Rigging research results

I was mentally sleeping a bit and now see your log accelerometer alone was 5 or 6x log weight so the tip load is mucho big. Pretty hard catch.

30 years ago I made a few load cells. All that good stuff like surface prep, we used cyanoacrylate with accelerator (surprised me - crazy glue!) matching gauge coefficients to the metal and hitting the target location. And then its "mostly" linear. And for a dose of humour, imagine in a Mr. Rogers voice "Can you say Transverse Sensitivity children?" Coolest integrated strain gauges I ever saw were in the fingers of a dexterous robotic hand, MIT or some such. I knew the poor buggers were struggling with zero drift because amplifiers weren't stable enough yet. Since then amps have self zeroing functions. Magic. We struggled with drifting zeroing. First mini cell I did was as long as the end of your thumb (last joint to nail tip). Wasn't very good. Young and dumb.

If you've got two load cells, anchor a rope on one, route the rope 180 degree U turn through the aerial friction device (i.e. like a rigging tip) and put the second load cell between a "puller" and the rope. That way you get the tension on either side of the device. You could get the tension ratios for the aerial friction devices you used. Would be enlightening. I used an advantage lever to crank up the force for my measurements. An added feature is a linear pot or some such to capture the rope travel as it stretches under load. I think, short of a porty, the highest ratio device on the market is the Morgan block at 5 to 10, or BMS Belay @2 1/2 wraps 18 I think.

Am I a nerd if this sort of thing breaks up the doldrums? :)
 
evo said:
Hey there @Matt Follett , I think I saw you present with Scott Baker many years ago. I tried really hard to look you up, searching for the results of the research you were doing at that time with cell phone accelerometers on tree branches and different pruning methods. Did that ever pan out?
I’ll be sure to take a closer look at this thread and sorry for the side track
Click to expand...
Yes, that's me. That work has been presented in conference, but I've still to write it up. It's a big complex thing that I put effort into for a while, then throw my hands in the air and go do something else. ;) I'm hoping to replicate it this summer with a bit better measures, and less wires that can be chewed by tree dwelling rodentia... ;)

@Bart_

;) Crazy glue and hot glue gun potting!
 
Did you sneak into my garage and use my stuff on my milling machine? :) Uncanny. But my mill has variable speed dc drive. I hot rodded it. Spindle's a bit different.
 
It's interesting the numbers show the safeblock not changing the forces much vs rings. I'm curious what size rigging line you were using, as in my by the seat of my pants testing, the safeblock doesn't seem to add much additional fricition until you're using 5/8+ rope. The triple thimble on the other hand, works much better with smaller diameter 1/2 inch rope.

If you get around to doing more testing this summer, I would gladly loan you one to do your testing with.

Also you've got a thunder sling pictured... but no test data? run out of time to test it?
 
@theatertech87

Yes, we ran out of time for the thunder sling... basically had one working day (rig has to come down at end of day) and would be hard to justify going back for one device... also volunteer time etc. I had a triple thimble planned too, but time. ;)

As noted, the rope was 9/16 stable braid. I would not say the safeblock does not differ from the rings... if you look at the lead rope load, notice it is more variable and higher in general. I would argue that the increased friction in the safeblock means we loose some stretch in the fall of the rope and there's the chance for a greater acceleration ("de-acceleration"). Our robot groundie also had a harder time with the safebloc... needs some more AI learning ;)

I'd love to go back and go through more devices. It might happen, but I think for now, we got the results we needed. All in due time.

@Bart_
lol, my RF-30 (MT3 taper) has seen better days, glorified drill press... needs a new spindle drive, and ways scraped and and and.. but now runs a DRO. I have some DC stuff, and am thinking that route, maybe cnc, but not yet (want a Schaublin 13 or Deckle fp1 but $$$). The Colchester Master is the workhorse in the shop... good for a thou or less over a decent run.
 
