Printable View
Uprooting a tree using a 45:1 pulley system.
https://www.youtube.com/watch?v=vM24klVyxFk
Previously:
https://www.homemadetools.net/forum/...0797#post73160
https://www.homemadetools.net/forum/...569#post128217
https://www.homemadetools.net/forum/...708#post123831
https://www.homemadetools.net/forum/...9299#post89007
https://www.homemadetools.net/forum/...724#post111399
https://www.homemadetools.net/forum/...3411#post99026
Hmmmm?
Remembering my high school physics class I believe you add your compound systems not multiply. I think your system is about 10 or 11 to 1 and not 45 to 1. What was your input pull? Let’s just guess 100lbs. In a 10-1 system you’d be pulling at about 1000lbs and not 4500lbs as first stated judging by the way the tree came out of the ground my guess is you were pulling at the lower number? IMHO. it’s been a long time since high school physics class.
I'm fairly certain it's a 35:1 system, assuming he actually has a 5:1 at the end. Let's say he pulls with 1lb, that's 5lb out the purple pulley. The line out the purple pulley terminates at the tree, still tensioned at 5lb. That line also runs through that middle pulley, causing the line out to be 10lb. That runs through a red pulley at the tree pulling the tree with 20lb. That runs back and terminates at the tree again, with 10lb of tension.
So just the tension at the tree: 5+10+20=35lb from 1lb initial force.
I tried drawing up a diagram, but a nice way to represent it in 2d eludes me lol.
Kinda reinforces the perception of the power of the wind in a blow down.
If he put a weight on a rope and threw it over an upper limb he probably could have done a direct pull with a small truck, or a two to one pull with the lawn tractor.
All that rope connected that close to the ground shows an idiot at work. He also has little directional control that far down.
Hi Gang: Here's how I figure it:
1) Tractor pulls on rope #1 (with force "T") with four lines to the Purple pulley: Purple pulley pulls with 4T force.
2) rope #2 pulls on Green pulley #1 and loop back to Green pulley #2: Green pulley pulls rope #3 with 8T force.
3) rope #3 pulls on Red pulley attached to tree for 16T force at 8 foot up the tree.
4) rope #2 passes Green pulley #2 and finally to the tree at 4 foot up the trunk with 4T force.
5) rope #3 loops back to the tree at 6 foot up the tree with 8T force.
So the tree sees 16T + 8T + 4T = 28T a ration of 1:28
If we add a simple torque reaction at the stump base we have (16Tx8')+(8Tx6')+(4T+4')=(128')+(48T')+(16T')=192T'
If the tractor pulls with 100 pounds of force, the top point sees 1600 pounds, the mid point 800 pounds and the bottom point 400 pounds.
Adding the torque ration the top has 12.8K ft/lb, mid 4.8K ft/lb, and bottom 1.6K ft/lb.
So the top point has 8 times more effect than the bottom point. Everything tied higher in the tree would have been more effective.
In the end it worked fine and the tree came down.
Congratulations!
Carl.
I very much doubt that the chain saw and stump grinder markets are threatened.