle ground.

I have vague recollection of mass per unit length and elasticity (or not) and of course tension being in some physics equation for wave speed and shape. But in our case the rope tension goes from near zero where you hold the rope to max, maybe rope weight (plus tension effect from wave energy?) at the branch where we want it to jump. There's also the dynamic consideration of to get a jump, the (mass of the) whip leg of the rope has to lift ie accelerate/move upwards so it's not just overcoming the weight of the rope leg. Also if in contact, any ratios of tension within 1/1.3 to (reversed) 1.3/1 the rope won't slide as the fiction will hold it still. Greater ratios will slide, maintaining the ratio (measuring this is where the ratio came from!). And the contact force/weight is directly affected by the throw weight and the weight/length of it's rope leg. Also the throw bag side has to f = m x a itself downwards during the whip wave's release action at the branch contact. Also if the whip action just makes the bag rise up towards the branch that's a fail! (I've seen that happen!)

So my brain isn't likely to solve this. Maybe you or some (Professor) you know could. I friendly throw out the gauntlet.

Half marks (technically still a passing grade) if it is solved empirically by field experiment. Bonus marks if an analytical solution is verified.

In this scenario, I have learned to clove hitch the rope to one one of a pole/stick and use it to extend your arm/lever. Whipping it with a 6' stick using the power of both hands to whip it hard let's you get over at considerable heights.

 

[Bart_]

Strength if the whipping action is certainly one of the parameters. I figure defining that is part of the solution. Part of the DARPA exoskeleton activity was defining human leg/walking power.
Maybe a new gizmo could be a Mythbusters/SmarterEveryDay style ridiculous power rope whipper.

edit - watched a bunch of rope wave vids. Almost to a T they all use constant tension, small off-straight angle deviations and small angle trig substitutions/approximations. One mentioned that constant tension goes poof for eg gym whip?ropes with big waves - ie like we do. Some clues and notions but I'm still stumped. Can put limits on unequal rope legs via tension ratio, can substitute throw bag weight for equivalent length of rope. I do recall the hump getting faster as it got smaller going up to a very high branch. Matches the speed eqn. One YT prof calculated kinetic and spring energy in the wave - might be a lead.

edit2 - language barrier but getting closer

edit3 - this guy includes rope bending loss (damping) but - language barrier/traumatic flashback!