I went simple. Big 4" x about foot surplus dc motor 4 brush, potentiometer/opamp/PWM/single IGBT. Low kHz, you can hear it whine. Added a current sense resistor and an ammeter for seeing load. And hour meter. DPDT cross wired for reversing for tapping. Used to have a tach for speed regulation feedback. Stopped using it. I think it's heading on 30 years, winter summer, 500? hrs runtime. Still haven't blown the IGBT good for about 25A motor side. Switched right off wall 180V sine wave after a rectifier. Of course you can just buy a speed control :) But reversing for tapping is sweet. R8, one step from baby size.

Did you characterize the stable braid for modulus like the Buccaneer in the HSE report? Samson's data sheet works out nonsensically, giving values that contradict their own rising rate example graph. I'm talking about the EA method off the three percentage and load values 10, 20, 30%.
 
Here's a teaser:
log fall.png

Haven't done the analysis yet. I'm working on the similarities one of which is the rope. There's reason to match the rope to the log weight(s) which were 56.5 kg nominal and 223 kg. For the rope there's -cut at 8m height for 223 kg log using 14mm buccaneer- and cut at 4m above the ground for the lab 56.5 kg logs also same buccaneer rope. I found the buccaneer spec pg 240 as 258 kN modulus or 58,000 lbs imperial.

I've found my block moves quite a bit due to sling stretch even though I've got a much beefier sling than "rope". This is a significant factor which will mess with the whole works. It was only 16 mm sling vs 14 mm rope in the HSE data. Any chance of knowing roughly how many cm the block stretch-moved during the peak force vs just before in the HSE or other video data you've got? I'd like to match a base line before moving forward.

Another oddity is for kevlar, vectran and nylon braids I've tested I get one modulus with rising rate just like the Samson graph but after the initial tensioning the "rope" sometimes rises to about double the modulus with varying hysteresis. I haven't been able to get my hands on any right sized polyester braid yet though I wish I could. I also found big modulus difference between same diameter lines with different braid patterns.

Gonna be a challenge to pursue this with the weather changing over.
 
Well, let's just say I have informal confirmation of Samson's non-recommendation for nylon rigging ropes.

Boing!

I went to a less stiff line to try to lower the force spike. I actually expected it to break. Sproing. Altered the trajectory substantially. Turns out all the fudging around slippage imperfection of rigging is a helpful contributor to lowering the force spike. So far so good but having trouble getting to the 5G's baseline. Rope characteristics is a bit of a topic itself. Manufacturers aren't very public with that info, re specifics that is.

By the way, measured 1.1 tension ratio with fine kevlar through the block, 10:1 (big!!) groove diameter to line diameter, but back nearer to 1.2 tension ratio with fatter line. Block has needle bearings.
 
So based on this info it looks like I should purchase some rigging rings to help take strain of the truck instead of just using my blocks all the time, any one have any recommendations, I always work with a groundie so I'm not worried about having to adjust friction at the rigging point.
 
Vicente, I was just testing a mini safe block and dug up a reference for what the tension ratio should be for a rigging ring. Looks like it should be about 1.5 whereas a rigging pulley is already 1.2 so it's not hugely different. Connection being that using a single hole of the safeblock is the same as a rigging ring. The friction jump from one hole to two is moderate but the jump from two to 3 holes is more substantial, around 4 or 5 tension ratio. That's getting into morgan block territory but the safeblock is designed for abuse and larger loads.

Just remember if you ever want to lift, aerial friction devices are not your friend. They would amplify the rig tip loading if you did e.g. a grcs lift.
 
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Good news Matt in the form of corroboration. Due to my load cell I wasn't getting much porty/portysling slippage, but I dialled in block sling slippage, got in a bit of log half hitch slippage and am using a rope modulus about matched to the log mass - zeroed in on 5G's!! I wasn't that far off before. One factor I tuned was the throat length on the block sling which was proposed (if excess due to sticking a load cell in there) to be a source of excess fall distance and hence higher forces. On my first try I had it substantially too long. Custom fabrication...
Trajectory looks good. Kinetic energies seem ok.
It's getting more interesting now. :)

I even had a failure run where the block sling went for a boogie downward. Lost about 1G from that.
 
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