Recent content by davespencer

  1. davespencer

    Canada's Greatest Know It All

    Re: Canada\'s Greatest Know It All Thomas is now a close friend of mine! We skype at least twice a month. I don't know if dropbox has limitations on bandwidth or not but Ill post this link for my american friends who can not see the show due to stupid licensing rules...
  2. davespencer

    Birthday zipline

    Just a suggestion but if you put the pulley on a webbing loop long enough that people can not touch the pulley, you will never have to worry about pinched or burnt fingers.
  3. davespencer

    tipping trees

    tree video We had some warm weather melting snow, rain and some winds, I got home from a night shift the other morning and decided the tree was probably coming down today. It just depended on whether or not I cut it or it fell. The video shows the ground moving around and the best part is...
  4. davespencer

    Shock load

    Moray, you have a great point. There is definitely a lot missing from the math here at this point. I know that a final equation for this is beyond the power of my brain. If someone comes up with it I would sure like to take a gander though. It is easy to calculate the energy of a falling...
  5. davespencer

    tipping trees

    Back when I ran my own tree company. I ran across a few trees that had been blown over a bit after a heavy rain had supersaturated the root area. My solution to this was to guy the tree, re-saturate the root area, and use the guys to straighten the tree back up, leaving the guys until the...
  6. davespencer

    Shock load

    I gotta disagree with you here spydey. 4 ft of stopping distance is 4 ft of stopping distance, no matter what causes that final distance, be it stretch, sway or braking. This is not something that can be used to predict in advance but if the formula is correct and the distances can be measured...
  7. davespencer

    Shock load

    [ QUOTE ] [ QUOTE ] ...impact force=weight * fall distance * stopping distance. [/ QUOTE ] I think the formula isn't quite right, but the idea is. The essential notion is that the ratio of fall distance to stopping distance is related to the ratio of impact force to weight. [/ QUOTE ] I...
  8. davespencer

    Shock load

    Holy crap, I spent a couple hours last night trying to figure out this formula. I converted velocity and mass into joules and newtons, it was getting too complicated to understand but I figured I finally had it. In proving the formula I found a discrepancy due to the formulas being based on an...
  9. davespencer

    Shock load

    Theoretically if you had a long enough distance you could drop a 100 lb log 10 ft and then decelerate it very slowly and the force on the anchor could (theoretically) be 201 lbs (rope tension could be 100.5 lbs). Conversely, You could drop a 100 lb log 1 ft onto a steel cable with no stretch...
  10. davespencer

    saw for hire tv show?

    I hate to be the one who points this out but I think that Nosak is more of the typical north american tree company than any of you guys out here. Before you all get upset here, know that that was meant as a compliment. Ive done my fair share of traveling around the US and Canada and I can't...
  11. davespencer

    Rope demo at TCIA

    True Story, Working during the 97 ice storm in Ottawa. A good buddy of mine and I were working with a young fella and his dad as foreman (working for municipality) Young guy was late for work and really hung over when he did arrive. Dad was furious as it was not the first time. We told him...
  12. davespencer

    The physics of rope bends

    I am surprised by the above statement about the rope breaking on the inside. It has been my experience with testing and in field failures (of which I've witnessed a few) that the rope will break a couple of inches in front of the knot. I have no idea as to why it happens this way, I have...
  13. davespencer

    The physics of rope bends

    [ QUOTE ] I think in the main this is on the right track, but the devil is in the details. First, the difference between the inner and outer circumference doesn't vary with the bend radius--it is constant. [/ QUOTE ] Maybe we are thinking about two different things here so I will give an...
  14. davespencer

    The physics of rope bends

    [ QUOTE ] Please explain how the rope gains and loses strength as it bends. I am referring to both knots and over pulleys, friction savers, biners etc. How do you calculate the strength loss say of a rope girth hitched over a limb to be used as a footlock line? Why do some ropes lose strength...
  15. davespencer

    Blocks sharing loads through differing angles

    Let me clarify what I have done here. Of course Spydey caught me on something I didn't think anyone would notice :) Thanks for keeping me honest. The math I have done here assumes that there is no pulley sheave that the rope is going around. This would slightly affect the angle of the rope...
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