Muggs
Been here much more than a while
- Location
- Canuckistan
2 load cells, fiddle block on a trucker's hitch, pulleys, carabiners, kilonewtons. Nerd stuff...
Trucker's Hitch Pull Testing, 6 Different Variations
- Thread starter Muggs
- Start date
Treeaddict
Participating member
- Location
- Bel Air
Happy to see a new video from you. I just rewatched many of them yesterday including the truckers hitch, fiddle block, and the 3X MA with 2 pulleys vids.
Mick Dempsey
Carpal tunnel level member
- Location
- France
Thanks, answered a lot of questions that I’ve asked myself.
Lot of work there.
Lot of work there.
Muggs
Been here much more than a while
- Location
- Canuckistan
I had a calibration issue with the output load cell so it seems like all of the resultant pulls were 25-50 lbs overstated, hard to say. I do believe that the relative ratios for each setup are accurate in terms of efficiency. I'm going to redo them, but here's the results I got:
Trucker's Hitch construction:
The final setup testing at 3.09:1 is why I'm doubting the calibration, but hopefully they are all off by the same amount.
Maybe the most interesting takeaway for me in this test is how, as I added hardware and made the system more efficient, it became harder and harder to input that same 2 kN starting pull on the fiddle block. Efficiency in a hauling system is a two edged sword. On the one hand, a higher percentage of your input is amplified and transmitted through the system all the way to the output. On the other hand, as friction decreases, the system makes it easier for the load to "pull back" and oppose your input force. This is true even with progress capture built in, because the progress capture doesn't engage until the active pull lets up.
Without the 2nd load cell on the input, I would probably have just thought that I was fatigued from pulling so much on the fiddle block. But it was very clear that getting back to that starting input of 2 kN was getting more and more difficult as I went along. Very interesting...
Trucker's Hitch construction:
| Front (Load end) | Back (anchor end) | Input (kN) | Output (kN) | Result Ratio |
| rope on rope | carabiner | 2.0 | 3.9 | 1.95:1 |
| rope on rope | pulley | 1.85 | 4.3 | 2.32:1 |
| carabiner | carabiner | 1.94 | 3.9 | 2.01:1 |
| carabiner | pulley | 1.9 | 4.45 | 2.34:1 |
| pulley | carabiner | 2.0 | 5.15 | 2.58:1 |
| pulley | pulley | 1.84 | 5.7 | 3.09:1 |
The final setup testing at 3.09:1 is why I'm doubting the calibration, but hopefully they are all off by the same amount.
Maybe the most interesting takeaway for me in this test is how, as I added hardware and made the system more efficient, it became harder and harder to input that same 2 kN starting pull on the fiddle block. Efficiency in a hauling system is a two edged sword. On the one hand, a higher percentage of your input is amplified and transmitted through the system all the way to the output. On the other hand, as friction decreases, the system makes it easier for the load to "pull back" and oppose your input force. This is true even with progress capture built in, because the progress capture doesn't engage until the active pull lets up.
Without the 2nd load cell on the input, I would probably have just thought that I was fatigued from pulling so much on the fiddle block. But it was very clear that getting back to that starting input of 2 kN was getting more and more difficult as I went along. Very interesting...
Last edited:
chris_girard
Branched out member
- Location
- Gilmanton, N.H.
Great info Patrick! The use of a trucker's hitch aka Z-Rig I feel is one thing that a lot of new tree guys don't even know about in this age of technology, and if they know about it, then they don't know the mechanics behind it.
Nerdy stuff to some, but to hardcore rigging enthusiasts like me, awesome stuff!
Nerdy stuff to some, but to hardcore rigging enthusiasts like me, awesome stuff!
- Location
- Chardon, OH
I am not an expert, but I will tip-toe into this discussion . . . . .
How would high efficiency / ball bearing pulleys improve the setup ?
Years ago, I attended a short presentation by Taylor Hamel; expert climber & DMM rep, on Mechanical advantage & friction.
He used a load cell to show how much friction effected the MA:
1. simple carabineer redirects
2. standard pulleys
3. very high efficiency (low friction) pulleys.
I don't know if he has published, or if anything is on YouTubed, etc.
The effect of friction was mind-boggling, at least to me.
The effect, demonstrated by the load cell, was HUGE ! Totally unexpected !
My "take-away" was that I would never bother with a cheap, or even standard pulley fiddle block.
It added almost nothing to the MA for lifting, because of friction ! ! !
The friction would aid in holding or lowering a load; but would not aid in lifting.
(Unless very high efficiency (low friction) pulleys are used.)
How would high efficiency / ball bearing pulleys improve the setup ?
Years ago, I attended a short presentation by Taylor Hamel; expert climber & DMM rep, on Mechanical advantage & friction.
He used a load cell to show how much friction effected the MA:
1. simple carabineer redirects
2. standard pulleys
3. very high efficiency (low friction) pulleys.
I don't know if he has published, or if anything is on YouTubed, etc.
The effect of friction was mind-boggling, at least to me.
The effect, demonstrated by the load cell, was HUGE ! Totally unexpected !
My "take-away" was that I would never bother with a cheap, or even standard pulley fiddle block.
It added almost nothing to the MA for lifting, because of friction ! ! !
The friction would aid in holding or lowering a load; but would not aid in lifting.
(Unless very high efficiency (low friction) pulleys are used.)
Muggs
Been here much more than a while
- Location
- Canuckistan
Hoping to post that today, already planned it out...
Muggs, check out the SRT Basal Anchor TIP forces thread. You can apply the tension ratio type analysis directly to each of your devices, even directly as my friction measurements were with 180 degree bends like you used in the 3:1 system you set up for the video.
You have to be careful with settling of the system because tiny rope motions can change the amount of friction based on direction of rope travel. Try watching both load cells maybe by videos and see the friction loss reverse with the direction of rope travel. I set up a tiny zip line with tenex tec (double braid polyester) I think and it constantly slowly sagged. That type of thing can mess with your results. If you overshoot and settle back you'll also get a different answer/measurement. If you want to see both sides of the same coin do a video recording of the load cell readouts during a "lift" and during a "lower". The tension ratios principle will hold for both scenarios.
The tension ratio is the ratio of tension on each side of the device, be it a pulley, carabiner, rigging ring, Morgan block, tree crotch etc. You use it multiplicatively. e.g. 1.2 through a pulley, "lifting" you pull 120 lbs and get 100 lbs out the other side. I tested a whole bunch of stuff for their ratios. Made a few conclusions. One conclusion was that minimalist carabiners used as a pulley really sucked.
You have to be careful with settling of the system because tiny rope motions can change the amount of friction based on direction of rope travel. Try watching both load cells maybe by videos and see the friction loss reverse with the direction of rope travel. I set up a tiny zip line with tenex tec (double braid polyester) I think and it constantly slowly sagged. That type of thing can mess with your results. If you overshoot and settle back you'll also get a different answer/measurement. If you want to see both sides of the same coin do a video recording of the load cell readouts during a "lift" and during a "lower". The tension ratios principle will hold for both scenarios.
The tension ratio is the ratio of tension on each side of the device, be it a pulley, carabiner, rigging ring, Morgan block, tree crotch etc. You use it multiplicatively. e.g. 1.2 through a pulley, "lifting" you pull 120 lbs and get 100 lbs out the other side. I tested a whole bunch of stuff for their ratios. Made a few conclusions. One conclusion was that minimalist carabiners used as a pulley really sucked.
